Subject: Re: [Idr] Fw: Old transport-layer protocols to Historic?

From: David Freedman <[email-masked]>
Date: Mon, 10 Jan 2011 11:30:46 +0000

(apologies in advance for duplicates)

Ilya Varlashkin wrote:
> > Jakob,
> >
> > very valid points. Please see comments below.
> >
>> >> "deprecate" is too wussy. It does nothing.
>> >> We need a recommendation of what to do when we receive one.
>> >> Suggestions:
>> >> 1. Replace the AS-SET with the AS number of the sending speaker
> >
> > what if AS-SET is not the last element of the AS-PATH? e.g. an
announcement went through some routers which don't yet know that AS-SET
has been depricated? doesn't sound like a good idea
> >
>> >> 2. Replace the AS-SET with a special ASN that means "there was an
AS-SET here"
> >
> > this appeals to me as the best possible solution. While removing
AS-SET we should probably also remove AGGREGATOR and ATOMIC_AGGREGATE.
IANA section should be updated then and we need early allocation ASAP.
>> >> 3. drop the AS-SET

Well, just thinking about dropping it, its used heavily in aggregation,
meaning we should probably remove at least ATOMIC_AGGREGATE in this case
(any valid use cases these days?)

Also the tie breaking algorithm (4271 9.1.2.2),

"Remove from consideration all routes that are not tied for
         having the smallest number of AS numbers present in their
         AS_PATH attributes.  Note that when counting this number, an
         AS_SET counts as 1, no matter how many ASes are in the set."

So in this case, we need something in its place else we change
tie-breaking behaviour.

In short, (2) seems to cause the least disruption, though it is annoying
we have to carry this for backward compatibility, even more annoying we
have to reserve something for it...

Dave.