[geeks] Switch incompatibilities

[Fogg, James]

stp (spanning tree) is only to prevent loops. If you can be golden-sure you
won't accidentally create loops, leave it off.

My Christhall Bhall shows me you have macintosh's or dhcp'ing older
windblows machines. One fluke of the Cisco switch is that spanning-tree
portfast is disabled by default. This means that the port, though up/up, is
NOT forwarding for up to 45 seconds when the attached host brings the link
up. Also, you can do sh int f0/x and check that your link stats are what you
think they are, then do sh span int f0/x and make sure its forwarding.

Macs look for a network number from the (pardon my poor memory about
ethertalk) something master. When it doesn't find the network (or whatever)
master, it assumes that IT is the network master and will dole out network
numbers. It fails to find the network (or zone) master because its looking
for it while the cisco port is not forward but is actually up. When you have
bunches of network numbers you are doomed. Only hosts with the same network
numbers can talk to each other without a zone router. Older versions of
windblows on slow hardware sometimes have problems dhcp'ing for simular
reasons.

In config mode on each interface you can do "no spanning-tree portfast". If
you don't trust yourself to prevent loops don't turn off spanning tree
portfast on inter-switch or inter-hub links. For the SMC, turn ON spanning
tree portfast for inter-switch links.

Another possiblity is that you HAVE loops, in which case you will surely
have a broadcast storm going on and you won't pass traffic.

If none of this helps, write back.

> I'm at my wits end here.
> 
> I have a Cisco Series 3500 XL 24-port switch, and an SMC EZ 
> Switch 10/100
> 5-port, and I want them to talk. They both support IEEE 802.3x,
> autonegotiation, simple enough I thought.
> 
> Both switches show 100 megabit, full duplex link. Cisco says 
> the port is
> up/up. I can ping IPs on the other side of each switch, and 
> the Cisco shows
> MAC addresses. I can sniff the network and see ARP broadcasts. 
> 
> But I can't see any IP whatsoever. Pings don't work. Nothing 
> which is IP
> seems to work. I've tried turning off spanning tree. I've 
> tried hardcoding
> speed and duplex on the Cisco switch to every possible 
> combination. I've
> powercycled everything. No avail. I get link, and everything says it
> *should* work, but it doesn't.
> 
> Help?
> 
> David
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