Ecmp Support For Ldp - Nokia 7705 SAR-W Series Manual

Label Distribution Protocol
To prevent these performance and security issues, the 7705 SAR can be configured
for an optional behavior in which LDP installs a prefix binding in the LDP FIB by
performing a longest prefix match with an aggregate prefix in the routing table (RIB).
This behavior is described in RFC 5283, LDP Extension for Inter-Area Label
Switched Paths. The LDP prefix binding continues to be advertised on a per-
individual /32 prefix basis.
When the longest prefix match option is enabled and an LSR receives a FEC-label
binding from an LDP neighbor for a prefix-address FEC element, FEC1, it installs the
binding in the LDP FIB if:
When the FEC-label binding has been installed in the LDP FIB, LDP programs an
NHLFE entry in the egress data path to forward packets to FEC1. LDP also
advertises a new FEC-label binding for FEC1 to all its LDP neighbors.
When a new prefix appears in the RIB, LDP checks the LDP FIB to determine if this
prefix is a closer match for any of the installed FEC elements. If a closer match is
found, this may mean that the LSR used as the next hop will change; if so, the
NHLFE entry for that FEC must be changed.
When a prefix is removed from the RIB, LDP checks the LDP FIB for all FEC
elements that matched this prefix to determine if another match exists in the routing
table. If another match exists, LDP must use it. This may mean that the LSR used as
the next hop will change; if so, the NHLFE entry for that FEC must be changed. If
another match does not exist, the LSR removes the FEC binding and sends a label
withdraw message to its LDP neighbors.
If the next hop for a routing prefix changes, LDP updates the LDP FIB entry for the
FEC elements that matched this prefix. It also updates the NHLFE entry for the FEC
elements.

5.1.9 ECMP Support for LDP

Equal-Cost Multipath Protocol (ECMP) support for LDP performs load balancing for
services that use LDP-based LSPs as transport tunnels, by having multiple equal-
cost outgoing next hops for an IP prefix.
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• the routing table (RIB) contains an entry that matches FEC1. Matching can
either be a longest IP match of the FEC prefix or an exact match.
• the advertising LDP neighbor is the next hop to reach FEC1
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