Route filtering passive interface





Cisco IOS provides several ways to control updates traffic. Passive interface, distribute list, prefix list route maps. In this section we take look at passive interface in RIPv2, EIGRP, and OSPF.

Passive interface command is used in al routing protocol to disable sending updates out from a specific interface. However the command behavior varies from one protocol to another.



EIGRP Passive interface

EIGRP do not send any hello messages on passive interface. EIGRP router ignores any EIGRP messages received on the interface its means no neighbors relation but EIGRP still advertises about the connected subnet only if matched with an EIGRP network command.





Topology:









configure the topology as per the diagram

configure EIGRP 65001 and advertise interface

configure router 3 interface serial 3/1 passive interface

make sure router 3 drop neighbourship and prevent routes















R3#show ip interface brief Interface IP-Address OK? Method Status Protocol FastEthernet0/0 30.1.1.1 YES manual up up Serial3/1 2.1.1.2 YES manual up up











R2(config)#router eigrp 65001 R2(config-router)#network 20.0.0.0 R2(config-router)#network 2.0.0.0 R2(config-router)#network 1.0.0.0

*Mar 18 13:43:20.971: %DUAL-5-NBRCHANGE: EIGRP-IPv4 65001: Neighbor 1.1.1.1 (Serial3/0) is up: new adjacency

R2(config-router)#end





R3(config)#router eigrp 65001 R3(config-router)#network 2.0.0.0



*Mar 18 13:44:10.655: %DUAL-5-NBRCHANGE: EIGRP-IPv4 65001: Neighbor 2.1.1.1 (Serial3/1) is up: new adjacency

R3(config-router)# network 30.0.0.0 R3(config-router)#end





D 30.0.0.0/8 [90/2684416] via 1.1.1.2, 00:00:16, Serial3/0







R2#show ip route eigrp Codes: L - local, 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, H - NHRP, l - LISP + - replicated route, % - next hop override

Gateway of last resort is not set

D 10.0.0.0/8 [90/2172416] via 1.1.1.1, 00:04:00, Serial3/0 D 30.0.0.0/8 [90/2172416] via 2.1.1.2, 00:00:40, Serial3/1





R3#show ip route eigrp Codes: L - local, 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, H - NHRP, l - LISP + - replicated route, % - next hop override

Gateway of last resort is not set



D 1.0.0.0/8 [90/2681856] via 2.1.1.1, 00:00:58, Serial3/1 D 10.0.0.0/8 [90/2684416] via 2.1.1.1, 00:00:58, Serial3/1 D 20.0.0.0/8 [90/2172416] via 2.1.1.1, 00:00:58, Serial3/1

1 2.1.1.2 Se3/1 14 00:01:19 21 126 0 7









*Mar 18 13:50:02.303: %DUAL-5-NBRCHANGE: EIGRP-IPv4 65001: Neighbor 2.1.1.2 (Serial3/1) is down: interface passive









R2#show ip route eigrp Codes: L - local, 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, H - NHRP, l - LISP + - replicated route, % - next hop override



Gateway of last resort is not set

D 10.0.0.0/8 [90/2172416] via 1.1.1.1, 00:07:56, Serial3/0





R2#show ip eigrp neighbors EIGRP-IPv4 Neighbors for AS(65001) H Address Interface Hold Uptime SRTT RTO Q Seq (sec) (ms) Cnt Num 0 1.1.1.1 Se3/0 13 00:08:29 32 192 0 7







Goal:R1#show ip interface briefInterface IP-Address OK? Method Status ProtocolFastEthernet0/0 10.1.1.1 YES manual up upSerial3/0 1.1.1.1 YES manual up upR2#show ip interface briefInterface IP-Address OK? Method Status ProtocolFastEthernet0/0 20.1.1.1 YES manual up upSerial3/0 1.1.1.2 YES manual up upSerial3/1 2.1.1.1 YES manual up upR1(config)#router eigrp 65001R1(config-router)#network 1.0.0.0R1(config-router)#network 10.0.0.0R1(config-router)#exitR1#show ip route eigrpCodes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGPD - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter areaN1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2E1 - OSPF external type 1, E2 - OSPF external type 2i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2ia - IS-IS inter area, * - candidate default, U - per-user static routeo - ODR, P - periodic downloaded static route, H - NHRP, l - LISP+ - replicated route, % - next hop overrideGateway of last resort is not setD 2.0.0.0/8 [90/2681856] via 1.1.1.2, 00:03:36, Serial3/0D 20.0.0.0/8 [90/2172416] via 1.1.1.2, 00:03:36, Serial3/0R2#show ip eigrp neighborsEIGRP-IPv4 Neighbors for AS(65001)H Address Interface Hold Uptime SRTT RTO Q Seq(sec) (ms) Cnt Num0 1.1.1.1 Se3/0 10 00:04:39 27 162 0 6R2(config)#router eigrp 65001R2(config-router)#passive-interface serial 3/1R2(config-router)#endR1#show ip route eigrpCodes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGPD - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter areaN1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2E1 - OSPF external type 1, E2 - OSPF external type 2i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2ia - IS-IS inter area, * - candidate default, U - per-user static routeo - ODR, P - periodic downloaded static route, H - NHRP, l - LISP+ - replicated route, % - next hop overrideGateway of last resort is not setD 2.0.0.0/8 [90/2681856] via 1.1.1.2, 00:07:22, Serial3/0D 20.0.0.0/8 [90/2172416] via 1.1.1.2, 00:07:22, Serial3/0