Alcatel-Lucent 7450 Configuration Manual page 58

Weighted Load Balancing IGP, BGP, and Static Route Prefix Packets over IGP Shortcut
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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:
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:
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
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.
If one or more LSP in the ECMP set of a prefix static route does not have a weight configured, the
regular ECMP spraying for the prefix will be performed.
ECMP is also supported when resolving in TTM the same static route with multiple user-entered
indirect next-hops each binding to the same or different tunnel types. The system picks as many
tunnel next-hops as available in RTM beginning from the first indirect next-hop and up to the value
of the ecmp option in the system. In this case, the weighted load-balancing will be applied directly
using the weights of the selected set of tunnel next-hops. If one or more LSP in the ECMP set of a
prefix static route does not have a weight configured, or if one or more of the indirect next-hops
binds to an LDP LSP, the regular ECMP spraying for the prefix will be performed.
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Feature Behavior on page 54
7450 ESS Router Configuration Guide
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