Cisco IOS XR Routing Configuration Guide, Release 3.5 - Implementing IS-IS on Cisco IOS XR Software [Cisco IOS XR Software]

Table Of Contents

Implementing IS-IS on Cisco IOS XR Software

Contents

Prerequisites for Implementing IS-IS on Cisco IOS XR Software

Restrictions for Implementing IS-IS on Cisco IOS XR Software

Information About Implementing IS-IS on Cisco IOS XR Software

IS-IS Functional Overview

Key Features Supported in the Cisco IOS XR IS-IS Implementation

IS-IS Configuration Grouping

IS-IS Configuration Modes

IS-IS Interfaces

Multitopology Configuration

IPv6 Routing and Configuring IPv6 Addressing

Limit LSP Flooding

Flood Blocking on Specific Interfaces

Mesh Group Configuration

Maximum LSP Lifetime and Refresh Interval

Overload Bit Configuration During Multitopology Operation

Single-Topology IPv6 Support

Multitopology IPv6 Support

IS-IS Authentication

Nonstop Forwarding

Multi-Instance IS-IS

Multiprotocol Label Switching Traffic Engineering

Overload Bit on Router

Default Routes

Attached Bit on an IS-IS Instance

IS-IS Support for Route Tags

Multicast-Intact Feature

Multicast Topology Support Using IS-IS

MPLS Label Distribution Protocol IGP Synchronization

MPLS LDP-IGP Synchronization Compatibility with LDP Graceful Restart

MPLS LDP-IGP Synchronization Compatibility with IGP Nonstop Forwarding

Label Distribution Protocol IGP Auto-configuration

MPLS TE Forwarding Adjacency

MPLS TE Interarea Tunnels

IP Fast Reroute

How to Implement IS-IS on Cisco IOS XR Software

Enabling IS-IS and Configuring Level 1 or Level 2 Routing

Prerequisites

Configuring Single Topology for IS-IS

Restrictions

Configuring Multitopology for IS-IS

Controlling LSP Flooding for IS-IS

Configuring Nonstop Forwarding for IS-IS

Configuring Authentication for IS-IS

Configuring Keychains for IS-IS

Configuring MPLS Traffic Engineering for IS-IS

Prerequisite

Restrictions

Tuning Adjacencies for IS-IS

Setting SPF Interval for a Single-Topology IPv4 and IPv6 Configuration

Customizing Routes for IS-IS

Configuring MPLS LDP IS-IS Synchronization

Enabling Multicast-Intact

Tagging IS-IS Interface Routes

Setting the Priority for Adding Prefixes to the RIB

Configuring IP Fast Reroute Loop-free Alternate

Restrictions

Configuration Examples for Implementing IS-IS on Cisco IOS XR Software

Configuring Single-Topology IS-IS for IPv6: Example

Configuring Multitopology IS-IS for IPv6: Example

Redistributing IS-IS Routes Between Multiple Instances: Example

Tagging Routes: Example

Where to Go Next

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Implementing IS-IS on Cisco IOS XR Software

Integrated Intermediate System-to-Intermediate System (IS-IS), Internet Protocol Version 4 (IPv4), is a standards-based Interior Gateway Protocol (IGP).

Cisco IOS XR implements the IP routing capabilities described in International Organization for Standardization (ISO)/International Engineering Consortium (IEC) 10589 and RFC 1995, and adds the standard extensions for single topology and multitopology IS-IS for IP Version 6 (IPv6).

This module describes the new and revised tasks you need to implement IS-IS (IPv4 and IPv6) on your Cisco IOS XR network.

Note For more information about IS-IS on Cisco IOS XR software and complete descriptions of the IS-IS commands listed in this module, you can refer to the "Related Documents" section of this module. To locate documentation for other commands that might appear while of executing a configuration task, search online in the Cisco IOS XR software master command index.

Feature History for Implementing IS-IS on Cisco IOS XR Software

Release

Modification

Release 2.0

This feature was introduced on the Cisco CRS-1.

Release 3.0

No modification.

Release 3.2

Support was added for the Cisco XR 12000 Series Router. The ability to configure a broadcast medium connecting two networking devices as a point-to-point link was added.

Release 3.3.0

LDP IGP synchronization support was added for IPv4 unicast address families. See the "MPLS Label Distribution Protocol IGP Synchronization" section and "Configuring MPLS LDP IS-IS Synchronization" section for more information.

The ispf startup-delay command was removed from the "Setting SPF Interval for a Single-Topology IPv4 and IPv6 Configuration" section.

Release 3.4.0

Support was added for the following features:

•MPLS TE forwarding adjacency

•MPLS TE interarea tunnels

•Multicast topology

Release 3.5.0

Support was added for the following features:

•IS-IS keychain support for hello and LSP authentication and hitless key rollover

•IP fast reroute loop-free alternates computation

•Label Distribution Protocol (LDP) Interior Gateway Protocol (IGP) auto-configuration

Contents

•Prerequisites for Implementing IS-IS on Cisco IOS XR Software

•Restrictions for Implementing IS-IS on Cisco IOS XR Software

•Information About Implementing IS-IS on Cisco IOS XR Software

•How to Implement IS-IS on Cisco IOS XR Software

•Configuration Examples for Implementing IS-IS on Cisco IOS XR Software

•Where to Go Next

•Additional References

Prerequisites for Implementing IS-IS on Cisco IOS XR Software

You must be in a user group associated with a task group that includes the proper task IDs for IS-IS commands. For detailed information about user groups and task IDs, see the Configuring AAA Services on Cisco IOS XR Software module of Cisco IOS XR System Security Configuration Guide.

Restrictions for Implementing IS-IS on Cisco IOS XR Software

When multiple instances of IS-IS are being run, an interface can be associated with only one instance (process). Instances may not share an interface.

Information About Implementing IS-IS on Cisco IOS XR Software

To implement IS-IS you need to understand the following concepts:

•IS-IS Functional Overview

•Key Features Supported in the Cisco IOS XR IS-IS Implementation

•IS-IS Configuration Grouping

•IS-IS Configuration Modes

•Multitopology Configuration

•IPv6 Routing and Configuring IPv6 Addressing

•Limit LSP Flooding

•Maximum LSP Lifetime and Refresh Interval

•Overload Bit Configuration During Multitopology Operation

•Single-Topology IPv6 Support

•Multitopology IPv6 Support

•IS-IS Authentication

•Nonstop Forwarding

•Multi-Instance IS-IS

•Multiprotocol Label Switching Traffic Engineering

•Overload Bit on Router

•Default Routes

•Attached Bit on an IS-IS Instance

•IS-IS Support for Route Tags

•Multicast-Intact Feature

•Multicast Topology Support Using IS-IS

•MPLS Label Distribution Protocol IGP Synchronization

•Label Distribution Protocol IGP Auto-configuration

•MPLS TE Forwarding Adjacency

•MPLS TE Interarea Tunnels

•IP Fast Reroute

IS-IS Functional Overview

Small IS-IS networks are typically built as a single area that includes all routers in the network. As the network grows larger, it may be reorganized into a backbone area made up of the connected set of all Level 2 routers from all areas, which is in turn connected to local areas. Within a local area, routers know how to reach all system IDs. Between areas, routers know how to reach the backbone, and the backbone routers know how to reach other areas.

The IS-IS routing protocol supports the configuration of backbone Level 2 and Level 1 areas and the necessary support for moving routing information between the areas. Routers establish Level 1 adjacencies to perform routing within a local area (intra-area routing). Routers establish Level 2 adjacencies to perform routing between Level 1 areas (interarea routing).

For Cisco IOS XR software, each IS-IS instance can support either a single Level 1 or Level 2 area, or one of each. By default, all IS-IS instances automatically support Level 1 and Level 2 routing. You can change the level of routing to be performed by a particular routing instance using the is-type command.

Key Features Supported in the Cisco IOS XR IS-IS Implementation

The Cisco IOS XR implementation of IS-IS conforms to the IS-IS Version 2 specifications detailed in RFC 1195 and the IPv6 IS-IS functionality based on the Internet Engineering Task Force (IETF) IS-IS Working Group draft-ietf-isis-ipv6.txt document.

The following list outlines key features supported in the Cisco IOS XR implementation:

•Single topology IPv6

•Multitopology

•Nonstop forwarding (NSF), both Cisco proprietary and IETF

•Three-way handshake

•Mesh groups

•Multiple IS-IS instances

•Configuration of a broadcast medium connecting two networking devices as a point-to-point link

•Fast-flooding with different threads handling flooding and shortest path first (SPF).

Note For information on IS-IS support for Bidirectional Forwarding Detection (BFD), see Cisco IOS XR Interface and Hardware Configuration Guide and Cisco IOS XR Interface and Hardware Command Reference.

IS-IS Configuration Grouping

Cisco IOS XR groups all of the IS-IS configuration in router IS-IS configuration mode, including the portion of the interface configurations associated with IS-IS. To display the IS-IS configuration in its entirety, use the show running router isis command. The command output displays the running configuration for all configured IS-IS instances, including the interface assignments and interface attributes.

IS-IS Configuration Modes

The following sections show how to enter each of the configuration modes. From a mode, you can enter the ? command to display the commands available in that mode.

Router Configuration Mode

The following example shows how to enter router configuration mode:
RP/0/RP0/CPU0:router# configuration
RP/0/RP0/CPU0:router(config)# router isis isp
RP/0/RP0/CPU0:router(config-isis)# 
Router Address Family Configuration Mode

The following example shows how to enter router address family configuration mode:
RP/0/RP0/CPU0:router(config)# router isis isp
RP/0/RP0/CPU0:router(config-isis)# address-family ipv6 unicast
RP/0/RP0/CPU0:router(config-isis-af)#
Interface Configuration Mode

The following example shows how to enter interface configuration mode:
RP/0/RP0/CPU0:router(config)# router isis isp
RP/0/RP0/CPU0:router(config-isis)# interface POS0/3/0/0
RP/0/RP0/CPU0:router(config-isis-if)# 
Interface Address Family Configuration Mode

The following example shows how to enter interface address family configuration mode:
RP/0/RP0/CPU0:router(config)# router isis isp
RP/0/RP0/CPU0:router(config-isis)# interface POS0/3/0/0
RP/0/RP0/CPU0:router(config-isis-if)# address-family ipv4 unicast
RP/0/RP0/CPU0:router(config-isis-if-af)#
IS-IS Interfaces

IS-IS interfaces can be configured as one of the following types:

•active—advertises connected prefixes and forms adjacencies. This is the default for interfaces.

•passive—advertises connected prefixes but does not form adjacencies. The passive command is used to configure interfaces as passive. Passive interfaces should be used sparingly for important prefixes such as loopback addresses that need to be injected into the IS-IS domain. If many connected prefixes need to be advertised then the redistribution of connected routes with the appropriate policy should be used instead.

•suppressed—does not advertise connected prefixes but forms adjacencies. The suppress command is used to configure interfaces as suppressed.

•shutdown—does not advertise connected prefixes and does not form adjacencies. The shutdown command is used to disable interfaces without removing the IS-IS configuration.

Multitopology Configuration

Cisco IOS XR software supports multitopology for IPv6 IS-IS unless single topology is explicitly configured in IPv6 address-family configuration mode.

Note IS-IS supports IP routing and not Open Systems Interconnection (OSI) Connectionless Network Service (CLNS) routing.

