Segment Routing & Traffic-Engineering (SR/SR-TE)

Segment routing extends link-state IGPs by carrying forwarding instructions as labels across the domain, not using hello messages or adjacencies, with a well-documented SR-MPLS model and an IPv6-only service option.

Highlights why segment routing enables traffic engineering by letting the source compute an SR policy and label stack, avoiding LDP and RSVP state on hops and enabling scalable load balancing.

Enable and configure segment routing in the ISIS IPv4 unicast domain, set srgb base and prefix index values, and verify mappings, label tables, and traceroute outcomes.

Explore how the segment routing global block reserves the srgb in the label switching database, how prefix sets determine labels, and how global versus instance-specific configuration shifts label values.

Explore how the prefix set in segment routing guides traffic to the advertised prefix along the shortest path using the associated MPLS label.

Explore how prefix-SID index versus absolute values, P and E flags, and explicit nulls shape LSP behavior and SRGB configurations.

Explore anycast in segment routing by advertising the same prefix from multiple nodes, using adjacency sets in ISIS, and clearing the N flag to ensure precise SR-TE path selection.

Explore adjacency sets in segment routing, where R1 advertises per-neighbor, locally significant labels (24,000–1,000,000), with protected and unprotected options, and 30-minute persistence, enabling fast failover and local policy control.

Explore ti-lfa concepts, including rsvp-based backup tunnels for link or node failure, loop-free alternate routing with lfa, and topology-independent backups using segment routing to precompute loop-free paths.

Learn how alpha segment routing enables fast backup paths for traffic engineering, with a primary route via R5 and a backup via R9, using tiebreakers and srlg disjointness.

Demonstrates interworking of segment routing and mpls ldp, showing ldp label binding, label preference, and how to configure sr preference to influence imposition across edge and core routers.

Learn how segment routing and LDP interwork across two domains, with R3 as the segment routing mapping server, to form end-to-end LSP and merge LDP and SR forwarding.

Configure a segment routing mapping server to advertise 8.8.8.one/32 with index eight, enabling sr labels for end-to-end traffic and interworking with an ldp domain.

Explore how to troubleshoot segment routing LSPs with MPLS using ping and traceroute to test IP connectivity and observe TTL and ICMP behaviors.

Explore classic traceroute in MPLS networks by capturing and analyzing label switched path behavior, MPLS labels transport and VPN V4, and TTL-exceeded ICMP messages in a Cisco Modeling Labs setup.

Validate end-to-end lsp with mpls ping and echo replies; track IPv4 prefix, downstream mapping, and labels across r1 to r7. Mpls traceroute reveals labeled vs unlabeled paths and equal-cost paths.

Capture and analyze MPLS traceroute PCAPs from R1 to 7.7.7.one, revealing TTL-based hops, downstream mapping, FIB next hops, and multipath equal-cost paths.

Explore troubleshooting segment routing with practical lab tests using ping, traceroute, and MPLS traceroute to verify labels and data plane behavior across routers three, five, and seven.

Demonstrate manual traceroute MPLS paths by attaching a label stack (16,007 and 16,008) and assigning output interfaces, next hops, and sources, per RFC 4379.

Breaks end-to-end to observe route changes after forcing a 1000 cost on R3–R5 and disabling segment routing, exposing ip-only paths, unlabeled interfaces, and the need to rollback SR with traceroute.

Explore how MPLS traceroute discovers multiple equal-cost paths and tests the data plane with fixed labels using Nilfisk, illustrating multipath routes and downstream mapping.

Explore segment routing traffic engineering with color extended communities attached to VPNv4 routes. Use policies to match color and next hop and select lowest-delay or shortest-path paths.

Explore automated steering with segment routing policies, attaching color extended communities to VPN v4 routes and applying policies to traffic, then verify topology and path selection.

Explore segment routing with sr-te paths, comparing dynamic and explicit paths, with metrics like IGP and delay, and constraints such as affinity, srlg, and disjointness, plus load-balanced explicit paths.

