Re: revised draft of BGP-4

[Curtis Villamizar <[e-mail]>]

In message <[e-mail]>et>, "Michael F. Nittmann" writ
es:
> 
> Following case: assume a multihomed AS splits up due to internal 
> connectivity loss. Both parts announce routes to systems with transit 
> agreement. 
> By accepting routes with the own AS path, the other part of the AS can be 
> reached via the transit system.
> this shouls be the default.

Partition repair is possible, but should not be the default.  Would
you like to repair an AS690 partition (can't happen, just hypothetic :)

> The limitation in this paragraph is only important for single homed AS 
> systems, which are not the majority case.
> 
> I would suggest to invert this, that the default behaviour will be to 
> accept routes with the same AS path, but not to duplicate the same route 
> at all, e.g.
> 
> 	1.0.0.0 is announced by two routers of AS 0 to AS 1 and AS 2 .
> 	
> 	AS 0 splits due to internal connectivity loss (split means, the 
> 	fallback link is too slow to take all traffic)
> 	
> 	Router A announces 1.0.0.0, router B (of AS 0) lost the route due to 
> 	the split and picks it up from AS 2, which has a transit agreement with
> 	AS 0.
> 
> 	Router B can announce to the severed part of AS 0 that 1.0.0.0 is 
> 	now not reachable best via the internal 'natural' link, but via AS 2.

Having an agreement to do partition repair may be a different from a
transit agreement.  Some providers (us) don't announce you back to
yourself so you can't prefer our backbone in favor of your own or
intentionally partition your own backbone to overcome congestion
(unless you default at us, which we also prohibit in our agreement).

Partition repair (accepting your AS in the path exactly once) can be
configured but should not be the default.  If you have an agreement
with your provider to do partition repair, then configure it.

Curtis