Segment Routing over MPLS

Table 1. Feature History Table

Feature name

Release information

Feature description

Segment Routing over MPLS

Release 26.2.1

Starting from Cisco IOS XE Release 26.2.1, you can configure Segment Routing over Multiprotocol Label Switching (SR-MPLS) on supported WAN ports. SR-MPLS encodes an ordered list of segments in the packet and integrates with MPLS services such as Layer 3 VPN and Ethernet VPN.

Segment Routing over MPLS

Segment Routing over Multi-protocol Label Switching (SR-MPLS) on WAN ports is a routing architecture that provides a flexible and scalable approach to source routing. It allows the source to define a path and encode it in the packet header as an ordered list of segments. Each segment is identified by a Segment ID (SID). When operating using the MPLS dataplane, segment routing integrates with the multi-service capabilities of MPLS, including Layer 3 VPN (L3VPN) and Ethernet VPN (EVPN).


Note

SR-MPLS is applied specifically to the WAN ports of the supported routers. Ensure the WAN interfaces are active and configured with the appropriate routing protocols (OSPF or IS-IS) before proceeding.

Benefits of using SR-MPLS

SR-MPLS helps in:

  • Scalability: The network does not need to maintain per-application or per-flow states.

  • Traffic Engineering: Offers lower latency and more effective bandwidth utilization than traditional MPLS networks.

  • Automatic Protection: Provides automatic traffic protection against link and node failures without requiring additional signaling.

Prerequisites

Before configuring SR-MPLS on your router, you must ensure that:

  • Cisco Catalyst IR1101 or IR8340 routers with active WAN ports are used.

  • The software image supports SR-MPLS configuration for these routers.

  • Intermediate System to Intermediate System (IS-IS) and Open Shortest Path First (OSPF) routing protocols are enabled and configured for SR-MPLS operation.

Configure Segment Routing over MPLS

Use this task to enable SR-MPLS mode.

Procedure

Step 1

Use the configure terminal command to enter the global configuration mode.

Example:

Router# configure terminal

Step 2

Use the segment-routing mpls command to enable segment routing MPLS.

Example:

Router(config)# segment-routing mpls

Step 3

Use the global-block start-range end-range command to enable Segment Routing Global Block (SRGB) to define the label range for Prefix-SIDs.

Example:

Router(config)# global-block 16000 23999

For more information, see Segment Routing Global Block

Step 4

Use the connected-prefix-sid-map command to enter the sub-mode for configuring address-family specific mappings.

Example:

Router(config-srmpls)# connected-prefix-sid-map

Step 5

Use the address-family ipv4 command to specify the IPv4 address family.

Example:

Router(config-srmpls-conn)# address-family ipv4

Step 6

Use the ip-address/mask index sid-index range range-value command to associate a Segment Identifier (SID) with the IP address.

Example:

Router(config-srmpls-conn-af)# 4.4.4.4/32 index 4 range 1

Step 7

Use the exit-address-family command to exit the address family configuration mode and return to the connected-prefix-sid-map sub-mode.

Example:

Router(config-srmpls-conn-af)# exit-address-family

Configure Segment Routing MPLS on OSPF network

Use this task to define the network topology, select OSPF as the control protocol, and configure the necessary SID mappings.

Procedure

Step 1

Use the configure terminal command to enter global configuration mode.

Example:

Router# configure terminal

Step 2

Use the router ospf process-id command to enable the OSPF routing process.

Example:

Router(config)# router ospf 10

Step 3

Use the router-id id command to manually configure the OSPF router ID.

Example:

Router(config-router)# router-id 10.0.0.1

Step 4

Use the segment-routing mpls command to enable segment routing under the OSPF process.

Example:

Router(config-router)# segment-routing mpls

Step 5

Use the segment-routing area area-id mpls command to configure segment routing MPLS mode for a specific OSPF area.

Example:

Router(config-router)# segment-routing area 0 mpls

Configure Prefix-SID for OSPF

This task allows you to map a specific Prefix-SID to a loopback or interface address. Mapping the Prefix-SID to a loopback address creates a Node-SID, which serves as the node's unique identity. This enables other routers to forward traffic to this specific prefix using the associated SID label.

Before you begin

Ensure that segment routing is enabled on the corresponding address family.

Procedure

Step 1

Use the configure terminal command to enter global configuration mode.

Example:

Router# configure terminal

Step 2

Use the segment-routing mpls command to enable segment routing MPLS mode.

Example:

Router(config)# segment-routing mpls

Step 3

Use the connected-prefix-sid-map command to enter the sub-mode for configuring address-family specific mappings.

Example:

Router(config-srmpls)# connected-prefix-sid-map

Step 4

Use the address-family ipv4 command to specify the IPv4 address family.

Example:

Router(config-srmpls-conn)# address-family ipv4

Step 5

Use the ip-address/mask index sid-index range range-value command to associate a SID with the specified IPv4 prefix.

Example:

Router(config-srmpls-conn-af)# 10.1.1.1/32 index 100 range 1

Step 6

Use the exit command to exit to global configuration mode.

Example:

Router(config-srmpls-conn-af)# exit

Verify SR-MPLS configuration

Use this task to validate connectivity, path establishment, and resilience of your SR-MPLS deployment.

Before you begin

Verify the node SID reachability to ensure each node in the SR-MPLS domain can reach its designated node SID.

Procedure

Step 1

Use the show segment-routing mpls connected-prefix-sid-map local ipv4 command to verify the SR-MPLS configuration on the router.

Example:

Router# show segment-routing mpls connected-prefix-sid-map local ipv4

Step 2

Use the show mpls forwarding-table command to check the MPLS label table.

Example:

Router# show mpls forwarding-table

Step 3

Use the ping mpls command to validate the end-to-end connectivity between critical devices.

Note

 

  • You can simulate link or node failures to ensure traffic is automatically rerouted along available alternate paths.

  • You can also test adjacency SID reachability between adjacent nodes.