IPv6 Routing and Configuring IPv6 Addressing

By default, IPv6 routing is disabled in the Cisco IOS XR software. To enable IPv6 routing, you must assign IPv6 addresses to individual interfaces in the router using the ipv6 enable or ipv6 address command. See the Network Stack IPv4 and IPv6 Commands on Cisco IOS XR Software module of Cisco IOS XR IP Addresses and Services Command Reference.

Limit LSP Flooding

Limiting link-state packets (LSP) may be desirable in certain "meshy" network topologies. An example of such a network might be a highly redundant one such as a fully meshed set of point-to-point links over a nonbroadcast multiaccess (NBMA) transport. In such networks, full LSP flooding can limit network scalability. One way to restrict the size of the flooding domain is to introduce hierarchy by using multiple Level 1 areas and a Level 2 area. However, two other techniques can be used instead of or with hierarchy: Block flooding on specific interfaces and configure mesh groups.

Both techniques operate by restricting the flooding of LSPs in some fashion. A direct consequence is that although scalability of the network is improved, the reliability of the network (in the face of failures) is reduced because a series of failures may prevent LSPs from being flooded throughout the network, even though links exist that would allow flooding if blocking or mesh groups had not restricted their use. In such a case, the link-state databases of different routers in the network may no longer be synchronized. Consequences such as persistent forwarding loops can ensue. For this reason, we recommend that blocking or mesh groups be used only if specifically required, and then only after careful network design.

Flood Blocking on Specific Interfaces

With this technique, certain interfaces are blocked from being used for flooding LSPs, but the remaining interfaces operate normally for flooding. This technique is simple to understand and configure, but may be more difficult to maintain and more error prone than mesh groups in the long run. The flooding topology that IS-IS uses is fine-tuned rather than restricted. Restricting the topology too much (blocking too many interfaces) makes the network unreliable in the face of failures. Restricting the topology too little (blocking too few interfaces) may fail to achieve the desired scalability.

To improve the robustness of the network in the event that all nonblocked interfaces drop, use the csnp-interval command in interface configuration mode to force periodic complete sequence number PDUs (CSNPs) packets to be used on blocked point-to-point links. The use of periodic CSNPs enables the network to become synchronized.

Mesh Group Configuration

Configuring mesh groups (a set of interfaces on a router) can help to limit flooding. All routers reachable over the interfaces in a particular mesh group are assumed to be densely connected with each router having at least one link to every other router. Many links can fail without isolating one or more routers from the network.

In normal flooding, a new LSP is received on an interface and is flooded out over all other interfaces on the router. With mesh groups, when a new LSP is received over an interface that is part of a mesh group, the new LSP is not flooded over the other interfaces that are part of that mesh group.

Maximum LSP Lifetime and Refresh Interval

By default, the router sends a periodic LSP refresh every 15 minutes. LSPs remain in a database for 20 minutes by default. If they are not refreshed by that time, they are deleted. You can change the LSP refresh interval or maximum LSP lifetime. The LSP interval should be less than the LSP lifetime or else LSPs time out before they are refreshed. In the absence of a configured refresh interval, the software adjusts the LSP refresh interval, if necessary, to prevent the LSPs from timing out.

Overload Bit Configuration During Multitopology Operation

Because the overload bit applies to forwarding for a single topology, it may be configured and cleared independently for IPv4 and IPv6 during multitopology operation. For this reason, the overload is set from the router address family configuration mode. If the IPv4 overload bit is set, all routers in the area do not use the router for IPv4 transit traffic. However, they can still use the router for IPv6 transit traffic.

Single-Topology IPv6 Support

Single-topology IPv6 support on Cisco IOS XR software allows IS-IS for IPv6 to be configured on interfaces along with an IPv4 network protocol. All interfaces must be configured with the identical set of network protocols, and all routers in the IS-IS area (for Level 1 routing) or the domain (for Level 2 routing) must support the identical set of network layer protocols on all interfaces.

When single-topology support for IPv6 is used, only narrow link metrics, also known as old-style type, length, and value (TLV) arguments, may be employed. During single-topology operation, one shortest path first (SPF) computation for each level is used to compute both IPv4 and IPv6 routes. Using a single SPF is possible because both IPv4 IS-IS and IPv6 IS-IS routing protocols share a common link topology.

Multitopology IPv6 Support

Multitopology IPv6 support on Cisco IOS XR software for IS-IS assumes that multitopology support is required as soon as it detects interfaces configured for both IPv6 and IPv4 within the IS-IS stanza.

Because multitopology is the default behavior in the software, you must explicitly configure IPv6 to use the same topology as IPv4 to enable single-topology IPv6. Configure the single-topology command in IPv6 router address family configuration submode of the IS-IS router stanza.

IS-IS Authentication

Authentication is available to limit the establishment of adjacencies by using the hello-password command, and to limit the exchange of LSPs by using the lsp-password command.

IS-IS supports plain-text authentication, which does not provide security against unauthorized users. Plain-text authentication allows you to configure a password to prevent unauthorized networking devices from forming adjacencies with the router. The password is exchanged as plain text and is potentially visible to an agent able to view the IS-IS packets.

When an HMAC-MD5 password is configured, the password is never sent over the network and is instead used to calculate a cryptographic checksum to ensure the integrity of the exchanged data.

IS-IS stores a configured password using simple encryption. However, the plain-text form of the password is used in LSPs, sequence number protocols (SNPs), and hello packets, which would be visible to a process that can view IS-IS packets. The passwords can be entered in plain text (clear) or encrypted form.

To set the domain password, configure the lsp-password command for Level 2; to set the area password, configure the lsp-password command for Level 1.

The keychain feature allows IS-IS to reference configured keychains. IS-IS key chains enable hello and LSP keychain authentication. Keychains can be configured at the router level (in the case of the lsp-password command) and at the interface level (in the case of the hello-password command) within IS-IS. These commands reference the global keychain configuration and instruct the IS-IS protocol to obtain security parameters from the global set of configured keychains.

IS-IS is able to use the keychain to implement hitless key rollover for authentication. ey rollover specification is time based, and in the event of clock skew between the peers, the rollover process is impacted. The configurable tolerance specification allows for the accept window to be extended (before and after) by that margin. This accept window facilitates a hitless key rollover for applications (for example, routing and management protocols).

See Cisco IOS XR System Security Guide for information on keychain management.

Nonstop Forwarding

On Cisco IOS XR software, NSF minimizes the amount of time a network is unavailable to its users following a route processor (RP) failover. The main objective of NSF is to continue forwarding IP packets and perform a graceful restart following an RP failover.

When a router restarts, all routing peers of that device usually detect that the device went down and then came back up. This transition results in what is called a routing flap, which could spread across multiple routing domains. Routing flaps caused by routing restarts create routing instabilities, which are detrimental to the overall network performance. NSF helps to suppress routing flaps in NSF-aware devices, thus reducing network instability.

NSF allows for the forwarding of data packets to continue along known routes while the routing protocol information is being restored following an RP failover. When the NSF feature is configured, peer networking devices do not experience routing flaps. Data traffic is forwarded through intelligent line cards while the standby RP assumes control from the failed active RP during a failover. The ability of line cards to remain up through a failover and to be kept current with the Forwarding Information Base (FIB) on the active RP is key to NSF operation.

When the Cisco IOS XR router running IS-IS routing performs an RP failover, the router must perform two tasks to resynchronize its link-state database with its IS-IS neighbors. First, it must relearn the available IS-IS neighbors on the network without causing a reset of the neighbor relationship. Second, it must reacquire the contents of the link-state database for the network.

The IS-IS NSF feature offers two options when configuring NSF:

•IETF NSF

•Cisco NSF

If neighbor routers on a network segment are NSF aware, meaning that neighbor routers are running a software version that supports the IETF Internet draft for router restartability, they assist an IETF NSF router that is restarting. With IETF NSF, neighbor routers provide adjacency and link-state information to help rebuild the routing information following a failover.

In Cisco IOS XR software, Cisco NSF checkpoints (stores persistently) all the state necessary to recover from a restart without requiring any special cooperation from neighboring routers. The state is recovered from the neighboring routers, but only using the standard features of the IS-IS routing protocol. This capability makes Cisco NSF suitable for use in networks in which other routers have not used the IETF standard implementation of NSF.

Note If you configure IETF NSF on the Cisco IOS XR router and a neighbor router does not support IETF NSF, the affected adjacencies flap, but nonstop forwarding is maintained to all neighbors that do support IETF NSF. A restart reverts to a cold start if no neighbors support IETF NSF.

Multi-Instance IS-IS

You may configure as many IS-IS instances as system resources (memory and interfaces) allow. Each interface may be associated with only a single IS-IS instance, and MPLS may be enabled for only a single IS-IS instance. Cisco IOS XR software prevents the double-booking of an interface by two instances at configuration time—two instances of MPLS configuration causes an error.

Because the Routing Information Base (RIB) treats each of the IS-IS instances as equal routing clients, you must be careful when redistributing routes between IS-IS instances. The RIB does not know to prefer Level 1 routes over Level 2 routes. For this reason, if you are running Level 1 and Level 2 instances, you must enforce the preference by configuring different administrative distances for the two instances.

Multiprotocol Label Switching Traffic Engineering

The MPLS TE feature enables an MPLS backbone to replicate and expand the traffic engineering capabilities of Layer 2 ATM and Frame Relay networks. MPLS is an integration of Layer 2 and Layer 3 technologies.

For IS-IS, MPLS TE automatically establishes and maintains MPLS TE label-switched paths across the backbone by using Resource Reservation Protocol (RSVP). The route that a label-switched path uses is determined by the label-switched paths resource requirements and network resources, such as bandwidth. Available resources are flooded by using special IS-IS TLV extensions in the IS-IS. The label-switched paths are explicit routes and are referred to as traffic engineering (TE) tunnels.

Overload Bit on Router

The overload bit is a special bit of state information that is included in an LSP of the router. If the bit is set on the router, it notifies routers in the area that the router is not available for transit traffic. This capability is useful in four situations:

1. During a serious but nonfatal error, such as limited memory.

2. During the startup and restart of the process. The overload bit can be set until the routing protocol has converged. However, it is not employed during a normal NSF restart or failover because doing so causes a routing flap.

3. During a trial deployment of a new router. The overload bit can be set until deployment is verified, then cleared.

4. During the shutdown of a router. The overload bit can be set to remove the router from the topology before the router is removed from service.

Default Routes

You can force a default route into an IS-IS routing domain. Whenever you specifically configure redistribution of routes into an IS-IS routing domain, the Cisco IOS XR software does not, by default, redistribute the default route into the IS-IS routing domain. The default-information originate command generates a default route into IS-IS, which can be controlled by a route policy. You can use the route policy to identify the level into which the default route is to be announced, and you can specify other filtering options configurable under a route policy. You can use a route policy to conditionally advertise the default route, depending on the existence of another route in the routing table of the router.

Attached Bit on an IS-IS Instance

The attached bit is set in a router that is configured with the is-type command and level-1-2 keyword. The attached bit indicates that the router is connected to other areas (typically through the backbone). This functionality means that the router can be used by Level 1 routers in the area as the default route to the backbone. The attached bit is usually set automatically as the router discovers other areas while computing its Level 2 SPF route. The bit is automatically cleared when the router becomes detached from the backbone.

Note If the connectivity for the Level 2 instance is lost, the attached bit in the Level 1 instance LSP would continue sending traffic to the Level 2 instance and cause the traffic to be dropped.

To simulate this behavior when using multiple processes to represent the level-1-2 keyword functionality, you would manually configure the attached bit on the Level 1 process.

