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Example: Configuring Segment Routing Global Blocks in SPRING for IS-IS to Increase Network Speed

This example shows how to define the segment routing label block (SRGB) label range for segment packet routing in networking (SPRING) or segment routing (SR) for the IS-IS protocol. This configuration ensures that the labels are more predictable across the segment routing domain and thereby increasing the speed of the network.

Requirements

This example uses the following hardware and software components:

  • Two MX Series routers

  • Junos OS Release 17.2 or later running on all devices

Before you configure the SRGB label range for SPRING in the IS-IS domain, be sure you configured the routing and signaling protocols.

Overview

Currently, Junos OS allows you to configure only node segment indices. The value of the start label depends on the dynamic label available in the system. Because there is no predictability of the dynamic label range being allocated to the SRGB, Junos OS allows you to configure the SRGB label range used by SPRING. The labels in the SRGB range are used for SPRING in the IS-IS domain. This means the labels advertised are more predictable and deterministic across the SPRING domain.

Topology

Figure 1 shows SRGB configured on router R1 and router R2.

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

R1

R2

Configuring Device R1

Step-by-Step Procedure

The following example requires that you navigate various levels in the configuration hierarchy. For information about navigating the CLI, see Using the CLI Editor in Configuration Mode in the Junos OS CLI User Guide.

To configure device R1:

Note:

Repeat this procedure for device R2 after modifying the appropriate interface names, addresses, and other parameters.

  1. Configure enhanced-ip mode on the MX Series because the SRGB functionality is supported on routers with MPCs and MIC interfaces only. A system reboot is required after you commit this configuration.

  2. Configure the interfaces.

  3. Configure the MPLS protocol on the interface. For SR to work, you can configure any of the statements under the [edit protocols mpls] hierarchy. For example, abstract-hop, class-of-service, label-range, optimize-switchover-delay, et cetra.

  4. Configure the start label and index range of SRGB.

    Note:
    • Ensure that the MPLS label for a binding segment ID (SID) is the sum of the SRGB start label and SID index value. In addition, SID index value must be less than or equal to the index-range value specified in the configuration.

    • Junos does not check whether the SID index is within the SRGB's range when the SID index is assigned through an ISIS export policy. If you configure an index that is out of range of the configured SRGB, you won’t see any error message in the logs or while committing the configuration. Junos OS shows a commit error only when you configure the SID under the [edit protocols isis source-packet-routing] hierarchy level.

  5. Configure the IPv4 index value of the node segment.

  6. Configure the IPv6 index value of the node segment.

  7. Disable level 1, configure the IS-IS protocol on the interface, and configure loopback interface lo0.0 as passive..

Results

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

Verification

Confirm that the configuration is working properly.

Verifying IS-IS Neighbors

Purpose

Verify IS-IS neighbors.

Action

From operational mode, run the show isis adjacency command to display the IS-IS neighbor information.

user@R1> show isis adjacency

Meaning

The output displays the IS-IS neighbor information of device R1.

Verifying the IS-IS Overview Information

Purpose

Verify the IS-IS overview information.

Action

From operational mode, run the show isis overview command to display the IS-IS overview information.

Meaning

The output displays the IS-IS overview information along with SPRING information.

Verifying the IS-IS Configuration

Purpose

Verify the IS-IS configuration.

Action

From operational mode, run the show route protocol isis command to display the IS-IS route information.

Meaning

The output displays the IS-IS route information along with segment routing information.

Verifying the Route Information of SRGB Label

Purpose

Verify the route information of SRGB label 402002 of IPv4 node 2002.

Action

From operational mode, run the show route label 402002 extensive command to display the route information of label 402002 of IPv4 node 2002.

Meaning

The output displays the details of the SRGB label 402002 of IPv4 node 2002.

Verifying the Forwarding Table of SRGB Label 402002

Purpose

Verify the forwarding table information of SRGB label 402002.

Action

Meaning

The output displays forwarding table information of SRGB label 402002 of IPv4 node 2002.

Verifying the Route of SRGB Label

Purpose

Verify the route of SRGB label of IPv6 node 3002.

Action

Meaning

The output displays forwarding table information of SRGB label 403002 of IPv6 node 3002.

Verifying the Forwarding Table of SRGB Label 403002

Purpose

Verify the forwarding table information of SRGB label 403002.

Action

Meaning

The output displays forwarding table information of SRGB label 403002 of IPv6 node 3002.