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Configuring Multiple Instances of IS-IS

You can configure multiple instances of IS-IS for administrative separation.

To configure multiple routing instances, perform the following tasks:

Configure the IS-IS default instance at the [edit protocols isis] or [edit logical-systems logical-system-name protocols isis] hierarchy levels with the statements needed for your network so that routes are installed in inet.0 and in the forwarding table. Make sure to include the routing table group.
Configure an IS-IS routing instance for each additional IS-IS routing entity, configuring the following items:
- Interfaces
- Routing options
- IS-IS protocol statements belonging to that entity
- Routing table group
Configure a routing table group to install routes from the routing instance into the inet.0 routing table. You can do this in two ways:
- Create a common routing table group so that either one of two conditions is configured:
  - Routes from the routing instances are installed in inet.0 and therefore installed in the forwarding table.
  - Routes from one router in a routing instance are forwarded to another router in the same routing instance.
- Create a routing table group with just the routing table from one instance and inet.0 to keep the routes from going to other instances.
Create an export policy to export routes with a specific tag and to use that tag to export routes back into the instances. For more information, see the JUNOS Policy Framework Configuration Guide.

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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