# Lab: Drain Traffic From an IS-IS Node Before Starting Maintenance

DevFeed: [Lab: Drain Traffic From an IS-IS Node Before Starting Maintenance](<https://devfeed.tech/articles/lab-drain-traffic-from-an-is-is-node-before-starting-maintenance-11260.md>)

Original publisher: [Read original article](<https://blog.ipspace.net/2025/10/isis-lab-overload-maintenance/>)

Published: 2025-10-23T05:09:00Z

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>), [Protocol (disambiguation)](<https://devfeed.tech/topics/protocol.md>)

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

## AI overview

This lab demonstrates how to drain traffic from an IS-IS node before maintenance by using the IS-IS overload bit. The bit signals other routers to stop using the node for transit traffic, allowing routing tables to adjust before traffic is disrupted.

## Source excerpt

Here's a cool feature every routing protocol should have: a flag that tells everyone a node is going down, giving them time to adjust their routing tables before disrupting traffic flow. OSPF never had such a feature; common implementations set the cost of all interfaces to a very high value to emulate it. BGP got it (the Graceful BGP Session Shutdown) almost 30 years after it was created. IS-IS had the overload bit from day one, and it's just what an IS-IS router needs to tell everyone else they should stop using it for transit traffic. You can try it out in the Drain Traffic Before Node Maintenance lab exercise. Read more ...