Re: [Idr] Last Call: <draft-ietf-idr-rfc4893bis-06.txt> (BGP Support for Four-octet AS Number Space) to Proposed Standard

[Claudio Jeker <[e-mail]>]

On Tue, Jun 12, 2012 at 08:38:29AM -0700, Robert Raszuk wrote:
> Hi Claudio,
> 
> One clarification question to your comment ...
> 
> >It forces bgp implementations that don't have
> >confederation support to strip out something that will cause an error in
> >the regular path and for those systems ignoring the AS4_PATH attribute
> >is perfectly fine.
> 
> Why are you saying that there will be an error in the regular
> AS_PATH ? As far as I can see the above quote refers only to
> AS4_PATH.

If an implementation does not support confederations then an AS_PATH with
confederation elements will cause an error. Sure an invalid AS4_PATH as
that does not imply that the AS_PATH will have the same structure.

> The motivation is that instead of dropping the session or treating
> as withdraw robust BGP speaker can just remove the unexpected bad
> elements from AS4_PATH. In that respect this paragraph seems to add
> value and should be kept.

It seems you did not finish reading the draft:

   The AS4_PATH attribute in an UPDATE message SHALL be considered
   malformed under the following conditions:

...

      - the path segment type in the attribute is not one of the
        types defined: AS_SEQUENCE, AS_SET.

   A NEW BGP speaker that receives a malformed AS4_PATH attribute in an
   UPDATE message from an OLD BGP speaker MUST discard the attribute,
   and continue processing the UPDATE message.  The error SHOULD be
   logged locally for analysis.

So there is no dropping of the session and also no treat as withdraw.
It will just remove a malformed AS4_PATH from the received attributes.
Since an AS4_PATH attribute MUST NOT include AS_CONFED_SEQUENCE and
AS_CONFED_SET (or anything else but AS_SEQUENCE and AS_SET) it can be
considered malformed.

What will we gain from having to add complex code for something that
should not happen in the first place instead of using the default of
reverting back to the regular 2-byte AS_PATH attribute because the
AS4_PATH attribute was considered malformed?

-- 
:wq Claudio