Re: [Bridge] delay in bridge learning when forward delay is 0

[Uli Luckas <u.luckas@road.de>]

Is any one willing to look into this problem? Or even aknowledege it's 
existence? 
If the description is not clear, please let me know.

Any response would be appreciated.

regards,
Uli

> Hi,
> In July 2007 Philip Craig reported the following issue with 'forward
> delay'=0 in great detail without receiving an answer. Has Philip's message
> got lost or was his analysis wrong?
> The problem becomes a real problem if you bridge a fast LAN to a slow port
> like a bluetooth pan for example.
>
>
> https://lists.linux-foundation.org/pipermail/bridge/2007-July/005476.html
> Philip Craig philipc at snapgear.com
>
> > Hi,
> >
> > If you set the bridge forward delay to 0 with:
> >         brctl setfd br0 0
> > then the bridge does not learn addresses for the first 20 seconds,
> > and so it floods everything during this time.
> >
> > The reason for this is that hold_time() returns 0 after a topology
> > change, br_fdb_update() is a no-op if hold_time() is 0 (so that
> > 'brctl setmaxage br0 0' can be used to disable learning), and the
> > topology change flag isn't cleared for max_age seconds, so nothing
> > is learnt during that time.
> >
> > It seems that the intent of hold_time() is to expire entries that are
> > older than forward_delay seconds at the time of the topology change,
> > which it does, but then it keeps on checking this expiry again for
> > max_age seconds, and bases these checks on the current time rather
> > than the time of the change.
> >
> > A quick fix for the forward delay 0 case would be to skip the
> > topology change check if stp is disabled, but if I understand things
> > correctly then the expiry isn't right for non-zero cases either.
>
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