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

[Enke Chen <[e-mail]>]

Hi, Claudio:

Not sure if you are aware of the large scale outage that occurred a few 
years ago from the leak of the confed related segments by one 
implementation. At the time quite a few implementations were resetting 
the sessions when receiving such updates.

While discarding the whole AS4_PATH would be simpler and less disruptive 
(than session resetting), it would still lose the vital as-path info 
contained in the AS4_PATH which can otherwise be recovered by 
"repairing" the attribute.  That is why the approach specified in the 
rfc4893bis is adopted, and it has been implemented widely.

-- Enke

On 6/12/12 10:14 AM, Claudio Jeker wrote:
> 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?
>