5.11. IS-IS Command Reference

This command administratively disables the entity. When disabled, an entity does not change, reset, or remove any configuration settings or statistics. Many entities must be explicitly enabled using the no shutdown command.

The operational state of the entity is disabled as well as the operational state of any entities contained within. Many objects must be shut down before they can be deleted.

Unlike other commands and parameters where the default state is not indicated in the configuration file, shutdown and no shutdown are always indicated in system-generated configuration files.

The no form of the command puts an entity into the administratively enabled state.

This command activates an IS-IS instance on the router and enables access to the context to define IS-IS parameters.

Instance 0, the base instance, is enabled when the isis command is run without specifying an isis-instance. Multiple IS-IS instances are enabled by including an isis-instance value.

The no form of the command deletes the IS-IS instance and removes all configuration parameters.

This command enables the forwarding adjacency feature. With this feature, IS-IS advertises an RSVP-TE LSP as a link so that other routers in the network can include it in their SPF calculations. The RSVP-TE LSP is advertised as an unnumbered point-to-point link and the link-state PDU (LSP) has no traffic engineering opaque sub-TLVs as per RFC 3906.

The forwarding adjacency feature can be enabled independently from the IGP shortcut feature (rsvp-shortcut). If both features are enabled for a given IS-IS instance, the forwarding adjacency feature takes precedence.

When this feature is enabled, each node advertises a point-to-point unnumbered link for each best-metric tunnel to the router ID of any endpoint node. The node does not include the tunnels as IGP shortcuts in the SPF calculation directly. Instead, when the LSP advertising the corresponding point-to-point unnumbered link is installed in the local routing database, the node performs an SPF calculation using the link like any other link LSP.

The link bidirectional check requires that a regular link or tunnel link exists in the reverse direction for the tunnel to be used in the SPF calculation.

An RSVP-TE LSP can be excluded from being used as a forwarding adjacency with the config>router>mpls>lsp>no igp-shortcut command.

The no form of this command disables forwarding adjacency and therefore disables the advertisement of RSVP-TE LSPs into IS-IS.

This command configures the area ID portion of the Network Service Access Point (NSAP) address, which identifies a point of connection to the network, such as a router interface.

Addresses in the IS-IS protocol are based on the ISO NSAP addresses and Network Entity Titles (NETs), not IP addresses. NET addresses are constructed similarly to NSAPs with the exception that the selector ID is always 00. NET addresses are exchanged in Hello and LSP PDUs. All NET addresses configured on the node are advertised to its neighbors.

Up to three area addresses can be configured.

NSAP addresses are divided into three parts. Only the area ID portion is configurable:

For level 1 interfaces, neighbors can have different area IDs, but they must have at least one area ID (AFI + area) in common. Sharing a common area ID, they become neighbors and area merging between the potentially different areas can occur.

For level 2 interfaces, neighbors can have different area IDs. However, if they have no area IDs in common, they become only level 2 neighbors and only level 2 LSPs are exchanged.

For level 1/2 interfaces, neighbors can have different area IDs. If they have at least one area ID (AFI + area) in common, they become neighbors. In addition to exchanging level 2 LSPs, area merging between potentially different areas can occur.

If multiple area-id commands are entered, the system ID of all subsequent entries must match the system ID of the first area address.

The no form of the command removes the area address.

This command associates an authentication keychain with the IS-IS instance or level. The keychain is a collection of keys used to authenticate IS-IS messages from remote peers. The keychain allows the rollover of authentication keys during the lifetime of a session and also supports stronger authentication algorithms than clear text and MD5.

The keychain must already be defined in the config>system>security>keychain context.

Either the authentication-key command or the auth-keychain command can be used by IS-IS, but both cannot be supported at the same time. If both commands are configured, the auth-keychain configuration will be applied and the authentication-key command will be ignored.

By default, authentication is not enabled.

This command sets an authentication check to reject PDUs that do not match the type or key requirements.

The default behavior when authentication is configured is to reject all IS-IS protocol PDUs that have a mismatch in either the authentication type or authentication key.

When no authentication-check is configured, authentication PDUs are generated and IS-IS PDUs are authenticated on receipt. However, although mismatches cause an event to be generated, the mismatches will not be rejected.

