4.10. IS-IS Command Reference

This command enables the context to configure the Intermediate-System-to-Intermediate-System (IS-IS) protocol instance.

The IS-IS protocol instance is enabled with the no shutdown command in the config>router>isis context. Alternatively, the IS-IS protocol instance is disabled with the shutdown command in the config>router>isis context.

The no form of this command deletes the IS-IS protocol instance. Deleting the protocol instance removes all configuration parameters for this IS-IS instance.

Note: The platforms as described in this document allow for the configuration of a single IS-IS instance at any time. The instance ID can be any number other than 0. This enables these platforms to be used in a network where multi-instance IS-IS is deployed, and the node needs to use an instance ID other than the default instance ID of 0.

This command administratively disables an entity. When disabled, an entity does not change, reset, or remove any configuration settings or statistics.

The operational state of the entity and entities contained within is disabled. Many objects must be shut down before they may be deleted.

The no form of this command administratively enables an entity.

This command enables and disables IS-IS to advertise only prefixes that belong to passive interfaces.

The no form of this command disables IS-IS to advertise only prefixes that belong to passive interfaces.

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

The area and as keywords control the scope of the capability advertisements.

The no form of this command disables this advertisement capability.

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, mismatches cause an event to be generated and will not be rejected.

The no form of this command allows authentication mismatches to be accepted and generate a log event.

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 statement must also be included.

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.

The no form of this command removes the authentication key.

This command enables either simple password or message digest authentication or must go in either 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 statement must also be included.

Configure the authentication type on 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 this command disables authentication.

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

For more information about the protocols and platforms that support BFD, see the 7210 SAS-D, Dxp, K 2F1C2T, K 2F6C4T, K 3SFP+ 8C Router Configuration Guide.

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

This command configures the route tag for the default route.

This command enables authentication of individual ISIS packets of the complete sequence number PDUs (CSNP) type.

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

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

By default, CSN PDUs are sent every 10 seconds for LAN interfaces and every 5 seconds for point-to-point interfaces

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

This command configures the default metric used for IPv4 routes for both level 1 and level 2 on the interface, only when IS-IS multi-topology is configured for use.

To calculate the lowest cost to reach a specific destination, each configured level on each interface must have a cost. The costs for each level on an interface may be different. The value specified with this command is used only if the metric is not specified using the CLI command ipv4-unicast-metric under the specific level.

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

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

This command configures the default metric used for IPv6 routes for both level 1 and level 2 on the interface, only when IS-IS multi-topology is configured for use.

To calculate the lowest cost to reach a specific destination, each configured level on each interface must have a cost. The costs for each level on an interface may be different. The value specified with this command is used only if the metric is not specified using the command ipv6-unicast-metric under the specific level.

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

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

This command specifies the configurable default metric used for all IS-IS interfaces on this level. This value is not used if a metric is configured for an interface.

This command disables the IGP-LDP synchronization feature on all interfaces participating in the IS-IS routing protocol. When this command is executed, IGP immediately advertises the actual value of the link cost for all interfaces which have the IGP-LDP synchronization enabled if the currently advertised cost is different. It then disables IGP-LDP synchronization for all interfaces. This command does not delete the interface configuration. The no form of this command has to be entered to re-enable IGP-LDP synchronization for this routing protocol.

For information about LDP synchronization, refer to “IGP-LDP and static route-LDP synchronization on the 7210 SAS-K 2F6C4T and 7210 SAS-K 3SFP+ 8C” and the ldp-sync and ldp-sync-timer commands in the 7210 SAS-D, Dxp, K 2F1C2T, K 2F6C4T, K 3SFP+ 8C Router Configuration Guide.

The no form of this command restores the default settings and re-enables IGP-LDP synchronization on all interfaces participating in the IS-IS routing protocol and for which the ldp-sync-timer is configured.

This command configures export routing policies that determine the routes exported from the routing table to IS-IS.

If no export policy is defined, 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 overrides the previous command. A maximum of five policy names can be specified.

If an aggregate command is also configured in the config>router context, the aggregation is applied before the export policy is applied.

Routing policies are created in the config>router>policy-options context.

The no form of this command removes the specified policy-name or all policies from the configuration if no policy-name is specified.

This command configures the maximum number of routes (prefixes) that can be exported into IS-IS from the route table.

The no form of this command removes the parameters from the configuration.

This command configures the external route preference for the IS-IS level.

The external-preference command configures the preference level of either IS-IS level 1 or IS-IS level 2 external routes. By default, the preferences are as listed in Table 44.

