P2MP LSP Data Plane
Page 158 7450 ESS MPLS Guide
Procedures at Egress LER Node
The following procedures occur at the leaf node of the P2MP LSP (egress LER):
• The egress LER performs a pop operation. An ILM entry is programmed at the ingress of
the egress LER to map an incoming label to a list of next-hop/OIF.
The following is an exception handling procedure for control packets received on an ILM in an
egress LER.
• The packet is sent to the CPM for further processing if there is any of the IP header
exception handling conditions set after the label is popped: 127/8 destination address,
router alert option set, or any other options set.
Procedures at BUD LSR Node
The following are procedures at an LSR node which is both a branch node and an egress leaf node
(bud node):
• The bud LSR performs a pop operation on one or many replications of the received packet
and a swap operation of the remaining replications. An ILM entry is programmed at
ingress of the LSR to map the incoming label to list of NHLFE/OIF and next-hop/OIF.
Note however, the exact same packets are replicated to an LSP leaf and to a local interface.
The following are the exception handling procedures for control packets received on an ILM in a
bud LSR:
• Packets which arrive with the TTL in the outer label expiring are sent to the CPM and are
not copied to the LSP branches.
• Packets whose TTL does not expire are copied to all branches of the LSP. The local copy
of the packet is sent to the CPM for further processing if there is any of the IP header
exception handling conditions set after the label is popped: 127/8 destination address,
router alert option set, or any other options set.
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