[routing-wg] New on RIPE Labs: BGP Zombies

> One of the issues we found (Philip Smith and I) "back then" was indeed
> router bugs.  The combination of "export policy is changed" with "an 
> update is queued for this neighbour right then" led to control-plane 
> confusion and missing withdraws.  This was fixed.

cool

> My conclusion then was that something along the following line happens
> 
>  - router R1 remembers where an UPDATE was sent to
>  - export policy on R1 is changed, changing whether or not a given
>    peer would receive an UPDATE for a given prefix
>  - R1 receives withdraw from his best (and only) path, prefix is gone
>  - R1 sends withdraw to "all peers it remembers"
>  - and something goes wrong if that list of peers is not reflecting the
>    real set of peers, possibly due to "BGP internal state not fully in
>    sync between 'export policy is changed' and 'withdraw comes in'", so
>    R1 is no longer aware that one of his neighbours received the prefix
>    originally.

believable conjecture.  could and should be tested in lab.

but does not explain the cases where we see stuck routes on devices
which have no config changes for a loooong time (if you believe rancid).

randy