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 advertisement of a router’s capabilities to its neighbors for informational and troubleshooting purposes. A TLV as defined in RFC 4971 advertises the TE Node Capability Descriptor capability.

The parameters (area and as) control the scope of the capability advertisements.

The no form of this command disables this capability.

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 enables the population of the extended TE database (TE-DB) with the link-state information from the IS-IS instance.

The extended TE-DB is used as a central point for importing all link-state, link, node, and prefix information from IGP instances on the router and exporting the information to BGP-LS on the router. This information includes the IGP, TE, SID sub-TLV, and adjacency SID sub-TLV.

The no form of this command disables database exportation.

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 enables the context for the configuration of entropy label capabilities (ELC) for the routing protocol.

This command configures the ability to override any received entropy label capability advertisements. When enabled, the system assumes that all nodes for an IGP domain are capable of receiving and processing the entropy label on segment routed tunnels. This command can only be configured if entropy-label is enabled via the config>router>isis>segment-routing>entropy-label command.

The no version of this command disables the override. The system assumes entropy label capability for other nodes in the IGP instance if capability advertisements are received.

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 this level 1 router will ignore the attached (ATT) bit in received level 1 link-state PDUs (LSPs) and therefore will not install the default route to the level 1/2 router that set the ATT bit.

The no form of the command specifies that the router will install the default route to the closest level 1/2 router.

This command specifies that the router will ignore 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 63.

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 63.

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-entry context. 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 63. 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 64 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 for the IS-IS routing protocol.

When this command is enabled, it instructs the IGP SPF to attempt to precompute both a primary next hop and an 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 user enables the remote LFA next-hop calculation by the IGP LFA SPF by using the remote-lfa option. When this option is enabled in an IGP instance, SPF performs the additional remote LFA computation that follows the regular LFA next-hop calculation when the latter calculation results in no protection for one or more prefixes that resolve to a particular interface.

Remote LFA extends the protection coverage of LFA-FRR to any topology by automatically computing and establishing or tearing-down shortcut tunnels, also referred to as repair tunnels, to a remote LFA node that puts the packets back into the shortest path without looping them back to the node that forwarded them over the repair tunnel. The remote LFA node is referred to as a PQ node. A repair tunnel can, in theory, be an RSVP-TE LSP, an LDP-in-LDP tunnel, or a segment routing (SR) tunnel. In this command, remote-lfa is restricted to using an SR repair tunnel to the remote LFA node.

The remote LFA algorithm is a per-link LFA SPF calculation and not a per-prefix calculation like the regular LFA algorithm. The remote LFA algorithm provides protection for all destination prefixes that share the protected link by using the neighbor on the other side of the protected link as a proxy for all the destinations.

The Topology-independent LFA (TI-LFA) further improves the protection coverage of a network topology by computing and automatically instantiating a repair tunnel to a Q node that is not in the shortest path from the computing node. The repair tunnel uses the shortest path to the P node and a source-routed path from the P node to the Q node.

The TI-LFA repair tunnel can have a maximum of three labels pushed in addition to the label of the destination node or prefix. The user can set a lower maximum value for the additional FRR labels by configuring the max-sr-frr-labels option. The default value is 2.

The no form of this command disables the LFA computation by the IGP SPF.

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 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.

This command configures IS-IS in the overload state upon boot-up until one of the following events occurs:

When the router is in an overload state, the router is used only if there is no other router to reach the destination.

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 the use of the Purge Originator Identification (POI) TLV for this IS-IS instance. The POI is added to purges and contains the system ID of the router that generated the purge, which simplifies troubleshooting and determining what caused the purge.The no form of this command removes the POI 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 enables the context to configure segment routing parameters within an IGP instance.

Segment routing adds to IS-IS and OSPF routing protocols the ability to perform shortest path routing and source routing using the concept of abstract segment. An abstract segment can represent a local prefix of a node, a specific adjacency of the node (interface or next-hop), a service context, or a specific explicit path over the network. For each segment, the IGP advertises an identifier referred to as the segment ID (SID).