IS-IS Support for Route Tags

The IS-IS Support for route tags feature provides the capability to associate and advertise a tag with an IS-IS route prefix. Additionally, the feature allows you to prioritize the order of installation of route prefixes in the RIB based on a tag of a route. Route tags may also be used in route policy to match route prefixes (for example, to select certain route prefixes for redistribution).

Multicast-Intact Feature

The multicast-intact feature provides the ability to run multicast routing (PIM) when IGP shortcuts are configured and active on the router. Both OSPFv2 and IS-IS support the multicast-intact feature. MPLS TE and IP multicast coexistence is supported in Cisco IOS XR software by using the mpls traffic-eng multicast-intact IS-IS or OSPF router command.

You can enable multicast-intact in the IGP when multicast routing protocols (PIM) are configured and IGP shortcuts are configured on the router. IGP shortcuts are MPLS tunnels that are exposed to IGP. The IGPs route the IP traffic over these tunnels to destinations that are downstream from the egress router of the tunnel (from an SPF perspective). PIM cannot use IGP shortcuts for propagating PIM joins because reverse path forwarding (RPF) cannot work across a unidirectional tunnel.

When you enable multicast-intact on an IGP, the IGP publishes a parallel or alternate set of equal-cost next-hops for use by PIM. These next-hops are called mcast-intact next-hops. The mcast-intact next-hops have the following attributes:

•They are guaranteed not to contain any IGP shortcuts.

•They are not used for unicast routing but are used only by PIM to look up an IPv4 next-hop to a PIM source.

•They are not published to the FIB.

•When multicast-intact is enabled on an IGP, all IPv4 destinations that were learned through link-state advertisements are published with a set equal-cost mcast-intact next-hops to the RIB. This attribute applies even when the native next-hops have no IGP shortcuts.

•In IS-IS, the max-paths limit is applied by counting both the native and mcast-intact next-hops together. (In OSPFv2, the behavior is slightly different.)

Multicast Topology Support Using IS-IS

Multicast topology support allows for the configuration of IS-IS multicast topologies for IPv4 or IPv6 routing. IS-IS maintains a separate topology for multicast and runs a separate Shortest Path First (SPF) over the multicast topology. IS-IS multicast inserts routes from the IS-IS multicast topology into the multicast-unicast Routing Information Base (muRIB) table in the RIB for the corresponding address family. Since PIM uses the muRIB, PIM uses routes from the multicast topology instead of routes from the unicast topology.

MPLS Label Distribution Protocol IGP Synchronization

Multiprotocol Label Switching (MPLS) Label Distribution Protocol (LDP) Interior Gateway Protocol (IGP) Synchronization ensures that LDP has completed label exchange before the IGP path is used for switching. MPLS traffic loss can occur in the following two situations:

•When an IGP adjacency is established, the router begins forwarding packets using the new adjacency before LDP has exchanged labels with peers on that link.

•When an LDP session closes, the router continues to forward traffic using the link associated with the LDP peer rather than using an alternate path with an established LDP session.

This feature provides a mechanism to synchronize LDP and IS-IS to minimize MPLS packet loss. The synchronization is accomplished by changing the link metric for a neighbor IS-IS link-state packet (LSP), based on the state of the LDP session.

When an IS-IS adjacency is established on a link but the LDP session is lost or LDP has not yet completed exchanging labels, IS-IS advertises the maximum metric on that link. In this instance, LDP IS-IS synchronization is not yet achieved.

Note In IS-IS, a link with a maximum wide metric (0xFFFFFF) is not considered for shortest path first (SPF). Therefore, the maximum wide metric of -1 (0XFFFFFE) is used with MPLS LDP IGP synchronization.

When LDP IS-IS synchronization is achieved, IS-IS advertises a regular (configured or default) metric on that link.

MPLS LDP-IGP Synchronization Compatibility with LDP Graceful Restart

LDP graceful restart protects traffic when an LDP session is lost. If a graceful restart-enabled LDP session fails, MPLS LDP IS-IS synchronization is still achieved on the interface while it is protected by graceful restart. MPLS LDP IGP synchronization is eventually lost under the following circumstances:

•LDP fails to restart before the LDP graceful restart reconnect timer expires.

•The LDP session on the protected interface fails to recover before the LDP graceful restart recovery timer expires.

MPLS LDP-IGP Synchronization Compatibility with IGP Nonstop Forwarding

IS-IS nonstop forwarding (NSF) protects traffic during IS-IS process restarts and route processor (RP) failovers. LDP IS-IS synchronization is supported with IS-IS NSF only if LDP graceful restart is also enabled over the interface. If IS-IS NSF is not enabled, the LDP synchronization state is not retained across restarts and failovers.

Label Distribution Protocol IGP Auto-configuration

Label Distribution Protocol (LDP) Interior Gateway Protocol (IGP) auto-configuration simplifies the procedure to enable LDP on a set of interfaces used by an IGP instance. LDP IGP auto-configuration can be used on a large number interfaces (for example, when LDP is used for transport in the core) and on multiple IGP instances simultaneously.

This feature supports the IPv4 address family for the default VPN routing and forwarding (VRF) instance.

LDP IGP auto-configuration can also be explicitly disabled on individual interfaces under LDP using the igp auto-config disable command. This allows LDP to receive all IGP interfaces except the ones explicitly disabled.

See Cisco IOS XR Multiprotocol Label Switching Configuration Guide for information on configuring LDP IGP auto-configuration.

MPLS TE Forwarding Adjacency

MPLS TE forwarding adjacency allows a network administrator to handle a traffic engineering, label switch path (LSP) tunnel as a link in an Interior Gateway Protocol (IGP) network, based on the Shortest Path First (SPF) algorithm. A forwarding adjacency can be created between routers in the same IS-IS level. The routers can be located multiple hops from each other. As a result, a TE tunnel is advertised as a link in an IGP network, with the cost of the link associated with it. Routers outside of the TE domain see the TE tunnel and use it to compute the shortest path for routing traffic throughout the network.

MPLS TE forwarding adjacency is considered in IS-IS SPF only if a two-way connectivity check is achieved. This is possible if the forwarding adjacency is bidirectional or the head end and tail end routers of the MPLS TE tunnel are adjacent.

The MPLS TE forwarding adjacency feature is supported by IS-IS. For details on configuring MPLS TE forwarding adjacency, see Cisco IOS XR Multiprotocol Label Switching Configuration Guide.

MPLS TE Interarea Tunnels

MPLS TE interarea tunnels allow you to establish MPLS TE tunnels that span multiple IGP areas (Open Shorted Path First [OSPF]) and levels (IS-IS), removing the restriction that required that both the tunnel headend and tailend routers be in the same area. The IGP can be either IS-IS or OSPF. See the "Configuring MPLS Traffic Engineering for IS-IS" section for information on configuring MPLS TE for IS-IS.

For details on configuring MPLS TE interarea tunnels, see Cisco IOS XR Multiprotocol Label Switching Configuration Guide.

IP Fast Reroute

The IP Fast Reroute (IPFRR) loop-free alternate (LFA) computation provides protection against link failure. Locally computed repair paths are used to prevent packet loss caused by loops that occur during network reconvergence after a failure. See IETF draft-ietf-rtgwg-ipfrr-framework-06.txt and draft-ietf-rtgwg-lf-conv-frmwk-00.txt for detailed information on IPFRR LFA.

Note IPFRR is supported on the Cisco CRS-1 router.

IPFRR LFA is different from Multiprotocol Label Switching (MPLS) as it is applicable to networks using conventional IP routing and forwarding. See Multiprotocol Label Switching Configuration Guide for information on configuring MPLS IPFRR.

How to Implement IS-IS on Cisco IOS XR Software

This section contains the following procedures:

•Enabling IS-IS and Configuring Level 1 or Level 2 Routing (required)

•Configuring Single Topology for IS-IS (optional)

•Configuring Multitopology for IS-IS (optional)

•Controlling LSP Flooding for IS-IS (optional)

•Configuring Nonstop Forwarding for IS-IS (optional)

•Configuring Authentication for IS-IS (optional)

•Configuring Keychains for IS-IS (optional)

•Configuring MPLS Traffic Engineering for IS-IS (optional)

•Tuning Adjacencies for IS-IS (optional)

•Setting SPF Interval for a Single-Topology IPv4 and IPv6 Configuration (optional)

•Customizing Routes for IS-IS (optional)

•Configuring MPLS LDP IS-IS Synchronization (optional)

•Enabling Multicast-Intact (optional)

•Tagging IS-IS Interface Routes (optional)

•Setting the Priority for Adding Prefixes to the RIB (optional)

•Configuring IP Fast Reroute Loop-free Alternate (optional)

Note To save configuration changes, you must commit changes when the system prompts you.

Enabling IS-IS and Configuring Level 1 or Level 2 Routing

This task explains how to enable IS-IS and configure the routing level for an area.

Note Configuring the routing level in Step 4 is optional, but is highly recommended to establish the proper level of adjacencies.

Prerequisites

Although you can configure IS-IS before you configure an IP address, no IS-IS routing occurs until at least one IP address is configured.

SUMMARY STEPS

1. configure

2. router isis instance-id

3. net network-entity-title

4. is-type {level-1 | level-1-2 | level-2-only}

5. end
or
commit

6. show isis [instance instance-id] protocol

DETAILED STEPS
Command or Action

Purpose

Step 1

configure
Example:

RP/0/RP0/CPU0:router# configure

Enters global configuration mode.

Step 2

router isis instance-id
Example:

RP/0/RP0/CPU0:router(config)# router isis isp

Enables IS-IS routing for the specified routing instance, and places the router in router configuration mode.

•By default, all IS-IS instances are automatically Level 1 and Level 2. You can change the level of routing to be performed by a particular routing instance by using the is-type router configuration command.

Step 3

net network-entity-title
Example:

RP/0/RP0/CPU0:router(config-isis)# net 47.0004.004d.0001.0001.0c11.1110.00

Configures network entity titles (NETs) for the routing instance.

•Specify a NET for each routing instance if you are configuring multi-instance IS-IS.

•This example configures a router with area ID 47.0004.004d.0001 and system ID 0001.0c11.1110.00.

•To specify more than one area address, specify additional NETs. Although the area address portion of the NET differs, the systemID portion of the NET must match exactly for all of the configured items.

Step 4

is-type {level-1 | level-1-2 | level-2-only}
Example:

RP/0/RP0/CPU0:router(config-isis)# is-type level-2-only

(Optional) Configures the system type (area or backbone router).

•By default, every IS-IS instance acts as a level-1-2 router.

•The level-1 keyword configures the software to perform Level 1 (intra-area) routing only. Only Level 1 adjacencies are established. The software learns about destinations inside its area only. Any packets containing destinations outside the area are sent to the nearest level-1-2 router in the area.

•The level-2-only keyword configures the software to perform Level 2 (backbone) routing only, and the router establishes only Level 2 adjacencies, either with other Level 2-only routers or with level-1-2 routers.

•The level-1-2 keyword configures the software to perform both Level 1 and Level 2 routing. Both Level 1 and Level 2 adjacencies are established. The router acts as a border router between the Level 2 backbone and its Level 1 area.
Step 5

end
or

commit
Example:

RP/0/RP0/CPU0:router(config-isis)# end
or

RP/0/RP0/CPU0:router(config-isis)# commit
Saves configuration changes.

•When you issue the end command, the system prompts you to commit changes:
Uncommitted changes found, commit them before 
exiting(yes/no/cancel)? 
[cancel]:
–Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

–Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

–Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

•Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.
Step 6

show isis [instance instance-id] protocol
Example:

RP/0/RP0/CPU0:router# show isis protocol

(Optional) Displays summary information about the IS-IS instance.
Configuring Single Topology for IS-IS

After an IS-IS instance is enabled, it must be configured to compute routes for a specific network topology.

