SRv6 uSID Flex-Algo Lab

Segment Routing over IPv6 (SRv6) is the successor to SR-MPLS. SRv6 natively utilizes the IPv6 data plane to deliver Segment Routing capabilities, significantly simplifying network deployments. It employs source routing by encoding the path in the packet header. SRv6 utilizes the IPv6 Routing Extension Header to carry multiple IPv6 addresses, which can include multiple SRv6 SIDs. SRv6 uSID takes this concept further by allowing a single 128-bit IPv6 destination address to carry up to six individual SIDs, or in MPLS terms, labels.

This lab is the second part of a two-part SRv6 uSID course, with the first lab being the SRv6 uSID Lab. In this lab, we will explore the use of Flexible Algorithm (FA) with SRv6 uSID and BGP L3VPNs. If you are not familiar with Flex-Algo (FA), we recommend checking out the SR-MPLS With Flex-Algo Lab. This lab delves into Flex-Algo in detail, and we assume a certain level of understanding with Flex-Algo in this lab. 

This lab is the second part of a two-part SRv6 uSID course, following the SRv6 uSID Lab. In this lab, you'll learn how to configure SRv6 uSID with Flex-Algo on eight Cisco IOS XRv9000 routers to establish a L3VPN over BGPv6 peering. This lab assumes you're familiar with IPv6 and SRv6 uSID. We discussed transitioning to IPv6 and SRv6 uSID in our previous labs, Deploying IPv6 with ISIS and SRv6 uSID Lab. It's recommended that you complete part one of the SRv6 uSID Lab to understand SRv6 and BGP VPNV4 uSID function assignments. However, we will still be assigning functions for BGP as part of Flex-Algo. If you're not overly familiar with IPv6, you might also want to check out the Deploying IPv6 with ISIS.

In this lab, you'll configure transport routers with SRv6 uSIDs, similar to the configuration you performed in the previous lab. However, unlike the SRv6 uSID Lab, we'll configure Flex-Algo (FA) on all routers to establish different paths and implement prefix matching to enhance control over the IGP default path, a Flex-Algo Delay-based path, and a constraint-based path.

In this lab, you'll gain hands-on experience configuring SRv6 uSID Flex-Algo on Cisco IOS XRv9000 routers, particularly with IS-IS since no vendors support RFC 9513 OSPFv3 Extensions for Segment Routing over IPv6 or are unlikely to do so in the future. You'll create virtual routing functions (VRFs) for IPv4 peering with the CE routers. Subsequently, you'll configure SRv6 to transport all VPNv4 traffic through multiple different Flex-Algo paths.

This document is composed of the following sections:

• Introduction
• Physical Topology
• Lab Access Details
• Performance Monitoring - Link Delay & Constraint
• SRv6 uSID Flex-Algo Configuration
• SRv6 uSID Flex-Algo Verification
• SRv6 uSID Flex-Algo L3VPN Configuration
• SRv6 uSID Flex-Algo L3VPN Verification
• Conclusion

• Eight Cisco IOS XRv9000 v24.1.2 routers
• Two Cisco IOS-XE Routers running  15.5(2)S