A route can be learned by the router by different protocols, in which case, the costs are not comparable. When this occurs, the preference decides the route to use.

Different protocols should not be configured with the same preference. If this occurs, the tiebreaker is dependent on the default preference table. 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 the route to use is determined by the configuration of ecmp in the config>router context.

This command enables graceful-restart helper support for IS-IS. The router will act as a helper to neighbors who are graceful-restart-capable and are restarting.

When the control plane of a graceful-restart-capable router fails, the neighboring routers (graceful-restart helpers) temporarily preserve adjacency information so packets continue to be forwarded through the failed graceful-restart router using the last known routes. If the control plane of the graceful-restart router comes back up within the timer limits, the routing protocols reconverge to minimize service interruption.

The no form of this command disables graceful restart and removes all graceful restart configurations in the IS-IS instance.

This command disables the helper support for graceful restart.

When graceful-restart is enabled, the router can act as a helper router (the router is helping a neighbor to restart) or a restarting router or both. The router supports only helper mode. This facilitates the graceful restart of neighbors but the router does not act as a restarting router (meaning that the router will not help the neighbors to restart).

The no form of this command enables helper support and is the default when graceful-restart is enabled.

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

The IGP SPF is instructed to precompute both a primary next-hop and an LFA 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 IGP LFA SPF uses the remote-lfa option to enable the remote LFA next-hop calculation. When this option is enabled in an IGP instance, SPF performs the remote LFA additional computation following the regular LFA next-hop calculation when the latter results in no protection for one or more prefixes that are resolved to a specific interface.

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

Unlike the regular LFA algorithm, which is per-prefix, the remote LFA algorithm is a per-link LFA SPF calculation. It provides protection to all destination prefixes that share the protected link by using the neighbor on the other side of the protected link as a proxy for those prefixes.

This command instructs IGP to exclude a specific interface or all interfaces participating in a specific IS-IS level or OSPF area from the SPF LFA computation. This reduces the LFA SPF calculation where it is not needed.

When an interface is excluded from the LFA SPF in IS-IS, it is excluded in both level 1 and level 2. When it is excluded from the LFA SPF in OSPF, it is excluded in all areas. However, the preceding OSPF command can only be executed under the area in which the specified interface is primary and when enabled, the interface is excluded in that area and in all other areas where the interface is secondary. If the user attempts to apply it to an area where the interface is secondary, the command will fail.

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

This command enables authentication of individual IS-IS hello packets.

The no form of this command suppresses authentication of hello packets.

This command specifies whether the Instance Identifier (IID) TLV has been enabled or disabled for this IS-IS instance.

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 hello authentication type on a segment must match. The hello-authentication-type must be specified.

To configure the hello authentication key in the interface context, 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 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).

When the hello authentication key is configured in the config>router>isis>interface context, it applies to all levels configured for the interface.

The no form of this command removes the 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 authentication-key statement must also be included.

To configure the hello authentication type at the interface context, use the hello-authentication-type command in the config>router>isis>interface context.

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

The no form of this command disables hello authentication.

This command configures the interval between IS-IS Hello PDUs issued on the interface at this level. The hello-interval command, along with the hello-multiplier command, 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 to reverts to the default value.

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

The hold time is the time during 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 default metric used for IPv6 routes for both level 1 and level 2 on the interface, only when IS-IS multi-topology is configured for use.

To calculate the lowest cost to reach a specific 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 of 10 is used unless reference bandwidth is configured.

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

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 separate areas.

When the interface is a POS channel, the OSINCP is enabled when the interface is created and removed when the interface is deleted.

The shutdown command in the config>router>isis>interface context administratively disables IS-IS on the interface without affecting the IS-IS configuration.

The no form of this command removes IS-IS from the interface.

This command configures a route tag to the specified IP address of an interface.

This command configures the default metric used for IPv6 routes for both level 1 and level 2 on the interface, only when IS-IS multi-topology is configured for use.

Use this command to set the interface type of an Ethernet link to point-to-point to avoid having to carry the designated IS-IS overhead if the link is used as a point-to-point.

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

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

This command specifies whether this IS-IS instance supports IPv4.

The no form of this command disables IPv4 on the IS-IS instance.

This command enables IPv6 routing.

The no form of this command disables support for IS-IS IPv6 TLVs for IPv6 routing.

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

A router can be configured as a Level 1, Level 2, or Level 1-2 system. 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.

