[uClinux-dev] Serial Connection of Ethernet Switches

[Dennison, Eric]

> Remco Poelstra wrote:
> > Mark Phillips schreef:
> > >HI All,
> > >
> > >Sorry to do this but usual my contacts can't give me a answer to
this
> > >question.
> > >
> > >
> > >I have a series of switches connected in series. That is port B of
> > >switch 1 is connected to port A of switch 2, and port B of switch 2
is
> > >connected to port A of switch 3 ....
> > >
> > >What is the maximum number of switches.
> > >I need a reference ie RFC, Standard etc.
> >
> > I think that is pretty unlimited, since a switch creates a seperate
> > collision domain.
> 
> Yes.  It's hubs which have a strict limitation, due to the maximum
> time to detect collisions.
> 
> For switches the MAC address learning capacity and spanning tree
> capacity of the switches - but that's to do with the number of devices
> connected.  I'm not sure if the spanning tree protocol has a daisy
> chain limitation due to its timeouts.
> 

There is a limitation for daisy chaining if spanning tree protocol is
used. If you want to daisy chain switches *and* introduce redundant
paths (e.g. a ring topology), which would require spanning tree
protocol, then you will run into trouble. The exact limit depends on the
spanning tree implementation, but I think you will find the limit to be
somewhere in the neighborhood of 20-30 switches. There are some
industrial Ethernet vendors selling switches with customized RSTP that
extend the limit.

Eric