The problem is that you do not have provider independent space, and
therefore you are breaking CIDR rules when you advertise the more specific
route through provider B.
So... out on the internet, there are two routes appearing in everyone's BGP
tables. One is to provider A's aggregate. The other is to your subnet.
Longest match rule applies here. Your /23 is more specific than provider A's
/18 ( or whatever ) So yes, I suppose that if the bulk of internet activity
is from the outside towards you, your more specific route will attract that
traffic through provider B. On the other hand, if the bulk of your traffic
is from your site out to the internet, then this might not be a problem.
Of course, there is a bright side. So far, at least your route is being
advertised. I seem to recall reading someplace that a lot of providers, in
order to encourage aggregation, do not advertise anything longer than a /19
or so.
Chuck
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On Behalf Of
Martin-Guy Richard
Sent: Friday, September 15, 2000 9:09 AM
To: cisco
Subject: BGP question - Multihoming
I have a tricky version for you guys:
I am multihomed to two provider. I got a /23 from Provider1. I
announce my /23 two Provider1 and Provider2. Since my /23 comes from
Provider1, he is supposed to aggregate in in is /16 CIDR. But, I have
to announce my /23 to my other provider. Somebody told me that the
longest prefix becomes something of a traffic magnet (or something like
that). So, all of my traffic would come from Provider2 and not
Provider1. How is it so, since BGP use aggregation?
I don't understand!
MGR
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