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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...

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. ;)


                                 Marshall Eubanks

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T.M. Eubanks
Multicast Technologies, Inc.
10301 Democracy Lane, Suite 410
Fairfax, Virginia 22030
Phone : 703-293-9624       Fax     : 703-293-9609
e-mail : [email protected]

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