IP Router Configuration Command Reference
200 Router Configuration Guide
SRLG is used to tag IP or MPLS interfaces which share a specific fate with the same identifier. For
example, an SRLG group identifier could represent all links which use separate fibers but are carried
in the same fiber conduit. If the conduit is accidentally cut, all the fiber links are cut which means all
interfaces using these fiber links will fail.
The user first configures locally on each router the name and identifier of each SRLG group. A
maximum of 1024 SRLGs can be configured per system.
The user then configures the SRLG membership of an interface. The user can apply SRLGs to an IES,
VPRN, network IP, or MPLS interface. A maximum of 64 SRLGs can be applied to a given interface.
When SRLGs are applied to MPLS interfaces, CSPF at an LER will exclude the SRLGs of interfaces
used by the LSP primary path when computing the path of the secondary path. CSPF at an LER or LSR
will also exclude the SRLGs of the outgoing interface of the primary LSP path in the computation of
the path of the FRR backup LSP. This provides path disjointness between the primary path and the
secondary path or FRR backup path of an LSP.
When SRLGs applied to IES, VPRN, or network IP interfaces, they are evaluated in the route next-hop
selection by adding the srlg-enable option in a route next-hop policy template applied to an interface
or a set of prefixes. For instance, the user can enable the SRLG constraint to select a LFA next-hop for
a prefix which avoids all interfaces that share fate with the primary next-hop.
The following provisioning rules are applied to SRLG configuration. The system will reject the
creation of a SRLG if it re-uses the same name but with a different group value than an existing group.
The system will also reject the creation of an SRLG if it re-uses the same group value but with a
different name than an existing group.
Only the SRLGs bound to an MPLS interface are advertised area-wide in TE link TLVs and sub-TLVs
when the traffic-engineering option is enabled in IS-IS or OSPF. IES and VPRN interfaces do not
have their attributes advertised in TE TLVs.
A user may specify a penalty weight (penalty-weight) associated with an SRLG. This controls the
likelihood of paths with links sharing SRLG values with a primary path being used by a bypass or
detour LSP. The higher the penalty weight, the less desirable it is to use the link with a given SRLG.
Parameters group-name — Specifies the name of the group, up to 32 characters. The association of group
name and value should be unique within an IP/MPLS domain.
value group-value — Specifies the integer value associated with the group. The association of
group name and value should be unique within an IP/MPLS domain.
Values 0 to 4294967295
penalty-weight penalty-weight — Specifies the integer value of the penalty weight that is assigned
to the SRLG group.
Values 0 to 65535
Default 0
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