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Terry Slattery

What is Segment Routing?

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.

Terry Slattery

Terry Slattery

Principal Architect

Terry Slattery is a Principal Architect at NetCraftsmen, an advanced network consulting firm that specializes in high-profile and challenging network consulting jobs. Terry is currently working on network management, SDN, business strategy consulting, and interesting legal cases. He is the founder of Netcordia, inventor of NetMRI, has been a successful technology innovator in networking during the past 20 years, and is co-inventor on two patents. He has a long history of network consulting and design work, including some of the first Cisco consulting and training. As a consultant to Cisco, he led the development of the current Cisco IOS command line interface. Prior to Netcordia, Terry founded Chesapeake Computer Consultants, which became a Cisco premier training and consulting partner. At Chesapeake, he co-invented and patented the v-LAB system to provide hands-on access to real hardware for the hands-on component of internetwork training classes. Terry co-authored the successful McGraw-Hill text "Advanced IP Routing in Cisco Networks," is the second CCIE (1026) awarded, and is a regular speaker at Enterprise Connect and Interop. He blogs at nojitter.com and netcraftsmen.com.

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