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Example: Configuring IS-IS Multicast Topology

 

IS-IS Multicast Topologies Overview

Most multicast routing protocols perform a reverse-path forwarding (RPF) check on the source of multicast data packets. If a packet comes in on the interface that is used to send data to the source, the packet is accepted and forwarded to one or more downstream interfaces. Otherwise, the packet is discarded and a notification is sent to the multicast routing protocol running on the interface.

In certain instances, the unicast routing table used for the RPF check is also the table used for forwarding unicast data packets. Thus, unicast and multicast routing are congruent. In other cases, where it is preferred that multicast routing be independent of unicast routing, the multicast routing protocols are configured to perform the RPF check using an alternate unicast routing table inet.2.

You can configure IS-IS to calculate an alternate IPv4 multicast topology, in addition to the normal IPv4 unicast topology, and add the corresponding routes to inet.2. The IS-IS interface metrics for the multicast topology can be configured independently of the unicast metrics. You can also selectively disable interfaces from participating in the multicast topology while continuing to participate in the regular unicast topology. This enables you to exercise control over the paths that multicast data takes through a network so that it is independent of unicast data paths. You can also configure IS-IS to calculate an alternate IPv6 multicast topology, in addition to the normal IPv6 unicast topology.

Note

IS-IS only starts advertising the routes when the interface routes are in inet.2.

Note

For the multicast metric commands, these are interface-specific settings, not global.

Table 1 lists the various IPv4 statements you can use to configure IS-IS topologies.

Table 1: IPv4 Statements

Statement

Description

ipv4-multicast

Enables an alternate IPv4 multicast topology.

ipv4-multicast-metric number

Configures the multicast metric for an alternate IPv4 multicast topology.

no-ipv4-multicast

Excludes an interface from the IPv4 multicast topology.

no-unicast-topology

Excludes an interface from the IPv4 unicast topologies.

Table 2 lists the various IPv6 statements you can use to configure IS-IS topologies.

Table 2: IPv6 Statements

Statement

Description

ipv6-multicast

Enables an alternate IPv6 multicast topology.

ipv6-unicast

Enables an alternate IPv6 unicast topology.

ipv6-multicast-metric number

Configures the multicast metric for an alternate IPv6 multicast topology.

ipv6-unicast-metric number

Configures the unicast metric for an alternate IPv6 multicast topology.

no-ipv6-multicast

Excludes an interface from the IPv6 multicast topology.

no-ipv6-unicast

Excludes an interface from the IPv6 unicast topologies.

For a list of hierarchy levels at which you can include these statements, see the statement summary sections for these statements.

Example: Configuring IS-IS Multicast Topology

This example shows how to configure a multicast topology for an IS-IS network.

Requirements

Before you begin, configure IS-IS on all routers. See Example: Configuring IS-IS for information about the required IS-IS configuration.

This example uses the following hardware and software components:

  • Junos OS Release 7.3 or later

  • M Series, MX Series, and T Series routers

Overview

This example shows an IS-IS multicast topology configuration. Three routers are connected to each other. A loopback interface is configured on each router.

Figure 1 shows the sample network.

Figure 1: Configuring IS-IS Multicast Topology
Configuring IS-IS Multicast Topology

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.

Router R1

Router R2

Router R3

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 IS-IS multicast topologies:

  1. Enable the multicast topology for IS-IS by using the ipv4-multicast statement.

    Routers R1, R2, and R3

  2. Enable multicast metrics on the first SONET/SDH Interface by using the ipv4-multicast-metric statement.

    Router R1

    Router R2

    Router R3

  3. Enable multicast metrics on a second sonet Interface by using the ipv4-multicast-metric statement.

    Router R1

    Router R2

    Router R3

  4. Disable the out-of-band management port, fxp0.

    Routers R1, R2, and R3

  5. If you are done configuring the routers, commit the configuration.

    Routers R1, R2, and R3

Results

From configuration mode, confirm your configuration by using the show protocols isis statement. If the output does not display the intended configuration, repeat the instructions in this example to correct the configuration.

Router R1

user@R1# show protocols isis

Router R2

user@R2# show protocols isis

Router R3

user@R3# show protocols isis

Verification

Confirm that the configuration is working properly.

Verifying the Connection Between Routers R1, R2, and R3

Purpose

Make sure that Routers R1, R2, and R3 are connected to each other.

Action

Ping the other two routers from any router, to check the connectivity between the three routers as per the network topology.

user@R1> ping 10.0.3.9
user@R1> ping 10.0.3.10
user@R2> ping 10.0.2.9
user@R2> ping 10.0.2.10
user@R3> ping 10.0.1.10
user@R3> ping 10.0.1.9

Meaning

Routers R1, R2, and R3 have a peer relationship with each other.

Verifying That IS-IS Is Configured

Purpose

Make sure that the IS-IS instance is running on Routers R1, R2, and R3, and that they are adjacent to each other.

Action

Use the show isis adjacency detail command to check the adjacency between the routers.

Router R1

user@R1> show isis adjacency detail

Router R2

user@R2> show isis adjacency detail

Router R3

user@R3> show isis adjacency detail

Meaning

IS-IS is configured on Routers R1, R2, and R3, and they are adjacent to each other.

Verifying the Configured Multicast Metric Values

Purpose

Make sure that the SPF calculations are accurate as per the configured multicast metric values on Routers R1, R2, and R3.

Action

Use the show isis spf results command to check the SPF calculations for the network.

Router R1

user@R1> show isis spf results

Router R2

user@R2> show isis spf results

Router R3

user@R3> show isis spf results

Meaning

The configured multicast metric values are used in SPF calculations for the IS-IS network.

Verifying the Configuration of the Multicast Topology

Purpose

Make sure that the multicast topology is configured on Routers R1, R2, and R3.

Action

Use the show isis database detail command to verify the multicast topology configuration on the routers.

Router R1

user@R1> show isis database detail

Router R2

user@R2> show isis database detail

Router R3

user@R3> show isis database detail

Meaning

Multicast topology is configured on Routers R1, R2, and R3.