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Example: Configuring a Routing Policy to Redistribute BGP Routes with a Specific Community Tag into IS-IS

 

This example defines a policy that takes BGP routes from the Edu community and places them into IS-IS with a metric of 63.

Requirements

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

Overview

Figure 1 shows the topology used in this example.

Figure 1: Redistributing BGP Routes with a Specific Community Tag into IS-IS
Redistributing BGP Routes with
a Specific Community Tag into IS-IS

In this example, Device A, Device B, Device C, and Device D are in autonomous system (AS) 1 and are running IS-IS. All of the AS 1 devices, except Device D, are running internal BGP (IBGP).

Device E is in AS 2 and has an external BGP (EBGP) peering session with Device C. Device E has two static routes, 10.2.0.0/16 and 10.3.0.0/16. These routes are tagged with the Edu 2:5 community attribute and are advertised by way of EBGP to Device C.

Device C accepts the BGP routes that are tagged with the Edu 2:5 community attribute, redistributes the routes into IS-IS, and applies an IS-IS metric of 63 to these routes.

CLI Quick Configuration shows the configuration for all of the devices in Figure 1. The section Step-by-Step Procedure describes the steps on Device C and Device E.

Configuration

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 A

Device B

Device C

Device D

Device E

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 Device E:

  1. Configure the interfaces.
  2. Configure the statics policy, which adds the Edu community attribute to the static routes.
  3. Configure EBGP and apply the statics policy.
  4. Configure the static routes.
  5. Configure the router ID and the AS number.

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 Device C:

  1. Configure the interfaces.
  2. Configure IBGP.
  3. Configure the Edu-to-isis policy, which redistributes the Edu-tagged BGP routes learned from Device E and applies a metric of 63.
  4. Enable IS-IS on the interfaces, and apply the Edu-to-isis policy.
  5. Configure the send-isis-and-direct policy, which redistributes routes to Device E, through EBGP.

    Without this policy, Device E would not have connectivity to the networks in AS 1.

  6. Configure EBGP and apply the send-isis-and-direct policy.
  7. Configure the router ID and the autonomous system (AS) number.

Results

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

Device E

Device C

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

Verification

Confirm that the configuration is working properly.

Verifying the IS-IS Neighbor

Purpose

Verify that the BGP routes from Device E are communicated on the IS-IS network in AS 1.

Action

From operational mode, enter the show route protocol isis command.

user@D> show route protocol isis

Meaning

As expected, the 10.2.0.0/16 and 10.3.0.0/16 routes are in Device D’s routing table as IS-IS external routes with a metric of 73. If Device C had not added 63 to the metric, Device D would have a metric of 10 for these routes.

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