13-1 passive-interface interface-name interface-number

13-1 passive-interface interface- name interface-number

Syntax Description:

• interface-name ” Name of the interface.

• interface-number ” Number of the interface.

Purpose: To prevent OSPF packets from being sent on the specified interface.

Initial Cisco IOS Software Release: 10.0

Configuration Example: Using a Passive Interface to Reduce Protocol Traffic

In Figure 13-1, Router B has a BGP neighbor relationship with Router C. The BGP routes learned by Router B from Router C are redistributed into OSPF. The network between Routers B and C needs to be advertised by OSPF to Router A so there is IP connectivity between Routers A and C. There is no need to send OSPF protocol packets to Router C. Therefore, the Serial 1 interface on Router B can be made passive under OSPF. The network between Routers B and C could also be advertised by redistributing connected routes on Router B. The redistributed networks would be advertised as OSPF external routes.

Figure 13-1. OSPF Will Advertise the Network Assigned to an Interface if the Interface Is Included in One of the OSPF network Statements. If the Interface Does Not Have Any OSPF Neighbors, then the Interface Can Be Made Passive

 Router A  interface Loopback0   ip address 1.1.1.1 255.255.255.255   !   interface Serial0/1   bandwidth 64   ip address 10.1.1.1 255.255.255.252   clock rate 64000   !   router ospf 1   network 1.1.1.1 0.0.0.0 area 1   network 10.1.1.0 0.0.0.3 area 0  ________________________________________________________________ Router B  interface Loopback0   ip address 2.2.2.2 255.255.255.255   !   interface Serial0   ip address 10.1.1.2 255.255.255.252   !   interface Serial1   ip address 10.1.1.5 255.255.255.252   clock rate 64000   !   router ospf 1   redistribute bgp 1 subnets    passive-interface Serial1    network 2.2.2.2 0.0.0.0 area 2   network 10.1.1.0 0.0.0.3 area 0   network 10.1.1.4 0.0.0.3 area 0   !   router bgp 1   neighbor 10.1.1.6 remote-as 2  ________________________________________________________________ Router C  interface Loopback0   ip address 3.3.3.3 255.255.255.255   !   interface Serial0   ip address 10.1.1.6 255.255.255.252   !   router bgp 2   network 3.3.3.3 mask 255.255.255.255   neighbor 10.1.1.5 remote-as 1   !   ip route 0.0.0.0 0.0.0.0 Serial0  

The OSPF configuration on Router B contains the following statement:

  network 10.1.1.4 0.0.0.3 area 0  

This statement enables OSPF on the Serial 1 interface on Router B and causes OSPF to advertise the network 10.1.1.4. OSPF protocol packets will be sent from the Serial 1 interface on Router B. Router C is not running OSPF, so there is no need to send protocol packets over this network. The passive-interface command prevents the OSPF packets from being sent while allowing the network to be advertised into OSPF. The redistribution of BGP into OSPF on Router B allows Router A to reach the 3.3.3.3 network on Router C. The static default route on Router C allows Router C to reach the 1.1.1.1 network on Router A.

Verification

Verify that the Serial 1 interface is a passive OSPF interface.

 rtrB#  show ip ospf interface serial 1  Serial1 is up, line protocol is up   Internet Address 10.1.1.5/30, Area 0   Process ID 1, Router ID 2.2.2.2, Network Type POINT_TO_POINT, Cost: 1562   Transmit Delay is 1 sec, State POINT_TO_POINT,   Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5  No Hellos (Passive interface)  Neighbor Count is 0, Adjacent neighbor count is 0   Suppress hello for 0 neighbor(s) 

Verify that the 10.1.1.4 network is being advertised to Router A via OSPF.

 rtrA#  show ip route  Codes: C - connected, S - static, I - IGRP, 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, E - EGP        i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default        U - per-user static route, o - ODR Gateway of last resort is not set      1.0.0.0/32 is subnetted, 1 subnets C       1.1.1.1 is directly connected, Loopback0      2.0.0.0/32 is subnetted, 1 subnets O IA    2.2.2.2 [110/1563] via 10.1.1.2, 03:30:49, Serial0/1      3.0.0.0/32 is subnetted, 1 subnets O E2    3.3.3.3 [110/1] via 10.1.1.2, 03:30:49, Serial0/1      172.16.0.0/24 is subnetted, 1 subnets C       10.1.1.0 is directly connected, Serial0/1  O       10.1.1.4 [110/3124] via 10.1.1.2, 03:30:49, Serial0/1  

Verify that Routers A and C can reach each other's attached networks.

 rtrA#  ping 3.3.3.3  Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 3.3.3.3, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 56/58/60 ms ________________________________________________________________ rtrC#  ping 1.1.1.1  Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 56/57/60 ms 

Troubleshooting

Step 1. Verify that the intended interface has been made passive. A common mistake is to make the wrong OSPF interface passive.