Tue, May 08, 2001 at 05:35:21PM +0100, Stephen J. Wilcox:
Cant comment on verios policys but...
1. Since Verio says they would not accept /24 nets drawn from Class B space, I assume this means that they don't insert a /16 into their tables so that the /24 nets appear to Verio customers as unreachable. In this case, a design that wants to extend connectivity to verio customers (and any other ISP with similar policies) must include a /16 advertisement from at least one of the sites.
if you have a /16 why would it be broken down to /24? i would assume the only reason you advertise /24 is because that is the size of your assignment from the NIC, in which case you cannot advertise the /16.
if you do own the /16 then yes of course you can advertise it.
s/can/should/
2. Suppose a customer of a Verio-like ISP, wishes to go to ftp. foo.org. DNS returns 169.61.201.155 (in amsterdam, see above). Verio passes the traffic to the neighbor it received the /16 advertisement from. At this point, the best thing that could happen is if that neighbor has the /16 and /24 networks in its route table, right? That means, a path exists for that user to the amsterdam server and the only problem with routing to Amsterdam is that Verio possibly handed the traffic to a sub-optimal neighbor. Am I understanding this issue correctly?
maybe, see above, if they cant advertise the /16 then theres no route. if its a verio customer then if verio dont advertise the /24 then no bgp will propogate and no routes will be valid.
no allocations have been made by RIRs in B space longer than /16, so they have the /16 to announce.
dont forget for traffic going TO the customer the traffic needs to find verio first and then the next hop will be the customer so verio wont pass it to anyone.
if it were possible to advertise both via different providers and the other provider accepted the /24 then the verio routes will be only used where the /24s dont propogate so there will be a shift in traffic to the other provider, if these are both transits so the routes are advertised out then your not going to get any traffic giong over verio.
I think you're forgetting that inbound packets and outbound packets are independent in finding their way through a network, a bidirectional flow does not mean that in and out go the same way..
in your example above you'll have packets going out nicely balanced but coming back in will just be through the /24 acceptor and not verio.
Steve
I'm new to BGP. I've tried to get a handle on this issue on my own and by working with Genuity, Internap and Cisco. No disrespect to those companies but each of them had this vague memory of Verio's policy but couldnt really tell me in plain language how it might affect the above scenario. Obviously, I wasn't talking to chief engineers. Someone from the CCIE mailing list suggested I browse the archives of this list, which I did. But I didnt find a clear enough answer to my questions--perhaps because they are too basic to be discussed here or I'm not good at using this lists archive search engine. Either way, any guidance on the above scenario is greatly appreciated.
-BM
-- Stephen J. Wilcox IP Services Manager, Opal Telecom http://www.opaltelecom.co.uk/ Tel: 0161 222 2000 Fax: 0161 222 2008