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Example: Configuring Mesh Groups of IS-IS Interfaces

This example shows how to configure mesh groups of IS-IS interfaces.


No special configuration beyond device initialization is required before configuring this example.


When link-state PDUs are being flooded throughout an area, each router within a mesh group receives only a single copy of a link-state PDU instead of receiving one copy from each neighbor, thus minimizing the overhead associated with the flooding of link-state PDUs.

To create a mesh group and designate that an interface be part of the group, assign a mesh-group number to all the routing device interfaces in the group:

To prevent an interface in the mesh group from flooding link-state PDUs, configure blocking on that interface:

Figure 1 shows the topology used in this example.

Figure 1: IS-IS Mesh TopologyIS-IS Mesh Topology

CLI Quick Configuration shows the configuration for all of the devices in Figure 1. The section #configuration663__isis-mesh-step-by-step describes the steps on Device R1.



CLI Quick Configuration

To quickly configure this example, copy the following commands, paste them into a text file, remove any line breaks, change any details necessary to match your network configuration, and then copy and paste the commands into the CLI at the [edit] hierarchy level.

Device R1

Device R2

Device R3

Device R4

Step-by-Step Procedure

The following example requires you to navigate various levels in the configuration hierarchy. For information about navigating the CLI, see Using the CLI Editor in Configuration Mode in the CLI User Guide.

To configure an IS-IS mesh group:

  1. Configure the interfaces.

  2. Enable IS-IS on the interfaces, and assign a mesh group number.


From configuration mode, confirm your configuration by entering the show interfaces and show protocols commands. If the output does not display the intended configuration, repeat the instructions in this example to correct the configuration.

If you are done configuring the device, enter commit from configuration mode.


Confirm that the configuration is working properly.

Checking the Interface Mesh Group


Verify that the mesh group is enabled on the IS-IS interfaces.


From operational mode, enter the show isis interface extensive command.


Mesh group: 1 in the output shows that the mesh group is enabled as expected.

Checking the IS-IS Statistics


Verify that the number of link-state PDUs received and sent is less than what it would be if the mesh group were not enabled.


From operational mode, enter the show isis statistics command.


After the adjacencies have been up for about 38 minutes, the output shows that Device R1 has received 73 link-state PDUs and sent 37 link-state PDUs. In the same topology in the same amount of time without the mesh group enabled, Device R1 would have received roughly 156 link-state PDUs and sent roughly 117 link-state PDUs.