When segment routing is used together with the MPLS data plane, the SID is a standard MPLS label. A router forwarding a packet using segment routing will push one or more MPLS labels.

Segment routing using MPLS labels can be used in both shortest path routing applications and traffic engineering applications. On the 7705 SAR, segment routing implements the shortest path forwarding application.

After segment routing is successfully enabled in the IS-IS or OSPF instance, the router will perform the following operations:

When the user enables segment routing in an IGP instance, the main SPF and LFA SPF are computed normally and the primary next hop and LFA backup next hop for a received prefix are added to the RTM without the label information advertised in the prefix SID sub-TLV.

This command configures a timer to hold the ILM or LTN of an adjacency SID following a failure of the adjacency.

When an adjacency to a neighbor fails, the IGP will withdraw the advertisement of the link TLV information as well as its adjacency SID sub-TLV. However, the ILM or LTN record of the adjacency SID must be kept in the data path to maintain forwarding using the LFA or remote LFA backup for a sufficient length of time to allow the ingress LER and other routers that use this adjacency SID to activate a new path after the IGP converges.

If the adjacency is restored before the timer expires, the timer is aborted as soon as the new ILM or LTN records are updated with the new primary and backup NHLFE information.

The no form of the command removes the adjacency SID hold time.

This command, when used with the force-disable keyword, instructs the system to ignore any received IGP advertisements of entropy label capability relating to remote nodes in the network. The command also prevents a user from configuring override-tunnel-elc for the IGP instance.

The no version of this command enables the processing of any received IGP advertisements of entropy label capability. Using the enable keyword has the same effect.

This command enables the exporting of LDP tunnels from the TTM to an IGP instance for the purpose of stitching an SR tunnel to an LDP FEC for the same destination IPv4 /32 prefix.

When this command is enabled, the IGP monitors the LDP tunnel entries in the TTM. Whenever an LDP tunnel destination matches a prefix for which IGP received a prefix SID sub-TLV from the mapping server, the IGP instructs the SR module to program the SR ILM and to stitch it to the LDP tunnel endpoint.

The no form of this command disables the exporting of LDP tunnels to the IGP instance.

This command enables the context to enable the SR mapping server feature for an IS-IS instance.

The mapping server feature allows the configuration and advertisement via IS-IS of the node SID index for IS-IS prefixes of routers that are in the LDP domain. The router that is acting as a mapping server uses a prefix SID sub-TLV within the SID/Label Binding TLV in IS-IS to advertise a node SID index.

The no form of this command deletes the mapping server.

This command configures the SR mapping server database for an IS-IS instance.

The node-sid index can be configured for one prefix or a range of prefixes by specifying the index value or a value range.

Only the first prefix in a consecutive range of prefixes must be entered. If the first prefix has a mask lower than 32, the SID/Label Binding TLV is advertised but the router does not resolve the prefix SIDs; a trap is originated instead.

The set-flags s option indicates to the IS-IS network routers that the flooding of the SID/Label Binding TLV applies to the entire domain. A router that receives the TLV advertisement leaks it between IS-IS levels 1 and 2. If leaked from level 2 to level 1, the D-flag must be set; this prevents the TLV from being leaked back into level 2. The S-flag is not defined by default; if it is not configured, the TLV is not leaked by routers receiving the mapping server advertisement.

The level option specifies the mapping server’s flooding scope for the generated SID/Label Binding TLV using t. The default flooding scope of the mapping server is level 1/2.

The no form of this command deletes the range of node SIDs beginning with the specified index value.

This command configures the prefix SID index range and offset label value for an IGP instance.

The key parameter is the configuration of the prefix SID index range and the offset label value that this IGP instance will use. Because each prefix SID represents a network global IP address, the SID index for a prefix must be unique network-wide. Therefore, all routers in the network are expected to configure and advertise the same prefix SID index range for an IGP instance. However, the label value used by each router to represent this prefix, that is, the label programmed in the ILM, can be local to that router by the use of an offset label, referred to as a start label:

Local Label (Prefix SID) = start-label + {SID index}

The label operation in the network is very similar to LDP when operating in the independent label distribution mode (RFC 5036, LDP Specification), with the difference that the label value used to forward a packet to each downstream router is computed by the upstream router based on the advertised prefix SID index using the above formula.

