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Table Of Contents
Designated Intermediate System
High Availability and Graceful Restart
Licensing Requirements for IS-IS
Guidelines and Limitations for IS-IS
Configuring IS-IS on an Interface
Shutting Down IS-IS on an Interface
Configuring IS-IS Authentication in an Area
Configuring IS-IS Authentication on an Interface
Configuring a Designated Intermediate System
Configuring Dynamic Host Exchange
Configuring the Transient Mode for Hello Padding
Limiting the Number of Redistributed Routes
Configuring a Graceful Restart
Verifying the IS-IS Configuration
Configuration Examples for IS-IS
Configuring IS-IS
This chapter describes how to configure Integrated Intermediate System-to-Intermediate System (IS-IS) on the Cisco NX-OS device.
This chapter includes the following sections:
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Licensing Requirements for IS-IS
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Information About IS-IS
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.
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This section includes the following topics:
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IS-IS Overview
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.
IS-IS Areas
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.
NET and System ID
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.
Designated Intermediate System
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.
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IS-IS Authentication
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:
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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.
Mesh Groups
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 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.
Overload Bit
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 may want to use the overload bit in these situations:
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Route Summarization
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
Route Redistribution
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 Chapter 16 "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.
Load Balancing
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.
BFD
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.
Virtualization Support
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 Chapter 14 "Configuring Layer 3 Virtualization."
High Availability and Graceful Restart
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:
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A graceful restart is used in the following scenarios:
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Note
Multiple IS-IS Instances
Cisco NX-OS supports a maximum of four instances of the IS-IS protocol that run on the same node. You cannot configure multiple instances over the same interface. Every instance uses the same system router ID.
Licensing Requirements for IS-IS
The following table shows the licensing requirements for this feature:
Prerequisites for IS-IS
IS-IS has the following prerequisites:
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Guidelines and Limitations for IS-IS
IS-IS has the following configuration guidelines and limitations:
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Default Settings
Table 9-1 lists the default settings for IS-IS parameters.
Configuring IS-IS
To configure IS-IS, follow these steps:
Step 1
Step 2
Step 3
Step 4
This section contains the following topics:
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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.
This section includes the following topics:
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Router Configuration Mode
This example shows how to enter router configuration mode:
switch#: configure terminalswitch(config)# router isis ispswitch(config-router)#Router Address Family Configuration Mode
This example shows how to enter router address family configuration mode:
switch(config)# router isis ispswitch(config-router)# address-family ipv4 unicastswitch(config-router-af)#Enabling the IS-IS Feature
You must enable the IS-IS feature before you can configure IS-IS.
BEFORE YOU BEGIN
Ensure that you are in the correct VDC (or use the switchto vdc command).
SUMMARY STEPS
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2.
3.
4.
DETAILED STEPS
To disable the IS-IS feature and remove all associated configuration, use the following command in configuration mode.
no feature isis
Example:
switch(config)# no feature isis
Disables the IS-IS feature and removes all associated configuration.
Creating an IS-IS Instance
You can create an IS-IS instance and configure the area level for that instance.
BEFORE YOU BEGIN
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).
SUMMARY STEPS
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DETAILED STEPS
To remove the IS-IS instance and the associated configuration, use the following command in configuration mode.
no router isis instance-tag
Example:
switch(config)# no router isis Enterprise
Deletes the IS-IS instance and all associated configuration.
Note
You can configure the following optional parameters for IS-IS:
distance value
Example:
switch(config-router)# distance 30
Sets the administrative distance for IS-IS. The range is from 1 to 255. The default is 115. See the "Administrative Distance" section.
log-adjacency-changes
Example:
switch(config-router)# log-adjacency-changes
Sends a system message whenever an IS-IS neighbor changes the state.
lsp-mtu size
Example:
switch(config-router)# lsp-mtu 600
Sets the MTU for LSPs in this IS-IS instance. The range is from 128 to 4352 bytes. The default is 1492.
maximum-paths number
Example:
switch(config-router)# maximum-paths 6
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.
reference-bandwidth bandwidth-value {Mbps | Gbps}
Example:
switch(config-router)# reference-bandwidth 100 Gbps
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# configure terminal
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:
Restarting an IS-IS Instance
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:
restart isis instance-tag
Example:
switch(config)# restart isis Enterprise
Restarts the IS-IS instance and removes all neighbors.
Shutting Down IS-IS
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:
Configuring IS-IS on an Interface
You can add an interface to an IS-IS instance.
BEFORE YOU BEGIN
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).
SUMMARY STEPS
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DETAILED STEPS
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# configure terminal
switch(config)# interface ethernet 1/2
switch(config-if)# ip router isis Enterprise
switch(config-if)# copy running-config startup-config
Shutting Down IS-IS on an Interface
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:
switch(config-if)# isis shutdown
Example:
switch(config-router)# isis shutdown
Disables IS-IS on this interface. The IS-IS interface configuration remains.
Configuring IS-IS Authentication in an Area
You can configure IS-IS to authenticate LSPs in an area.
BEFORE YOU BEGIN
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).
SUMMARY STEPS
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6.
DETAILED STEPS
This example shows how to configure cleartext authentication on an IS-IS instance:
switch# configure terminal
switch(config)# router isis Enterprise
switch(config-router)# authentication-type cleartext level-2
switch(config-router)# authentication key-chain ISISKey level-2
switch(config-router)# copy running-config startup-config
Configuring IS-IS Authentication on an Interface
You can configure IS-IS to authenticate Hello packets on an interface.
