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This chapter describes how to configure Integrated Intermediate System-to-Intermediate System (IS-IS) on the Cisco NX-OS device.
IS-IS is an Interior Gateway Protocol (IGP) based on Standardization (ISO)/International Engineering Consortium (IEC) 10589. Cisco NX-OS supports Internet Protocol version 4 (IPv4). IS-IS is a dynamic link-state routing protocol that can detect changes in the network topology and calculate loop-free routes to other nodes in the network. Each router maintains a link-state database that describes the state of the network and sends packets on every configured link to discover neighbors. IS-IS floods the link-state information across the network to each neighbor. The router also sends advertisements and updates on the link-state database through all the existing neighbors.
Note Cisco NX-OS does not support IPv6 for IS-IS.
This section includes the following topics:
IS-IS sends a hello packet out every configured interface to discover IS-IS neighbor routers. The hello packet contains information, such as the authentication, area, and supported protocols, which the receiving interface uses to determine compatibility with the originating interface. The hello packets are also padded to ensure that IS-IS establishes adjacencies only with interfaces that have matching maximum transmission unit (MTU) settings. Compatible interfaces form adjacencies, which update routing information in the link-state database through link-state update messages (LSPs). By default, the router sends a periodic LSP refresh every 10 minutes and the LSPs remain in the link-state database for 20 minutes (the LSP lifetime). If the router does not receive an LSP refresh before the end of the LSP lifetime, the router deletes the LSP from the database.
The LSP interval must be less than the LSP lifetime or the LSPs time out before they are refreshed.
IS-IS sends periodic hello packets to adjacent routers. If you configure transient mode for hello packets, these hello packets do not include the excess padding used before IS-IS establishes adjacencies. If the MTU value on adjacent routers changes, IS-IS can detect this change and send padded hello packets for a period of time. IS-IS uses this feature to detect mismatched MTU values on adjacent routers. For more information, see the “Configuring the Transient Mode for Hello Padding” section.
You can design IS-IS networks as a single area that includes all routers in the network or as multiple areas that connect into a backbone or Level 2 area. Routers in a nonbackbone area are Level 1 routers that establish adjacencies within a local area (intra-area routing). Level 2 area routers establish adjacencies to other Level 2 routers and perform routing between Level 1 areas (inter-area routing). A router can have both Level 1 and Level 2 areas configured. These Level 1/Level 2 routers act as area border routers that route information from the local area to the Level 2 backbone area (see Figure 9-1).
Within a Level 1 area, routers know how to reach all other routers in that area. The Level 2 routers know how to reach other area border routers and other Level 2 routers. Level 1/Level 2 routers straddle the boundary between two areas, routing traffic to and from the Level 2 backbone area. Level1/Level2 routers use the attached (ATT) bit signal Level 1 routers to set a default route to this Level1/Level2 router to connect to the Level 2 area.
In some instances, such as when you have two or more Level1/Level 2 routers in an area, you may want to control which Level1/Level2 router that the Level 1 routers use as the default route to the Level 2 area. You can configure which Level1/Level2 router sets the attached bit. For more information, see the “Verifying the IS-IS Configuration” section.
Each IS-IS instance in Cisco NX-OS supports 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.
Figure 9-1 IS-IS Network Divided into Areas
An autonomous system boundary router (ASBR) advertises external destinations throughout the IS-IS autonomous system. External routes are the routes redistributed into IS-IS from any other protocol.
Each IS-IS instance has an associated network entity title (NET). The NET is comprised of the IS-IS system ID, which uniquely identifies this IS-IS instance in the area and the area ID. For example, if the NET is 47.0004.004d.0001.0001.0c11.1111.00, the system ID is 0000.0c11.1111.00 and the area is ID 47.0004.004d.0001.
IS-IS uses a designated intermediate system (DIS) in broadcast networks to prevent each router from forming unnecessary links with every other router on the broadcast network. IS-IS routers send LSPs to the DIS, which manages all the link-state information for the broadcast network. You can configure the IS-IS priority that IS-IS uses to select the DIS in an area.
Note No DIS is required on a point-to-point network.
