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 This e-mail may contain confidential and proprietary information of Multicast Technologies, Inc, subject to Non-Disclosure Agreements T.M. Eubanks Multicast Technologies, Inc. 10301 Democracy Lane, Suite 410 Fairfax, Virginia 22030 Phone : 703-293-9624 Fax : 703-293-9609 e-mail : tme@multicasttech.com http://www.multicasttech.com Test your network for multicast : http://www.multicasttech.com/mt/ Status of Multicast on the Web : http://www.multicasttech.com/status/index.html
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
Until such time as vendor C determines that RPF lookups should use the MRIB first, then the URIB, rather than the final RIB, the following will help: router bgp distance mbgp 19 19 19 ip mroute 0.0.0.0 0.0.0.0 bgp Null0 20 or if using 12.1: router bgp address-family ipv4 multicast distance bgp 19 19 19 ip mroute 0.0.0.0 0.0.0.0 bgp Null0 20 not having looked at vendor J's multicast, I can't speak to it. This does, however, make absolutely certain that only MBGP routes determine RPF choices. If you expect or desire unicast routes to drive multicast routing decisions, the above is not for you. I had to do this to get around a bunch of RPF hedge cases.
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Marshall Eubanks