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Re: /8s and filtering

  • From: Marshall Eubanks
  • Date: Tue Dec 10 09:55:36 2002

Here is one reason for some to care :

If you want to do interdomain multicast, and your
address space is not announced globally (say because you have a /24 that is
not from the swamp), you are likely to be black-holed
due to RPF failures (as your unicast and multicast routing is likely to be different).

This has caused problems from time to time...

Regards
Marshall Eubanks

On Tuesday, December 10, 2002, at 05:58 AM, David Schwartz wrote:



I was also curious about this - if I am a customer who wants to
multihome and can justify only a /24, I would go to an ISP
which has an allocation from the Class C space rather than one from the
Class A space.




It doesn't matter. For all practical purposes, basement
multihomers only

care that their two or three providers have their route.




Do ISPs get to choose where the allocation comes from?




Ask your ISP if they'll let you choose. But it usually doesn't
matter, if

you can only justify a /24, you'll find about the same filtering
policies in

both traditional class A space and class C space.



But again, it doesn't matter. So long as each of your providers
will honor

your route (and why wouldn't they, you're paying them to) you
shouldn't have

a problem.



Just pick your most reliable provider, and the one you're pretty
sure you're

going to stay with the longest, and get your IP space from them. Make
sure

they don't mind you advertising your block through other providers.



And give some thought to hiring a competent consultant to help
you. You can

hire a consultant even if you are the consultant. In fact, no competent

consultant would do otherwise outside his or her area of expertise.
Don't

learn to multihome at your client's expense. ;)



DS








                                 Regards
                                 Marshall Eubanks

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T.M. Eubanks
Multicast Technologies, Inc.
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