You can configure authentication to control adjacencies and the exchange of LSPs. Routers that want to become neighbors must exchange the same password for their configured level of authentication. IS-IS blocks a router that does not have the correct password. You can configure IS-IS authentication globally or for an individual interface for Level 1, Level 2, or both Level 1/Level 2 routing.
IS-IS supports the following authentication methods:
To provide protection against passive attacks, IS-IS never sends the MD5 secret key as cleartext through the network. In addition, IS-IS includes a sequence number in each packet to protect against replay attacks.
You can use also keychains for hello and LSP authentication. See the Cisco Nexus 7000 Series NX-OS Security Configuration Guide, Release 5.x , for information on keychain management.
A mesh group is a set of interfaces in which all routers reachable over the interfaces have at least one link to every other router. Many links can fail without isolating one or more routers from the network.
In normal flooding, an interface receives a new LSP and floods the LSP out over all other interfaces on the router. With mesh groups, when an interface that is part of a mesh group receives a new LSP, the interface does not flood the new LSP over the other interfaces that are part of that mesh group.
Note You may want to limit LSPs in certain mesh network topologies to improve network scalability. Limiting LSP floods might also reduce the reliability of the network (in case of failures). For this reason, we recommend that you use mesh groups only if specifically required, and then only after you make a careful network design.
You can also configure mesh groups in block mode for parallel links between routers. In this mode, all LSPs are blocked on that interface in a mesh group after the routers initially exchange their link-state information.
IS-IS uses the overload bit to tell other routers not to use the local router to forward traffic but to continue routing traffic destined for that local router.
You can configure a summary aggregate address. Route summarization simplifies route tables by replacing a number of more-specific addresses with an address that represents all the specific addresses. For example, you can replace 10.1.1.0/24, 10.1.2.0/24, and 10.1.3.0/24 with one summary address, 10.1.0.0/16.
If more specific routes are in the routing table, IS-IS advertises the summary address with a metric equal to the minimum metric of the more specific routes.
Note Cisco NX-OS does not support automatic route summarization.
You can use IS-IS to redistribute static routes, routes learned by other IS-IS autonomous systems, or routes from other protocols. You must configure a route map with the redistribution to control which routes are passed into IS-IS. A route map allows you to filter routes based on attributes such as the destination, origination protocol, route type, route tag, and so on. For more information, see Chapter16, “Configuring Route Policy Manager”
Whenever you redistribute routes into an IS-IS routing domain, Cisco NX-OS does not, by default, redistribute the default route into the IS-IS routing domain. You can generate a default route into IS-IS, which can be controlled by a route policy.
You also configure the default metric that is used for all imported routes into IS-IS.
You can use load balancing to allow a router to distribute traffic over all the router network ports that are the same distance from the destination address. Load balancing increases the utilization of network segments and increases the effective network bandwidth.
Cisco NX-OS supports the Equal Cost Multiple Paths (ECMP) feature with up to 16 equal-cost paths in the IS-IS route table and the unicast RIB. You can configure IS-IS to load balance traffic across some or all of those paths.
This feature supports bidirectional forwarding detection (BFD). BFD is a detection protocol designed to provide fast forwarding-path failure detection times. BFD provides subsecond failure detection between two adjacent devices and can be less CPU-intensive than protocol hello messages because some of the BFD load can be distributed onto the data plane on supported modules. See the Cisco Nexus 7000 Series NX-OS Interfaces Configuration Guide, Release 5.x , for more information.
Cisco NX-OS supports multiple instances of the IS-IS protocol that runs on the same system. IS-IS supports virtual routing and forwarding (VRF) instances. VRFs exist within virtual device contexts (VDCs). You can configure up to four IS-IS instances in a VDC.
By default, Cisco NX-OS places you in the default VDC and default VRF unless you specifically configure another VDC and VRF. See the Cisco Nexus 7000 Series NX-OS Virtual Device Context Configuration Guide, Release 5.x, and Chapter14, “Configuring Layer 3 Virtualization”
Cisco NX-OS provides a multilevel high-availability architecture. IS-IS supports stateful restart, which is also referred to as non-stop routing (NSR). If IS-IS experiences problems, it attempts to restart from its previous run-time state. The neighbors would not register any neighbor event in this case. If the first restart is not successful and another problem occurs, IS-IS attempts a graceful restart as per RFC 3847. A graceful restart, or non-stop forwarding (NSF), allows IS-IS to remain in the data forwarding path through a process restart. When the restarting IS-IS interface is operational again, it rediscovers its neighbors, establishes adjacency, and starts sending its updates again. At this point, the NSF helpers recognize that the graceful restart has finished.
