Command:

isis mesh-group


Mode:

Router(config-if)#


Syntax:

isis mesh-group [number | blocked]
no isis mesh-group

 

Syntax Description:

number (Optional) A number identifying the mesh group of which this interface is a member.
blocked (Optional) Specifies that no LSP flooding will take place on this subinterface.

 

Command Description:

To optimize link-state packet (LSP) flooding in nonbroadcast multiaccess (NBMA) networks with highly meshed, point-to-point topologies, use the isis mesh-group command in interface configuration mode. To remove a subinterface from a mesh group, use the no form of this command.

The interface performs normal flooding by default.

LSPs that are first received on subinterfaces that are not part of a mesh group are flooded to all other subinterfaces in the usual way.

LSPs that are first received on subinterfaces that are part of a mesh group are flooded to all interfaces except those in the same mesh group. If the blocked keyword is configured on a subinterface, then a newly received LSP is not flooded out over that interface.

To minimize the possibility of incomplete flooding, you should allow unrestricted flooding over at least a minimal set of links in the mesh. Selecting the smallest set of logical links that covers all physical paths results in very low flooding, but less robustness. Ideally, you should select only enough links to ensure that LSP flooding is not detrimental to scaling performance, but enough links to ensure that under most failure scenarios no router will be logically disconnected from the rest of the network. In other words, blocking flooding on all links permits the best scaling performance, but there is no flooding. Permitting flooding on all links results in very poor scaling performance.


Example:

In the following example six interfaces are configured in three mesh groups. LSPs received are handled as follows:

LSPs received first via ATM 1/0.1 are flooded to all interfaces except ATM 1/0.2 (which is part of the same mesh group) and ATM 1/2.1, which is blocked.

LSPs received first via ATM 1/1.2 are flooded to all interfaces except ATM 1/1.1 (which is part of the same mesh group) and ATM 1/2.1, which is blocked.

LSPs received first via ATM 1/2.1 are not ignored, but flooded as usual to all interfaces. LSPs received first via ATM 1/2.2 are flooded to all interfaces, except ATM 1/2.1, which is blocked.

Router(config)# interface atm 1/0.1
Router(config-subif)# ip router isis
Router(config-subif)# isis mesh-group 10

Router(config)# interface atm 1/0.2
Router(config-subif)# ip router isis
Router(config-subif)# isis mesh-group 10

Router(config)# interface atm 1/1.1
Router(config-subif)# ip router isis
Router(config-subif)# isis mesh-group 11

Router(config)# interface atm 1/1.2
Router(config-subif)# ip router isis
Router(config-subif)# isis mesh-group 11

Router(config)# interface atm 1/2.1
Router(config-subif)# ip router isis
Router(config-subif)# isis mesh-group blocked

Router(config)# interface atm 1/2.2
Router(config-subif)# ip router isis


Misconceptions:

None


Related Commands:

router isis

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