Re: [Idr] RFC-4893 handling malformed AS4_PATH attributes

On Mon, Dec 15, 2008 at 02:36:34PM -0500, John G. Scudder wrote:
> Discarding updates without processing them as Cayle describes violates the 
> loop free property.  Consider the fact that an advertisement of a route is 
> also an implicit withdrawal of any previous advertisement, and also 
> consider that an update can also carry explicit withdrawals.  Simply 
> discarding an update is thus equivalent to ignoring a withdrawal.  It's not 
> difficult to construct a scenario in which persistent forwarding loops 
> ensue.  A scenario with a persistent blackhole is trivial.

That was a point I clearly hadn't thought through: This may affect
implicit withdrawals along with other bundled reachability.

At the risk of missing something else obvious in a quick reply, presume
instead of dropping the update that the withdrawn routes field is processed
and that all reachability covered by the path attributes is deleted
instead of being installed or updated.  I believe this would have the
effect I was originally intending without leaving stale information in
the system.

> This has generally been my position in past iterations of this annual 
> debate.  I'm starting to moderate it based on the demonstrated operational 
> problems caused in particular by bad optional/transitives.

I think we're all there with you.

I suspect if the WG put our collective heads together we'd probably
arrive at some consensus on having more survivable sessions.  It'd
probably result in a re-spin of the previous INFORM specification,
perhaps renaming the attribute WTF.

-- Jeff
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