# Lab: Summarizing IS-IS Level-1 Routes

DevFeed: [Lab: Summarizing IS-IS Level-1 Routes](<https://devfeed.tech/articles/lab-summarizing-is-is-level-1-routes-11362.md>)

Original publisher: [Read original article](<https://blog.ipspace.net/2026/04/isis-summary/>)

Published: 2026-04-03T07:02:00Z

Content type: tutorial

Language: en

Sources: [ipSpace.net blog](<https://devfeed.tech/sources/ipspace-net-blog.md>)

Topics: [IS-IS](<https://devfeed.tech/topics/is-is.md>), [networking](<https://devfeed.tech/topics/networking.md>), [Routing (disambiguation)](<https://devfeed.tech/topics/routing.md>), [Internet Engineering Task Force (IETF)](<https://devfeed.tech/topics/ietf.md>)

Tags: [is-is](<https://devfeed.tech/tags/is-is.md>), [netlab](<https://devfeed.tech/tags/netlab.md>), [networking](<https://devfeed.tech/tags/networking.md>), [protocol](<https://devfeed.tech/tags/protocol.md>), [routing](<https://devfeed.tech/tags/routing.md>)

## AI overview

This tutorial explains why IS-IS does not provide prefix summarization by default in IP networks and points readers to a lab for practicing Level-1 route summarization into the Level-2 backbone.

## Source excerpt

IS-IS was designed to carry node addresses (NSAPs) between level-1 routers (called Intermediate Systems) within an area and area prefixes between level-2 routers, resulting in a perfect separation of concerns and forwarding information summarization. When IETF tried to use the same routing protocol for a networking stack with a completely different addressing mentality, something had to give. Read more ...