This task explains how to configure the operation of the IS-IS protocol on an interface for an IPv4 or IPv6 topology.

Restrictions

To enable the router to run in single-topology mode, configure each of the IS-IS interfaces with all of the address families enabled and "single-topology" in the address-family IPv6 unicast in the IS-IS router stanza. You can use either the IPv6 address family or both IPv4 and IPv6 address families, but your configuration must represent the set of all active address families on the router. Additionally, explicitly enable single-topology operation by configuring it in the IPv6 router address family submode.

Two exceptions to these instructions exist:

1. If the address-family stanza in the IS-IS process contains the adjacency-check disable command, then an interface is not required to have the address family enabled.

2. The single-topology command is not valid in the ipv4 address-family submode.

The default metric style for single topology is narrow metrics. However, you can use either wide metrics or narrow metrics. How to configure them depends on how single topology is configured. If both IPv4 and IPv6 are enabled and single topology is configured, the metric style is configured in the address-family ipv4 stanza. You may configure the metric style in the address-family ipv6 stanza, but it is ignored in this case. If only IPv6 is enabled and single topology is configured, then the metric style is configured in the address-family ipv6 stanza.

SUMMARY STEPS

1. configure

2. interface type number

3. ipv4 address address mask
or
ipv6 address ipv6-prefix/prefix-length [eui-64]
or
ipv6 address ipv6-address {/prefix-length | link-local}
or
ipv6 enable

4. exit

5. router isis instance-id

6. net network-entity-title

7. address-family ipv6 [unicast]

8. single-topology

9. exit

10. interface type instance

11. circuit-type {level-1 | level-1-2 | level-2-only}

12. address-family {ipv4 | ipv6} [unicast | multicast]

13. end
or
commit

14. show isis [instance instance-id] interface [type instance] [detail] [level {1 | 2}]

15. show isis [instance instance-id] topology [systemid system-id] [level {1 | 2}] [summary]

DETAILED STEPS
Command or Action

Purpose

Step 1

configure
Example:

RP/0/RP0/CPU0:router# configure

Enters global configuration mode.

Step 2

interface type number
Example:

RP/0/RP0/CPU0:router(config)# interface POS 0/1/0/3

Enters interface configuration mode.
Step 3
ipv4 address address mask
or

ipv6 address ipv6-prefix/prefix-length [eui-64]
or

ipv6 address ipv6-address {/prefix-length | link-local}
or

ipv6 enable
Example:

RP/0/RP0/CPU0:router(config-if)# ipv4 address 10.0.1.3 255.255.255.0
or
RP/0/RP0/CPU0:router(config-if)# ipv6 address 
3ffe:1234:c18:1::/64 eui-64
or

RP/0/RP0/CPU0:router(config-if)# ipv6 address FE80::260:3EFF:FE11:6770 link-local
or

RP/0/RP0/CPU0:router(config-if)# ipv6 enable
Defines the IPv4 address for the interface. An IP address is required on all interfaces in an area enabled for IS-IS if any one interface is configured for IS-IS routing.

or

Specifies an IPv6 network assigned to the interface and enables IPv6 processing on the interface with the eui-64 keyword.

or

Specifies an IPv6 address assigned to the interface and enables IPv6 processing on the interface with the link-local keyword.

or

Automatically configures an IPv6 link-local address on the interface while also enabling the interface for IPv6 processing.

•The link-local address can be used only to communicate with nodes on the same link.

•Specifying the ipv6 address ipv6-prefix/prefix-length interface configuration command without the eui-64 keyword configures site-local and global IPv6 addresses.

•Specifying the ipv6 address ipv6-prefix/prefix-length command with the eui-64 keyword configures site-local and global IPv6 addresses with an interface ID in the low-order 64 bits of the IPv6 address. Only the 64-bit network prefix for the address needs to be specified; the last 64 bits are automatically computed from the interface ID.

•Specifying the ipv6 address command with the link-local keyword configures a link-local address on the interface that is used instead of the link-local address that is automatically configured when IPv6 is enabled on the interface.
Step 4

exit
Example:

RP/0/RP0/CPU0:router(config-if)# exit

Exits interface configuration mode, and returns the router to global configuration mode.

Step 5

router isis instance-id
Example:

RP/0/RP0/CPU0:router(config)# router isis isp

Enables IS-IS routing for the specified routing instance, and places the router in router configuration mode.

•By default, all IS-IS instances are Level 1 and Level 2. You can change the level of routing to be performed by a particular routing instance by using the is-type command.

Step 6

net network-entity-title
Example:

RP/0/RP0/CPU0:router(config-isis)# net 47.0004.004d.0001.0001.0c11.1110.00

Configures NETs for the routing instance.

•Specify a NET for each routing instance if you are configuring multi-instance IS-IS. You can specify a name for a NET and for an address.

•This example configures a router with area ID 47.0004.004d.0001 and system ID 0001.0c11.1110.00.

•To specify more than one area address, specify additional NETs. Although the area address portion of the NET differs, the system ID portion of the NET must match exactly for all of the configured items.

Step 7

address-family ipv6 [unicast]
Example:

RP/0/RP0/CPU0:router(config-isis)# address-family ipv6 unicast

Specifies the IPv6 address family and enters router address family configuration mode.

•This example specifies the unicast IPv6 address family.

Step 8

single-topology
Example:

RP0/0/RP0/CPU0:router(config-isis-af)# single-topology

(Optional) Configures the link topology for IPv4 when IPv6 is configured.

•The single-topology command is valid only in IPv6 submode. The command instructs IPv6 to use the single topology rather than the default configuration of a separate topology in the multitopology mode.

•See the "Single-Topology IPv6 Support" section for more information.

Step 9

exit
Example:

RP/0/RP0/CPU0:router(config-isis-af)# exit

Exits router address family configuration mode, and returns the router to router configuration mode.

Step 10

interface type instance
Example:

RP/0/RP0/CPU0:router(config-isis)# interface POS 0/1/0/3

Enters interface configuration mode.

Step 11

circuit-type {level-1 | level-1-2 | level-2-only}
Example:

RP/0/RP0/CPU0:router(config-isis-if)# circuit-type level-1-2

(Optional) Configures the type of adjacency.

•The default circuit type is the configured system type (configured through the is-type command).

•Typically, the circuit type must be configured when the router is configured as only level-1-2 and you want to constrain an interface to form only level-1 or level-2-only adjacencies.

Step 12

address-family {ipv4 | ipv6} [unicast | multicast]
Example:

RP/0/RP0/CPU0:router(config-isis-if)# address-family ipv6 unicast

Specifies the IPv4 or IPv6 address family, and enters interface address family configuration mode.

•This example specifies the unicast IPv6 address family on the interface.
Step 13

end
or

commit
Example:

RP/0/RP0/CPU0:router(config-isis-if-af)# end
or

RP/0/RP0/CPU0:router(config-isis-if-af)# commit
Saves configuration changes.

•When you issue the end command, the system prompts you to commit changes:
Uncommitted changes found, commit them before 
exiting(yes/no/cancel)? 
[cancel]:
–Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

–Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

–Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

•Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.
Step 14

show isis [instance instance-id] interface [type instance] [detail] [level {1 | 2}]
Example:

RP/0/RP0/CPU0:router# show isis interface POS0/1/0/1

(Optional) Displays information about the IS-IS interface.

Step 15

show isis [instance instance-id] topology [systemid system-id] [level {1 | 2}] [summary]
Example:

RP/0/RP0/CPU0:router# show isis topology

(Optional) Displays a list of connected routers in all areas.
Configuring Multitopology for IS-IS

Multitopology is configured in the same way as the single topology for IPv4 and IPv6 address families. However, the single- topology command is omitted, invoking the default multitopology behavior. This task is optional.

Controlling LSP Flooding for IS-IS

Flooding of LSPs can limit network scalability. You can control LSP flooding by tuning your LSP database parameters on the router globally or on the interface. This task is optional.

Many of the commands to control LSP flooding contain an option to specify the level to which they apply. Without the option, the command applies to both levels. If an option is configured for one level, the other level continues to use the default value. To configure options for both levels, use the command twice. For example:
RP/0/RP0/CPU0:router(config-isis)# lsp-refresh-interval 1200 level 2
RP/0/RP0/CPU0:router(config-isis)# lsp-refresh-interval 1100 level 1
SUMMARY STEPS

1. configure

2. router isis instance-id

3. lsp-refresh-interval seconds [level {1 | 2}]

4. lsp-check-interval seconds [level {1 | 2}]

5. lsp-gen-interval {[initial-wait initial | secondary-wait secondary | maximum-wait maximum] ...}[level {1 | 2}]

6. lsp-mtu bytes [level {1 | 2}]

7. max-lsp-lifetime seconds [level {1 | 2}]

8. ignore-lsp-errors disable

9. interface type instance

10. lsp-interval milliseconds [level {1 | 2}]

11. csnp-interval seconds [level {1 | 2}]

12. retransmit-interval seconds [level {1 | 2}]

13. retransmit-throttle-interval milliseconds [level {1 | 2}]

14. mesh-group {number | blocked}

15. end
or
commit

16. show isis interface [type instance | level {1 | 2}] [brief]

17. show isis [instance instance-id] database [level {1 | 2}] [detail | summary | verbose] [* | lsp-id]

18. show isis [instance instance-id] lsp-log [level {1 | 2}]

19. show isis database-log [level {1 | 2}]

DETAILED STEPS
Command or Action

Purpose

Step 1

configure
Example:

RP/0/RP0/CPU0:router# configure

Enters global configuration mode.

Step 2

router isis instance-id
Example:

RP/0/RP0/CPU0:router(config)# router isis isp

Enables IS-IS routing for the specified routing instance, and places the router in router configuration mode.

•You can change the level of routing to be performed by a particular routing instance by using the is-type router configuration command.

Step 3

lsp-refresh-interval seconds [level {1 | 2}]
Example:

RP/0/RP0/CPU0:router(config-isis)# lsp-refresh-interval 10800

(Optional) Sets the time between regeneration of LSPs that contain different sequence numbers

•The refresh interval should always be set lower than the max-lsp-lifetime command.

Step 4

lsp-check-interval seconds [level {1 | 2}]
Example:

RP/0/RP0/CPU0:router(config-isis)# lsp-check-interval 240

(Optional) Configures the time between periodic checks of the entire database to validate the checksums of the LSPs in the database.

•This operation is costly in terms of CPU and so should be configured to occur infrequently.

Step 5

lsp-gen-interval {[initial-wait initial | secondary-wait secondary | maximum-wait maximum] ...} [level {1 | 2}]
Example:

RP/0/RP0/CPU0:router(config-isis)# lsp-gen-interval maximum-wait 15 initial-wait 5

(Optional) Reduces the rate of LSP generation during periods of instability in the network. Helps reduce the CPU load on the router and number of LSP transmissions to its IS-IS neighbors.

•During prolonged periods of network instability, repeated recalculation of LSPs can cause an increased CPU load on the local router. Further, the flooding of these recalculated LSPs to the other Intermediate Systems in the network causes increased traffic and can result in other routers having to spend more time running route calculations.

Step 6

lsp-mtu bytes [level {1 | 2}]
Example:

RP/0/RP0/CPU0:router(config-isis)# lsp-mtu 1300

(Optional) Sets the maximum transmission unit (MTU) size of LSPs.

