MPLS - need labels for MPLS neighbors only?

[vv0bbLeS]

Hello all,

We are implementing a new MPLS core between a few of our sites (let's say sites A, B, C, with respective subnets A, B, C at each site). Originally, we were advertising subnets A, B, and C to the MPLS routers so that MPLS labels would be created for subnets A, B, and C, but then someone told us in MPLS we only need labels created for our MPLS neighbor IP's, i.e. we only need MPLS labels created for our LDP peering IP's.

This doesn't make sense to me, as I would think I want LDP labels for all my subnets (A, B, and C), so the MPLS routers know where to route traffic for those subnets?

[MHM Cisco World]

Between CE and PE there is no need for PE to PE you need ldp

How PE send label for prefix we use mp-bgp for that

MHM

[Giuseppe Larosa · Accepted solution]

Hello @vv0bbLeS ,

it depends on how the prefixes for subnet A,B,C are advertised.

if subnets A,B,C are advertised in the IGP ( for example OSPF) then you need also MPLS labels for them.

if subnets A,B,C are advertised in BGP even using IBGP in standard AF ipv4 unicast then each router uses the LSP to the BGP next-hop that has to be the loopback address the same used for LDP.

The same happens if using MPLS based services like L3 VPN also in this case we use MP BGP with address family vpnv4 towards other PE nodes. In this case we use a stack of labels and the more internal label is a VPN label that is associated to the prefix in VRF by the advertising PE node.

In this third scenario the external label also called IGP label points to the BGP next-hop and it is the loopback address of the advertising PE node.

Hope to help

Giuseppe

[vv0bbLeS]

@Giuseppe Larosa yes that helps! thank you!