Controlling outbound traffic in a multihomed BGP environment

Mon Mar 17 16:39:11 UTC 2003

Routing based on source address is called "Policy Routing".  IF you are on a cisco box, create an extended access-list specifying the source Ip's, and then match that access list in a route map to set the next hop.  Apply the route map on ports facing that customer, building a chain from edge (facing the customer) to border (facing the internet.

Good Luck,
Ejay

-----Original Message-----
From: Daniel Abbey [mailto:dabbey at edeltacom.net]
Sent: Monday, March 17, 2003 10:20 AM
To: nanog at merit.edu
Cc: cisco-digest at groupstudy.com; isp-outsourcing at isp-outsourcing.com
Subject: FW: Controlling outbound traffic in a multihomed BGP
environment

How can you control outbound traffic from a single subnet - meaning forcing
all its outbound traffic out a single bgp edge router in a multihomed
environment.

Here is the scenario:

1. Inbound traffic is engineered using prepends - meaning to force inbound
traffic through a particular router, we are using prepends to make one path
seem better than the other on the outside.

2. Local preferences are set to control general outbound traffic to specific
ISPs - those that are one or two hops away.

3. Now, I have a customer whose traffic I'll prefer to force out a single
bgp edge router - all his traffic, no specific ones. The IGP is OSPF, and
there are several different distribution routers between the access IGP
router and the core/edge bgp routers.