This command sets the authentication key used to verify PDUs sent by neighboring routers on the interface. Neighboring routers use passwords to authenticate PDUs sent from an interface. For authentication to work, both the authentication key and the authentication type on a segment must match. The authentication-type command must also be entered.

To configure authentication on the global level, configure this command in the config>router>isis context. When this parameter is configured on the global level, all PDUs are authenticated, including the Hello PDU.

To override the global setting for a specific level, configure the authentication-key command in the config>router>isis>level context. When configured within the specific level, Hello PDUs are not authenticated.

By default, no authentication key is configured.

Either the authentication-key command or the auth-keychain command can be used by IS-IS, but both cannot be supported at the same time. If both commands are configured, the auth-keychain configuration will be applied and the authentication-key command will be ignored.

The no form of the command removes the authentication key.

This command enables either simple password or message-digest authentication in the global IS-IS or IS-IS level context. Both the authentication key and the authentication type on a segment must match. The authentication-key command must also be entered.

Configure the authentication type at the global level in the config>router>isis context. Configure or override the global setting by configuring the authentication type in the config>router>isis>level context.

The no form of the command disables authentication.

This command enables authentication of individual IS-IS packets of complete sequence number PDUs (CSNPs).

The no form of the command suppresses authentication of CSNP packets.

This command disables the IGP-LDP synchronization feature on all interfaces participating in the OSPF or IS-IS routing protocol. When this command is executed, the IGP immediately advertises the actual value of the link cost for all interfaces that have the IGP-LDP synchronization enabled if the currently advertised cost is different. IGP-LDP synchronization will then be disabled for all interfaces. This command does not delete the interface configuration.

The no form of this command restores the default settings and re-enables IGP-LDP synchronization on all interfaces participating in the OSPF or IS-IS routing protocol and for which the ldp-sync-timer is configured (refer to the 7705 SAR Router Configuration Guide for information on configuring the ldp-sync-timer).

This command associates export route policies to determine which routes are exported from the route table to IS-IS.

If no export policy is specified, non-IS-IS routes are not exported from the routing table manager to IS-IS.

If multiple policy names are specified, the policies are evaluated in the order they are specified. The first policy that matches is applied. If multiple export commands are issued, the last command entered will override the previous command. A maximum of five policy names can be specified.

The no form of the command removes all policies from the configuration.

Refer to the 7705 SAR Router Configuration Guide for information on defining route policies.

This command enables authentication of individual IS-IS Hello PDUs.

The no form of the command suppresses authentication of Hello PDUs.

This command specifies that the router will ignore IS-IS link-state PDUs (LSPs) with internal checksum errors rather than purging the LSPs.

The no form of the command specifies that LSPs with internal checksum errors will be purged, which will cause the originator to resend the LSPs.

This command specifies whether the Instance Identifier (IID) TLV is enabled or disabled for this IS-IS instance so an interface can be used in multiple IS-IS instances.

When enabled, each IS-IS instance marks its packets with the IID TLV containing its unique 16-bit IID for the routing domain. You must use a shutdown/no shutdown command sequence on the IS-IS instance to make the change operational.

The no form of the command disables the IID TLV marking of packets.

This command enables or disables IPv4 routing on the IS-IS instance.

This command enables or disables single topology (native) IPv6 routing on the IS-IS instance. In native mode, IPv6 routing information is exchanged within IS-IS using IS-IS IPv6 TLVs.

This command enables the context to configure IS-IS level 1 or level 2 area attributes.

To reset global and/or interface level parameters to the default, the following commands must be entered independently:

This command configures the preference for IS-IS external routes for the IS-IS level. The preference for internal routes is set with the preference command.

The command configures the preference level for either level 1 or level 2 external routes. The default preferences are listed in Table 50.

A route can be learned by the router from different protocols, in which case, the costs are not comparable. When this occurs, the preference is used to decide which route will be used.

Different protocols should not be configured with the same preference. If this occurs, the tiebreaker is based on the default preferences as listed in Table 50.

If multiple routes are learned with an identical preference using the same protocol, the lowest-cost route is used. If multiple routes are learned with an identical preference using the same protocol and the costs (metrics) are equal, the decision of which route to use is determined by the configuration of ECMP in the config>router context. Refer to the 7705 SAR Router Configuration Guide for information on ECMP.

