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19. Route Filtering

Ok, now that BGP has been covered, lets talk about filtering routes received

from our neighbor. Here I have created some additional Loopbacks on R2 that

are being advertised to R1:

RP/0/7/CPU0:R1#sh ip route /jointfilesconvert/356165/bgp

Fri Mar 30 13:13:36.797 UTC

B 200.100.200.100/32 [20/0] via 2.2.2.2, 00:00:42

B 200.200.200.200/32 [20/0] via 2.2.2.2, 13:45:00

B 200.200.200.203/32 [20/0] via 2.2.2.2, 00:00:42

B 200.200.200.204/32 [20/0] via 2.2.2.2, 00:00:42

B 200.200.200.205/32 [20/0] via 2.2.2.2, 00:00:42

B 200.200.200.206/32 [20/0] via 2.2.2.2, 00:00:42

B 200.200.200.207/32 [20/0] via 2.2.2.2, 00:00:42

B 200.200.200.208/32 [20/0] via 2.2.2.2, 00:00:42

B 200.200.200.209/32 [20/0] via 2.2.2.2, 00:00:42

B 200.200.200.210/32 [20/0] via 2.2.2.2, 00:00:42

RP/0/7/CPU0:R1#

As you can see, we are getting a bunch of 200.200.200.x/32 routes now as well

as a 200.100.200.100/32 route. For this exercise, lets filter our all the

200.200.200.x routes we are receiving from our neighbor.

Ok, lets create a prefix-set for the loopback we want to permit:

RP/0/7/CPU0:R1(config)#conf t

RP/0/7/CPU0:R1(config)#prefix-set R2Loopbacks

In IOS XR you can add comments via the #

RP/0/7/CPU0:R1(config-pfx)## These are the R2 Loopbacks that we will allow

RP/0/7/CPU0:R1(config-pfx)#200.100.200.100/32

RP/0/7/CPU0:R1(config-pfx)#end-set

Now that we have the prefix-set done we can create the route-policy

RP/0/7/CPU0:R1(config)#route-policy R2Loopbacks

Notice that IOS XR can use IF statements, you can just imagine how powerful

IF and ELSE statements can be when route filtering.

RP/0/7/CPU0:R1(config-rpl)#if destination in R2Loopbacks then

RP/0/7/CPU0:R1(config-rpl-if)#pass

RP/0/7/CPU0:R1(config-rpl-if)#endif

RP/0/7/CPU0:R1(config-rpl)#end-policy

After we end the policy, we need to commit it

RP/0/7/CPU0:R1(config)#commit

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Cisco Router IOS XR Manuale Utente Pagina 69