Users Guide

● To deny only /8 prefixes, enter deny x.x.x.x/x ge 8 le 8
● To permit routes with the mask greater than /8 but less than /12, enter permit x.x.x.x/x ge 8 le 12
● To deny routes with a mask less than /24, enter deny x.x.x.x/x le 24
● To permit routes with a mask greater than /20, enter permit x.x.x.x/x ge 20
The following rules apply to prefix-lists:
● A prefix-list without permit or deny filters allows all routes
● An implicit deny is assumed — the route drops for all route prefixes that do not match a permit or deny filter
● After a route matches a filter, the filter’s action applies and no additional filters apply to the route
NOTE: Use prefix-lists in processing routes for routing protocols such as open shortest path first (OSPF), route table
manager (RTM), and border gateway protocol (BGP).
To configure a prefix-list, use commands in PREFIX-LIST and ROUTER-BGP modes. Create the prefix-list in PREFIX-LIST mode
and assign that list to commands in ROUTER-BGP modes.
Route-maps
Route-maps are a series of commands that contain a matching criterion and action. They change the packets meeting the
matching criterion. ACLs and prefix-lists can only drop or forward the packet or traffic while route-maps process routes for
route redistribution. For example, use a route-map to filter only specific routes and to add a metric.
●
Route-maps also have an implicit deny. Unlike ACLs and prefix-lists where the packet or traffic drops, if a route does not
match the route-map conditions, the route does not redistribute.
● Route-maps process routes for route redistribution. For example, to add a metric, a route-map can filter only specific routes.
If the route does not match the conditions, the route-map decides where the packet or traffic drops. The route does not
redistribute if it does not match.
● Route-maps use commands to decide what to do with traffic. To remove the match criteria in a route-map, use the no
match command.
● In a BGP route-map, if you repeat the same match statements; for example, a match metric, with different values in the
same sequence number, only the last match and set values are taken into account.
Configure match metric
OS10(config)# route-map hello
OS10(conf-route-map)# match metric 20
View route-map
OS10(conf-route-map)# do show route-map
route-map hello, permit, sequence 10
Match clauses:
metric 20
Change match
OS10(conf-route-map)# match metric 30
View updated route-map
OS10(conf-route-map)# do show route-map
route-map hello, permit, sequence 10
Match clauses:
metric 30
To filter the routes for redistribution, combine route-maps and IP prefix lists. The following table explains the action performed
for multiple match commands under a single route-map.
Table 133. Multiple match commands under a single route-map
Route-map
clause
Prefix list Incoming
Route
Action
permit permit
MATCH The route is permitted.
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