Command:

isis circuit-type


Mode:

Router(config-if)#


Syntax:

isis circuit-type [level-1 | level-1-2 | level-2-only]
no isis circuit-type

 

Syntax Description:

level-1 (Optional) Configures a router for Level 1 adjacency only.
level-1-2 (Optional) Configures a router for Level 1 and Level 2 adjacency.
level-2-only (Optional) Configures a router for Level 2 adjacency only.

 

Command Description:

To configure the type of adjacency, use the isis circuit-type command in interface configuration mode. To reset the circuit type to Level l and Level 2, use the no form of this command.

By default, a Level 1 and Level 2 adjacency is established.

Normally, this command need not be configured. The proper way is to configure a router as a Level 1-only, Level 1-2, or Level 2-only system. Only on routers that are between areas (Level 1-2 routers) should you configure some interfaces to be Level 2-only to prevent wasting bandwidth by sending out unused Level 1 hello packets. Note that on point-to-point interfaces, the Level 1 and Level 2 hellos are in the same packet.

A Level 1 adjacency may be established if there is at least one area address in common between this system and its neighbors. Level 2 adjacencies will never be established over this interface.

A Level 1 and Level 2 adjacency is established if the neighbor is also configured as level-1-2 and there is at least one area in common. If there is no area in common, a Level 2 adjacency is established. This is the default.

Level 2 adjacencies are established if the other routers are Level 2 or Level 1-2 routers and their interfaces are configured for Level 1-2 or Level 2. Level 1 adjacencies will never be established over this interface.


Example:

In the following example, other routers on Ethernet interface 0 are in the same area. Other routers on Ethernet interface 1 are in other areas, so the router will stop sending Level 1 hellos.

Router(config-if)# interface ethernet 0
Router(config-if)# ip router isis
Router(config-if)# interface ethernet 1
Router(config-if)# isis circuit-type level-2-only


Misconceptions:

None


Related Commands:

None

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