[KLUG Members] switches vs. hubs

[Adam Tauno Williams]

> > Have you tried to assign a static IP address on a workstation on the
> > second switch to see if the workstation can see the rest of the
> > network?  
> On the first replaced switch, I could move a connection for a single box 
> from switch two to switch one and then both could work fine.  Returning 
> to the original setup wouldn't work, so the switch was replaced.  On the 
> second second switch (i.e. switch number two, now replaced) that didn't 
> work.  Neither did assigning static IP addresses.  As mentioned before, 
> swapping the entire switch 2 out with a hub worked instantly, so I'm 
> convinced it's not cabling, computer configuration, etc.

It sounds like two bad switches,  which while terribly unlikely, seems the only
explanation.

> > There is nothing in a switch that should be blocking DHCP. 
> > The only thing I can think of is if you have spanning tree running
> > and the port is in blocking mode (it is a real streach).  
> Translate "spanning tree" and "blocking mode" please

"Spanning Tree" is a mechanism where switches 'share' their MAC routing tables
with each other so you can cross-link/mesh the switches to increase bandwidth
and redundancy.  "Spanning Tree", by neccesity, introduces the concept of
"blocking mode" where a given port does not permit broadcast packets because
broadcast packets are assumed to ingress and egress the span at an alternative
port.

> > I would
> > first verify hardware connectivity using the switch without DHCP. 
> Tried that, sigh, doesn't work on this replaced switch.

So do you get any connectivity from a host on switch #1 and a host on switch
#2?

> > Since DHCP is broadcast traffic the switch should simply flood the
> > request.
> > One other thing.... is it possible you have a vlan conflict (assuming
> > you are running a switch with vlans)?
> A vlan?

A vLan is a virtual-LAN.  For example: Our main distribution switch has 50
ports,  but these are divided, via the configuration of the switch, into
multiple 'switchlets'.  So ports 1-36,49,50 act like one switch and 36-42
behave like a seperate switch, and so on.  So a host plugged into port 24
cannot communicate with a host plugged into port 37.  Ports 1-36 are the "LAN",
while 36-42 have a link to the firewall and all the wireless WAPS, and ports
43-47 are the internet DMZ. (48 is a monitoring port).   One should note,
however, that there are several different types of vLAN technology and ways it
can be used.

If you paid less than $200 for your switch it is VERY unlikely it even supports
things like spanning tree or vLans.