There are two mutually exclusive modes of operation for the prefix SID range on the router: global mode and per-instance mode.

In global mode, the user configures the global value and the IGP instance assumes that the start label value is the lowest label value in the Segment Routing Global Block (SRGB) and the prefix SID index range size is equal to the range size of the SRGB. When one IGP instance selects the global option for the prefix SID range, all IGP instances on the system must do the same. The user must shut down the segment routing context and disable the prefix-sid-range command in all IGP instances in order to change the SRGB. When the SRGB is changed, the user must re-enable the prefix-sid-range command. The SRGB range change will fail if an already allocated SID index/label goes out of range.

In per-instance mode, the user partitions the SRGB into non-overlapping sub-ranges among the IGP instances. The user configures a subset of the SRGB by specifying the start label value and the prefix SID index range size. All resulting net label values (start-label + index) must be within the SRGB or the configuration will fail. The 7705 SAR checks for overlaps of the resulting net label value range across IGP instances and will strictly enforce no overlapping of these ranges. The user must shut down the segment routing context of an IGP instance in order to change the SID index/label range of that IGP instance using the prefix-sid-range command. A range change will fail if an already allocated SID index/label goes out of range. The user can change the SRGB without shutting down the segment routing context as long as it does not reduce the current per-IGP instance SID index/label range defined with the prefix-sid-range command. Otherwise, the user must shut down the segment routing context of the IGP instance, and disable and re-enable the prefix-sid-range command.

This command configures the MTU of all SR tunnels within each IGP instance.

The MTU of an SR tunnel populated into the TTM is determined in the same way as the MTU of an IGP tunnel (for example, an LDP LSP) based on the outgoing interface MTU minus the label stack size. Remote LFA can add, at most, one more label to the tunnel for a total of two labels. There is no default value for this command. If the user does not configure an SR tunnel MTU, the MTU, in bytes, is determined by IGP as follows:

SR_Tunnel_MTU = MIN {Cfg_SR_MTU, IGP_Tunnel_MTU – (1 + frr-overhead)× 4}

where:

The SR tunnel MTU is dynamically updated whenever any of the above parameters used in its calculation changes. This includes if the set of the tunnel next hops changes or the user changes the configured SR MTU or interface MTU value.

This command configures the TTM preference of shortest path SR tunnels created by the IGP instance. This is used for BGP shortcuts, VPRN auto-bind, or BGP transport tunnel when the tunnel binding commands are configured to the any value, which parses the TTM for tunnels in the protocol preference order. The user can choose either the global TTM preference or explicitly list the tunnel types they want to use. If the user lists the tunnel types explicitly, the TTM preference is still used to select one type over the other. In both cases, a fallback to the next preferred tunnel type is performed if the selected type fails. A reversion to a more preferred tunnel type is performed as soon as one is available.

The segment routing module adds to the TTM an SR tunnel entry for each resolved remote node SID prefix and programs the data path having the corresponding LTN with the push operation pointing to the primary and LFA backup NHLFEs.

The default preference for shortest path SR tunnels in the TTM is set lower than LDP tunnels but higher than BGP tunnels to allow controlled migration of customers without disrupting their current deployment when they enable segment routing. The following list shows the value of the default preference for the various tunnel types. This includes the preference of SR tunnels based on shortest path (referred to as SR-ISIS and SR-OSPF).

Note: The preference of the SR-TE LSP is not configurable and is the second most preferred tunnel type after RSVP-TE. The preference is the same whether the SR-TE LSP was resolved in IS-IS or OSPF.

The global default TTM preference for the tunnel types is as follows:

The default value for SR-ISIS or SR-OSPF is the same regardless of whether one or more IS-IS or OSPF instances programmed a tunnel for the same prefix. The selection of an SR tunnel in this case is based on the lowest IGP instance ID.

