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Example: IS-IS Flood Reflector

 

This example shows how to configure flood reflectors in an IS-IS network. Flood reflection mainly reduces the redundancy in flooding paths and enhances the efficiency of IS-IS updates in large fabric topologies.

Requirements

This example uses the following hardware and software components:

  • Eleven PTX Series routers.

  • Junos OS Release 20.4R1 or later running on all devices.

Overview

Starting in Junos OS Release 20.4R1, you can configure flood-reflector interfaces in an IS-IS network. Flood reflection enables you to create IS-IS topologies where Level 1 areas provide transit forwarding for Level 2 destinations within a Level 2 topology. This is accomplished by creating Level 2 flood-reflection adjacencies within each Level 1 area.

A flood-reflector adjacency reflects Level 2 link-state packet data units (PDUs) and they are used in the Level 2 shortest-path-first (SPF) computation. However, they are not used for forwarding.

To establish IS-IS adjacency for flood-reflection, flexible tunnel interfaces (FTI) are designated as flood-reflector interfaces. These tunnels utilize UDP encapsulation.

Topology

Figure 1 shows a flood-reflector topology for IPv4 traffic and Figure 2 shows a flood-reflector topology for IPv6 traffic in which Router R6 is the flood reflector. Routers R0, R1, R2, R3 are the flood-reflector clients that have FTI tunnels to R6. All of the FTI tunnels have metric 10 and are configured as flood-reflector interfaces. Routers R0, R1, R2, R3 are configured to redistribute Level 2 routes into Level 1 as Level 1/Level 2 inter-area routes. Routers R4 and R5 are Level 2 routers. Routers R7, R8, R9, R10 use the Level 1 route as they do not participate in flood reflection. The Level 1 metric is 100.

Figure 1: Flood-Reflector Topology for IPv4 Traffic
Flood-Reflector Topology for IPv4 Traffic
Figure 2: Flood-Reflector Topology for IPv6 addresses
Flood-Reflector Topology for IPv6 addresses

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, copy and paste the commands into the CLI at the [edit] hierarchy level, and then enter commit from the configuration mode.

Device R0

Device R1

Device R2

Device R3

Device R4

Device R5

Device R6

Device R7

Device R8

Device R9

Device R10

Configuring the Flood-Reflector Client

Step-by-Step Procedure

To configure the flood-reflector client R0, perform these tasks:

  1. Configure the device interfaces to enable IP and ISO transport.
  2. Configure the loopback interface (lo0) with IPv4 and IPv6 addresses that are used as router ID for IS-IS sessions. Configure an ISO network entity title (NET) address on the loopback interface for the router to support IS-IS.
  3. Configure routing options to identify the router in the domain.
  4. Configure the source address for the FTI with UDP encapsulation. The source address is the router ID of the tunnel source.
  5. Configure the destination address for the FTI. The destination address is the router ID of the tunnel endpoint.
  6. Specify the source IP address of the tunnel and the UDP port value of the destination that identifies the tunnel endpoint. Specify the value of destination-udp-port from 1 through 65,535.
  7. Configure a policy in the Level 2 area to leak routes into the Level 1 area.
  8. Enable IS-IS Level 2 and disable Level 1 on the interface that connects to an interface of R4 at Level 2. Configure a metric of 10 for the Level 2 interface.
  9. Enable IS-IS Level 1 and disable Level 2 on the interface that connects to interfaces of R7 and R8 at Level 1. Configure a metric of 100 for the Level 1 interfaces.
  10. Configure the IS-IS interfaces to behave like point-to-point interfaces.
  11. Disable Level 1 on the FTI and configure the flood reflector client at Level 2 by including the cluster identifier.
  12. Configure wide-metrics for IS-IS to allow wider range of metric values.
  13. Configure the loopback interface as passive to ensure the protocols do not run over the loopback interface and that the loopback interface is advertised correctly throughout the network.
  14. Enter commit from the configure mode on R0 device.

In addition to configuring these steps on flood-reflector client R0, repeat these steps for the flood-reflector clients R1, R2, R3 within the cluster that you configure.

Results

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

Configuring the Flood Reflector

Step-by-Step Procedure

To configure the flood-reflector device R6, perform these tasks:

  1. Configure the device interfaces to enable IP and ISO transport.
  2. Configure the loopback interface (lo0) with IPv4 and IPv6 addresses that are used as router ID for IS-IS sessions. Configure an ISO network entity title (NET) address on the loopback interface for the router to support IS-IS.
  3. Configure routing options to identify the router in the domain.
  4. Configure the source address for the FTI with UDP encapsulation. The source address is the router ID of the tunnel source.
  5. Configure the destination addresses for the FTI per unit. The destination addresses are the router IDs of the tunnel endpoints.
  6. Specify the source IP address of the tunnel and the UDP port value of the destination that identifies the tunnel endpoint per unit. Specify the value of destination-udp-port from 1 through 65,535.
  7. Configure a policy in the Level 2 area to leak routes into the Level 1 area.
  8. Enable IS-IS Level 1 and disable Level 2 on the interfaces and configure a metric of 100 on the Level 1 interface.
  9. Configure the IS-IS interfaces to behave like point-to-point interfaces.
  10. Disable Level 1 on the FTI and configure the flood-reflector client at Level 2 by including the cluster identifier.
  11. Configure wide-metrics for IS-IS to allow wider range of metric values.
  12. Configure the loopback interface as passive to ensure the protocols do not run over the loopback interface and that the loopback interface is advertised correctly throughout the network.
  13. Enter commit from the configure mode on R6 device.