A stateful restart is used in the following scenarios:
A graceful restart is used in the following scenarios:
Note Graceful restart is on by default, and we strongly recommended that it not be disabled.
The following table shows the licensing requirements for this feature:
IS-IS has the following prerequisites:
IS-IS has the following configuration guidelines and limitations:
To configure IS-IS, follow these steps:
Step 1 Enable the IS-IS feature (see the “Enabling the IS-IS Feature” section).
Step 2 Create an IS-IS instance (see the “Creating an IS-IS Instance” section).
Step 3 Add an interface to the IS-IS instance (see the “Configuring IS-IS on an Interface” section).
Step 4 Configure optional features, such as authentication, mesh groups, and dynamic host exchange.
This section contains the following topics:
Note If you are familiar with the Cisco IOS CLI, be aware that the Cisco NX-OS commands for this feature might differ from the Cisco IOS commands that you would use.
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.
This example shows how to enter router address family configuration mode:
To disable the IS-IS feature and remove all associated configuration, use the following command in configuration mode.
You can create an IS-IS instance and configure the area level for that instance.
You must enable IS-IS (see the “Enabling the IS-IS Feature” section).
Ensure that you are in the correct VDC (or use the switchto vdc command).
4. (Optional) is-type {l evel-1 | level-2 | level-1-2 }
To remove the IS-IS instance and the associated configuration, use the following command in configuration mode.
Note You must also remove any IS-IS commands that are configured in interface mode to completely remove all configuration for the IS-IS instance.
You can configure the following optional parameters for IS-IS:
Sets the administrative distance for IS-IS. The range is from 1 to 255. The default is 115. See the “Administrative Distance” section. |
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Sends a system message whenever an IS-IS neighbor changes the state. |
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Sets the MTU for LSPs in this IS-IS instance. The range is from 128 to 4352 bytes. The default is 1492. |
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Configures the maximum number of equal-cost paths that IS-IS maintains in the route table. The range is from 1 to 16. The default is 4. |
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Sets the default reference bandwidth used for calculating the IS-IS cost metric. The range is from 1 to 4000 Gbps. The default is 40 Gbps. |
The following example shows how to create an IS-IS instance in a level 2 area:
switch(config)# router isis Enterprise
switch(config-router)# net 47.0004.004d.0001.0001.0c11.1111.00
switch(config-router)# is-type level 2
switch(config-router)# copy running-config startup-config
To clear neighbor statistics and remove adjacencies, use the following command in router configuration mode:
You can restart an IS-IS instance. This action clears all neighbors for the instance.
To restart an IS-IS instance and remove all associated neighbors, use the following command:
You can shut down the IS-IS instance. This action disables this IS-IS instance and retains the configuration.
To shut down the IS-IS instance, use the following command in router configuration mode:
You must enabled IS-IS (see the “Enabling the IS-IS Feature” section).
Ensure that you are in the correct VDC (or use the switchto vdc command).
2. interface interface-type slot/port
3. (Optional) medium { broadcast | p2p }
4. ip router isis instance-tag
5. (Optional) show isis [ vrf vrf-name ] [ instance-tag ] interface [ interface-type slot/port ]
You can configure the following optional parameters for IS-IS in interface mode:
This example shows how to add Ethernet 1/2 interface to an IS-IS instance:
switch(config)# interface ethernet 1/2
You can gracefully shut down IS-IS on an interface. This action removes all adjacencies and stops IS-IS traffic on this interface but preserves the IS-IS configuration.
To disable IS-IS on an interface, use the following command in interface configuration mode:
You must enable IS-IS (see the “Enabling the IS-IS Feature” section).
Ensure that you are in the correct VDC (or use the switchto vdc command).