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 Level 2 or a Level 1-2 router with interfaces configured as Level 1-2 or Level 2. Level 1 adjacencies are not established over this interface.

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

This command configures the routing level for an instance of the IS-IS routing process.

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

Table 45 displays configuration combinations and the potential adjacencies that can be formed.

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

This command configures the interval between LSP PDUs sent from this interface.

To avoid bombarding adjacent neighbors with excessive data, pace the Link State Protocol Data Units (LSPs). If a value of zero is configured, no LSPs are sent from the interface.

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

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

Each LSP received is maintained in an LSP database until the lsp-lifetime expires, unless the originating router refreshes the LSP. By default, each router refreshes its LSPs every 20 minutes (1200 seconds) so other routers will not age out the LSP.

The LSP refresh timer is derived from the following formula:

lsp-lifetime/2

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

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

Note: Using the exec command to execute a configuration file to change the LSP MTU size from the default value will automatically bounce IS-IS for the change to take effect.

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

This command is used to customize IS-IS 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.

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 a 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. Configure mesh groups carefully. It is easy to created isolated islands that do not receive updates as (other) links fail.

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

This command enables IS-IS multi-topology support.

The no form of this command disables IS-IS multi-topology support.

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. Also, assigning an identical 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 extracted from the range configured for this IGP instance. When the global mode of operation is used , a new segment routing module checks that the same index or label value is not assigned to more than one loopback interface address. When the per-instance mode of operation is used, this check is not required because the index and label ranges of the various IGP instances are not allowed to overlap.

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

This command enables multi-topology TLVs.

This no form of this command disables multi-topology TLVs.

This command configures the metric used for the level on the interface.

To calculate the lowest cost to reach a specific 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 of 10 is used, unless reference bandwidth is configured.

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

This command specifies the MAC address to use for all L1 IS-IS routers. The MAC address should be a multicast address. The user should configure shutdown and no shutdown in the IS-IS instance to make the change operational.

The MAC address, 01-80-C2-00-02-11, is used in the IS-IS base instance ID (ID==0). This cannot be modified by the user.

This command specifies the MAC address to use for all L2 IS-IS routers. The MAC address should be a multicast address. The user should configure shutdown and no shutdown in the IS-IS instance to make the change operational.

The MAC address, 01-80-C2-00-01-00, is used in the IS-IS base instance ID (ID==0). This cannot be modified by the user.

This command was previously named the net network-entity-title command. The area-id command enables the context to configure the area ID portion of Network Service Access Point (NSAP) addresses, which identify 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.

A maximum of 3 area addresses can be configured.

NSAP addresses are divided into the three following parts; only the area ID portion is configurable:

The NET is constructed like an NSAP but the selector byte contains a 00 value. NET addresses are exchanged in Hello and LSP PDUs. All NET addresses configured on the node are advertised to its neighbors.

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

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

For Level 1 and Level 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 first area address.

The no form of this command removes the area address.

This command applies a route next-hop policy template to an OSPF or 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.

However, the command in an OSPF interface context can only be executed under the area in which the specified interface is primary, and then applied in that area and in all other areas where the interface is secondary. If the user attempts to apply it to an area where the interface is secondary, the command will fail.

If the user excluded the interface from LFA using the command loopfree-alternate-exclude, the LFA policy, if applied to the interface, has no effect.

Finally, if the user applied a route next-hop policy template to a loopback interface or to the system interface, the command will not be rejected, but it will result in no action being taken.

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

This command instructs IGP to exclude a specific interface or all interfaces participating in a specific IS-IS level or OSPF area in the SPF LFA computation. This provides a way of reducing the LFA SPF calculation where it is not needed.

When an interface is excluded from the LFA SPF in IS-IS, it is excluded in both Level 1 and Level 2. When it is excluded from the LFA SPF in OSPF, it is excluded in all areas. However, the preceding OSPF command can only be executed under the area in which the specified interface is primary and when enabled, the interface is excluded in that area and in all other areas where the interface is secondary. If the user attempts to apply it to an area where the interface is secondary, the command will fail.

The no form of this command reinstates the default value for this command.

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 before executing a shutdown command to divert traffic around the router.

The no form of this 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 the IGP upon bootup in the overload state until one of the following events occurs.

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

This state can be cleared with the config>router>isis>no overload command.

If a timeout value is specifies, 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 the system stays in overload:

The overload state can be cleared before the timeout expires with the no overload command. Use the show router isis status commands to display the administrative and operational state as well as all timers.

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

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.

When 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 this command removes the passive attribute.

