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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical RE: Opinions about InterNAP
> /24's are sufficient to multihome with most if not all providers out > there. Why not conventionally multi-home to 2 large well established > providers? > > -Dave People sometimes forget that you can multihome effectively with just a single /24 provided: 1) You pick two (or more) providers that meet with each other directly in several places (or at least are well-connected to whoever is announcing the larger block the /24 comes from). 2) Both (or all) providers agree to accept/announce your /24. 3) Your /24 is inside a larger routable block advertised by a provider that is unlikely to ever withdraw the route entirely. Your two providers are extremely unlikely to lose contact with each other. This provides all the benefits of multihoming with your own block with only four disadvantages: 1) You aren't quite as well protected against certain complex multiple failure scenarios. (For example, if the provider who owns the block your IPs come from withdraws that route, or if you lose your link to that provider at the same time it loses all its links to the provider you still have connectivity to.) 2) You can't as easily add or delete providers (they have to, at least, agree to announce your /24 and you need to make sure they have good connectivity to whoever is announcing the larger block the /24 comes from) and you are to some extent controlled by the ISP who assigned you the addresses you are using (you can't stop getting service from them without renumbering). 3) You may experience finger pointing in the even that you are having connectivity problems. Because of the unusualness of the setup, it tends to be harder to figure out who is really at fault than when you multihome with your own block. 4) Your setup is a bit more fragile with your providers. You run the risk that a configuration change will somehow break your setup, and it's more likely with this type of setup to wind up blackholing traffic then with a convnetional setup where it's more likely to just not carry traffic. Even providers that filter your /24 will still have the route to the larger block it is part of. So they will still get your traffic closer to you, which is good enough to ensure full connectivity. DS
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