BEFORE YOU BEGIN
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).
SUMMARY STEPS
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6.
DETAILED STEPS
This example shows how to configure cleartext authentication on an IS-IS instance:
switch# configure terminal
switch(config)# interface ethernet 1/2
switch(config-if)# isis authentication-type cleartext level-2
switch(config-if)# isis authentication key-chain ISISKey
switch(config-if)# copy running-config startup-config
Configuring a Mesh Group
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:
isis mesh-group {blocked | mesh-id}
Example:
switch(config-if)# isis mesh-group 1
Adds this interface to a mesh group. The range is from 1 to 4294967295.
Configuring a Designated Intermediate System
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:
isis priority number {level-1 | level-2}
Example:
switch(config-if)# isis priority 100 level-1
Sets the priority for DIS selection. The range is from 0 to 127. The default is 64.
Configuring Dynamic Host Exchange
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:
hostname dynamic
Example:
switch(config-router)# hostname dynamic
Enables dynamic host exchange.
Setting the Overload Bit
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:
Configuring the Attached Bit
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:
[no] attached-bit
Example:
switch(config-router)# no attached-bit
Configures the Level 1/Level 2 router to set the attached bit. This feature is enabled by default.
Configuring the Transient Mode for Hello Padding
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:
Configuring a Summary Address
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.
BEFORE YOU BEGIN
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).
SUMMARY STEPS
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DETAILED STEPS
This example shows how to configure an IPv4 unicast summary address for IS-IS:
switch# configure terminal
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
Configuring Redistribution
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.
BEFORE YOU BEGIN
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).
SUMMARY STEPS
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2.
3.
4.
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6.
7.
8.
DETAILED STEPS
Step 1
configure terminal
Example:
switch# configure terminal
switch(config)#
Enters configuration mode.
Step 2
router isis instance-tag
Example:
switch(config)# router isis Enterprise
switch(config-router)#
Creates a new IS-IS instance with the configured instance tag.
Step 3
address-family ipv4 unicast
Example:
switch(config-router)# address-family ipv4 unicast
switch(config-router-af)#
Enters address family configuration mode.
Step 4
redistribute {bgp as | {eigrp | isis | ospf | ospfv3 | rip} instance-tag | static | direct} route-map map-name
Example:
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.
Step 5
default-information originate [always] [route-map map-name]
Example:
switch(config-router-af)# default-information originate always
(Optional) Generates a default route into IS-IS.
Step 6
distribute {level-1 | level-2} into {level-1 | level-2} {route-map route-map | all}
Example:
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.
Step 7
show isis [vrf vrf-name] ip route ip-prefix [detail | longer-prefixes [summary | detail]]
Example:
switch(config-router-af)# show isis ip route
(Optional) Shows the routes IS-IS.
Step 8
copy running-config startup-config
Example:
switch(config-router-af)# copy running-config startup-config
(Optional) Saves this configuration change.
This example shows how to redistribute EIGRP into IS-IS:
switch# configure terminal
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
Limiting the Number of Redistributed Routes
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:
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BEFORE YOU BEGIN
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).
SUMMARY STEPS
1.
2.
3.
4.
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6.
DETAILED STEPS
This example shows how to limit the number of redistributed routes into IS-IS:
switch# configure terminal
switch(config)# router eigrp isis Enterprise
switch(config-router)# redistribute bgp route-map FilterExternalBGP
switch(config-router)# redistribute maximum-prefix 1000 75
Configuring a Graceful Restart
You can configure a graceful restart for IS-IS.
BEFORE YOU BEGIN
You must enable IS-IS (see the "Enabling the IS-IS Feature" section).
Create the VDCs and VRFs.
Ensure that you are in the correct VDC (or use the switchto vdc command).
SUMMARY STEPS
1.
2.
3.
4.
5.
6.
DETAILED STEPS
This example shows how to enable a graceful restart:
switch# configure terminal
switch(config)# router isis Enterprise
switch(config-router)# graceful-restart
switch(config-router)# copy running-config startup-config
Configuring Virtualization
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
BEFORE YOU BEGIN
You must enable IS-IS (see the "Enabling the IS-IS Feature" section).
Create the VDCs.
Ensure that you are in the correct VDC (or use the switchto vdc command).
SUMMARY STEPS
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DETAILED STEPS
The following example shows how to create a VRF and add an interface to the VRF:
switch# configure terminal
switch(config)# vrf context NewVRF
switch(config-vrf)# exit
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
switch(config-if)# ip router isis Enterprise
switch(config-if)# copy running-config startup-config
Tuning IS-IS
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:
You can use the following optional commands in interface configuration mode to tune IS-IS:
Verifying the IS-IS Configuration
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.
Monitoring IS-IS
To display IS-IS statistics, use the following commands:
To clear IS-IS configuration statistics, perform one of the following tasks:
Configuration Examples for IS-IS
The following example shows how to configure IS-IS:
router isis Enterpriseis-type level-1net 49.0001.0000.0000.0003.00graceful-restartaddress-family ipv4 unicastdefault-information originateinterface ethernet 2/1ip address 192.0.2.1/24isis circuit-type level-1ip router isis EnterpriseRelated Topics
See the Chapter 16 "Configuring Route Policy Manager" for more information on route maps.
Additional References
For additional information related to implementing IS-IS, see the following sections:
Related Documents
Standards
No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.
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Feature History for IS-IS
Table 9-2 lists the release history for this feature.
