Home > Tech in general, VPN > MPLS and Loopback Address

MPLS and Loopback Address

February 21st, 2009 Leave a comment Go to comments

 

Our team just started working on technology involving MPLS and stuff, so we were talking about MPLS networks, then came a question as to why do we always see loopback addresses in examples and is it like a strict requirement? We couldn’t find a solid answer or answers, owing to the fact that we are a bunch of security experts just landed into this MPLS

 

So the question is, Is it a must to have Loopback addresses for MPLS to work? Well, I got the following from  [Here]

 

"Loopback" IP address

Although not a strict requirement, it is advisable to configure routers participating in MPLS network with "loopback" IP addresses (not attached to any real network interface) to be used by LDP to establish sessions.

This serves 2 purposes:

    • As there is only one LDP session between any 2 routers, no matter how many links connect them, loopback IP address ensures that LDP session is not affected by interface state or address changes
    • Use of loopback address as LDP transport address ensures proper penultimate hop popping behaviour when multiple labels are attached to packet as in case of VPLS
 

Is there any other reason that you think should be there? Would appreciate if you could comment.

Categories: Tech in general, VPN Tags:
  1. Naeem Maniar
    February 26th, 2009 at 13:18 | #1
    Reply | Quote

    Another reason is specific to Juniper (not sure about Cisco routes)

    Juniper Routers (by default) advertises only loopback address as an FEC which allows all LDP routers in the network to establish an LSP to the loopback address of every
    other router in the network. If loopback address is not configured then route id (lowest interface IP) with /32 prefix will be advertised as an FEC then receiving router will first try to locate reachbility to advertised FEC through IGP and obviously won’t find reachability as address is advertised with /32 prefix, as a result no LSP will be established.

  1. No trackbacks yet.