Re: [Bier] Possible conflict between nibble value in RFC 8296 and IANA registry of IP version number

Eric C Rosen <erosen@juniper.net> Fri, 23 March 2018 17:10 UTC

To: Greg Mirsky <gregimirsky@gmail.com>, BIER WG <bier@ietf.org>, Loa Andersson <loa@pi.nu>
References: <CA+RyBmUnsjo015FuSQO6BzouA=S-MDoJ8H38-AVRF7_+Yigihw@mail.gmail.com>
From: Eric C Rosen <erosen@juniper.net>
Message-ID: <f7527f88-0ab6-7396-398a-18706df83756@juniper.net>
Date: Fri, 23 Mar 2018 13:09:54 -0400
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Subject: Re: [Bier] Possible conflict between nibble value in RFC 8296 and IANA registry of IP version number
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This issue was discussed extensively on the mailing list in April of 
2016.  You may wish to consult the archives, look for the subject "The 
first nibble issue associated with MPLS encapsulation".

The conflict you mention below does not exist because the first nibble 
of the BIER encapsulation is not a value taken from the "IP Version 
Number" registry.

BTW,  ST was actually deployed in the 1970's and it is possible that a 
few ST implementations were still around in the early-to-mid 1980's.





On 3/23/2018 8:10 AM, Greg Mirsky wrote:
> Dear All,
> RFC 8296 explains the nibble field on BIER header as:
>    Nibble:
>
>       This field is set to the binary value 0101; this ensures that the
>       MPLS ECMP logic will not confuse the remainder of the BIER header
>       with an IP header or with the header of a pseudowire packet.  In
>       an MPLS network, if a BFR receives a BIER packet with any other
>       value in the first nibble after the label stack, it SHOULD discard
>       the packet and log an error.
>
> But IANA registry for IP version numbers 
> <https://urldefense.proofpoint.com/v2/url?u=https-3A__www.iana.org_assignments_version-2Dnumbers_version-2Dnumbers.xhtml&d=DwMFaQ&c=HAkYuh63rsuhr6Scbfh0UjBXeMK-ndb3voDTXcWzoCI&r=-DXB84eU9m4cIlq2OOcCJCQQAwJXQQswyu3F0kG0VNo&m=qBfmUmqT2F34aAOWqRNReo3_XIMvcBGSqsnmIh1Z5oM&s=BX_OgisR1iQa9oJZq_YDewd6VDPmLJIYWVHeWk69SeA&e=> 
> reflects allocation of 5 for ST RFC 1819 (thanks to Loa for pointing 
> me to the registry):
>
> Decimal Keyword Version Reference
> 0-1Reserved[Jon_Postel][RFC4928]
> 2-3Unassigned[Jon_Postel]
> 4IPInternet Protocol[RFC791][Jon_Postel]
> 5STST Datagram Mode[RFC1819][Jim_Forgie]
> 6IPv6Internet Protocol version 6[RFC8200]
> 7TP/IXTP/IX: The Next Internet[RFC6814]
> 8PIPThe P Internet Protocol[RFC1621]
> 9TUBATUBA[RFC1347]
> 10-14Unassigned[Jon_Postel]
> 15Reserved[Jon_Postel]
>
> Perhaps ST Datagram never saw the light of deployment but, as it 
> looks, we may have formal conflict at hand. The way to remedy the 
> situation may be to re-assign value 5 to BIER or, at the minimum, make 
> it reserved.
> What do you think?
>
> Regards,
> Greg
>
>
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[Bier] Possible conflict between nibble value in … Greg Mirsky
Re: [Bier] Possible conflict between nibble value… 徐小虎(义先)
Re: [Bier] Possible conflict between nibble value… Eric C Rosen