What is Segment Routing?

Terry Slattery
Principal Architect

Do you remember source routing, used in token ring bridging networks? If you’re relatively new to networking, you may not know about it. In source routing, the hosts determine the path to take through the network and build a frame header that specifies the forwarding nodes that the frame should pass through as it goes from source to destination. The token ring implementation typically used special frames called explorer packets to discover the set of paths from source to destination. Too many explorer packets could cause overloading problems with the network nodes (source route bridges) and with the hosts that had to process them, much like a broadcast storm in Ethernet networks.

Segment Routing

When I first heard about segment routing and that it was based on source routing technology, I was initially curious, because of my history with token ring source route bridging. But fortunately, segment routing is completely different. It doesn’t use explorer packets and it isn’t bridging.

I’ve written a good deal about segment routing, so a good introduction to this subject would be those posts. A great start is my post at nojitter.com, where I write a monthly article.

Then move on to this post at Tech Target. It includes more information about how applications and the network can communicate with each other to select optimum traffic paths. I also recommend a white paper on the technology from Cisco.

Finally, there are more links at the Segment Routing Tech Field Day site.


A number of new innovations to networking are being created and the network world is in a state of transition. It will be interesting to see which technologies make it and which ones wind up in the dustbin of history. Segment routing may make it because of its scalability over other technologies.

Leave a Reply