Re: [Idr] Benoit Claise's Discuss on draft-ietf-idr-large-community-11: (with DISCUSS and COMMENT)

Ignas Bagdonas <> Wed, 04 January 2017 15:26 UTC

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To: Benoit Claise <>, The IESG <>
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From: Ignas Bagdonas <>
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Date: Wed, 4 Jan 2017 15:26:43 +0000
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Subject: Re: [Idr] Benoit Claise's Discuss on draft-ietf-idr-large-community-11: (with DISCUSS and COMMENT)
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Hi Benoit,

Thank you for reviewing.

Global Administrator field is a 4 octet integer that is used to carry AS 
number but it is not mandatory to interpret it as an AS number only 
(while a typical use case is for carrying AS number) - two peers can 
agree on any value that has meaning between those peers. Representation 
on the wire is in network byte order, and 2 byte AS number will get 
naturally padded with two zero bytes in front. Virtually all deployments 
today are AS4 capable and use AS4 encoding even for AS number values 
that fit into 16 bit value range therefore AS number is a 4 octet entity 

The topics of 2 byte padding and any integer value in global 
administrator field have been discussed in the WG.


On 04/01/2017 14:52, Benoit Claise wrote:
> Benoit Claise has entered the following ballot position for
> draft-ietf-idr-large-community-11: Discuss
> When responding, please keep the subject line intact and reply to all
> email addresses included in the To and CC lines. (Feel free to cut this
> introductory paragraph, however.)
> Please refer to
> for more information about IESG DISCUSS and COMMENT positions.
> The document, along with other ballot positions, can be found here:
> ----------------------------------------------------------------------
> ----------------------------------------------------------------------
> I see from the abstract: "The attribute is suitable for use with
> four-octet ASNs."
> I also see this text, which doesn't mention four-octet ASNs
>     The Global Administrator field is intended to allow different
>     Autonomous Systems to define BGP Large Communities without
> collision.
>     This field SHOULD be an Autonomous System Number (ASN), in which
> case
>     the Local Data Parts are to be interpreted as defined by the owner
> of
>     the ASN.  The use of Reserved ASNs (0 [RFC7607], 65535 and
> 4294967295
>     [RFC7300]) is NOT RECOMMENDED.
> What if the ASN is two bytes, we use padding? How?
> Even if we would say: "This field SHOULD be an four-octet Autonomous
> System Number (ASN)", it doesn't preclude inserting a two-octet ASN in
> the Global Administrator field.
> Isn't it better to specify how?
> >From RFC 6793:
>     Currently assigned two-octet AS numbers are converted into
> four-octet
>     AS numbers by setting the two high-order octets of the four-octet
>     field to zero.  Such a four-octet AS number is said to be mappable
> to
>     a two-octet AS number.
> ----------------------------------------------------------------------
> ----------------------------------------------------------------------
> Thanks John for an excellent shepherd writeup.