Configure S-IS Routing Control

Configuration Condition

Before configuring the IS-IS routing feature, first complete the following tasks:

• Configure the IP address of the interface to enable the neighboring nodes to be reachable at the network layer.
• Enable the IS-IS protocol.

Configure IS-IS Metric Style

Initially, the IS-IS only has the narrow metric style. When the narrow metric style is used, the maximum metric value is 63. With the expansion of the network scale, the metric style cannot satisfy the requirements. Therefore, the wide metric style emerges whose metric value can reach 16777214. Devices use different metric styles cannot advertise and learn the routing information from each other. To realize the transition between the two metric styles, the configuration method for the transition metric style is provided.

The wide metric style is recommended.

Table 9-8: Configure the IS-IS metric style

Configure IS-IS Interface Metric Value

When the IS-IS protocol is enabled on the interface, the IS-IS routing metric is the global metric value. The following command can be used to specify a metric value for each interface.

Table 9-9 Configure the interface metric value

Configure IS-IS Administrative Distance

The system chooses the primary routing based on the administrative distance. The smaller the administrative distance is, the higher priority the routing has.

Table 9-10 Configure the IS-IS administrative distance

Configure IS-IS Route Summary

The route summary summarizes multiple pieces of routing information as a piece of routing information. After the route summary is configured for the IS-IS, the number of advertisements to the subnet reduces effectively and the link status database and routing table size reduce. This effectively saves the memory and CPU resources. This configuration is generally applied to the Level-1-2 edge device, reducing the routing information of layer advertisement.

Table 9-11 Configure the IS-IS route summary

Configure the maximum number of load-balanced routes for the IS-IS

There are multiple paths of the same cost to the same destination IP address. These ECMP (equal cost multipath routing) can improve the link utilization rate. The user can control the maximum number of the IS-IS ECMPs.

Table 9-12 Configure the maximum number of load-balanced routes for the IS-IS

Configure IS-IS Inter-layer Route Leakage

By default, the IS-IS only leak the Level-1 routing to the Level-2, but the Level-1 area cannot know the routing of the Level-2 area. The inter-layer route leakage can be configured to introduce the Level-2 routing to the Level-1 area. When configuring the inter-layer route leakage, the routing policy can be specified to only leak the route that matches the condition.

Table 9-13 Configure the IS-IS inter-layer route leakage

Configure IS-IS ATT-bit

In the Level-1-2 device, the ATT-bit is used to inform other nodes whether this node has the connection to other areas. If yes, the ATT-bit will be set to 1 automatically and other nodes will generate a default route to this node. This increases the service load of this node. To avoid this situation, the ATT-bit can be forcibly set to 0.

Table 9-14 Configure the IS-IS ATT-bit