Step 7

max-lsp-lifetime seconds [level {1 | 2}]
Example:

RP/0/RP0/CPU0:router(config-isis)# max-lsp-lifetime 11000

(Optional) Sets the initial lifetime given to an LSP originated by the router.

•This is the amount of time that the LSP persists in the database of a neighbor unless the LSP is regenerated or refreshed.

Step 8

ignore-lsp-errors disable
Example:

RP/0/RP0/CPU0:router(config-isis)# ignore-lsp-errors disable

(Optional) Sets the router to purge LSPs received with checksum errors.

Step 9

interface type instance
Example:

RP/0/RP0/CPU0:router(config-isis)# interface POS 0/1/0/3

Enters interface configuration mode.

Step 10

lsp-interval milliseconds [level {1 | 2}]
Example:

RP/0/RP0/CPU0:router(config-isis-if)# lsp-interval 100

(Optional) Configures the amount of time between each LSP sent on an interface.

Step 11

csnp-interval seconds [level {1 | 2}]
Example:

RP/0/RP0/CPU0:router(config-isis-if)# csnp-interval 30 level 1

(Optional) Configures the interval at which periodic CSNP packets are sent on broadcast interfaces.

•Sending more frequent CSNPs means that adjacent routers must work harder to receive them.

•Sending less frequent CSNP means that differences in the adjacent routers may persist longer.

Step 12

retransmit-interval seconds [level {1 | 2}]
Example:

RP/0/RP0/CPU0:router(config-isis-if)# retransmit-interval 60

(Optional) Configures the amount of time that the sending router waits for an acknowledgment before it considers that the LSP was not received and subsequently resends.

Step 13

retransmit-throttle-interval milliseconds [level {1 | 2}]
Example:

RP/0/RP0/CPU0:router(config-isis-if)# retransmit-throttle-interval 1000

(Optional) Configures the amount of time between retransmissions on each LSP on a point-to-point interface.

•This time is usually greater than or equal to the lsp-interval command time because the reason for lost LSPs may be that a neighboring router is busy. A longer interval gives the neighbor more time to receive transmissions.

Step 14

mesh-group {number | blocked}
Example:

RP/0/RP0/CPU0:router(config-isis-if)# mesh-group blocked

(Optional) Optimizes LSP flooding in NBMA networks with highly meshed, point-to-point topologies.

•This command is appropriate only for an NBMA network with highly meshed, point-to-point topologies.
Step 15

end
or

commit
Example:

RP/0/RP0/CPU0:router(config-isis-if)# end
or

RP/0/RP0/CPU0:router(config-isis-if)# commit
Saves configuration changes.

•When you issue the end command, the system prompts you to commit changes:
Uncommitted changes found, commit them before 
exiting(yes/no/cancel)? 
[cancel]:
–Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

–Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

–Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

•Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.
Step 16

show isis interface [type instance | level {1 | 2}] [brief]
Example:

RP/0/RP0/CPU0:router# show isis interface POS0/1/0/1 brief

(Optional) Displays information about the IS-IS interface.

Step 17

show isis [instance instance-id] database [level {1 | 2}] [detail | summary | verbose] [* | lsp-id]
Example:

RP/0/RP0/CPU0:router# show isis database level 1

(Optional) Displays the IS-IS LSP database.

Step 18

show isis [instance instance-id] lsp-log [level {1 | 2}]
Example:

RP/0/RP0/CPU0:router# show isis lsp-log

(Optional) Displays LSP log information.

Step 19

show isis database-log [level {1 | 2}]
Example:

RP/0/RP0/CPU0:router# show isis database-log level 1

(Optional) Display IS-IS database log information.
Configuring Nonstop Forwarding for IS-IS

This task explains how to configure your router with NSF that allows the Cisco IOS XR software to resynchronize the IS-IS link-state database with its IS-IS neighbors after a process restart. The process restart could be due to an:

•RP failover (for a warm restart)

•Simple process restart (due to an IS-IS reload or other administrative request to restart the process)

•IS-IS software upgrade

In all cases, NSF mitigates link flaps and loss of user sessions. This task is optional.

SUMMARY STEPS

1. configure

2. router isis instance-id

3. nsf {cisco | ietf}

4. nsf interface-expires number

5. nsf interface-timer seconds

6. nsf lifetime seconds

7. end
or
commit

8. show running-config [command]

DETAILED STEPS
Command or Action

Purpose

Step 1

configure
Example:

RP/0/RP0/CPU0:router# configure

Enters global configuration mode.

Step 2

router isis instance-id
Example:

RP/0/RP0/CPU0:router(config)# router isis isp

Enables IS-IS routing for the specified routing instance, and places the router in router configuration mode.

•You can change the level of routing to be performed by a particular routing instance by using the is-type router configuration command.

Step 3

nsf {cisco | ietf}
Example:

RP/0/RP0/CPU0:router(config-isis)# nsf ietf

Enables NSF on the next restart.

•Enter the cisco keyword to run IS-IS in heterogeneous networks that might not have adjacent NSF-aware networking devices.

•Enter the ietf keyword to enable IS-IS in homogeneous networks where all adjacent networking devices support IETF draft-based restartability.

Step 4

nsf interface-expires number
Example:

RP/0/RP0/CPU0:router(config-isis)# nsf interface-expires 1

Configures the number of resends of an acknowledged NSF-restart acknowledgment.

•If the resend limit is reached during the NSF restart, the restart falls back to a cold restart.

Step 5

nsf interface-timer seconds
Example:

RP/0/RP0/CPU0:router(config-isis) nsf interface-timer 15

Configures the number of seconds to wait for each restart acknowledgment.

Step 6

nsf lifetime seconds
Example:

RP/0/RP0/CPU0:router(config-isis)# nsf lifetime 20

Configures the maximum route lifetime following an NSF restart.

•This command should be configured to the length of time required to perform a full NSF restart because it is the amount of time that the Routing Information Base (RIB) retains the routes during the restart.

•Setting this value too high results in stale routes.

•Setting this value too low could result in routes purged too soon.
Step 7

end
or

commit
Example:

RP/0/RP0/CPU0:router(config-isis)# end
or

RP/0/RP0/CPU0:router(config-isis)# commit
Saves configuration changes.

•When you issue the end command, the system prompts you to commit changes:
Uncommitted changes found, commit them before 
exiting(yes/no/cancel)? 
[cancel]:
–Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

–Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

–Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

•Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.
Step 8
show running-config [command]
Example:

RP/0/RP0/CPU0:router# show running-config router isis isp
(Optional) Displays the entire contents of the currently running configuration file or a subset of that file.

•Verify that "nsf" appears in the IS-IS configuration of the NSF-aware device.

•This example shows the contents of the configuration file for the "isp" instance only.
Configuring Authentication for IS-IS

This task explains how to configure authentication for IS-IS. This task is optional.

SUMMARY STEPS

1. configure

2. router isis instance-id

3. lsp-password {hmac-md5 | text} {clear | encrypted} password [level {1 | 2}] [send-only] [snp send-only]

4. interface type instance

5. hello-password {hmac-md5 | text} {clear | encrypted} password [level {1 | 2}] [send-only]

6. end
or
commit

DETAILED STEPS
Command or Action

Purpose

Step 1

configure
Example:

RP/0/RP0/CPU0:router# configure

Enters global configuration mode.

Step 2

router isis instance-id
Example:

RP/0/RP0/CPU0:router(config)# router isis isp

Enables IS-IS routing for the specified routing instance, and places the router in router configuration mode.

•You can change the level of routing to be performed by a particular routing instance by using the is-type command.

Step 3

lsp-password {hmac-md5 | text} {clear | encrypted} password [level {1 | 2}] [send-only] [snp send-only]
Example:

RP/0/RP0/CPU0:router(config-isis)# lsp-password hmac-md5 clear password1 level 1

Configures the LSP authentication password.

•The hmac-md5 keyword specifies that the password is used in HMAC-MD5 authentication.

•The text keyword specifies that the password uses cleartext password authentication.

•The clear keyword specifies that the password is unencrypted when entered.

•The encrypted keyword specifies that the password is encrypted using a two-way algorithm when entered.

•The level 1 keyword sets a password for authentication in the area (in Level 1 LSPs and Level SNPs).

•The level 2 keywords set a password for authentication in the backbone (the Level 2 area).

•The send-only keyword adds authentication to LSP and sequence number protocol data units (SNPs) when they are sent. It does not authenticate received LSPs or SNPs.

•The snp send-only keyword adds authentication to SNPs when they are sent. It does not authenticate received SNPs.

Note To disable SNP password checking, the snp send-only keywords must be specified in the lsp-password command.

Step 4

interface type instance
Example:

RP/0/RP0/CPU0:router(config-isis)# interface POS 0/1/0/3

Enters interface configuration mode.

Step 5

hello-password {hmac-md5 | text} {clear | encrypted} password [level {1 | 2}] [send-only]
Example:

RP/0/RP0/CPU0:router(config-isis-if)#
hello-password text clear mypassword

Configures the authentication password for an IS-IS interface.
Step 6

end
or

commit
Example:

RP/0/RP0/CPU0:router(config-isis-if)# end
or

RP/0/RP0/CPU0:router(config-isis-if)# commit
Saves configuration changes.

•When you issue the end command, the system prompts you to commit changes:
Uncommitted changes found, commit them before 
exiting(yes/no/cancel)? 
[cancel]:
–Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

–Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

–Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

•Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.
Configuring Keychains for IS-IS

This task explains how to configure keychains for IS-IS. This task is optional.

Keychains can be configured at the router level (lsp-password command) and at the interface level (hello-password command) within IS-IS. These commands reference the global keychain configuration and instruct the IS-IS protocol to obtain security parameters from the global set of configured keychains. The router-level configuration (lsp-password command) sets the keychain to be used for all IS-IS LSPs generated by this router, as well as for all Sequence Number Protocol Data Units (SN PDUs). The keychain used for HELLO PDUs is set at the interface level, and may be set differently for each interface configured for IS-IS.

SUMMARY STEPS

1. configure

2. router isis instance-id

3. lsp-password keychain keychain-name [level {1 | 2}] [send-only] [snp send-only]

4. interface type instance

5. hello-password keychain keychain-name [level {1 | 2}] [send-only]

6. end
or
commit

DETAILED STEPS
Command or Action

Purpose

Step 1

configure
Example:

RP/0/RP0/CPU0:router# configure

Enters global configuration mode.

Step 2

router isis instance-id
Example:

RP/0/RP0/CPU0:router(config)# router isis isp

Enables IS-IS routing for the specified routing instance, and places the router in router configuration mode.

•You can change the level of routing to be performed by a particular routing instance by using the is-type command.

Step 3

lsp-password keychain keychain-name [level {1 | 2}] [send-only] [snp send-only]
Example:

RP/0/RP0/CPU0:router(config-isis)# lsp-password keychain isis_a level 1

Configures the keychain.

Step 4

interface type instance
Example:

RP/0/RP0/CPU0:router(config-isis)# interface POS 0/1/0/3

Enters interface configuration mode.

Step 5

hello-password keychain keychain-name [level {1 | 2}] [send-only]
Example:

RP/0/RP0/CPU0:router(config-isis-if)#
hello-password keychain isis_b

Configures the authentication password for an IS-IS interface.
Step 6

end
or

commit
Example:

RP/0/RP0/CPU0:router(config-isis-if)# end
or

RP/0/RP0/CPU0:router(config-isis-if)# commit
Saves configuration changes.

