From: adiment@xxxxxxxxxx
Date: Fri Apr 27 2001 - 12:51:59 GMT-3
They better. A lot of our customers multihome with full BGP to different
ISPs to get redundancy. If both ISPs did not advertise their networks they
would not get redundancy. In some cases the ISPs required them to put an
aggregate address command under "router bgp xxxxx" Here is an actual config
from a customers router I'm working on right now, address and AS numbers I
have to omit. They have 2 router each connected to a different service
provider and the routers are linked to each other with a x-over ethernet
cable. The as-path filter is to make sure they don't become a transit path
for the internet.
router bgp 20xxx
no synchronization
bgp log-neighbor-changes
aggregate-address 198.xxx.xxx.0 255.255.252.0 summary-only
neighbor xx.x.x.xxx remote-as 20xxx
neighbor 204.xx.xx.xxx remote-as 10xxx
neighbor 204.xx.xx.xxx filter-list 99 out
!
ip as-path access-list 99 permit ^$
ip as-path access-list 99 deny .*
-----Original Message-----
From: Murphy, Brennan [mailto:Brennan_Murphy@NAI.com]router
Sent: Friday, April 27, 2001 10:28 AM
To: 'ccielab@groupstudy.com'
Subject: real world BGP question
What is the smallest subnet that major carriers will exchange with one
another? /24..../26.../27?? I know that the real issue is the size of
the route table.
I'm just wondering about the reallity of scenarios that Habali describes
where an institution advertises an aggregate with specific subnets.
I know that when you're multi-homed to a carrier, that carrier will
sometimes
take your /26 and /27 nets to help route inbound traffic but that carrier
will not advertise those nets to its neighbors.....at least thats what I've
heard.
Anyone have any real world experience with this? Or is there a URL
I could read up on?
Thanks,
BM
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