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How can I know what is the next protocol in MPLS header? I do know that MPLS header does not provide any information about the next protocol, But I somehow need to know how to recognize it, as I am expanding existing RSS mechanism to support packets with MPLS header.

Thanks.

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  • No, the point of MPLS is that it only looks at the labels to switch the frames, and it simply does not care about the payload. It is like ethernet switching, where ethernet switching has no idea, nor does it care anything about the next protocol in order to switch the frames. It is only a host that needs to know about the next protocol carried in the frame payload.
    – Ron Maupin
    May 29, 2023 at 16:39
  • Has any answer solved your question? Then please accept it or your question will keep popping up here forever. Please also consider voting for useful answers.
    – Zac67
    Jun 29, 2023 at 18:10

1 Answer 1

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How can I know what is the next protocol in MPLS header?

You can't. MPLS doesn't carry a 'next-protocol' header. It doesn't have to.

MPLS is used to carry a certain type of payload, commonly either Ethernet or plain IP. The kind of payload is agreed upon by the endpoints, so there's no ambiguity.

A next-protocol header could indicate different types of payloads, so you could for instance run Ethernet and Fibre Channel concurrently on the same label path. MPLS doesn't do that - instead, you'd use multiple labels for different payload types.

You can of course run dual-stack IP on the same label as the first nibble of the IP header (=MPLS payload) is the version field.

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