•When you issue the end command, the system prompts you to commit changes:
Uncommitted changes found, commit them before 
exiting(yes/no/cancel)? 
[cancel]:
–Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

–Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

–Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

•Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.
Configuring MPLS Traffic Engineering for IS-IS

This task explains how to configure IS-IS for MPLS TE. This task is optional.

For a description of the MPLS TE tasks and commands that allow you to configure the router to support tunnels, configure an MPLS tunnel that IS-IS can use, and troubleshoot MPLS TE, see Implementing MPLS Traffic Engineering on Cisco IOS XR Software.

Prerequisite

Your network must support the MPLS Cisco IOS XR software feature before you enable MPLS TE for IS-IS on your router.

Note You must enter the commands in the following task list on every IS-IS router in the traffic-engineered portion of your network.

Restrictions

MPLS traffic engineering currently does not support routing and signaling of LSPs over unnumbered IP links. Therefore, do not configure the feature over those links.

SUMMARY STEPS

1. configure

2. router isis instance-id

3. address-family {ipv4 | ipv6} [unicast | multicast]

4. mpls traffic-eng level {1 | 2}

5. mpls traffic-eng router-id {ip-address | interface-name interface-instance}

6. metric-style wide [level {1 | 2}]

7. end
or
commit

8. show isis [instance instance-id] mpls traffic-eng tunnel

9. show isis [instance instance-id] mpls traffic-eng adjacency-log

10. show isis [instance instance-id] mpls traffic-eng advertisements

DETAILED STEPS
Command or Action

Purpose

Step 1

configure
Example:

RP/0/RP0/CPU0:router# configure

Enters global configuration mode.

Step 2

router isis instance-id
Example:

RP/0/RP0/CPU0:router(config)# router isis isp

Enables IS-IS routing for the specified routing instance, and places the router in router configuration mode.

•You can change the level of routing to be performed by a particular routing instance by using the is-type router configuration command.

Step 3

address-family {ipv4 | ipv6} [unicast | multicast]
Example:

RP/0/RP0/CPU0:router(config-isis)#
address-family ipv6 unicast

Specifies the IPv4 or IPv6 address family, and enters router address family configuration mode.

•This example specifies the unicast IPv6 address family.

Step 4

mpls traffic-eng level {1 | 2}
Example:

RP/0/RP0/CPU0:router(config-isis-af)# mpls traffic-eng level 1

Configures a router running IS-IS to flood MPLS TE link information into the indicated IS-IS level.

Step 5

mpls traffic-eng router-id {ip-address | interface-name interface-instance}
Example:

RP/0/RP0/CPU0:router(config-isis-af)# mpls traffic-eng router-id loopback0

Specifies that the MPLS TE router identifier for the node is the given IP address or an IP address associated with the given interface.

Step 6

metric-style wide [level {1 | 2}]
Example:

RP/0/RP0/CPU0:router(config-isis-af)# metric-style wide level 1

Configures a router to generate and accept only wide link metrics in the Level 1 area.
Step 7

end
or

commit
Example:

RP/0/RP0/CPU0:router(config-isis-af)# end
or

RP/0/RP0/CPU0:router(config-isis-af)# commit
Saves configuration changes.

•When you issue the end command, the system prompts you to commit changes:
Uncommitted changes found, commit them before 
exiting(yes/no/cancel)? 
[cancel]:
–Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

–Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

–Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

•Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.
Step 8

show isis [instance instance-id] mpls traffic-eng tunnel
Example:

RP/0/RP0/CPU0:router# show isis instance isp mpls traffic-eng tunnel

(Optional) Displays MPLS TE tunnel information.

Step 9

show isis [instance instance-id] mpls traffic-eng adjacency-log
Example:

RP/0/RP0/CPU0:router# show isis instance isp mpls traffic-eng adjacency-log

(Optional) Displays a log of MPLS TE IS-IS adjacency changes.

Step 10

show isis [instance instance-id] mpls traffic-eng advertisements
Example:

RP/0/RP0/CPU0:router# show isis instance isp mpls traffic-eng advertisements

(Optional) Displays the latest flooded record from MPLS TE.
Tuning Adjacencies for IS-IS

This task explains how to enable logging of adjacency state changes, alter the timers for IS-IS adjacency packets, and display various aspects of adjacency state. Tuning your IS-IS adjacencies increases network stability when links are congested. This task is optional.

For point-to-point links, IS-IS sends only a single hello for Level 1 and Level 2, which means that the level modifiers are meaningless on point-to-point links. To modify hello parameters for a point-to-point interface, omit the specification of the level options.

The options configurable in the interface submode apply only to that interface. By default, the values are applied to both Level 1 and Level 2.

The hello-password command can be used to prevent adjacency formation with unauthorized or undesired routers. This ability is particularly useful on a LAN, where connections to routers with which you have no desire to establish adjacencies are commonly found.

SUMMARY STEPS

1. configure

2. router isis instance-id

3. log adjacency changes

4. interface type number

5. hello-padding {disable | sometimes} [level {1 | 2}]

6. hello-interval seconds [level {1 | 2}]

7. hello-multiplier multiplier [level {1 | 2}]

8. hello-password {hmac-md5 | text} {clear | encrypted} password [level {1 | 2}] [send-only]

9. end
or
commit

10. show isis [instance instance-id] adjacency [interface-type interface-instance] [detail] [systemid system-id]

11. show isis adjacency-log

12. show isis [instance instance-id] interface [type instance] [brief | detail] [level {1 | 2}]

13. show isis [instance instance-id] neighbors [interface-type interface-instance] [summary] [detail] [systemid system-id]

DETAILED STEPS
Command or Action

Purpose

Step 1

configure
Example:

RP/0/RP0/CPU0:router# configure

Enters global configuration mode.

Step 2

router isis instance-id
Example:

RP/0/RP0/CPU0:router(config)# router isis isp

Enables IS-IS routing for the specified routing instance, and places the router in router configuration mode.

•You can change the level of routing to be performed by a particular routing instance by using the is-type command.

Step 3

log adjacency changes
Example:

RP/0/RP0/CPU0:router(config-isis)# log adjacency changes

Generates a log message when an IS-IS adjacency changes state (up or down).

Step 4

interface type number
Example:

RP/0/RP0/CPU0:router(config-isis)# interface POS 0/1/0/3

Enters interface configuration mode.

Step 5

hello-padding {disable | sometimes} [level {1 | 2}]
Example:

RP/0/RP0/CPU0:router(config-isis-if)# hello-paddi ng sometimes

Configures padding on IS-IS hello PDUs for an IS-IS interface on the router.

•Hello padding applies to only this interface and not to all interfaces.

Step 6

hello-interval seconds [level {1 | 2}]
Example:

RP/0/RP0/CPU0:router(config-isis-if)#
hello-interval 6

Specifies the length of time between hello packets that the software sends.

Step 7

hello-multiplier multiplier [level {1 | 2}]
Example:

RP/0/RP0/CPU0:router(config-isis-if)# hello-multiplier 10

Specifies the number of IS-IS hello packets a neighbor must miss before the router should declare the adjacency as down.

•A higher value increases the networks tolerance for dropped packets, but also may increase the amount of time required to detect the failure of an adjacent router.

•Conversely, not detecting the failure of an adjacent router can result in greater packet loss.

Step 8

hello-password {hmac-md5 | text} {clear | encrypted} password [level {1 | 2}] [send-only]
Example:

RP/0/RP0/CPU1:router(config-isis-if)#
hello-password text clear mypassword

Specifies that this system include authentication in the hello packets and requires successful authentication of the hello packet from the neighbor to establish an adjacency.
Step 9

end
or

commit
Example:

RP/0/RP0/CPU0:router(config-isis-if)# end
or

RP/0/RP0/CPU0:router(config-isis-if)# commit
Saves configuration changes.

•When you issue the end command, the system prompts you to commit changes:
Uncommitted changes found, commit them before 
exiting(yes/no/cancel)? 
[cancel]:
–Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

–Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

–Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

•Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.
Step 10

show isis [instance instance-id] adjacency [interface-type interface-instance] [detail] [systemid system-id]
Example:

RP/0/RP0/CPU0:router# show isis instance isp adjacency ipv4

(Optional) Displays IS-IS adjacencies.

Step 11

show isis adjacency-log
Example:

RP/0/RP0/CPU1:router# show isis adjacency-log

(Optional) Displays a log of the most recent adjacency state transitions.

Step 12

show isis [instance instance-id] interface [type instance] [brief | detail] [level {1 | 2}]
Example:

RP/0/RP0/CPU0:router# show isis interface POS 0/1/0/1 brief

(Optional) Displays information about the IS-IS interface.

Step 13

show isis [instance instance-id] neighbors [interface-type interface-instance] [summary] [detail] [systemid system-id]
Example:

RP/0/RP0/CPU0:router# show isis neighbors summary

(Optional) Displays information about IS-IS neighbors.
Setting SPF Interval for a Single-Topology IPv4 and IPv6 Configuration

This task explains how to make adjustments to the SPF calculation to tune router performance. This task is optional.

Because the SPF calculation computes routes for a particular topology, the tuning attributes are located in the router address family configuration submode. SPF calculation computes routes for Level 1 and Level 2 separately.

When IPv4 and IPv6 address families are used in a single-topology mode, only a single SPF for the IPv4 topology exists. The IPv6 topology "borrows" the IPv4 topology; therefore, no SPF calculation is required for IPv6. To tune the SPF calculation parameters for single-topology mode, configure the address-family ipv4 unicast command.

The incremental SPF algorithm can be enabled separately. When enabled, the incremental shortest path first (ISPF) is not employed immediately. Instead, the full SPF algorithm is used to "seed" the state information required for the ISPF to run. The startup delay prevents the ISPF from running for a specified interval after an IS-IS restart (to permit the database to stabilize). After the startup delay elapses, the ISPF is principally responsible for performing all of the SPF calculations. The reseed interval enables a periodic running of the full SPF to ensure that the iSFP state remains synchronized.

SUMMARY STEPS

1. configure

2. router isis instance-id

3. address-family {ipv4 | ipv6} [unicast | multicast]

4. spf-interval {[initial-wait initial | secondary-wait secondary | maximum-wait maximum] ...}[level {1 | 2}]

5. ispf [level {1 | 2}]

6. end
or
commit

7. show isis [instance instance-id] [[ipv4 | ipv6 | afi-all] [unicast | multicast | safi-all]] spf-log [level {1 | 2}] [ispf | fspf | prc | nhc] [detail | verbose] [last number | first number]

DETAILED STEPS
Command or Action

Purpose

Step 1

configure
Example:

RP/0/RP0/CPU0:router# configure

Enters global configuration mode.

Step 2

router isis instance-id
Example:

RP/0/RP0/CPU0:router(config)# router isis isp

Enables IS-IS routing for the specified routing instance, and places the router in router configuration mode.

•You can change the level of routing to be performed by a particular routing instance by using the is-type router configuration command.

Step 3

address-family {ipv4 | ipv6} [unicast | multicast]
Example:

RP/0/RP0/CPU0:router(config-isis)#
address-family ipv6 unicast

Specifies the IPv4 or IPv6 address family, and enters router address family configuration mode.

•This example specifies the unicast IPv6 address family.

Step 4

spf-interval {[initial-wait initial | secondary-wait secondary | maximum-wait maximum] ...} [level {1 | 2}]
Example:

RP/0/RP0/CPU0:router(config-isis-af)# spf-interval initial-wait 10 maximum-wait 30

(Optional) Controls the minimum time between successive SPF calculations.

•This value imposes a delay in the SPF computation after an event trigger and enforces a minimum elapsed time between SPF runs.

