IP Router Configuration
Router Configuration Guide 49
Weighted Load Balancing Static Route Packets over MPLS LSP
Feature Configuration
The configuration of the resolution of a static route prefix to set of MPLS LSPs is covered in
detail in Static Route Resolution Using Tunnels which also provides the selection rules
among multiple LSP types: RSVP-TE, SR-TE, LDP, SR-ISIS, and SR-OSPF. A given static
route of a prefix can only be resolved to a set of tunnel next-hops of the same type though for
each indirect next-hop.
In order to perform ECMP over a set of configured MPLS LSPs the user must enter two or
more LSP names to be used as tunnel next-hops. If automatic selection is performed, ECMP
is performed if two or more MPLS LSPs are found in TTM to the indirect next-hop of the
static route. All LSPs however must have the same LSP metric otherwise only the tunnel
next-hops with the same lowest metric will be activated for the static route.
The user can force the metric of an LSP to a constant value using the following command:
CLI Syntax: configure>router>mpls>lsp>metric
If the user enters for the same static route more LSP names with the same LSP metric than
the value of the router level ecmp option, only the first configured LSPs which number equals
the ecmp value will be selected. The remaining tunnel next-hops for the route will not be
activated. When automatic MPLS LSP selection is performed in TTM, the lower tunnel-id is
used as a tie-breaker among the same lowest metric LSPs.
In order to perform weighted load-balancing over the set of MPLS LSPs, either when the LSP
names are provided or when auto-selection in TTM is performed, the user must also enable
the weighted ECMP globally like for a static, IGP and BGP prefixes resolving to IGP
shortcuts:
CLI Syntax: configure>router>weighted-ecmp
Feature Behavior
The behavior of this feature in terms of RTM and IOM is exactly the same as in the case of
BGP, IGP, and static route prefixes resolving to IGP shortcuts. See Feature Behavior for the
details. In this case, the static route module computes the normalized weight for each prefix
tunnel next-hop of the static route indirect next-hop. The minimum value of the normalized
weight is 1 and the maximum if 64. The static route module updates the route in RTM with
the set of tunnel next-hops and normalized weights. RTM downloads the information to IOM
for inclusion in the FIB.
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