|
North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: Generally accepted announcement sizes
On Thu, 22 Jun 2000, Mike Heller wrote: > > Can anyone point me to a centralized resource for Tier 1 and Tier2 > providers' accept policies? I have found that when some of my circuits go > down various parts of the 'Net become unreachable and I attributed that to > the size of that announcement being a /24. I assume that the carriers I'm > having issue with are not using RADB as I registered all of my netblocks, Here's the deal. If you number out of Provider1's CIDR block but advertise your more-specific to Provider2 and the two Providers touch and Provider1 accepts the more-specific route from Provider2, you should have no problem reaching anyone. Here's the reason: Everyone accepts Provider1's announcement of the block. When your link to P1 is up, any traffic they recieve for your prefix gets routed over that link since they carry your more-specific internally. However, if other providers here the more-specific from P2, they'll send directly via P2 who sends it over the link to you. If your link to P1 goes down, P1 won't see the direct route to you but should see the route via P2 if P1 is accepting it. (Some may either block the announcement or have anti-spoofing packet filters at their borders that block the traffic itself). There are many misconceptions about this topic. Hopefully this explanation has helped someone. To find out exactly why your multi-homing set-up isn't working, I'd work with your providers' operations staff. Perhaps set up a time to test the fail over with them on hand to help you analyze by looking at the routes on both. It should be possible for them to help check the behavior of traffic over a third provider as well if the providers are worth their salt. Tony
|