Configure IS-IS Overload

There are some circumstances in which it is advantageous to have an IS-IS intermediate system not fully participate in forwarding traffic. For example:

• During startup this intermediate system may be temporarily too busy with the tasks associated with convergence to forward traffic.

• The intermediate system is in a test network that has connections to a production network. The overload bit prevents traffic from moving between the two networks.

You can configure the intermediate system to not forward traffic by enabling the overload bit.

When enabled, the overload bit instructs other intermediate systems not to use this intermediate system as an intermediate hop in their SPF computations. No paths through this intermediate system are visible to other intermediate systems in the domain. IP and CLNS prefixes directly connected to this intermediate system are reachable.

The command set protocols isis area-tag <text> [vrf <vrf-name>] set-overload-bit <true | false> can be used to configure the overload bit for non-pseudonode LSPs.

Configure Attached-bit

The ATT bit is a field in IS-IS LSP (Link State Packet) messages used to indicate whether a Level-1 area is connected to other areas. Level-1-2 routers set this field in their generated Level-1 LSPs to inform Level-1 routers within the same area that they are connected to other areas, specifically to the Level-2 backbone area. When routers in a Level-1 area receive Level-1 LSPs with the ATT bit set from Level-1-2 routers, they create a default route pointing to the Level-1-2 router as the destination, allowing data to be routed to other areas.

The set protocols isis area-tag <text> [vrf <vrf-name>] attached-bit send <true | false> command can be used to configure whether the Level-1 routers will send default routes in the routing table due to the ATT bit or not.

The following command configures the Level-1 routers to send default routes in the routing table due to the ATT bit.

Configure Default Metric Value for IS-IS Interface

IS-IS uses metrics to determine the best path to a destination. By configuring a default metric value, you influence the path selection process and ensure that traffic follows the desired route.

Configuring different metric values on multiple interfaces can facilitate load balancing. IS-IS can distribute traffic across multiple paths based on their metric values, allowing for efficient utilization of network resources.

The set protocols isis area-tag <text> interface <interface-name> metric <metric> command configures default metric value for IS-IS interface.

The following command configures the default metric value for IS-IS interface.

Configure the Priority for Designated Router Election

Configuring a priority for Designated Router (DR) election in an IS-IS network allows you to influence the selection process for the DR. By assigning different priority values to routers, you can control which routers are more likely to be elected as the DR or BDR. Routers with higher priority values have a greater chance of winning the election.

You can designate certain routers with higher priority values as the preferred DR for critical segments of the network. This ensures that key routers take on leadership roles and helps maintain network stability and performance.

The set protocols isis area-tag <text> interface <interface-name> priority <priority> command configures priority for Designated Router election.

The following command configures the priority for Designated Router election.

Configure IS-IS Passive Interface

Configuring an layer 3 interface as a passive IS-IS interface prevents the IS-IS process from sending or receiving IS-IS hello packets on the specified interface, effectively making it passive in the IS-IS routing process.

Passive interfaces do not participate actively in IS-IS routing updates. This can be useful in scenarios where you want to limit the exposure of your IS-IS topology to specific interfaces for security reasons.

By marking certain interfaces as passive, you can reduce the amount of IS-IS hello packets exchanged on those interfaces. This can help in conserving network resources and reducing unnecessary control plane traffic.

The set protocols isis area-tag <text> interface <interface-name> passive command configures the specified layer 3 interface as passive IS-IS interface.

The following command configures the specified layer 3 interface as passive IS-IS interface.