Discussion

9.2 Changing a Route’s Routing Information
Problem
You want to enforce your company’s BGP peering relationships and control the traffic
you receive from BGP peers by modifying the BGP LOCAL_PREF attribute and
associating a community with certain BGP routes.
Solution
Another function of routing policy is to modify the routing information associated
with BGP routes. First, match the routes to be affected:
[edit policy-options policy-statement from-my-customers term 1]
aviva@router1# set from neighbor 10.0.31.2/32
Use the then clause to modify the route’s routing information:
[edit policy-options policy-statement from-my-customers term 1]
aviva@router1# set then local-preference 300
aviva@router1# set then community set 65500:12345
aviva@router1# set then accept
Finally, apply the policy to a BGP group:
[edit protocols bgp]
aviva@router1# set group external-group import from-my-customers
Discussion
For BGP routes, routing policy allows you to modify the BGP routing information
associated with each route, including the BGP local preference, community, and origin
attributes, and the AS paths in each route. You typically do this to manage customer
traffic and peering arrangements with other ISPs. Table 9-4 lists the actions
you can include in a policy to change a route’s routing information. Most of these
actions are specific to BGP.
Table 9-4. Actions that change routing information in matching routes
Action term
as-path-prepend path
as-path-expand last-as count number
community + names
community add names
community – names
community delete names
community = names
community set names
damping name
Description
Add AS numbers to the beginning of the BGP AS path.
Add the last AS number to the BGP AS path the specified number of
times before adding the local AS number.
Add BGP community names.
Delete BGP community names.
Set the specific BGP community name.
Configure BGP route flap damping.
290 | Chapter 9: Routing Policy and Firewall Filters
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