Demonstrate dynamic path selection with ecmp, showing how R1 balances traffic across two equal-cost paths to R7 using s-r policy and IGP metrics.

Modify the segment routing traffic engineering policy to switch metric types and observe how path selection and accumulated metrics respond, including trace routes and advertised weights.

Configure affinity maps in segment routing to steer SPF-driven paths with bit position affinities. Apply include any or include all policies for red and blue links and verify path changes.

Explore dynamic path selection in segment routing and traffic engineering within MPLS TE. Apply affinity-like constraints to avoid shared fiber, learn about SRP and flex algorithms.

Explore explicit path in segment routing traffic engineering, building segment lists from IP addresses or labels to direct traffic from R1 to R7 via hops, using policy and trace routes.

Configure two explicit paths with the same preference under a segment routing traffic engineering policy, observe hash-based load balancing and the effect of weights on traffic distribution.

Show how explicit paths using adjacency sets in segment routing can steer traffic from R1 via R6 to R7, replacing prefix-only routing and validating with trace routes.

Learn segment routing traffic engineering policies, using higher preference to select dynamic paths, with explicit paths as backups, and apply affinity constraints to red links.

Explore flex algo, building a new logical topology atop the physical network and advertising prefixed values for algorithms such as 128 and 129 to shape dynamic or explicit SR paths.

Explore flex-algo in SR-TE by configuring on-demand next-hops, advertised definitions for algos 128 and 129, color ten, and blue affinity to steer shortest-path traffic in a lab.

Demonstrate multi-domain topology by applying and verifying ISIS and BGP configurations across multiple routers, reapplying the ISIS apply group after reboot, and validating loopback prefixes and color policies in SR/TE.

Explore segment routing for traffic engineering in an IPv4 topology, showing a color-matched policy between R1 and R7 that is down because the node 7.7.7.one is not in the topology.

Configure BGP egress engineering across nodes to establish end-to-end LSP paths, assigning MPLS labels and next hops for each peering.

Configure explicit paths for inter-domain lsp traffic by creating a segment list and policy on r1 and r7; validate with traceroute and enable mpls traffic engineering on interfaces.

Understand how dynamic path works across two routing domains using BGP link state and segment routing, with a path computation element delivering segment lists for end-to-end LSP.

Configure BGP link state sessions across multiple routers using loopback sources, distribute ISIS link-state into segment routing traffic engineering topology, and interpret BGP LS topology updates.

Explore how link-state advertising supports BGP egress engineering and reveals router IDs, BGP link-state details, and the need for matching router IDs and distance instance IDs across ISIS and EBGP.

Explore how the segment routing path computation element offloads path computation from PCCs to the SR PCE, enabling seed list based routes and dynamic policy-driven path updates in multi-domain topologies.

Demonstrates SR TE policy instantiation with PCE, configuring explicit and dynamic segment lists, verifying LSPs, and using trace routes to validate paths.

Configure disjoint paths in segment routing traffic engineering to prevent node sharing between color 10 and color 20 policies, using a group ID and node-disjointness constraint.

Explore multi-domain segment routing and traffic engineering by reviewing a configured topology, verifying BGP and ISIS session states, VPNv4 services, disjoint SR policies, and validating with LSP summaries.

Analyze how OSPF uses opaque LSAs (types 9–11) with area, link, and AS scopes to advertise traffic engineering data, including opaque types 1, 4, 7, 8 for MPLS SR.

On multi-access OSPF segments, advertise adjacency sets and lan adjacency sets via dr and bdr roles, illustrated by ddrs and pdr on r3 and r4 using extended link type eight.

Examine OSPF prefix and adjacency flags in segment routing, decode extended prefix LSA TLV values for A and N flags, and show explicit null effects on the LSA.

Configure R3 as a segment routing mapping server and advertise 9.9.9.1 mappings under OSPF with a segment routing prefix; verify 9.9.9.1 routes from the mapping server with label 16009.