Subject: Re: [Idr] issue: bgp4-23: route resolvability and discard/null0 routes (fwd)

From: Pekka Savola <[email-masked]>
Date: Tue, 23 Mar 2004 16:42:36 +0200 (EET)

There were no follow-ups to this and the spec has entered IETF Last 
Call.

So, let me ask again; is there opposition for adding a clarification
like:

   If a route's (Rte1) next-hop (Rte2) or next-hop interface would
   lead to packets being discarded by the same router, the route
   (Rte1) SHOULD be considered unresolvable.

or:

   When considering resolvable routes or referenced interfaces,
   if packets through the route would be discarded by the router,
   the route SHOULD be considered unresolvable.

in 9.1.2.1, after the two points about the route resolvability 
condition (as justified by below) ?

---------- Forwarded message ----------
Date: Sat, 13 Mar 2004 09:57:15 +0200 (EET)
From: Pekka Savola <[email-masked]>
To: [email-masked]
Subject: Re: [Idr] issue: bgp4-23: route resolvability and discard/null0
    routes

On Fri, 12 Mar 2004, Jeffrey Haas wrote:
> On Fri, Mar 12, 2004 at 04:55:04AM -0500, Curtis Villamizar wrote:
> > I think the best way to handle this (from the standards standpoint) is
> > to write a separate draft.  The draft would provide a better "BGP next
> > hop resolvable test" but does not match any current implementation so
> > it does not belong in the BGP spec.  If changes are made to any
> > implementations they would remain fully interoperable with those that
> > go by the letter of the spec without any "better resolvable test".
> 
> I would agree with Curtis.  This is an operational/deployment issue
> and a draft covering such issues - and not just this one - may
> be a Good Thing.

There was already an off-list discussion about this, but I think I 
should clarify the issue here:

  The local router knows that route R2 is a discard/null0 route, and
  the nexthop of route R1 goes through R2 after the more specific
  route has been withdrawn from IGP.  Route R1 is considered valid 
  even though the router knows it goes through a discard route.

Many consider this an implementation bug; some have already said
they'd fix this, so the argument "there is no implementation" does not
hold.

What I want is that this gets fixed in the spec, because the spec can
be read both ways.  I want to avoid "local optimizations" by
implementations, and fix this in the specification.  It would be
irresponsible to have purposely ambiguous specifications.

One possible way to fix this could be, in 9.1.2.1:

----
   The route resolvability condition is defined as follows.

      1. A route Rte1, referencing only the intermediate network
      address, is considered resolvable if the Routing Table contains at
      least one resolvable route Rte2 that matches Rte1's intermediate
      network address and is not recursively resolved (directly or indi-
      rectly) through Rte1. If multiple matching routes are available,
      only the longest matching route SHOULD be considered.

      2. Routes referencing interfaces (with or without intermediate
      addresses) are considered resolvable if the state of the refer-
      enced interface is up and IP processing is enabled on this inter-
      face.
----

Add a clarifying paragraph afterwards:

   If a route's (Rte1) next-hop (Rte2) or next-hop interface would 
   lead to packets being discarded by the same router, the route 
   (Rte1) SHOULD be considered unresolvable.

or:
 
   When considering resolvable routes or referenced interfaces,
   if packets through the route would be discarded by the router,
   the route SHOULD be considered unresolvable.

-- 
Pekka Savola                 "You each name yourselves king, yet the
Netcore Oy                    kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings

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