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.

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.

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.

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 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.

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 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 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.

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.

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.

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.