Is per-platform label allocation necessary in MPLS VPN ?

[n.nandrekar]

In case of MPLS VPNs, can the PE devices ever be using per interface label allocation? Am asking this because, due to PHP, the egress PE will directly get a packet with the inner(VPN) label and that can arrive thru any interface . It cant bind a label to a perticular interface.

[pkhatri]

Hi,

In the context of MPLS VPNs, either per-platform or per-interface label space may be used for the tunnel (transport) label. What is important, as far as RFC4364 is concerned, is that the inner (VPN) label is understood by the PE, and is the same regardless of which interface the packet comes in on.

I don't believe there are too many implementations out there using per-interface label space anyway. It was more of a concern when LC-ATM interfaces were used and you had to have per-interface label space.

Paresh

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[n.nandrekar]

How does the PE differentiate between vpn label and and transport label? There is no difference in that. In per interface allocationa, suppose the PE has advertised label 'X' out int eth1 for tunnel label of a network of which it is a P router, and suppose X is also advertisesd thru mp-bgp for vpn label, whet will the PE do when it recieves pkt with X on ETH1? It could be an vpn label X due to php coming on that interface or it can be the tunnel label X for the remote network? what is it supposed to do in this case? pop and forward in VRF, or swap and fwd to other interface. Coz as far as i know, there is no seperate LFIB for vpn labels and tunnel labels.

[pkhatri]

That's exactly what I am getting at. When per-interface label space is used in the case of LC-ATM, then there is no concept of PHP (since ATM cells will not be ATM cells without a VPI/VCI :-). In such cases, the 'top' label is always the tunnel label and the inner label can be part of the per-platform label space.

Paresh