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Re: ISP Filter Policies--Effect is what?
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 188.8.131.52 (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 >