SR-MPLS With Flex-Algo Lab

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Solution Overview

Segment Routing MPLS, or SR-MPLS, makes the network more scalable and intelligent while improving capacity utilization, leading to lower cost and greater user satisfaction. Segment Routing Flexible Algorithm, also commonly called Flex-Algo, enables the router to assign a user-defined algorithm to the IGP — no traffic engineering, just a user-defined algorithm implemented dynamically and on-demand.

In conjunction with the performance monitoring, a feature that measures the round-trip time it takes a packet to get from Point A to Point B, Segment Routing Flex-Algo allows routers to deploy customized IGP algorithms for routing. With Flex-Algo, operators can now specify the metrics or parameters the IGP uses to route traffic instead of relying solely on bandwidth.

We can also add constraints to the algorithm, such as telling the router to avoid a link or set of links, which is useful when there is a link in the path that is desirable to be avoided for monetary or strategic reasons. This can all be accomplished without traffic engineering and with a single MPLS label used to transport the traffic end-to-end across the entire network. 

This lab provides a hands-on environment with Cisco XRv9000 routers to demonstrate some of the basic use cases of SR-MPLS with Flex-Algo. Since the performance monitoring feature is not dynamic in XRv9000 virtual routers, we will assign static values. The concept is the same; however, the routers cannot dynamically report the delay in real time, as would be the case on an ASR9000 or NCS5500 router.

Goals & Objectives

The purpose of this lab is to expose the user to Segment Routing, SR-MPLS with Flex-Algo concepts. The user will explore several use cases with Flex-Algo by using IGP custom-defined algorithms like delay-based paths, constrained paths and a combination of both. 

You will learn how to configure SR-MPLS with Flex-Algo on Cisco IOS XRv9000 routers with ISIS IGP along with BGP Color communities used to steer traffic along a Flex-Algo user-defined path. 

The configuration exercises include:

  • Enable Segment Routing and define prefix SIDs
  • Validate SR-MPLS label forwarding
  • Enable Performance Monitoring
  • Define Flex-Algo low-delay based path without constraints
  • Define Flex-Algo IGP Shortest Path with constraints
  • Define Flex-Algo IGP Shortest Path with constraints and excluded Node

Hardware & Software

Six Cisco IOS XRv9000 routers running 7.1.1