What is IS-IS?

Most network engineers know BGP, OSPF, and maybe EIGRP, but far fewer have hands-on experience with ISIS. In this episode of The Art of Network Engineering, Andy Lapteff sits down with Russ White and Mike Bushong for a deep, opinionated, and refreshingly honest discussion about routing protocol design in modern data centers.

We explore why BGP has become the default hammer for every networking nail, what we lose when we blend underlay and overlay into a single protocol, and why some of the largest networks in the world still rely on IS-IS for simplicity, scale, and resilience.

This isn’t a “which protocol is best” argument, it’s a design conversation. One about failure domains, operational reality, education gaps, and why many engineers never learn the protocols that quietly power hyperscale networks.

In this episode:

Why BGP is policy-rich but intentionally slow
The architectural value of separating underlay and overlay
How ISIS works and why it’s simpler than you think
TLVs, scalability, and protocol evolution
Why familiarity often beats good design (for better or worse)
Where RIFT fits and where it doesn’t
The cost of losing deep protocol knowledge as engineers retire

If you’ve ever wondered why networks are designed the way they are, or if you’ve felt uneasy about “just using BGP everywhere,” this conversation is for you.

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