MPLS LDP access-list to allow neighbors to form

LDP uses TCP port 646 for adjacency connection and label exchange…
LDP neighbors send hellos to multicast address (all routers on a subnet)…

R0(config-ext-nacl)#do sh ip access-list
Extended IP access list MPLS
10 permit icmp any any
11 permit ip host host (52 matches)
15 permit tcp any eq 646 host (3 matches)
20 deny ip any any (87 matches)

R0(config-ext-nacl)#do sh mpls ldp nei
Peer LDP Ident:; Local LDP Ident
TCP connection: –
State: Oper; Msgs sent/rcvd: 8/8; Downstream
Up time: 00:03:59
LDP discovery sources:
FastEthernet0/0, Src IP addr:
Addresses bound to peer LDP Ident:

When two LSRs are running LDP and they share one or more links between them, they should
discover each other by means of Hello messages. The second step is for them to establish a session
across a TCP connection. Across this TCP connection, LDP advertises the label mapping
messages between the two LDP peers. These label mapping messages are used to advertise,
change, or retract label bindings. LDP provides the means to notify the LDP neighbor of some
advisory and error messages by sending notification messages.


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