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Example: Configuring Multiple Routing Instances of IS-IS

Figure 4 shows how you can use multiple instances of IS-IS to segregate traffic within a large network. The network consists of three administrative entities: voice_policy, other_policy, and the backbone or core. Each entity is composed of several geographically separate sites that are connected by the backbone and managed by the backbone entity.

Figure 4: Configuration for Multiple Routing Instances

Image h1460.gif

Sites A and D belong to the voice_policy routing instance. Sites B and C belong to the other_policy instance. Router 1 and Router 3 at the edge of the backbone connect the routing instances. Each runs a separate IS-IS instance (one per entity).

Router 1 runs three IS-IS instances: one each for Site A (voice_policy), Site C (other_policy), and the backbone, otherwise known as the default instance. Router 3 also runs three IS-IS instances: one each for Site B (other_policy), Site D (voice_policy), and the backbone (default instance).

When Router 1 runs the IS-IS instances, the following occur:

Routes from the default instance routing table are placed in the voice_policy and other_policy instance routing tables.
Routes from the voice_policy routing instance are placed in the default instance routing table.
Routes from the other_policy routing instance are placed in the default instance routing table.
Routes from the voice_policy routing instance do not enter the other_policy instance routing table.
Routes from the other_policy routing instance do not enter the voice_policy instance routing table.

Configuring Router 1

The following sections describe how to configure Router 1 in the backbone entity with multiple routing instances.

Configure the routing instances for voice-policy and other-policy. Use all routes learned from the routing tables in the routing table group common. Export routes tagged as belonging to the routing instance.



[edit]
routing-instances {


voice-policy {
interface so-2/2/2.0;


protocols {


isis {
rib-group voice_to_inet;
export filter-on-voice-policy;


interface so-2/2/2.0 {
level 2 metric 20;
}


}


}


}


}
other-policy {
interface so-4/2/2.0;


protocols {


isis {
rib-group other_to_inet;
export filter-on-other-policy;


interface so-4/2/2.0 {
level 2 metric 20;
}


}


}


}

Configure the routing table group inet_to_voice_and_other to share routes with the inet.0 (in the backbone entity), voice-policy.inet.0, and other-policy.inet.0 routing tables:



[edit]
routing-options {


rib-groups {


inet_to_voice_and_other {
import-rib [ inet.0 voice-policy.inet.0 other-policy.inet.0
];
}


}


}

Configure the routing table group voice_to_inet to share routes with the inet.0 (in the backbone entity) and voice-policy.inet.0 routing tables:



[edit]
routing-options {


rib-groups {


voice_to_inet {
import-rib [ voice-policy.inet.0 inet.0];
}


}


}

Configure the routing table group other_to_inet to share routes with the inet.0 (in the backbone entity) and other-policy.inet.0 routing tables:



[edit]
routing-options {


rib-groups {


other_to_inet {
import-rib [ other-policy.inet.0 inet.0];
}


}


}

Configure the default IS-IS instance so that the routes learned from the routing instances are installed in inet.0 and the tagged routes are exported from voice-policy and other-policy:



[edit]
protocols {


isis {
export apply-tag;
rib-group inet_to_voice_and_other;


interface so-1/0/0.0 {
level 2 metric 20;
}




interface fxp0.0 {
disable;
}




interface lo0.0 {
passive;
}


}


}

Configure routing policy for the routes learned from the routing instances:



[edit]
policy-options {


policy-statement apply-tag {


term voice-policy {
from instance voice-policy;


then {
tag 10;
accept;
}


}




term other-policy {
from instance other-policy;


then {
tag 12;
accept;
}


}


}




policy-statement filter-on-voice-policy {


from {
tag 10;
protocol isis;
}




then {
accept;
}


}




policy-statement filter-on-other-policy {


from {
tag 12;
protocol isis;
}




then {
accept;
}


}


}

Configuring Router 3

The configuration for Router 3 is the same as for Router 1 except that the interface names might differ. In this topology, the interface so-5/2/2.0 belongs to other-policy, and so-3/2/2.0 belongs to voice-policy.

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