3. authentication-type { cleartext | md5 } {l evel-1 | level-2 }
4. authentication key-chain key { level-1 | level-2 }
This example shows how to configure cleartext authentication on an IS-IS instance:
switch(config)# router isis Enterprise
switch(config-router)# authentication-type cleartext level-2
switch(config-router)# authentication key-chain ISISKey level-2
You can configure IS-IS to authenticate Hello packets on an interface.
You must enable IS-IS (see the “Enabling the IS-IS Feature” section).
Ensure that you are in the correct VDC (or use the switchto vdc command).
2. interface interface-type slot/port
3. isis authentication-type { cleartext | md5 } { level-1 | level-2 }
4. isis authentication key-chain key { level-1 | level-2 }
5. (Optional) isis authentication-check { level-1 | level-2 }
This example shows how to configure cleartext authentication on an IS-IS instance:
switch(config)# interface ethernet 1/2
switch(config-if)# isis authentication-type cleartext level-2
You can add an interface to a mesh group to limit the amount of LSP flooding for interfaces in that mesh group. You can optionally block all LSP flooding on an interface in a mesh group.
To add an interface to a mesh group, use the following command in interface configuration mode:
You can configure a router to become the designated intermediate system (DIS) for a multiaccess network by setting the interface priority.
To configure the DIS, use the following command in interface configuration mode:
You can configure IS-IS to map between the system ID and the hostname for a router using dynamic host exchange.
To configure dynamic host exchange, use the following command in router configuration mode:
You can configure the router to signal other routers not to use this router as an intermediate hop in their shortest path first (SPF) calculations. You can optionally configure the overload bit temporarily on startup, until BGP converges.
In addition to setting the overload bit, you might also want to suppress certain types of IP prefix advertisements from LSPs for Level 1 or Level 2 traffic.
To set the overload bit, use the following command in router configuration mode:
You can configure the attached bit to control which Level 1/Level 2 router that the Level 1 routers use as the default route to the Level 2 area. If you disable setting the attached bit, the Level 1 routers do not use this Level 1/Level 2 router to reach the Level 2 area.
To configure the attached bit for a Level 1/Level 2 router, use the following command in router configuration mode:
You can configure the transient mode for hello padding to pad hello packets when IS-IS establishes adjacency and remove that padding after IS-IS establishes adjacency.
To configure the mode for hello padding, use the following command in router configuration mode:
You can create aggregate addresses that are represented in the routing table by a summary address. One summary address can include multiple groups of addresses for a given level. Cisco NX-OS advertises the smallest metric of all the more-specific routes.
You must enable IS-IS (see the “Enabling the IS-IS Feature” section).
Ensure that you are in the correct VDC (or use the switchto vdc command).
3. address-family ipv4 { unicast | multicast }
4. summary-address ip-prefix/mask-len { level-1 | level-2 | level-1-2 }
5. (Optional) show isis [ vrf vrf-name ] ip summary-address ip-prefix [ longer-prefixes ]
This example shows how to configure an IPv4 unicast summary address for IS-IS:
switch(config)# router isis Enterprise
switch(config-router)# address-family ipv4 unicast
switch(config-router-af)# summary-address 192.0.2.0/24 level-2
switch(config-router-af)# copy running-config startup-config
You can configure IS-IS to accept routing information from another routing protocol and redistribute that information through the IS-IS network. You can optionally assign a default route for redistributed routes.
You must enable IS-IS (see the “Enabling the IS-IS Feature” section).
Ensure that you are in the correct VDC (or use the switchto vdc command).
