Why MPLS Label do not have next header field?

[mukupatil]

MPLS Label do not have protocol filed like IP or Type field like ethernet, then how do router knows what is the next header?

[Peter Paluch · Accepted solution]

Hello,

If a router receives a labeled packet, that label value must have originally been assigned by that router itself. The router knows what does that particular label bind to (IPv4 network, IPv6 network, VPNv4 network, pseudowire, etc.) because it has created the binding itself. Therefore it is not necessary for an MPLS label to carry a protocol field (although, admittedly, it would do no harm).

Please feel welcome to ask further!

Best regards,

Peter