Results

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

Configuring the Non-Flood Reflector Device at Level 2

Step-by-Step Procedure

To configure the non-flood reflector device R4 at Level 2:

  1. Configure the device interfaces to enable IP and ISO transport.
  2. Configure the loopback interface (lo0) with IPv4 and IPv6 addresses that are used as router ID for IS-IS sessions. Configure an ISO network entity title (NET) address on the loopback interface for the router to support IS-IS.
  3. Configure routing options to identify the router in the domain.
  4. Enable IS-IS Level 2 and disable Level 1 on the interfaces and configure a metric of 10 and 11 on the Level 1 interfaces.
  5. Configure the IS-IS interfaces to behave like point-to-point interfaces.
  6. Configure wide-metrics for IS-IS to allow wider range of metric values.
  7. Configure the loopback interface as passive to ensure the protocols do not run over the loopback interface and that the loopback interface is advertised correctly throughout the network.
  8. Enter commit from the configure mode on R4 device.

In addition to configuring these steps on the Level 2 non-flood reflector device R4, repeat these steps for the non-flood reflector device R5.

Results

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

Configuring the Non-Flood Reflector Device at Level 1

Step-by-Step Procedure

To configure the non-flood reflector device R7 at Level 1:

  1. Configure the device interfaces to enable IP and ISO transport.
  2. Configure the loopback interface (lo0) with IPv4 and IPv6 addresses that are used as router ID for IS-IS sessions. Configure an ISO network entity title (NET) address on the loopback interface for the router to support IS-IS.
  3. Configure routing options to identify the router in the domain.
  4. Enable IS-IS Level 1 and disable Level 2 on the interfaces and configure a metric of 100 on the Level 1 interfaces.
  5. Configure the IS-IS interfaces to behave like point-to-point interfaces.
  6. Configure wide-metrics for IS-IS to allow wider range of metric values.
  7. Configure the loopback interface as passive to ensure the protocols do not run over the loopback interface and that the loopback interface is advertised correctly throughout the network.
  8. Enter commit from the configure mode on R7 device.

In addition to configuring these steps on the Level 1 non-flood reflector device R7, repeat these steps for the non-flood reflector devices R8, R9, R10.

Results

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

Verification

To confirm that the configuration is working properly, perform the following tasks:

Verify the IS-IS Adjacency

Purpose

Verify that the IS-IS instance is running on devices R0 and R6 and that they are adjacent to each other.

Action

From operational mode, run the show isis adjacency detail and show isis adjacency extensive commands.

On R0

user@R0>show isis r6 adjacency detail

On R0

user@R0>show isis r6 adjacency extensive

Meaning

  • The interface fti0.0 on the device R0 has established adjacency with the device R6.

Verify the Flood Reflector Status

Purpose

Verify that the flood reflector is enabled and verify its status.

Action

From operational mode, run the show isis interface fti0.0 detail and show isis interface fti0.0 extensive commands.

On R6

user@R6>show isis interface fti0.0 detail

On R6

user@R6>show isis interface fti0.0 extensive

Meaning

  • On R6, the flood reflector is enabled on fti0 at level 2 with cluster-id 100.

Verify Flood-Reflector Client Status

Purpose

Verify that the flood-reflector client is enabled and verify its status.

Action

From operational mode, run the show isis interface fti0.0 detail and show isis interface fti0.0 extensive commands.

On R0

user@R0>show isis interface fti0.0 detail

On R0

user@R0>show isis interface fti0.0 extensive

Meaning

  • On R0, the flood-reflector client is enabled on fti0 at level 2 with cluster-id 100.

Verify the IS-IS Database

Purpose

Verify the IS-IS database on the flood reflector and the flood-reflector clients.

Action

From operational mode, run the show isis database command.

On R0

user@R0>show isis database r0 extensive

On R6

user@R6>show isis database r6 extensive

Meaning

On R0 and R6, the IS-IS database shows the flood-reflector client and the flood reflector with cluster-id 100.

Verify the IS-IS Route

Purpose

Verify that the Level 2 routes learned on the FTI are not installed in the R0 routing table.

Action

From operational mode, run the show isis route command.

On R0

user@R0>show isis route

Meaning

The Level 2 routes learned on the FTI between R0 and R6 are not installed in the R0 routing table.

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