ISIS passive-interface default

There are three ways to advertise directly connected interfaces using ISIS routing protocol:

1.       Using redistribute connected, but then we need to use route-map to filter out advertisements:

 

router isis redistribute connected route-map RM_ISIS_CONNECTED

 

2.       Configure routing protocol on the interface and manually set passive-interface under routing process:

 

interface Fastethrnet 0/0 ip router isis ! router isis passive-interface fastethernt 0/0

 

 

3.       Configure passive-interface default under the routing process and manually disable passive-interface for ISIS adjacency required interfaces.

 

router isis passive-interface default no passive-interface fastethernt 0/0

 

The last method was implemented in order to ease the process of advertising large amount of interfaces which can be found on large SP or enterprise distribution routers.

The problem with this method is how can we disable or prevent interface IP address to be advertised using ISIS?

So let’s look on the following example:

 

 

 

R1 is configured with the following interfaces:

 

R1#show ip interface brief Interface                  IP-Address      OK? Method Status                Protocol FastEthernet0/0            10.1.12.1       YES manual up                    up FastEthernet0/1            unassigned      YES unset  administratively down down Loopback0                  1.1.1.1         YES manual up                   up Loopback1                  192.168.11.1    YES manual up                    up Loopback2                  192.168.12.1    YES manual up                    up Tunnel0                    10.10.10.10     YES manual up                    down

And with the following ISIS configuration:

router isis  net 49.0000.0000.0000.0001.00  metric-style wide  passive-interface default  no passive-interface FastEthernet0/0

R2 routing table:

R2#show 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 not set   i L2 192.168.12.0/24 [115/10] via 10.1.12.1, FastEthernet0/0      1.0.0.0/32 is subnetted, 1 subnets i L2    1.1.1.1 [115/10] via 10.1.12.1, FastEthernet0/0 i L2 192.168.11.0/24 [115/10] via 10.1.12.1, FastEthernet0/0      10.0.0.0/24 is subnetted, 1 subnets C       10.1.12.0 is directly connected, FastEthernet0/0

So let’s say that now I don’t want network 192.168.12.0/24 to be advertised at all, so I simply shutdown the routing process on the interface:

R1(config)#int loopback 2 R1(config-if)#isis protocol shutdown

And the result:

R2# show 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 not set        1.0.0.0/32 is subnetted, 1 subnets i L2    1.1.1.1 [115/10] via 10.1.12.1, FastEthernet0/0 i L2 192.168.11.0/24 [115/10] via 10.1.12.1, FastEthernet0/0      10.0.0.0/24 is subnetted, 1 subnets C       10.1.12.0 is directly connected, FastEthernet0/0

No 192.168.12.0/24 network in R2 routing table.