Ecmp Considerations; Disabling Ttl Propagation In An Lsp Shortcut - Alcatel-Lucent 7450 Manual

ECMP Considerations

When ECMP is enabled and multiple equal-cost next-hops exit for the IGP route, the ingress
forwarding engine sprays the packets for this route based on hashing routine currently supported
for IPv4 packets.
When the preferred RTM entry corresponds to an LDP shortcut route, spraying will be performed
across the multiple next-hops for the LDP FEC. The FEC next-hops can either be direct link LDP
neighbors or T-LDP neighbors reachable over RSVP LSPs in the case of LDP-over-RSVP but not
both. This is as per ECMP for LDP in existing implementation.
When the preferred RTM entry corresponds to a regular IP route, spraying will be performed
across regular IP next-hops for the prefix.

Disabling TTL Propagation in an LSP Shortcut

This feature provides the option for disabling TTL propagation from a transit or a locally
generated IP packet header into the LSP label stack when an LDP LSP is used as a shortcut for
BGP next-hop resolution, a static-route next-hop resolution, or for an IGP route resolution.
A transit packet is a packet received from an IP interface and forwarded over the LSP shortcut at
ingress LER.
A locally-generated IP packet is any control plane packet generated from the CPM and forwarded over the
LSP shortcut at ingress LER
TTL handling can be configured for all LDP LSP shortcuts originating on an ingress LER using
the following global commands:
config>router>ldp>[no] shortcut-transit-ttl-propagate
config>router>ldp>[no] shortcut-local-ttl-propagate
These commands apply to all LDP LSPs which are used to resolve static routes, BGP routes, and
IGP routes.
When the no form of the above command is enabled for local packets, TTL propagation is
disabled on all locally generated IP packets, including ICMP Ping, traceroute, and OAM packets
7450 ESS MPLS Guide
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Label Distribution Protocol
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