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Thread Index [isp-bgp] Re: Introduction, and questions
Anand, No-one will filter a Class C address (192.0.0.0/24 - 223.255.255.0/24) unless they have a very good reason for it. Some ISP's filter on their peering-points (Verio has some f(l)ame-status here) for filtering a class A (/8) or class B (/16) unless the more specific subnets are registered in the RADB database. If you are a transit ISP, there is nothing you can do about other isp's not accepting prefixes that do not originate from you.. If you allow your customers to announce prefixes out of your address space, the best you can guarantee those customers is that you will announce theirs, and your aggregate prefix. For some ISP's, we found out, it hepls to just announce the /16 or /8 -if you own it :) Ton S. Anand Buddhdev wrote: Hi everyone, I'm a network engineer for a company based in The Netherlands. I've recently started to use BGP with my upstream, and we announce a /20. At the moment, our configuration is very simple, since we don't do any transit or multi-homing, although this is going to change in just a few months, because we are getting a second upstream. I am a newbie with BGP, so there are some things that I am not too clear about. Perhaps someone with more experience can guide me. At the moment, we have a customer using a /22 and a /23 from our /20 assignment from RIPE. For various complex reasons this customer is moving to another provider, but needs to keep their IP addresses. If the other provider announces those /22 and /23 blocks via their AS, is that ok? Do I need to break up my /20 announcement into a /21 and /23? I have read that BGP will choose the most specific prefix, so if I understand it right, then I should be able to leave my /20 in place, while the customer can announce their more specific routes via the other provider. Can someone confirm this for me? Secondly, I have read that many providers often filter received routes, and typically reject anything more specific than a /22. We don't do that, so in our BGP table, I see many /24 networks too. May I hear opinion on what is common practice on the Internet these days? Since routers nowadays have more memory and power, is it necessary to filter more specific routes? I ask this question to understand the implications of what will happen to our customer when they announce their routes via the other provider, particularly the /23 they have. Thanks in advance to everyone for your valuable opinions.
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