2.1 KiB
Module 7: Traffic Engineering
Course: ISP Backbone Lab Course Previous: Module 6: Segment Routing Next: Module 8: Attack & Defense
Network Diagram
SR-TE explicit path steering — default shortest path vs policy-driven SID stack path with Flex-Algo
Why TE?
By default, IS-IS picks the shortest path. But what if:
- The shortest path is congested?
- You want to send VoIP traffic on a low-latency path and bulk data on a high-bandwidth path?
- A fiber cut takes out the shortest path and you need a pre-computed backup?
Traffic Engineering lets you define explicit paths through the network.
SR-TE (Segment Routing Traffic Engineering)
With SR, TE is just a stack of SIDs. Want traffic to go P1 → P2 → P-CORE → P4 instead of the direct path? Push labels [16002, 16005, 16004] onto the packet. Done. No RSVP tunnels, no signaling protocol, no state in the core.
Lab 7 Config: SR-TE Policy
PE-EDGE1 (force traffic to PE-EDGE4 via a specific path):
segment-routing traffic-eng
segment-list PATH-VIA-P2-PCORE
index 10 mpls label 16002 ! P2
index 20 mpls label 16005 ! P-CORE
index 30 mpls label 16014 ! PE-EDGE4
!
policy STEER-TO-PE4
color 100 end-point 10.0.0.14
candidate-paths
preference 200
explicit segment-list PATH-VIA-P2-PCORE
Flex-Algo (Advanced)
Flex-Algo lets you define multiple topologies on the same physical network. For example:
- Algorithm 0 (default): Shortest path by metric
- Algorithm 128: Low-latency path (uses delay metric)
- Algorithm 129: High-bandwidth path (avoids congested links)
Each algorithm creates a separate set of SIDs, so you can steer traffic into different topologies without explicit path lists.
Understanding Check
- How does SR-TE compare to RSVP-TE? What makes it simpler?
- What is a SID stack and how does it define a path?
- What is Flex-Algo and when would you use it over explicit SR-TE?
Next Module: Module 8: Attack & Defense Labs →