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Cyclades-PR4000
Chapter 11 - Routing Protocols 103
BGP-4 Configuration
The BGP-4 routing protocol is used for routing on the Internet, performed between Autonomous Systems (ASs).
An autonomous system is defined as:
· A set of routers and networks under the same administration.
· An interconnected network, where no router is reachable solely through a path exterior to the AS
Each AS is identified by a 16-bit AS number. This number is supplied by the service provider.
Steps
1. Complete the Global Parameters
2. Register the neighbors of the autonomous system, the routers with which it this router exchanges information.
At this point, the BGP-4 protocol is up and running. All remaining steps are fine tuning to improve performance
and reduce the size of the routing table.
If some routes that might be received are undesired, they can be filtered as they enter (or leave) so that they are
not placed in the routing table (or are not propagated to other autonomous systems).
This requires the following three steps:
3. Create an Access List
4. Add rules to the Access List
5. Return to the Neighbor configuration and match each list to the neighbor it should be applied to.
In some cases, a route should be accepted, but with changes determined by policies defined by the system
administrator. In this case, a route map should be created indicating which of the path attributes of the incoming
(or outgoing) message should be changed. This route map can be associated with a filter so that only specific
rules will be altered. The steps are the following:
6. Create a route map/sequence pair
7. Edit the neighbor definition to link it to the new route map