bird OSPF lsupd bug (FULL/EXCHANGE problem)

[Ondrej Filip]

On 10.9.2013 21:00, Alexander V. Chernikov wrote:
> Hello list!

Thank you, Alex! Adding to the main tree.

	Ondrej

> 
> There is a problem in OSPFv2/v3 lsupdate flooding code triggering
> incorrect state machine change.
> 
> The problem is triggered under the following OSPF instability conditions:
> a) bird falls down to init state
> b) DR router LSA seqnum immediately increases after that
> c) some problems (like CoPP/policer/high CPU load) preventing DR to
> send DBD packets fast.
> 
> In that case the following can happen:
> * Our local/remote fsm state is EXCHANGE
> * Some small number of LSA's are sent (so we have no outstanding
> LSRequests other than DR router LSA)
> * DR is a bit slow on sending the next portion
> * Given router LSA is received via other neighbor (so we have empty
> LSR list)
> * We are changing state to FULL while other side is stuck in EXCHANGE
> state.
> 
> (So in practice we can end with up to 50% neighbors stuck in EXCHANGE
> state (from DR point of view) in case of OSPF flapping..)
> 
> 
>