The MPLS WG Archive

[Yakov Rekhter <yakov@juniper.net>]

Bruno,

> A brief question about draft-rosen-rfc-2547bis-02:
> 
> What is the proper encoding of an MPLS label in a labeled vpnv4 prefix in an
> MP-REACH-NLRI attribute? Draft-rosen-rfc2547bis-02 refers to
> draft-ietf-mpls-bgp4-mpls-04  which says that the "label is encoded as 3
> octets, where the high-order bit contains bottom-of-stack. The following
> high-order three bits must be zero. The remaining 20 buts contain the label
> value."
> 
> Given this, I would expect label 1000 (decimal) to be encoded as 80.03.e8
> (hex). However, one major vendor encodes it as 00.3e.81 (hex). Similarly, I
> would expect label 28 (decimal) to be encoded as 80.00.1c (hex) but the
> major vendor encodes it as 00.01.c1 (hex).
> 
> Am I missing something, or does the vendor have a bug?

Looks like a bug to me, as without setting the bottom-of-stack to
1, there is no way to find out how many labels are carried in the
MP_REACH_NLRI, and therefore no way to find out where the address
prefix part of MPL_REACH_NLRI begins.

Yakov.