Note: To configure a preference for static routes, use the config>router>static-route command. Refer to the 7705 SAR Router Configuration Guide for information.

The no form of the command reverts to the default value.

This command instructs IS-IS to exclude a specific interface or all interfaces participating in a specific IS-IS level from the LFA SPF calculation. The LFA SPF calculation can therefore be run only where it is needed.

If an interface is excluded from the LFA SPF in IS-IS, it is excluded in both level 1 and level 2.

This command configures the preference for IS-IS level 1 or level 2 internal routes.

A route can be learned by the router from different protocols, in which case, the costs are not comparable. When this occurs, the preference is used to decide which route will be used.

Different protocols should not be configured with the same preference. If this occurs, the tiebreaker is based on the default preferences as listed in Table 50. If multiple routes are learned with an identical preference using the same protocol and the costs (metrics) are equal, the decision of which route to use is determined by the configuration of ECMP in the config>router context. Refer to the 7705 SAR Router Configuration Guide for information on ECMP.

The no form of the command reverts to the default value.

This command enables the exclusive use of wide metrics in the LSPs for the level number. Narrow metrics can have values between 1 and 63. IS-IS can generate two TLVs, one for the adjacency and one for the IP prefix. In order to support traffic engineering, wider metrics are required. When wide metrics are used, a second pair of TLVs are added for the adjacency and the IP prefix.

By default, both sets of TLVs are generated. When wide-metrics-only is configured, IS-IS only generates the pair of TLVs with wide metrics for that level.

The no form of the command reverts to the default value.

This command configures the routing level for the IS-IS instance.

An IS-IS router and IS-IS interface can operate at level 1, level 2, or both level 1 and level 2.

A level 1 adjacency can be established if there is at least one area address shared by this router and a neighbor. A level 2 adjacency cannot be established over this interface.

A level 1/2 adjacency is created if the neighbor is also configured as a level 1/2 router and has at least one area address in common. A level 2 adjacency is established if there are no common area IDs.

A level 2 adjacency is established if another router is configured as a level 2 or level 1/2 router with interfaces configured as level 1/2 or level 2. Level 1 adjacencies will not established over this interface.

Table 51 lists capability combinations and the potential adjacencies that can be formed.

The no form of the command removes the level capability from the configuration.

This command enables Loop-Free Alternate (LFA) computation by SPF under the IS-IS routing protocol instance.

When this command is enabled, the IS-IS SPF attempts to precalculate both a primary next hop and a LFA backup next hop for every learned prefix. When found, the LFA next hop is populated into the routing table along with the primary next hop for the prefix.

The no form of this command disables the LFA SPF calculation.

This command excludes from the LFA SPF calculation any prefixes that match a prefix entry in a prefix policy. If a prefix is excluded, it is not included in the LFA SPF calculation, regardless of its priority. Prefix policies are created with the command config>router> policy-options>prefix-list (for information on prefix lists, refer to the 7705 SAR Router Configuration Guide, “Route Policies”).

The default action of the loopfree-alternate-exclude command, when not explicitly specified in the prefix policy, is to “reject”. Therefore, even if the default-action reject statement was not explicitly stated for the prefix policy, a prefix that does not match any entry in the policy will be used in the LFA SPF calculation.

The no form of the command deletes the excluded prefix policy.

This command sets the time interval for LSPs originated by the router to be considered valid by other routers in the domain.

Each LSP received is maintained in an LSP database until the LSP lifetime expires, unless the originating router refreshes the LSP. Each router refreshes its LSPs at the half-life of the lsp-lifetime value (by default, every 10 min (600 s)), so that other routers will not age out the LSP.

The no form of the command reverts to the default value.

This command configures the LSP MTU size. If the MTU size is changed from the default value using the CLI or SNMP, IS-IS must be restarted in order for the change to take effect. This can be done by performing a shutdown command and then a no shutdown command in the config>router>isis context.

Note: If the MTU size is changed from the default value by using the exec command to execute a configuration file with the changed value, IS-IS will automatically bounce before the change takes effect.

The no form of the command reverts to the default value.

This command is used to customize the throttling of IS-IS LSP generation. Timers that determine when to generate the first, second, and subsequent LSPs can be controlled with this command.

