Segment Routing over IPv6 (SRv6) Flexible Algorithm allows operators to customize IGP shortest path computation according to their own needs. An operator can assign custom SR prefix-SIDs to realize forwarding beyond link-cost-based SPF. As a result, Flexible Algorithm provides a traffic engineered path automatically computed by the IGP to any destination reachable by the IGP.

The SR architecture associates prefix-SIDs to an algorithm which defines how the path is computed. Flexible Algorithm allows for user-defined algorithms where the IGP computes paths based on a user-defined combination of metric type and constraint.

See Configuring SRv6 IS-IS Flexible Algorithm.

This feature introduces support for Topology-Independent Loop-Free Alternate (TI-LFA) node protection and Shared Risk Link Groups (SRLG) protection using Segment Routing over IPv6 (SRv6) for the IS-IS protocol.

• TI-LFA node protection functionality provides protection from node failures. The neighbor node is excluded during the post convergence backup path calculation.

• TI-LFA SRLG protection functionality attempts to find the post-convergence backup path, which excludes the SRLGs of the protected link. All local links that share any SRLG with the protecting link are excluded during the post convergence backup path calculation.

See Configuring SRv6 IS-IS TI-LFA.

The Segment Routing over IPv6 (SRv6) Microloop Avoidance feature enables link-state routing protocols, such as IS-IS, to prevent or avoid microloops during network convergence after a topology change.

Microloops are brief packet loops that occur in the network following a topology change (link down, link up, or metric change events). Microloops are caused by the non-simultaneous convergence of different nodes in the network. If nodes converge and send traffic to a neighbor node that has not converged yet, traffic may be looped between these two nodes, resulting in packet loss, jitter, and out-of-order packets. If a node computes that a microloop could occur on the new topology, the node creates a loop-free path to the destination using a list of segments. After the RIB update delay timer expires, the explicit path is replaced with regular forwarding paths.

See Configuring SRv6 IS-IS Microloop Avoidance.

This feature provides enhanced Operations, Administration, and Maintenance (OAM) in Segment Routing Networks with IPv6 Data plane (SRv6).

Existing OAM mechanisms to ping and trace a remote IPv6 prefix, along the shortest path, continue to work without any modification in an SRv6 network.

However, classic IPv6 OAM cannot be used to ping or trace a remote SRv6 SID function. This feature augments ping and traceroute operations to target remote SRv6 SIDs. An SRv6-enabled router now allocates a new SRv6 OAM SID known as END.OP (OAM Endpoint with Punt).

A target remote SID include the following:

• END

• END.DT4/END.DX4 (used by L3 Services over SRv6)

• END.DX2 (used by L2 Services over SRv6)

See SRv6 OAM — SID Verification.

BGP-LS is used to report the topology of the domain using nodes, links, and prefixes. This feature adds the capability to report SRv6 Segment Identifier (SID) Network Layer Reachability Information (NLRI).

The following NLRI has been added to the BGP-LS protocol to support SRv6:

• Node NLRI: SRv6 Capabilities, SRv6 MSD types

• Link NLRI: End.X, LAN End.X, and SRv6 MSD types

• Prefix NLRI: SRv6 Locator

• SRv6 SID NLRI (for SIDs associated with the node): Endpoint Function, BGP-EPE Peer Node/Set and Opaque

See SRv6 SID Information in BGP-LS Reporting.

This feature provides active-active connectivity to a CE device in a L3VPN deployment. The CE device can be Layer-2 or Layer-3 device connecting to the redundant PEs over a single LACP LAG port.

See SRv6 Services: L3VPN VPNv4 Active-Active Redundancy.

IOS XR 6.6.1 supports IETF draft draft-dawra-idr-srv6-vpn-04, in which SRv6 Service SID information is carried in the SRv6-VPN SID TLV (TLV Type 4). This SID TLV is inconsistent with the SRv6 SID Structure.

In IOS XR 7.0.2 and later releases, the implementation is now compliant with draft-ietf-bess-srv6-services-00, where a new SRv6 Services TLV (TLV Type 5/6) and SRv6 SID Structure Sub-Sub-TLV are defined to address this inconsistency.

Functionality is also provided to allow for backward compatibility between the two TLV types.

See SRv6 Services: SRv6 Services TLV Type 5 Support.

This feature extends support of SRv6-based BGP services to include Internet (IPv4) services by implementing End.DT4 SRv6 functions at the PE node (draft-ietf-bess-srv6-services).

See SRv6 Services: BGP Global IPv4.

This feature allows IS-IS to advertise the maximum metric during the start-up phase until either BGP converges or the specified start-up timer expires.

When a router is configured with maximum metric at start up, IS-IS advertises the maximum metric for IS-IS links as well as for prefixes that originated from the routers. This configuration will make neighboring routers use this router as a transit-node of last resort. The maximum metric is advertised only during the start-up phase when the routing table has not converged. Once the start-up timer expires or the BGP converge signal is received, the normal metric is advertised. You can set maximum metric for default routes, SRv6 locator, or redistributed prefixes.

For narrow metrics, the maximum metric value is 63; for wide metrics, the maximum metric value is 16777214.

See IS-IS Maximum Metric on Start Up.

EVPN VPWS All-Active Multi-Homing over SRv6 provides an ELINE (P2P) service with all-active multihoming capability over an SRv6 network.

All-Active Multi-Homing enables an operator to connect a customer edge (CE) device to two or more provider edge (PE) devices to provide load balancing and redundant connectivity. With All-Active Multi-Homing, all the PEs can forward traffic to and from the multi-homed device.

See SRv6 Services: EVPN VPWS — All-Active Multi-Homing.

This feature allows the ingress EVPN VPWS PE to compute the flow label field of the outer-most IPv6 header based on the L2 and L3 fields of the incoming Ethernet frames.

See SRv6 Services: EVPN VPWS — IPv6 QoS Traffic-Class Marking.

This feature allows the ingress EVPN VPWS PE to copy the CoS value from the top-most VLAN header to the traffic-class (TC) field of the outer-most IPv6 header. This functionality enables prioritization of traffic in the IPv6 network.

To enable this feature, use the hw-module profile segment-routing srv6 encapsulation traffic-class propagate command. This command requires you to reload the router for the configuration to take effect.

See SRv6 Services: EVPN VPWS — IPv6 QoS Traffic-Class Marking.

Pseudo-wire traffic mirroring (known as PW-SPAN) is an extra functionality on the existing SPAN solutions. The existing SPAN solutions are monitored on a destination interface or through a GRE tunnel or RSPAN. In PW-SPAN, the traffic mirroring destination port is configured to be a pseudo-wire rather than a physical port. Here, the designated traffic on the source port is mirrored over the pseudo-wire to a central location. Mirroring the designated traffic on the source port over the pseudo-wire to a central location allows the centralization of expensive network traffic analysis tools.

See SPAN over Pseudo-Wire.

The MAC Mobility between the Bridge Ports using VRF Leaking feature supports EVPN MAC mobility across bridge ports with VRF leaking functionality. With both source and target VRFs located on the same router, when VM in the target VRF is migrated, this feature supports the host in source VRF to reach the migrated VM.

See MAC Mobility between the Bridge Ports using VRF Leaking.