•If this value is configured too low, the router can lose too many CPU resources when the network is unstable.

•Configuring the value too high delays changes in the network topology that result in lost packets.

•The SPF interval does not apply to the running of the ISPF because that algorithm runs immediately on receiving a changed LSP.

Step 5

ispf [level {1 | 2}]
Example:

RP/0/RP0/CPU0:router(config-isis-af)# ispf

(Optional) Configures incremental IS-IS ISPF to calculate network topology.
Step 6

end
or

commit
Example:

RP/0/RP0/CPU0:router(config-isis-af)# end
or

RP/0/RP0/CPU0:router(config-isis-af)# commit
Saves configuration changes.

•When you issue the end command, the system prompts you to commit changes:
Uncommitted changes found, commit them before 
exiting(yes/no/cancel)? 
[cancel]:
–Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

–Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

–Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

•Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.
Step 7

show isis [instance instance-id] [[ipv4 | ipv6 | afi-all] [unicast | multicast | safi-all]] spf-log [level {1 | 2}] [ispf | fspf | prc | nhc] [detail | verbose] [last number | first number]
Example:

RP/0/RP0/CPU0:router# show isis instance 1 spf-log ipv6

(Optional) Displays how often and why the router has run a full SPF calculation.
Customizing Routes for IS-IS

This task explains how to perform route functions that include injecting default routes into your IS-IS routing domain and redistributing routes learned in another IS-IS instance. This task is optional.

SUMMARY STEPS

1. configure

2. router isis instance-id

3. set-overload-bit [on-startup {delay | wait-for-bgp}] [level {1 | 2}]

4. address-family {ipv4 | ipv6} [unicast | multicast]

5. default-information originate [route-policy route-policy-name]

6. redistribute isis instance [level-1 | level-2 | level-1-2] [metric metric] [metric-type {internal | external}] policy policy-name]

7. summary-prefix address/prefix-length [level {1 | 2}]
or
summary-prefix ipv6-prefix/prefix-length [level {1 | 2}]

8. maximum-paths route-number

9. distance weight [address/prefix-length [route-list-name]]

10. set-attached-bit

11. end
or
commit

DETAILED STEPS
Command or Action

Purpose

Step 1

configure
Example:

RP/0/RP0/CPU0:router# configure

Enters global configuration mode.

Step 2

router isis instance-id
Example:

RP/0/RP0/CPU0:router(config)# router isis isp

Enables IS-IS routing for the specified routing process, and places the router in router configuration mode.

•By default, all IS-IS instances are automatically Level 1 and Level 2. You can change the level of routing to be performed by a particular routing instance by using the is-type command.

Step 3

set-overload-bit [on-startup {delay | wait-for-bgp}] [level {1 | 2}]
Example:

RP/0/RP0/CPU0:router(config-isis)# set-overload-bit

(Optional) Sets the overload bit.

Note The configured overload bit behavior does not apply to NSF restarts because the NSF restart does not set the overload bit during restart.

Step 4

address-family {ipv4 | ipv6} [unicast | multicast]
Example:

RP/0/RP0/CPU0:router(config-isis)# address-family ipv6 unicast

Specifies the IPv4 or IPv6 address family, and enters router address family configuration mode.

•This example specifies the unicast IPv6 address family.

Step 5

default-information originate [route-policy route-policy-name]
Example:

RP/0/RP0/CPU0:router(config-isis-af)# default-information originate

(Optional) Injects a default IPv4 or IPv6 route into an IS-IS routing domain.

•The route-policy keyword and route-policy-name argument specify the conditions under which the IPv4 or IPv6 default route is advertised.

•If the route-policy keyword is omitted, then the IPv4 or IPv6 default route is unconditionally advertised at Level 2.

Step 6

redistribute isis instance [level-1 | level-2 | level-1-2] [metric metric] [metric-type {internal | external}] [policy policy-name]
Example:

RP/0/RP0/CPU0:router(config-isis-af)# redistribute isis 2 level-1

(Optional) Redistributes routes from one IS-IS instance into another instance.

•In this example, an IS-IS instance redistributes Level 1 routes from another IS-IS instance.

Step 7

summary-prefix address/prefix-length [level {1 | 2}]
or

summary-prefix ipv6-prefix/prefix-length [level {1 | 2}]
Example:

RP/0/RP0/CPU0:router(config-isis-af)# summary-prefix 10.1.0.0/16 level 1
or

RP/0/RP0/CPU0:router(config-isis-af)# summary-prefix 3003:xxxx::/24 level 1

(Optional) Allows a Level 1-2 router to summarize Level 1 IPv4 and IPv6 prefixes at Level 2, instead of advertising the Level 1 prefixes directly when the router advertises the summary.

•This example specifies an IPv4 address and mask.

or

•This example specifies an IPv6 prefix, and the command must be in the form documented in RFC 2373 in which the address is specified in hexadecimal using 16-bit values between colons.

•Note that IPv6 prefixes must be configured only in the IPv6 router address family configuration submode, and IPv4 prefixes in the IPv4 router address family configuration submode.

Step 8

maximum-paths route-number
Example:

RP/0/RP0/CPU0:router(config-isis-af)# maximum-paths 16

(Optional) Configures the maximum number of parallel paths allowed in a routing table.

Step 9

distance weight [address/prefix-length [route-list-name]]
Example:

RP/0/RP0/CPU0:router(config-isis-af)# distance 90

(Optional) Defines the administrative distance assigned to routes discovered by the IS-IS protocol.

•A different administrative distance may be applied for IPv4 and IPv6.

Step 10

set-attached-bit
Example:

RP/0/RP0/CPU0:router(config-isis-af)# set-attached-bit

(Optional) Configures an IS-IS instance with an attached bit in the Level 1 LSP.
Step 11

end
or

commit
Example:

RP/0/RP0/CPU0:router(config-isis-af)# end
or

RP/0/RP0/CPU0:router(config-isis-af)# commit
Saves configuration changes.

•When you issue the end command, the system prompts you to commit changes:
Uncommitted changes found, commit them before 
exiting(yes/no/cancel)? 
[cancel]:
–Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

–Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

–Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

•Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.
Configuring MPLS LDP IS-IS Synchronization

This task explains how to enable Multiprotocol Label Switching (MPLS) Label Distribution Protocol (LDP) IS-IS synchronization. MPLS LDP synchronization can be enabled for an address family under interface configuration mode. Only IPv4 unicast address family is supported. This task is optional.

SUMMARY STEPS

1. configure

2. router isis instance-id

3. interface type instance

4. address-family ipv4 unicast

5. mpls ldp sync [level {1 | 2}]

6. end
or
commit

DETAILED STEPS
Command or Action

Purpose

Step 1

configure
Example:

RP/0/RP0/CPU0:router# configure

Enters global configuration mode.

Step 2

router isis instance-id
Example:

RP/0/RP0/CPU0:router(config)# router isis isp

Enables IS-IS routing for the specified routing process, and places the router in router configuration mode.

•By default, all IS-IS instances are automatically Level 1 and Level 2. You can change the level of routing to be performed by a particular routing instance by using the is-type command.

Step 3

interface type number
Example:

RP/0/RP0/CPU0:router(config-isis)# interface POS 0/1/0/3

Enters interface configuration mode.

Step 4

address-family ipv4 unicast
Example:

RP/0/RP0/CPU0:router(config-isis-if)# address-family ipv4 unicast

Specifies the IPv4 address family and enters router address family configuration mode.

Step 5

mpls ldp sync [level {1 | 2}]
Example:

RP/0/RP0/CPU0:router(config-isis-if-af)# mpls ldp sync level 1

Enables MPLS LDP synchronization for the IPv4 address family under interface POS 0/1/0/3.
Step 6

end
or

commit
Example:

RP/0/RP0/CPU0:router(config-isis-if-af)# end
or

RP/0/RP0/CPU0:router(config-isis-if-af)# commit
Saves configuration changes.

•When you issue the end command, the system prompts you to commit changes:
Uncommitted changes found, commit them before 
exiting(yes/no/cancel)? 
[cancel]:
–Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

–Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

–Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

•Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.
Enabling Multicast-Intact

This optional task describes how to enable multicast-intact for IS-IS routes that use IPv4 and IPv6 addresses.

SUMMARY STEPS

1. configure

2. router isis instance-id

3. address-family {ipv4 | ipv6} [unicast | multicast]

4. mpls traffic-eng multicast-intact

5. end
or
commit

DETAILED STEPS
Command or Action

Purpose

Step 1

configure
Example:

RP/0/RP0/CPU0:router# configure

Enters global configuration mode.

Step 2

router isis instance-id
Example:

RP/0/RP0/CPU0:router(config)# router isis isp

Enables IS-IS routing for the specified routing process, and places the router in router configuration mode. In this example, the IS-IS instance is called isp.

Step 3

address-family {ipv4 | ipv6} [unicast | multicast]
Example:

RP/0/RP0/CPU0:router(config-isis)# address-family ipv6 unicast

Specifies the IPv4 or IPv6 address family, and enters router address family configuration mode.

•This example specifies the unicast IPv6 address family.

Step 4

mpls traffic-eng multicast-intact
Example:

RP/0/RP0/CPU0:router(config-isis-af)# mpls traffic-eng multicast-intact

Enables multicast-intact.
Step 5

end
or

commit
Example:

RP/0/RP0/CPU0:router(config-isis-af)# end
or

RP/0/RP0/CPU0:router(config-isis-af)# commit
Saves configuration changes.

•When you issue the end command, the system prompts you to commit changes:
Uncommitted changes found, commit them before 
exiting(yes/no/cancel)? 
[cancel]:
–Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

–Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

–Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

•Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.
Tagging IS-IS Interface Routes

This optional task describes how to associate a tag with a connected route of an IS-IS interface.

SUMMARY STEPS

1. configure

2. router isis instance-id

3. address-family {ipv4 | ipv6} [unicast | multicast]

4. metric-style wide [transition] [level {1 | 2}]

5. exit

6. interface type number

7. address-family {ipv4 | ipv6} [unicast | multicast]

8. tag tag

9. end
or
commit

10. show isis [ipv4 | ipv6 | afi-all] [unicast | multicast | safi-all] route [detail]

DETAILED STEPS
Command or Action

Purpose

Step 1

configure
Example:

RP/0/RP0/CPU0:router# configure

Enters global configuration mode.

Step 2

router isis instance-id
Example:

RP/0/RP0/CPU0:router(config)# router isis isp

Enables IS-IS routing for the specified routing process, and places the router in router configuration mode. In this example, the IS-IS instance is called isp.

Step 3

address-family {ipv4 | ipv6} [unicast | multicast]
Example:

RP/0/RP0/CPU0:router(config-isis)# address-family ipv6 unicast

Specifies the IPv4 or IPv6 address family, and enters router address family configuration mode.

•This example specifies the unicast IPv6 address family.

Step 4

metric-style wide [transition] [level {1 | 2}]
Example:

RP/0/RP0/CPU0:router(config-isis-af)# metric-style wide level 1

Configures a router to generate and accept only wide link metrics in the Level 1 area.

Step 5

exit
Example:

RP/0/RP0/CPU0:router(config-isis-af)# exit

Exits router address family configuration mode, and returns the router to router configuration mode.

Step 6

interface type number
Example:

RP/0/RP0/CPU0:router(config-isis)# interface POS 0/1/0/3

Enters interface configuration mode.

Step 7

address-family {ipv4 | ipv6} [unicast | multicast]
Example:

RP/0/RP0/CPU0:router(config-isis-if)# address-family ipv6 unicast

Specifies the IPv4 or IPv6 address family, and enters address family configuration mode.