Subsequent LSPs are generated at increasing intervals of the lsp-second-wait timer until a maximum value is reached.

This command enables the submission of routes into the multicast Route Table Manager (RTM) by IS-IS.

The no form of the command disables the submission of routes into the multicast RTM.

This command administratively sets the IS-IS router to operate in the overload state for a specific time period, in seconds, or indefinitely.

During normal operation, the router may be forced to enter an overload state due to a lack of resources. When in the overload state, the router is only used if the destination is reachable by the router and will not be used for other transit traffic.

If a time period is specified, the overload state persists for the configured length of time. If no time is specified, the overload state operation is maintained indefinitely.

The overload command can be useful in circumstances where the router is overloaded or used prior to executing a shutdown command to divert traffic around the router.

The no form of the command causes the router to exit the overload state.

When the router is in an overload state, the router is used only if there is no other router to reach the destination. This command configures IS-IS in the overload state upon boot-up until one of the following events occurs:

The no overload command does not affect the overload-on-boot function. If the overload state is cleared with the no overload command, the router will still re-enter the overload state after rebooting.

If no timeout is specified, IS-IS will go into the overload state indefinitely after a reboot. After the reboot, the IS-IS status will display a permanent overload state:

This state can be cleared with the no overload command.

If a timeout value is specified, IS-IS will go into the overload state for the configured timeout after a reboot. After the reboot, the IS-IS status will display the remaining time that the system stays in overload:

The overload state can be cleared before the timeout expires with the no overload command.

The no form of the command removes the overload-on-boot functionality from the configuration.

This command enables authentication of individual IS-IS packets of partial sequence number PDUs (PSNPs).

The no form of the command suppresses authentication of PSNP packets.

This command configures the reference bandwidth used to calculate the default costs of interfaces based on their underlying link speed.

The default interface cost is calculated as follows:

cost = reference bandwidth/bandwidth

If the reference bandwidth is configured as 10 Gbytes (10 000 000 000), a 100 Mb/s interface has a default metric of 100. In order for metrics in excess of 63 to be configured, wide metrics must be deployed (see the wide-metrics-only command).

If the reference bandwidth is not configured, all interfaces have a default metric of 10.

The no form of the command resets the reference bandwidth to the default value.

This command enables the use of an RSVP-TE shortcut for resolving IS-IS routes. When the command is enabled, IS-IS includes RSVP-TE LSPs originating on this node and terminating on the router ID of a remote node as direct links with a metric equal to the operational metric provided by MPLS.

The SPF algorithm will always use the IGP metric to build the SPF tree, and the LSP metric value does not update the SPF tree calculation. During the IP reach to determine the reachability of nodes and prefixes, LSPs are overlaid and the LSP metric is used to determine the subset of paths that are of an equal lowest cost to reach a node or a prefix. If the relative-metric option for this LSP is enabled (in the config>router>mpls>lsp>igp-shortcut context), IS-IS will apply the shortest cost between the endpoints of the LSP plus the value of the offset, instead of the LSP operational metric, when calculating the cost of a prefix that is resolved to the LSP.

When a prefix is resolved to a tunnel next hop, the packet is sent labeled with the label stack corresponding to the NHLFE of the RSVP-TE LSP. Any network event that causes an RSVP-TE LSP to go down will trigger a full SPF calculation, which may result in a new route being installed over another RSVP-TE LSP shortcut as a tunnel next hop or over a regular IP next hop.

When the rsvp-shortcut command is enabled, all RSVP-TE LSPs originating on this node are eligible by default as long as the destination address of the LSP, as configured with the config>router>mpls> lsp>to command, corresponds to a router ID of a remote node. A specific LSP can be excluded from being used as a shortcut with the config>router>mpls>lsp>no igp-shortcut command.

If ECMP is enabled on the system and multiple equal-cost paths exist for the route over a set of tunnel next hops (based on the hashing routine supported for IPv4 packets), there are two possibilities:

ECMP is not performed across both the IP and tunnel next hops.

IS-IS can populate the multicast RTM with the prefix IP next hop when both rsvp-shortcut and multicast-import are enabled. The unicast RTM can still use the tunnel next hop for the same prefix.

