Re: [Bridge] STP bug, loop not detetcted

["Joakim Tjernlund" <Joakim.Tjernlund@transmode.se>]

> -----Original Message-----
> From: Stephen Hemminger [mailto:shemminger@vyatta.com]
> Sent: den 12 maj 2008 19:50
> To: joakim.tjernlund@transmode.se
> Cc: bridge@lists.linux-foundation.org; Francesco Dolcini
> Subject: Re: [Bridge] STP bug, loop not detetcted
> 
> On Mon, 12 May 2008 11:37:45 +0200
> Joakim Tjernlund <joakim.tjernlund@transmode.se> wrote:
> 
> >
> > On Thu, 2008-05-08 at 14:58 +0200, Joakim Tjernlund wrote:
> > > On Thu, 2008-05-08 at 14:13 +0200, Francesco Dolcini wrote:
> > > > Joakim Tjernlund wrote:
> > > > > On Thu, 2008-05-08 at 11:04 +0200, Francesco Dolcini wrote:
> > > > >> cisco and others solved this kind of problem using proprietary
> > > > >> unidirectional link detection protocols (see cisco informational rfc
> > > > >> 5171 for example). No standard exists as far as I know (BFD rfc does not
> > > > >> consider the layer 2 case).
> > > > >
> > > > > Are these proprietary unidirectional link detection protocols the only
> > > > > way to solve the problem?
> > > > spanning tree protocol, in the various IEEE incarnation (802.1D, 802.1Q)
> > > > and cisco (PVSTP) does not handle this problem, so an external mechanism
> > > > is needed.
> > >
> > > Do they explicitly ban it? Otherwise I don't see why not the kernel STP
> > > can be enchanted. You could even view it as an external mechanism.
> > >
> > > >
> > > > > Would STP break if the interface was set to "non forwarding" in this
> > > > > case until the bridge stops seeing its own STP messages?
> > > > At least this will not solve the more general problem of a
> > > > unidirectional link (rx working and tx broken).
> > >
> > > hmm, if TX is broken there won't be a loop anyway?
> > >
> > > Anyhow, even if my proposed change doesn't solve all cases it seems like
> > > a useful, very simple, ad don to STP. I am just concerned that it can
> > > break some other aspect of STP. So far it seems OK.
> > >
> > > What is the bridge maintainers view on this?
> >
> > Stephen, whats is your view about extending the bridge code according to
> > above? Also, after looking at the bride code I don't see where this
> > should be added, I must be getting old :(
> >
> >         Jocke
> 
> If you want to make STP vlan aware, then fine, a good place to start
> is getting a version of new RSTP and making it vlan aware.

No, that is not what I meant, forget about VLAN just consider what
happens if you loop 2 or more interfaces which is connected to the
same bridge. The loop is such that each TX is connected to its own
RX.

      Jocke