I don't think this is as simple as this ... Remember that when the
less specific (/24) goes away the AS4 must readvertise the more
specifics not to break routing. So therefor I do not think that any
simple policy would work. The choice/decision what to advertise and
what not must be done at best path run.
Sure --but won't best path be run when the best path towards a
specific destination falls out of the table?
Best path today does not compare /16 and /24. In Pedro's proposal it does.
Actually I am not that clear I understand this business reg
communities marking. How about we consider even much simpler and
ASBR local solution:
A local ASBR only solution won't work for various reasons, so let's
not. :-)
I think it works. The example is comparing all best path eligible
attributes of less and more specific during best path and if the less
specific would win suppress the more specific.
I am only not sure if we really need to compare all. For example I am
not sure that like in your proposal it really matters if the more
specific was received over the same session as less specific (provided
that actually happens that often as you say :-)
So what you are saying is that if a provider owns 10.1.0.0/16, and
gives out 10.1.1.0/24 to a customer to advertise through some other
provider the customer is connected to, the provider would never
advertise 10.1.1.0/24 as well as 10.1.0.0/16? Why not? Since the
longest match always wins, what you're saying is that the provider
that handed out the address space would end up routing through the
competing provider (the customer's other provider) to reach the
customer, because there is a longer match being advertised by the
customer through the competing provider.
That doesn't make any sense to me.
That has been for years common recommendation of any RIR ... That's the
value of PA addresses. Multihomers were told to get PI which indeed does
not make the BGP table smaller.
Examples:
"Announcement of initial allocation as a single entity"
http://meetings.ripe.net/ripe-53/presentations/rou-ps-rou.pdf
"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] and NOPEER [RFC-3765] or provider-specific
communities, as described in [RIPE-399] to limit the propagation of
more specific prefixes in the routing table."
SRC: ripe-532.txt
Just to be very clear .. VA (any of the VA drafts) does not talk
about the same problem. For one it does not stop BGP from
advertising anything and second it is intra-domain solution.
Right --the VA drafts increase stretch and don't reduce the total
table size for anyone.
It never intended to. It reduces the local RIB/FIB size. I am not even
sure why you are comparing apple to oranges here :)
Best,
R.
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