Re: [mpls] [sfc] The first nibble issue associated with MPLS encapsulation

[t.petch <[e-mail]>]

----- Original Message -----
From: "Eric C Rosen" <[e-mail]>
Sent: Monday, April 11, 2016 3:19 PM


> (Removed sfc from the cc-list, this seems out of scope for that WG.)
>
> In designing the BIER header, the BIER WG is free to mandate any value
> it chooses in the first nibble.  These values do not come from a
"first
> nibble" registry.
>
> It seems prudent to put a value like 5 for the following reasons:
>
> - If a BIER packet is being parsed by an off-line tool, this is a good
> hint (though just a hint) that the packet is actually a BIER packet;
>
> - If a BIER packet is traveling through an MPLS tunnel, and it
traverses
> a node that does its MPLS load splitting by guessing at the type of
the
> payload, then this is  a good hint that the MPLS payload is not IPv4,
> IPv6, or PW.
>
> This strategy does incur a risk.  Suppose IPv5 gets designed,
> implemented, and deployed, and folks start to deploy hardware that
does

Too late;  see


https://tools.ietf.org/html/draft-boucadair-ip-version-5-8-9-historic-00

Discussion on the int-area list.

Tom Petch



> MPLS load balancing by inspecting the IPv5 headers of the MPLS
> payloads.  If a BIER packet is traversing an MPLS tunnel,
inappropriate
> load splitting may occur if the hardware thinks the payload is IPv5
> rather than BIER.
>
> This particular risk doesn't seem very significant to me.
>
> Thus I don't think there's anything here that needs fixing.
>