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

t.petch <ietfc@btconnect.com> Wed, 13 April 2016 16:16 UTC

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From: t.petch <ietfc@btconnect.com>
To: <mpls@ietf.org>, Loa Andersson <loa@pi.nu>
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Subject: Re: [mpls] [sfc] The first nibble issue associated with MPLS encapsulation
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----- Original Message -----
From: "Loa Andersson" <loa@pi.nu>
To: <mpls@ietf.org>rg>; "tom p." <daedulus@btconnect.com>
Sent: Wednesday, April 13, 2016 1:15 PM

> Tom,
>
>
> On 2016-04-13 19:53, t.petch wrote:
> > ----- Original Message -----
> > From: "Eric C Rosen" <erosen@juniper.net>
> > 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
>
> Isn't this just in time - if IPv5 is made historic - we can safely use
> it.

I think not

'   A specification that has been superseded by a more recent
   specification or is for any other reason considered to be obsolete is
   assigned to the "Historic" level.  '

It doesn't mean it is not in use although that I-D does say

'Given that IPv6 is a deployment reality and there are no proven
   deployments of the aforementioned IP versions ...'

My point was that IPv5 exists, as of now, and still will, even when made
Historic.

The I-D says

' IANA is requested to deallocate the version numbers'

which I think wrong. If you are feeling paranoid - sometimes I do - then
you will think that somewhere the value 5 is given a significance and it
would be safer not to free it up for re-use.

Tom Petch

>
> /Loa
> >
> > 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.
> >>
> >
> > _______________________________________________
> > mpls mailing list
> > mpls@ietf.org
> > https://www.ietf.org/mailman/listinfo/mpls
> >