•This example specifies the unicast IPv6 address family.

Step 8

tag tag
Example:

RP/0/RP0/CPU0:router(config-isis-if-af)# tag 3

Sets the value of the tag to associate with the advertised connected route.
Step 9

end
or

commit
Example:

RP/0/RP0/CPU0:router(config-isis-if-af)# end
or

RP/0/RP0/CPU0:router(config-isis-if-af)# commit
Saves configuration changes.

•When you issue the end command, the system prompts you to commit changes:
Uncommitted changes found, commit them before 
exiting(yes/no/cancel)? 
[cancel]:
–Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

–Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

–Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

•Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.
Step 10

show isis [ipv4 | ipv6 | afi-all] [unicast | multicast | safi-all] route [detail]
Example:

RP/0/RP0/CPU0:router(config-isis-if-af)# show isis ipv6 detail

Displays tag information. Verify that all tags are present in the RIB.
Setting the Priority for Adding Prefixes to the RIB

This optional task describes how to set the priority (order) for which specified prefixes are added to the RIB. The prefixes can be chosen using an access list (ACL), prefix list, or by matching a tag value.

SUMMARY STEPS

1. configure

2. router isis instance-id

3. address-family {ipv4 | ipv6} [unicast | multicast]

4. metric-style wide [transition] [level {1 | 2}]

5. spf prefix-priority [level {1 | 2}] {critical | high | medium} {access-list-name | tag tag}

6. end
or
commit

DETAILED STEPS
Command or Action

Purpose

Step 1

configure
Example:

RP/0/RP0/CPU0:router# configure

Enters global configuration mode.

Step 2

router isis instance-id
Example:

RP/0/RP0/CPU0:router(config)# router isis isp

Enables IS-IS routing for the specified routing process, and places the router in router configuration mode. In this example, the IS-IS instance is called isp.

Step 3

address-family {ipv4 | ipv6} [unicast | multicast]
Example:

RP/0/RP0/CPU0:router(config-isis)# address-family ipv6 unicast

Specifies the IPv4 or IPv6 address family, and enters router address family configuration mode.

•This example specifies the unicast IPv6 address family.

Step 4

metric-style wide [transition] [level {1 | 2}]
Example:

RP/0/RP0/CPU0:router(config-isis-af)# metric-style wide level 1

Configures a router to generate and accept only wide link metrics in the Level 1 area.

Step 5

spf prefix-priority [level {1 | 2}] {critical | high | medium} {access-list-name | tag tag}
Example:

RP/0/RP0/CPU0:router(config-isis-af)# spf prefix-priority high tag 3

Installs all routes tagged with the value 3 first.
Step 6

end
or

commit
Example:

RP/0/RP0/CPU0:router(config-isis-af)# end
or

RP/0/RP0/CPU0:router(config-isis-af)# commit
Saves configuration changes.

•When you issue the end command, the system prompts you to commit changes:
Uncommitted changes found, commit them before 
exiting(yes/no/cancel)? 
[cancel]:
–Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

–Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

–Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

•Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.
Configuring IP Fast Reroute Loop-free Alternate

This optional task describes how to enable the IP fast reroute (IPFRR) loop-free alternate (LFA) computation to converge traffic flows around link failures.

Note To enable node protection on broadcast links, IPFRR and bidirectional forwarding detection (BFD) must be enabled on the interface under IS-IS.

Restrictions

IPFRR is supported on the Cisco CRS-1 router only. IPv4 address families and single-level interfaces are supported.

Multiprotocol Label Switching (MPLS) FRR and IPFRR cannot be configured on the same interface simultaneously.

SUMMARY STEPS

1. configure

2. router isis instance-id

3. interface type instance

4. circuit-type {level-1 | level-2-only}

5. address-family ipv4 [unicast]

6. ipfrr lfa {level {1 | 2}}

7. end
or
commit

DETAILED STEPS
Command or Action

Purpose

Step 1

configure
Example:

RP/0/RP0/CPU0:router# configure

Enters global configuration mode.

Step 2

router isis instance-id
Example:

RP/0/RP0/CPU0:router(config)# router isis isp

Enables IS-IS routing for the specified routing process, and places the router in router configuration mode. In this example, the IS-IS instance is called isp.

Step 3

interface type instance
Example:

RP/0/RP0/CPU0:router(config-isis)# interface POS 0/1/0/3

Enters interface configuration mode.

Step 4

circuit-type {level-1 | level-2-only}
Example:

RP/0/RP0/CPU0:router(config-isis-if)# circuit-type level-1

(Optional) Configures the type of adjacency.

Step 5

address-family ipv4 [unicast]
Example:

RP/0/RP0/CPU0:router(config-isis-if)# address-family ipv6 unicast

Specifies the IPv4 address family, and enters router address family configuration mode.

•This example specifies the unicast IPv6 address family.

Step 6

ipfrr lfa {level {1 | 2}}
Example:

RP/0/RP0/CPU0:router(config-isis-if-af)# ipfrr lfa level 1

Specifies the IP fast reroute loop-free alternate computation on link or node failures.
Step 7

end
or

commit
Example:

RP/0/RP0/CPU0:router(config-isis-if-af)# end
or

RP/0/RP0/CPU0:router(config-isis-af)# commit
Saves configuration changes.

•When you issue the end command, the system prompts you to commit changes:
Uncommitted changes found, commit them before 
exiting(yes/no/cancel)? 
[cancel]:
–Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

–Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

–Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

•Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.
Configuration Examples for Implementing IS-IS on Cisco IOS XR Software

This section provides the following configuration examples:

•Configuring Single-Topology IS-IS for IPv6: Example

•Configuring Multitopology IS-IS for IPv6: Example

•Redistributing IS-IS Routes Between Multiple Instances: Example

•Tagging Routes: Example

Configuring Single-Topology IS-IS for IPv6: Example

The following example shows single-topology mode being enabled. An IS-IS instance is created, the NET is defined, IPv6 is configured along with IPv4 on an interface, and IPv4 link topology is used for IPv6.

This configuration allows POS interface 0/3/0/0 to form adjacencies for both IPv4 and IPv6 addresses.
router isis isp
 net 49.0000.0000.0001.00
 address-family ipv6 unicast
  single-topology
 interface POS0/3/0/0
  address-family ipv4 unicast
  !
  address-family ipv6 unicast
  !
  exit
!
interface POS0/3/0/0
 ipv4 address 10.0.1.3 255.255.255.0
 ipv6 address 2001::1/64
Configuring Multitopology IS-IS for IPv6: Example

The following example shows multitopology IS-IS being configured in IPv6.
router isis isp
 net 49.0000.0000.0001.00
 interface POS0/3/0/0
  address-family ipv6 unicast
  metric-style wide level 1
  exit
!
interface POS0/3/0/0
 ipv6 address 2001::1/64
Redistributing IS-IS Routes Between Multiple Instances: Example

The following example shows usage of the set-attached-bit and redistribute commands. Two instances, instance "1" restricted to Level 1 and instance "2" restricted to Level 2, are configured.

The Level 1 instance is propagating routes to the Level 2 instance using redistribution. Note that the administrative distance is explicitly configured higher on the Level 2 instance to ensure that Level 1 routes are preferred.

Attached bit is being set for the Level 1 instance since it is redistributing routes into the Level 2 instance. Therefore, instance "1" is a suitable candidate to get from the area to the backbone.
router isis 1
  is-type level-2-only
 net 49.0001.0001.0001.0001.00
 address-family ipv4 unicast
  distance 116
  redistribute isis 2 level 2
!
interface POS0/3/0/0
 address-family ipv4 unicast
!
!
router isis 2
 is-type level-1
 net 49.0002.0001.0001.0002.00
 address-family ipv4 unicast
  set-attached-bit
!
interface POS0/1/0/0
 address-family ipv4 unicast
Tagging Routes: Example

The following example show how to tag routes.
route-policy isis-tag-55
end-policy
!
route-policy isis-tag-555
  if destination in (5.5.5.0/24 eq 24) then
    set tag 555
    pass
  else
    drop
  endif
end-policy
!
router static
 address-family ipv4 unicast
  0.0.0.0/0 2.6.0.1
  5.5.5.0/24 Null0
 !
!
router isis uut
 net 00.0000.0000.12a5.00
 address-family ipv4 unicast
  metric-style wide
  redistribute static level-1 route-policy isis-tag-555
  spf prefix-priority critical tag 13
  spf prefix-priority high tag 444
  spf prefix-priority medium tag 777
Where to Go Next

To implement more IP routing protocols, see the following document modules in Cisco IOS XR Routing Configuration Guide:

•Implementing OSPF on Cisco IOS XR Software

•Implementing BGP on Cisco IOS XR Software

•Implementing EIGRP on Cisco IOS XR Software

•Implementing RIP on Cisco IOS XR Software

Additional References

The following sections provide references related to implementing IS-IS on Cisco IOS XR software.

Related Documents

Related Topic

Document Title

IS-IS commands: complete command syntax, command modes, command history, defaults, usage guidelines, and examples

Cisco IOS XR Routing Command Reference, Release 3.5

MPLS TE feature information

Implementing MPLS Traffic Engineering on Cisco IOS XR Software module in the Cisco IOS XR Multiprotocol Label Switching Configuration Guide, Release 3.5

IS-IS TLVs

Intermediate System-to-Intermediate System (IS-IS) TLVs at:
http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094bbd.shtml

Bidirectional Forwarding Detection (BFD)

Cisco IOS XR Interface and Hardware Configuration Guide, Release 3.5 and Cisco IOS XR Interface and Hardware Command Reference, Release 3.5

Standards

Standards

Title

Draft-ietf-isis-ipv6-05.txt

Routing IPv6 with IS-IS, by Christian E. Hopps

Draft-ietf-isis-wg-multi-topology-06.txt

M-ISIS: Multi Topology (MT) Routing in IS-IS, by Tony Przygienda, Naiming Shen, and Nischal Sheth

Draft-ietf-isis-traffic-05.txt

IS-IS Extensions for Traffic Engineering, by Henk Smit and Toni Li

Draft-ietf-isis-restart-04.txt

Restart Signalling for IS-IS, by M. Shand and Les Ginsberg

Draft-ietf-isis-igp-p2p-over-lan-05.txt

Point-to-point operation over LAN in link-state routing protocols, by Naiming Shen

Draft-ietf-rtgwg-ipfrr-framework-06.txt

IP Fast Reroute Framework, by M. Shand and S. Bryant

Draft-ietf-rtgwg-lf-conv-frmwk-00.txt

A Framework for Loop-free Convergence, by M. Shand and S. Bryant

MIBs

MIBs

MIBs Link

—

To locate and download MIBs using Cisco IOS XR software, use the Cisco MIB Locator found at the following URL and choose a platform under the Cisco Access Products menu: http://cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml

RFCs

RFCs

Title

RFC 1142

OSI IS-IS Intra-domain Routing Protocol

RFC 1195

Use of OSI IS-IS for Routing in TCP/IP and Dual Environments

RFC 2763

Dynamic Hostname Exchange Mechanism for IS-IS

RFC 2966

Domain-wide Prefix Distribution with Two-Level IS-IS

RFC 2973

IS-IS Mesh Groups

RFC 3277

IS-IS Transient Blackhole Avoidance

RFC 3373

Three-Way Handshake for IS-IS Point-to-Point Adjacencies

RFC 3567

IS-IS Cryptographic Authentication

Technical Assistance

Description

Link

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http://www.cisco.com/techsupport