Configuring Passive Interfaces

You can configure an IS-IS passive interface. A passive interface only advertises its IP address in its LSPs; it does not send or receive IS-IS packets.

Optionally, you can set a route tag for an IS-IS passive interface by including the tag keyword and a numeric tag value in the passive-interface command.

Passive interfaces have a metric of zero by default. You can set a different metric for a particular passive interface by specifying the value along with the metric keyword. A global default metric set with the metric command does not affect any passive interface. Similarly, configuring a reference bandwidth for IS-IS has no effect on passive interfaces. Metrics specified for a passive interface apply to both level 1 and level 2 interfaces unless you restrict the metric to a single level.

passive-interface

• Use to configure an IS-IS interface so that its IP address is advertised in its link-state PDUs but no IS-IS packets are sent from or received on the interface.
• Use the optional tag keyword to specify a tag value for an IS-IS passive interface before the route is propagated to other routers in an IS-IS domain. The tag value must be a number in the range 1–4294967295.
• Use the optional metric keyword to specify a metric value for an IS-IS passive interface. The metric value must be a number in the range 1–16777215. This value overrides the default metric of zero.
• You can also accomplish the equivalent of the passive-interface command by using the redistribute command to redistribute a connected route to level 1.
• Example 1—Configures loopback 0 as a passive interface and enable IS-IS on subinterfaces ATM 2/0.1 and ATM 2/1.1. IS-IS advertises the IP address of loopback 0 in its link-state PDUs, but runs only on ATM 2/0.1 and ATM 2/1.1:

  host1(config)#router isis floor12

  host1(config-router)#net 47.0010.0000.0000.0000.0001.0001.1111.1111.1111.00

  host1(config-router)#passive-interface loopback 0

  host1(config-router)#exit

  host1(config)#interface atm 2/0.1

  host1(config-subif)#ip router isis floor12

  host1(config-subif)#exit

  host1(config)#interface atm 2/1.1

  host1(config-subif)#ip router isis floor12

  You can override the passive-interface configuration simply by issuing the complementary command. For example, suppose you issue the following commands after the previous configuration:

  host1(config-router)#passive-interface atm 2/0.1

  host1(config-router)#exit

  host1(config)#interface loopback 0

  host1(config-if)#ip router isis floor12

  Now IS-IS advertises the IP address of ATM 2/0.1 in its link-state PDUs, but runs only on loopback 0 and ATM 2/1.1.

• Example 2—Sets a route tag on the IS-IS passive interface configured in Example 1.

  host1(config)#router isis floor12

  host1(config-router)#passive-interface loopback 0 tag 12

• Example 3—Sets a metric and level on the IS-IS passive interface configured in Example 1.

  host1(config)#router isis floor12

  host1(config-router)#passive-interface loopback 0 metric 45 level-2

• Use the no version to delete the passive interface, or to remove the tag, metric, or both.
• See passive-interface

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