Reference Guide

For example, in 112.24.0.0/16, the rst 16 bits of the address 112.24.0.0 match all addresses between 112.24.0.0 to
112.24.255.255. Use permit or deny lters for specic routes with the le (less or equal) and ge (greater or equal) parameters, where
x.x.x.x/x represents a route prex:
• To deny only /8 prexes, 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 prex-lists:
• A prex-list without permit or deny lters allows all routes
• An “implicit deny” is assumed — the route drops for all route prexes that do not match a permit or deny lter
• After a route matches a lter, the lter’s action applies and no additional lters apply to the route
Use prex-lists in processing routes for routing protocols such as OSPF, RTM, and BGP.
To congure a prex-list, use commands in PREFIX-LIST and ROUTER-BGP modes. Create the prex-list in PREFIX-LIST mode and assign
that list to commands in ROUTER-BGP modes.
Route-maps
Route-maps a series of commands that contain a matching criterion and action. They change the packets meeting the matching criterion.
ACLs and prex-lists can only drop or forward the packet or trac while route-maps process routes for route redistribution. For example,
use a route-map to lter only specic routes and to add a metric.
• Route-maps also have an implicit deny. Unlike ACLs and prex-lists where the packet or trac is dropped, if a route does not match the
route-map conditions, the route is not redistributed.
• Route-maps process routes for route redistribution. For example, to add a metric, a route-map can lter only specic routes. If the route
does not match the conditions, the route-map decides where the packet or trac drops. The route is not redistributed if it does not
match.
• Route-maps use commands to decide what to do with trac. 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 dierent values in the same sequence
number, only the last match and set values are taken into account.
Congure 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
600
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