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Filter bgp default route generated by 'default-originate' command

benjaminyu
Level 1
Level 1

I have a question on BGP. I have a router speaking BGP to multiple neighbors. It is generating a default route using 'default-originate' command to all of its neighbors. I would like to have some neighbors stop receiving this default route. How can I filter this default route on a particular neighbor.

5 Replies 5

yuhuiyao
Level 1
Level 1

use neighbor x.x.x.x default-originate instead under router bgp.

The task I would like to do is to remove the all 0.0.0.0 entries learned from BGP on this particular router:

Router A#sh ip bgp

BGP table version is 14, local router ID is 2.2.2.1

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

r RIB-failure, S Stale

Origin codes: i - IGP, e - EGP, ? - incomplete

Network Next Hop Metric LocPrf Weight Path

* 0.0.0.0 5.5.5.1 0 6533 6511 6511 i

*> 5.5.5.1 0 0 6511 6511 i

r 1.1.1.0/24 5.5.5.1 0 6533 6511 i

r> 5.5.5.1 0 0 6511 i

r 1.1.2.0/24 5.5.5.1 0 6533 6511 i

r> 5.5.5.1 0 0 6511 i

*> 2.2.1.0/24 0.0.0.0 0 32768 i

*> 2.2.2.0/24 0.0.0.0 0 32768 i

*> 10.10.1.0/24 5.5.5.3 0 0 6533 i

* 5.5.5.3 0 6511 6533 i

*> 10.10.2.0/24 5.5.5.3 0 0 6533 i

* 5.5.5.3 0 6511 6533 i

r 30.30.2.0/24 5.5.5.1 0 6533 6511 i

r> 5.5.5.1 156160 0 6511 i

*> 70.70.70.0/24 5.5.5.3 25753600 0 6533 i

* 5.5.5.3 0 6511 6533 i

*> 222.222.222.0 5.5.5.3 0 0 6533 i

Router A#sh ip route

Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP

D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area

N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

E1 - OSPF external type 1, E2 - OSPF external type 2

i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2

ia - IS-IS inter area, * - candidate default, U - per-user static route

o - ODR, P - periodic downloaded static route

Gateway of last resort is 5.5.5.1 to network 0.0.0.0

200.200.200.0/30 is subnetted, 1 subnets

C 200.200.200.0 is directly connected, Serial0/0/1:0

B 222.222.222.0/24 [100/0] via 5.5.5.3, 00:05:57

C 211.211.211.0/24 is directly connected, GigabitEthernet0/1

1.0.0.0/24 is subnetted, 2 subnets

D 1.1.1.0 [90/156160] via 211.211.211.1, 03:37:37, GigabitEthernet0/1

D 1.1.2.0 [90/156160] via 211.211.211.1, 03:37:37, GigabitEthernet0/1

D EX 222.222.100.0/24

[170/30720] via 211.211.211.4, 01:49:46, GigabitEthernet0/1

2.0.0.0/24 is subnetted, 2 subnets

C 2.2.1.0 is directly connected, Loopback0

C 2.2.2.0 is directly connected, Loopback1

100.0.0.0/30 is subnetted, 1 subnets

C 100.100.100.0 is directly connected, Serial0/0/0:0

70.0.0.0/24 is subnetted, 1 subnets

B 70.70.70.0 [100/25753600] via 5.5.5.3, 00:05:59

80.0.0.0/24 is subnetted, 2 subnets

D 80.80.1.0 [90/156160] via 211.211.211.4, 03:37:40, GigabitEthernet0/1

D 80.80.2.0 [90/156160] via 211.211.211.4, 03:37:40, GigabitEthernet0/1

5.0.0.0/24 is subnetted, 1 subnets

C 5.5.5.0 is directly connected, GigabitEthernet0/0

111.0.0.0/30 is subnetted, 1 subnets

D 111.111.111.0

[90/2181120] via 211.211.211.3, 03:36:22, GigabitEthernet0/1

[90/2181120] via 211.211.211.1, 03:36:22, GigabitEthernet0/1

10.0.0.0/24 is subnetted, 2 subnets

B 10.10.1.0 [100/0] via 5.5.5.3, 00:05:59

B 10.10.2.0 [100/0] via 5.5.5.3, 00:05:59

30.0.0.0/24 is subnetted, 2 subnets

D 30.30.1.0 [90/156160] via 211.211.211.3, 03:36:24, GigabitEthernet0/1

D 30.30.2.0 [90/156160] via 211.211.211.3, 03:36:24, GigabitEthernet0/1

B* 0.0.0.0/0 [100/0] via 5.5.5.1, 00:06:00

Alameda#

create a filter list:

Something like this should work.

router bgp ASN

neighbor x.x.x.x route-map IN in

!

ip prefix-list IN seq 5 deny 0.0.0.0/0

!

route-map IN permit 10

match ip address prefix-list IN

Hello Rick,

good idea I would refine it in this way:

ip prefix-list def_route seq 5 permit 0.0.0.0/0

route-map IN deny 10

match ip address prefix-list def_route

+

route-map IN permit 20

to allow all other prefixes learned from the neighbor without the second clause all prefixes are denied.

Hope to help

Giuseppe

Your solution is great. It works for me.

I was running into the problem that you described. Without the second clause on the route-map, all prefixes will be denied.

Thank you all.

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