This command configures the preference level of either IS-IS Level 1 or IS-IS Level 2 internal routes. The default preferences are listed in the default values section.

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

Protocols should not be configured with the same preference. If this occurs, the default preferences defined in the following table are used as the tiebreaker. 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 route to use is determined by the configuration of the ecmp command in the config>router context.

This command configures the priority of the IS-IS router interface for designated router election on a multi-access network.

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

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

This command enables authentication of individual IS-IS packets of partial sequence number PDU (PSNP) type.

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

This command configures the reference bandwidth that provides the basis of bandwidth relative costing.

To calculate the lowest cost to reach a specific destination, each configured level on each interface must have a cost. If the reference bandwidth is defined, the cost is calculated using the following formula:

cost = reference-bandwidth ÷ bandwidth

If the reference bandwidth is configured as 10 Gigabits (10,000,000,000), a 100 Mb/s interface has a default metric of 100. For metrics in excess of 63 to be configured, wide metrics must be deployed. See wide-metrics-only for more information.

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

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

This command configures the minimum time between LSP PDU retransmissions on a point-to-point interface.

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

This command enables the context to configure segment routing parameters within an IGP instance.

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

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

Segment routing using MPLS labels is used in both shortest path routing applications and in traffic engineering applications. The commands in the segment-routing context configure the shortest path forwarding application.

After segment routing is configured in the IS-IS 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 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.

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

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

The user must configure the prefix SID index range and the offset label value that this IGP instance uses. Because each prefix SID represents a network global IP address, the SID index for a prefix must be unique in the network. Therefore, all routers in the network 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, as in the following:

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

The label operation in the network becomes similar to LDP when operating in the independent label distribution mode (RFC 5036), 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.

In the global mode of operation, the global value is configured and this IGP instance assumes that the start label value is the lowest label value in the 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 are restricted to do the same. The user must shut down the segment routing context and delete the prefix-sid-range command in all IGP instances to change the SRGB. After the SRGB is changed, the user must re-enter the prefix-sid-range command. The SRGB range change fails if an already allocated SID index or label goes out of range.

In the per-instance mode of operation, the user partitions the SRGB into non-overlapping sub-ranges among the IGP instances. The user therefore 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 be failed.

Furthermore, the code checks for overlaps of the resulting net label value range across IGP instances and strictly enforces that these ranges do not overlap. The user must shut down the segment routing context of an IGP instance to change the SID index or label range of that IGP instance using the prefix-sid-range command.

In addition, any range change will fail if an already allocated SID index or label goes out of range. The user can, however, change the SRGB on the fly as long as it does not reduce the current per-IGP instance SID index or label range defined in the prefix-sid-range command. Otherwise, the user must shut down the segment routing context of the IGP instance and delete and reconfigure the prefix-sid-range command.

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

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 for an IGP tunnel; for example, LDP LSP, based on the outgoing interface MTU minus the label stack size. Remote LFA can add at least two more labels to the tunnel for a total of three labels. There is no default value. If the user does not configure an SR tunnel MTU, the MTU will be determined by IGP.

The MTU of the SR tunnel in bytes is determined as follows:

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

Where:

The SR tunnel MTU is dynamically updated when any of the preceding parameters that are used in its calculation change. This includes when the set of the tunnel next-hops changes, or the user changes the configured SR MTU or interface MTU value.

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

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

The segment routing module adds an SR tunnel entry to the TTM for each resolved remote node SID prefix and programs the data path that has 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 is the setting of the default preference of the various tunnel types. This includes the preference of SR tunnels based on the shortest path (referred to as SR-ISIS).

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

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

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

This command configures the maximum interval between two consecutive SPF calculations in seconds. 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 milliseconds, and then the next SPF will run after 4000 milliseconds, and so on, until it reaches the spf-wait value.

The SPF interval stays 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 drops back to spf-initial-wait.

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. This command is used to prevent black-holing traffic when IPv4 and IPv6 topologies are different. When disabled (no strict-adjacency-check) a BFD session failure for either IPv4 or Ipv6 will cause the routes for the other address family to be removed as well.

The no form of this command disables the strict checking of address families. When strict checking of address families is disabled, both routers only need to have one common address family to establish the adjacency.

This command creates summary addresses.

This command enables or disables IS-IS to suppress the installation of default routes.

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

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. To support traffic engineering, wider metrics are required. When wide metrics are used, a second pair of TLVs are added, again, one for the adjacency and one for 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 this command reverts to the default value.