Thursday, 4 April 2019

Route filtering passive interface OSPF

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 all routing protocol to disable sending updates out from a specific interface. However the command behavior varies from one protocol to another.

Passive interface in OSPF

In OSPF passive-interface, work just like it does with EIGRP. OSPF do not send any hello messages on passive interface its means no neighborship but still advertises about the connected subnet if matched with an OSPF network command.

lets see the configure:


Topology:


Goal:



  • configure the topology as per the diagram 
  • configure ospf and advertise the network
  • configure interface serial 4/1 passive interface 



R1#show ip interface brief
Interface              IP-Address      OK? Method Status                Protocol
FastEthernet0/0        10.1.1.1        YES manual up                    up
Serial4/0                    1.1.1.1         YES manual up                    up

R2#show ip interface brief
Interface              IP-Address      OK? Method Status                Protocol
FastEthernet0/0        20.1.1.1        YES manual up                    up
Serial4/0                    1.1.1.2         YES manual up                    up
Serial4/1                    2.1.1.1         YES manual up                    up


R3#show ip interface brief
Interface              IP-Address      OK? Method Status                Protocol
FastEthernet0/0        30.1.1.1        YES manual up                    up
Serial4/1                    2.1.1.2         YES manual up                    up
Loopback0              13.0.0.1        YES manual up                    up
Loopback1              13.0.1.1        YES manual up                    up
Loopback2              13.0.2.1        YES manual up                    up
Loopback3              13.0.3.1        YES manual up                    up
Loopback4              13.0.4.1        YES manual up                    up


R1(config)#router ospf 1
R1(config-router)#network 10.0.0.0 0.255.255.255 area 0
R1(config-router)#network 1.0.0.0 0.255.255.255 area 0
R1(config-router)#exit

*Apr  4 14:25:00.243: %OSPF-5-ADJCHG: Process 1, Nbr 20.1.1.1 on Serial4/0 from LOADING to FULL, Loading Done

R2(config)#router ospf 1
R2(config-router)#network 1.0.0.0 0.255.255.255 area 0

*Apr  4 14:25:00.403: %OSPF-5-ADJCHG: Process 1, Nbr 10.1.1.1 on Serial4/0 from LOADING to FULL, Loading Done

R2(config-router)#network 20.0.0.0 0.255.255.255 area 0
R2(config-router)#network 2.0.0.0 0.255.255.255 area 0
R2(config-router)#exit

*Apr  4 14:27:09.607: %OSPF-5-ADJCHG: Process 1, Nbr 13.0.4.1 on Serial4/1 from LOADING to FULL, Loading Done


R3(config)#router ospf 1
R3(config-router)#network 30.0.0.0 0.255.255.255 area 0
R3(config-router)#network 30.0.0.0 0.255.255.255 area 0
R3(config-router)#network 13.0.0.0 255.0.0.0 area 0
R3(config-router)#network 2.0.0.0 0.255.255.255 area 0
R3(config-router)#exit

*Apr  4 14:27:09.567: %OSPF-5-ADJCHG: Process 1, Nbr 20.1.1.1 on Serial4/1 from LOADING to FULL, Loading Done

router 2 facing router 1 established connection  

router 2 facing router 3 established connection


  
lets see the routing table

R1#show ip route ospf
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

O     2.0.0.0/8 [110/128] via 1.1.1.2, 00:07:57, Serial4/0
      13.0.0.0/32 is subnetted, 5 subnets
O        13.0.0.1 [110/129] via 1.1.1.2, 00:07:57, Serial4/0
O        13.0.1.1 [110/129] via 1.1.1.2, 00:07:57, Serial4/0
O        13.0.2.1 [110/129] via 1.1.1.2, 00:07:57, Serial4/0
O        13.0.3.1 [110/129] via 1.1.1.2, 00:07:57, Serial4/0
O        13.0.4.1 [110/129] via 1.1.1.2, 00:07:57, Serial4/0
O     20.0.0.0/8 [110/65] via 1.1.1.2, 00:07:57, Serial4/0
O     30.0.0.0/8 [110/129] via 1.1.1.2, 00:07:57, Serial4/0



R2#show ip route ospf
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

O     10.0.0.0/8 [110/65] via 1.1.1.1, 00:11:44, Serial4/0
      13.0.0.0/32 is subnetted, 5 subnets
O        13.0.0.1 [110/65] via 2.1.1.2, 00:19:36, Serial4/1
O        13.0.1.1 [110/65] via 2.1.1.2, 00:19:36, Serial4/1
O        13.0.2.1 [110/65] via 2.1.1.2, 00:19:36, Serial4/1
O        13.0.3.1 [110/65] via 2.1.1.2, 00:19:36, Serial4/1
O        13.0.4.1 [110/65] via 2.1.1.2, 00:19:36, Serial4/1
O     30.0.0.0/8 [110/65] via 2.1.1.2, 00:19:36, Serial4/1


(configure passive interface serial 4/1 on router 2 facing router 3)

R2(config)#router ospf 1
R2(config-router)#passive-interface serial 4/1

*Apr  4 14:48:54.387: %OSPF-5-ADJCHG: Process 1, Nbr 13.0.4.1 on Serial4/1 from FULL to DOWN, Neighbor Down: Interface down or detached

R2(config-router)#end


R1#show ip route ospf
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

O     2.0.0.0/8 [110/128] via 1.1.1.2, 00:13:49, Serial4/0
O     20.0.0.0/8 [110/65] via 1.1.1.2, 00:13:49, Serial4/0

R2#show ip route ospf
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

O     10.0.0.0/8 [110/65] via 1.1.1.1, 00:17:28, Serial4/0

router 3 2.1.1.2 is sending hello messages but router 2 2.1.1.1 is not responding 



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