The forwarding adjacency feature (advertise-tunnel-link) can be enabled independently from the shortcuts feature. If both features are enabled for a given IS-IS instance, the forwarding adjacency feature takes precedence.

The no form of this command disables the resolution of IGP routes using RSVP shortcuts.

This command defines the maximum interval, in seconds and milliseconds, between two consecutive SPF calculations. Timers that determine when to initiate the first, second, and subsequent SPF calculations after a topology change occurs can be controlled with this command. Subsequent SPF runs (if required) will occur at doubling intervals of the spf-second-wait interval. For example, if the spf-second-wait interval is 1000, the next SPF will run after 2000 ms, and the next SPF after that will run after 4000 ms, and so on, until it reaches the spf-wait value. The SPF interval will stay at the spf-wait value until there are no more SPF runs scheduled in that interval. After a full interval without any SPF runs, the SPF interval will drop back to spf-initial-wait.

The timer must be entered in increments of 100 ms. Values entered that do not match this requirement will be rejected.

The no form of this command returns to the default.

This command enables strict checking of address families (IPv4 and IPv6) for IS-IS adjacencies. When enabled, adjacencies will not come up unless both routers have exactly the same address families configured. If there is an existing adjacency with unmatched address families, it will be torn down. By ensuring that adjacencies are only established if both routers have the same address families, this command prevents the blackholing of traffic that may occur when IPv4 and IPv6 topologies are different.

When the command is disabled, both routers only need to have one common address family to establish the adjacency. A BFD session failure for either IPv4 or IPv6 will cause the routes for the other address family to be removed as well.

This command creates summary addresses.

This command enables traffic engineering and determines if IGP shortcuts are required.

The no form of the command disables traffic-engineered route calculations.

This command allows one IGP to import its routes into the multicast RTM (also known as the RPF RTM [Reverse Path Forwarding - Route Table Manager]) while another IGP imports routes only into the unicast RTM. Import policies can redistribute routes from an IGP protocol into the RPF RTM. By default, the IGP routes will not be imported into the RPF RTM, since such an import policy must be explicitly configured.

The no form of the command enables importing IGP routes into the RPF RTM.

This command enables the context to configure an IS-IS interface.

When an area is defined, the interfaces belong to that area. Interfaces cannot belong to other areas.

If the interface is a POS channel, the OSI Network Layer Control Protocol (OSINLCP) is enabled when the interface is created and removed when the interface is deleted.

The no form of the command deletes the IS-IS interface configuration for this interface. The shutdown command in the config>router>isis>interface context can be used to disable an interface without removing the configuration for the interface.

This command enables the use of bidirectional forwarding (BFD) to control IPv4 adjacencies. By enabling BFD on a given IS-IS interface, the state of the interface is tied to the state of the BFD session between the local node and the remote node. The parameters used for BFD are set via the BFD command under the IP interface.

The no form of this command removes BFD from the associated IPv4 adjacency.

This command configures the interval, in seconds, to send complete sequence number PDUs (CSNPs) from the interface. IS-IS must send CSNPs periodically.

The no form of the command reverts to the default value.

This command associates a Hello authentication keychain with the IS-IS interface or interface level. The keychain is a collection of keys used to authenticate IS-IS messages from remote peers. The keychain allows the rollover of authentication keys during the lifetime of a session and also supports stronger authentication algorithms than clear text and MD5.

The keychain must already be defined in the config>system>security>keychain context.

Either the hello-authentication-key command or the hello-auth-keychain command can be used by IS-IS, but both cannot be supported at the same time. If both commands are configured, the hello-auth-keychain configuration will be applied and the hello-authentication-key command will be ignored.

This command configures the authentication key (password) for Hello PDUs. Neighboring routers use the password to verify the authenticity of Hello PDUs sent from this interface. Both the Hello authentication key and the Hello authentication type on a segment must match. The hello-authentication-type command must also be entered.

To configure the Hello authentication key for all levels configured for the interface, use the hello-authentication-key command in the config>router>isis>interface context.

To configure or override the Hello authentication key for a specific level, use the hello-authentication-key command in the config>router>isis>interface>level context.

If both IS-IS authentication and Hello authentication are configured, Hello messages are validated using Hello authentication. If only IS-IS authentication is configured, it will be used to authenticate all IS-IS protocol PDUs, including Hello PDUs.

