Keep in mind what is actually occurring when using BGP. You are
advertising prefixes from your AS into your provider's AS. They in turn
either include your specific prefix in their announcements to other
providers, or they aggregate your smaller prefix into larger
advertisements. It is at this stage that you need to worry about what
other providers are doing as far as filtering.
If your provider is advertising your specific prefix, a /24 for
instance, but the other companies won't accept anything less than a /22,
then you're up a creek. We are advertising a /24 to two separate
providers and I haven't seen any reachability problems from anywhere in
the world. As far as I'm concerned, if we can be reached by either path
from just about anywhere, especially in the US, then I'm happy.
I've been following your posts and I'm curious about your motivation
for adding a second provider. This adds a measure of complexity that
might not be necessary, depending on your goals. Can your current
provider give you a circuit that follows a separate path then your first
circuit? If so, that would eliminate a couple of issues.
First, you wouldn't even necessarily need to run BGP, although I would
prefer to do so. But instead of getting full routes, you could accept
defaults-only from your provider and advertise your addresses on both
links.
Second, you wouldn't worry about getting an entire /24--or
larger--block of addresses. In this scenario, your provider will
aggregate your prefix into their larger announcements, but when traffic
destined for your network arrives in their network, internally they'll
see two available paths. This has the additional benefit of not wasting
registered addresses since you probably don't really need an entire
/24.
Third, you won't have to apply for your own AS number from Arin. If
you run BGP over two links to the same provider, they will either let
you use their ASN or let you use a private ASN that will only be seen by
their network.
Would a solution like this work for you?
Regards,
John
----------------------------------------------------------
John Neiberger
Firstbank Data Corporation
12345 W. Colfax Ave.
Lakewood, CO 80215
(303) 235-1093
>>> "Daniel Wilson" 7/6/01 12:23:46 PM >>>
We are looking into multi-homing our network and running BGP on our
router.
I was told by some of you before that some ISPs won't advertise a block
of
IP's smaller than /22 and many won't do any smaller than /24. That
leads to
this question.
Are our ISPs the only ones that need to advertise our block? Or does
everybody out there need to advertise the block?
Thanks!
--
Daniel Wilson
CompuSoft Solutions and The Worthwhile Company
http://www.worthwhile.com
Your complete e-business solution partners.
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=11195&t=11191
--------------------------------------------------
FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html
Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
