Alcatel-Lucent 7450 ESS Series, Configuration Manual

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Page 72 7450 ESS OS Router Configuration Guide
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.
Spraying across regular IP next-hops and LDP-shortcut next-hops concurrently is not supported.
Handling of Control Packets
All control plane packets will not see the LDP shortcut route entry in RTM with the exception of
the following control packets which will be forwarded over an LDP shortcut when enabled:
• A locally generated or in transit ICMP Ping and trace route of an IGP route. The transit
message appears as a user packet to the ingress LER node.
• A locally generated response to a received ICMP ping or trace route message.
All other control plane packets that require an RTM lookup and knowledge of which destination is
reachable over the LDP shortcut will continue to be forwarded over the IP next-hop route in RTM.
Handling of Multicast Packets
Multicast packets cannot be forwarded or received from an LDP LSP. This is because there is no
support for the configuration of such an LSP as a tunnel interfaces in PIM. Only an RSVP P2MP
LSP is currently allowed.
If a multicast packet is received over the physical interface, the RPF check will not resolve to the
LDP shortcut as the LDP shortcut route in RTM is not made available to multicast application.
Interaction with LDP Shortcut for BGP Route Resolution
There is no interaction between an LDP shortcut for BGP next-hop resolution and the LDP
shortcut for IGP route resolution. BGP will continue to resolve a BGP next-hop to an LDP shortcut
if the user enabled the LDP shortcut option in BGP
BGP-Shortcut :
CLI Syntax:
config>router>bgp>igp-shortcut ldp