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BGP handling bug causes widespread internet routing instability

At 7AM (UTC) on Wednesday 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.

This incident was further amplified by Hutchison/AS9304 being on a large number of internet exchanges, meaning that the offending messages were sent to IX route servers that typically are running bird. While the root cause (or even perpetrator) is not entirely clear, the fact that it propagated over the internet at scale is a demonstration of the situation/risk that I described in my previous post “Grave flaws in BGP Error handling” - August 2023. This is a curious decision, in which JunOS will save itself from a remote induced session reset, but then forward such messages to other peers (or in business words, likely towards your customers).

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