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 suppresses the setting of the attached (ATT) bit in level 1 LSPs originated by this level 1/2 router to prevent all level 1 routers in the area from installing a default route to this router.

The no form of the command enables the setting of the ATT bit.

This command configures the IS-IS timer values.

This command is used to customize LSP generation throttling. 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 second lsp-wait timer until a maximum value is reached.

Note: The IS-IS timer granularity is 100 ms. Timer values are rounded down to the nearest supported value; for example, a configured value of 550 ms is internally rounded down to 500 ms.

This command defines the maximum interval, in 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 exponentially increasing 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, the 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 the spf-initial-wait value.

Note: The IS-IS timer granularity is 100 ms. Timer values are rounded down to the nearest supported value; for example, a configured value of 550 ms is internally rounded down to 500 ms.

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 hello-interval, along with the hello-multiplier, is used to calculate a hold time, which is communicated to a neighbor in a Hello PDU.

Note: The neighbor hold time is (hello multiplier × hello interval) on non-designated intermediate system broadcast interfaces and point-to-point interfaces and is (hello multiplier × hello interval / 3) on designated intermediate system broadcast interfaces. Hello values can be adjusted for faster convergence, but the hold time should always be > 3 to reduce routing instability.

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

This command configures a hello multiplier. The hello-multiplier, along with the hello-interval, is used to calculate a hold time, which is communicated to a neighbor in a Hello PDU.

The hold time is the time in which the neighbor expects to receive the next Hello PDU. If the neighbor receives a Hello within this time, the hold time is reset. If the neighbor does not receive a Hello within the hold time, it brings the adjacency down.

Note: The neighbor hold time is (hello multiplier × hello interval) on non-designated intermediate system broadcast interfaces and point-to-point interfaces and is (hello multiplier × hello interval / 3) on designated intermediate system broadcast interfaces. Hello values can be adjusted for faster convergence, but the hold time should always be > 3 to reduce routing instability.

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 assigns a node SID index or label value to the prefix representing the primary address of an IPv4 network interface of type loopback. Only a single node SID can be assigned to an interface. The secondary address of an IPv4 interface cannot be assigned a node SID index and does not inherit the SID of the primary IPv4 address.

This command fails if the network interface is not of type loopback or if the interface is defined in an IES or a VPRN context.

Assigning the same SID index or label value to the same interface in two different IGP instances is not allowed within the same node.

The value of the label or index SID is taken from the range configured for this IGP instance. When using the global mode of operation, the segment routing module checks that the same index or label value is not assigned to more than one loopback interface address. When using the per-instance mode of operation, this check is not required because the index, and therefore the label ranges, of IGP instances are not allowed to overlap.

This command assigns a node SID index or label value to the prefix representing the primary address of an IPv6 network interface of type loopback. Only a single node SID can be assigned to an IPv6 interface. When an IPv6 interface has multiple global addresses, the primary address is always the first one in the list, as displayed by the interface info command.

This command fails if the network interface is not of type loopback or if the interface is defined in an IES or a VPRN context.

Assigning the same SID index or label value to the same interface in two different IGP instances is not allowed within the same node.

The value of the label or index SID is taken from the range configured for this IGP instance. When using the global mode of operation, the segment routing module checks that the same index or label value is not assigned to more than one loopback interface address. When using the per-instance mode of operation, this check is not required because the index, and therefore the label ranges, of IGP instances are not allowed to overlap.

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.

This command enables or disables adjacency SID protection by LFA and remote LFA.

LFA and remote LFA Fast Reroute (FRR) protection is enabled for all node SIDs and local adjacency SIDs when the user enables the loopfree-alternate option in IS-IS or OSPF at the LER and LSR. However, there may be applications where the user never wants traffic to divert from the strict hop computed by CSPF for an SR-TE LSP. In this case, the user can disable protection for all adjacency SIDs formed over a particular network IP interface using this command.

The protection state of an adjacency SID is advertised in the B flag of the IS-IS or OSPF Adjacency SID sub-TLV.