Either the hello-authentication-key command or the hello-auth-keychain command can be used by IS-IS, but both cannot be supported at the same time. If both commands are configured, the hello-auth-keychain configuration will be applied and the hello-authentication-key command will be ignored.

The no form of the command removes the hello authentication key from the configuration.

This command enables Hello authentication at either the interface or level context. Both the hello authentication key and the hello authentication type on a segment must match. The hello-auth-keychain command must also be entered.

To configure the hello authentication type for all levels configured for the interface, use the hello-authentication-type command in the config>router>isis>interface context.

To configure or override the hello authentication type for a specific level, use the hello-authentication-type command in the config>router>isis>interface>level context.

The no form of the command disables Hello PDU authentication.

This command configures the interval between IS-IS Hello PDUs issued on the interface at this level.

The no form of this command reverts to the default value.

This command configures the number of missing Hello PDUs from a neighbor after which the router declares the adjacency down.

The no form of this command reverts to the default value.

This command configures the interface type to be either broadcast or point-to-point.

Use this command to set the interface type of an Ethernet link to point-to-point to avoid having to carry the broadcast adjacency maintenance overhead of the Ethernet link, provided the link is used as a point-to-point link.

If the interface type is not known when the interface is added to IS-IS, and the IP interface is subsequently bound (or moved) to a different interface type, this command must be entered manually.

The no form of the command reverts to the default value.

This command applies a route next-hop policy template to an IS-IS interface. When a route next-hop policy template is applied to an interface in IS-IS, it is applied in both level 1 and level 2.

If the interface has been excluded from LFA with the loopfree-alternate-exclude command, the LFA policy has no effect on the interface.

If the route next-hop policy template is applied to a loopback interface or to the system interface, the command will not be rejected, but the policy will have no effect on the interface.

The no form of the command deletes the mapping of a route next-hop policy template to an IS-IS interface.

This command configures the interval between link-state PDUs (LSPs) sent from this interface. Controlling the time between LSPs ensures that adjacent neighbors are not being bombarded with excessive data.

A value of 0 means that no LSPs are sent from the interface.

The no form of the command reverts to the default value.

This command assigns an interface to a mesh group. Mesh groups limit the amount of flooding that occurs when a new or changed LSP is advertised throughout an area.

All routers in a mesh group should be fully meshed. When LSPs need to be flooded, only a single copy is received rather than one copy per neighbor.

To create a mesh group, configure the same mesh group value for each interface that is part of the mesh group. All routers must have the same mesh group value configured for all interfaces that are part of the mesh group.

To prevent an interface from flooding LSPs, the optional blocked parameter can be specified.

Caution: Configure mesh groups carefully. It is easy to create isolated islands that will not receive updates if other links fail.

The no form of the command removes the interface from the mesh group.

This command configures the metric used for the level on this IS-IS interface.

To calculate the lowest cost to reach a given destination, each configured level on each interface must have a cost. The costs for each level on an interface may be different.

If the metric is not configured, the default value of 10 is used unless the reference-bandwidth is configured.

The no form of the command reverts to the default value.

This command adds the passive attribute to the IS-IS interface, which causes the interface to be advertised as an IS-IS interface without running the IS-IS protocol. Normally, only interface addresses that are configured for IS-IS are advertised as IS-IS interfaces at the level that they are configured.

If the passive mode is enabled, the interface or the interface at the specified level ignores ingress IS-IS protocol PDUs and will not transmit IS-IS protocol PDUs.

The no form of the command removes the passive attribute.

This command configures the priority of the IS-IS interface that is used in an election of the designated router (DIS) on a multi-access network.

This parameter is only used if the interface is a broadcast type.

The priority is included in Hello PDUs transmitted by the interface on a multi-access network. The router with the highest priority becomes the designated router. The designated router is responsible for sending LSPs about the network and the routers attached to it.

The no form of the command reverts to the default value.

This command specifies the interval, in seconds, that IS-IS will wait before retransmitting an unacknowledged LSP to an IS-IS neighbor.

If the retransmit interval expires and no acknowledgment has been received, the LSP will be retransmitted.

The no form of this command reverts to the default interval.