BGP handling bug causes widespread internet routing instability

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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.

https://blog.benjojo.co.uk/post/bgp-attr-40-junos-arista-session-reset-incident

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Comments

  • host_chost_c Hosting Provider

    Most implementations (IOS-XR/Nokia SR-OS) correctly filtered this out without causing any problems assuming their systems have been setup for RFC7606 (“BGP error tolerance”), however an interesting interaction with JunOS and Arista EOS caused JunOS to carry the corrupt message, and Arista EOS devices to reset sessions when receiving the message from (likely) a JunOS device.

    Now that is cool, in a wrong way, but still cool.

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