# SwiNOG 40: When a Routing Control Functions Is Too Fresh

DevFeed: [SwiNOG 40: When a Routing Control Functions Is Too Fresh](<https://devfeed.tech/articles/swinog-40-when-a-routing-control-functions-is-too-fresh-11249.md>)

Original publisher: [Read original article](<https://blog.ipspace.net/2025/09/swinog40-arista-rcf-bug/>)

Published: 2025-09-17T05:33:00Z

Content type: article

Language: en

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

Topics: [Integration testing](<https://devfeed.tech/topics/integration-testing.md>), [bug](<https://devfeed.tech/topics/bug.md>), [BGP](<https://devfeed.tech/topics/bgp.md>), [Routing Security](<https://devfeed.tech/topics/routing-security.md>), [Network](<https://devfeed.tech/topics/network.md>)

Tags: [bgp](<https://devfeed.tech/tags/bgp.md>), [bug](<https://devfeed.tech/tags/bug.md>), [integration](<https://devfeed.tech/tags/integration.md>), [integration-testing](<https://devfeed.tech/tags/integration-testing.md>), [routing](<https://devfeed.tech/tags/routing.md>), [routing-security](<https://devfeed.tech/tags/routing-security.md>), [rpki](<https://devfeed.tech/tags/rpki.md>), [video](<https://devfeed.tech/tags/video.md>)

## AI overview

The article highlights a bug encountered during integration testing of network devices: applying a newly defined Routing Control Function to BGP routing updates in the same Arista EOS configuration session can produce unexpected behavior. The related SwiNOG 40 video presentation notes that the bug has since been fixed.

## Source excerpt

During integration testing, I find unexpected quirks in network devices way too often. However, that's infinitely better than experiencing them in production (even after thoroughly testing stuff) while discovering that your peers don't care about routing security, RPKI, and similar useless stuff. For example, what happens if you define a new Routing Control Function (RFC) on Arista EOS and apply it to BGP routing updates in the same configuration session? You'll find out in the Sorry We Messed Up (video) presentation Stefan Funke had at SwiNOG 40 (note: the bug has been fixed in the meantime).