3. address-family ipv4 unicast
4. redistribute { bgp as | direct |{ eigrp | isis | ospf | ospfv3 | rip } instance-tag | static } route-map map-name
5. (Optional) default-information originate [ always ] [ route-map map-name ]
6. (Optional) distribute { level-1 | level-2 } into { level-1 | level-2 } { route-map route-map | all }
7. (Optional) show isis [ vrf vrf-name ] ip route ip-prefix [ detail | longer-prefixes [ summary | detail ]]
Creates a new IS-IS instance with the configured instance tag . |
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redistribute { bgp as | { eigrp | isis | ospf | ospfv3 | rip } instance-tag | static | direct } route-map map-name switch(config-router-af)# redistribute eigrp 201 route-map ISISmap |
Redistributes routes from other protocols into IS-IS. See the “Configuring Route Maps” section for more information about route maps. |
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default-information originate [ always ] [ route-map map-name ] switch(config-router-af)# default-information originate always |
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distribute { level-1 | level-2 } into { level-1 | level-2 } { route-map route-map | all } switch(config-router-af)# distribute level-1 into level-2 all |
(Optional) Redistributes routes from one IS-IS level to the other IS-IS level. |
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show isis [ vrf vrf-name ] ip route ip-prefix [ detail | longer-prefixes [ summary | detail ]] |
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copy running-config startup-config switch(config-router-af)# copy running-config startup-config |
This example shows how to redistribute EIGRP into IS-IS:
switch(config)# router isis Enterprise
switch(config-router)# address-family ipv4 unicast
switch(config-router-af)# redistribute eigrp 201 route-map ISISmap
switch(config-router-af)# copy running-config startup-config
Route redistribution can add many routes to the IS-IS route table. You can configure a maximum limit to the number of routes accepted from external protocols. IS-IS provides the following options to configure redistributed route limits:
You must enable IS-IS (see the “Enabling the IS-IS Feature” section).
Ensure that you are in the correct VDC (or use the switchto vdc command).
3. redistribute { bgp id | direct | eigrp id | isis id | ospf id | rip id | static } route-map map-name
4. redistribute maximum-prefix max [ threshold ] [ warning-only | withdraw [ num-retries timeout ]]
This example shows how to limit the number of redistributed routes into IS-IS:
switch(config)# router eigrp isis Enterprise
switch(config-router)# redistribute bgp route-map FilterExternalBGP
You must enable IS-IS (see the “Enabling the IS-IS Feature” section).
Ensure that you are in the correct VDC (or use the switchto vdc command).
Enables a graceful restart and the graceful restart helper functionality. Enabled by default. |
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Configures the graceful restart T3 timer. The range is from 30 to 65535 seconds. The default is 60. |
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This example shows how to enable a graceful restart:
switch(config)# router isis Enterprise
You can configure multiple IS-IS instances in each VDC. You can also create multiple VRFs within each VDC and use the same or multiple IS-IS instances in each VRF. You assign an IS-IS interface to a VRF.
You must configure a NET for the configured VRF.
Note Configure all other parameters for an interface after you configure the VRF for an interface. Configuring a VRF for an interface deletes all the configuration for that interface.
You must enable IS-IS (see the “Enabling the IS-IS Feature” section).
Ensure that you are in the correct VDC (or use the switchto vdc command).
10. ip address ip-prefix/length
11. ip router isis instance-tag
12. (Optional) show isis [ vrf vrf-name ] [ instance-tag ] interface [ interface-type slot/port ]
The following example shows how to create a VRF and add an interface to the VRF:
switch(config)# vrf context NewVRF
switch(config)# router isis Enterprise
switch(config-router)# vrf NewVRF
switch(config-router-vrf)# net 47.0004.004d.0001.0001.0c11.1111.00
switch(config-router-vrf)# interface ethernet 1/2
switch(config-if)# vrf member NewVRF
switch(config-if)# ip address 192.0.2.1/16
You can tune IS-IS to match your network requirements.
You can use the following optional commands in router configuration mode to tune IS-IS:
You can use the following optional command in router address configuration mode:
Performs an adjacency check to verify that an IS-IS instance forms an adjacency only with a remote IS-IS entity that supports the same address family. This command is enabled by default. |
You can use the following optional commands in interface configuration mode to tune IS-IS:
To display the IS-IS configuration, perform one of the following tasks:
For detailed information about the fields in the output from these commands, see the Cisco Nexus 7000 Series NX-OS Command Reference .
To display IS-IS statistics, use the following commands:
To clear IS-IS configuration statistics, perform one of the following tasks:
See the Chapter 16, “Configuring Route Policy Manager” for more information on route maps.
For additional information related to implementing IS-IS, see the following sections:
Table 9-2 lists the release history for this feature.