We have an office network with a sonicwall TZ190 firewall and four daisy-chained switches, the first three 24 port 3com switches, the last one an older 12 port Cisco switch. (I know this isn't a great setup, next time I think I'll insist on 2 48 port switches). The issue I've been having is that for two days now, at around the same time each day, DHCP suddenly stops working, and the firewall is unreachable (can't be pinged) by a computer if I release its DHCP address.
If I assign a computer a static IP in this case, the computer is immediately connected with the router. Sometime later in the day, this problem magically disappears and DHCP works again.
I thought maybe it was an issue with a switch loop, although I can't find any loops, and I'm not sure if STP is active on the 3Com switches (but it should be right?). When I do a packet trace, I can see STP packets coming from the Cisco switch (which is at the end of the chain) but only from it. Honestly, I'm not really sure how to connect to the 3com switches. I've done Cisco switches from the command line with no problem, but I can't find the 3Com switches at the IP addresses listed on them (169.254.xxx.xxx). There's a CD with the detect utility but it doesn't find them either.
Not sure if this is relevant at all, but the Cisco switch is about 100m away from the other switches in a separate room. There are two hubs and a wireless AP (or a wireless router in AP mode) also connected to the network, but I haven't found any looping issues there either.
So, any ideas? Any info I've left out that you'd like?