[routing-wg] IPv6 Routing Recommendations.

* Rob Evans:

> There is a valid need for some LIRs to advertise more than one IPv6
> PA prefix.  As either obtaining more address space and advertising
> more /32 prefixes, or advertising more specific prefixes within an
> already allocated /32 have the same impact on the routing table,
> it is suggested that the latter approach is taken to prevent address
> space wastage.

Another approach would be to leave the filtering recommendation at
/32, and give LIRs the full /29 (or so) which is currently reserved
for them.  This would result in better FIB aggregation in many cases.

But your proposal seems less controversial.

> Advertisement of more specific prefixes should not be used unless
> absolutely necessary and, where sensible, a covering aggregate
> should also be advertised.  Further, LIRs should use BGP methods
> such as NO_EXPORT [RFC-1997], [AS-PATHLIMIT], or provider-specific
> communities, as described in [RIPE-399] to limit the propagation of
> more specific prefixes in the routing table.

AS_PATHLIMIT is dead, as far as I know.  But NO_EXPORT actually works
in the case of the presence of a covering aggregate (it's a one of the
precious few use cases for it).

In any case, these recommendations should be prominently referenced
from pages which describe minimum allocation sizes (which must not be
used to construct filters).

-- 
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