[Benjojo] BGP handling bug causes widespread internet routing instability

At 7AM (UTC) on Tuesday May 20th 2025 a BGP message was propagated that triggered surprising (to many) behaviours with two major BGP implementations that are often used for carrying internet traffic.

This caused a large number of “internet facing” BGP sessions to automatically shut down, causing at the very least some routing instability, and at worst brief loss of connectivity for some networks.

What was the message?

Using the sessions that people feed to bgp.tools, we can see here a version of the update that caused this behaviour, it is a relatively unremarkable BGP Update for a /16, except it had a BGP Prefix-SID Attribute that was not only unwelcome (it is unexpected to see this on internet table BGP updates), but it was also corrupt with all of its internal data being 0x00.

BGP handling bug causes widespread internet routing instability