3com 2948 switches blocking PXE boot

[smithk2306]

I have recently been getting to know my way around WDS and have found a strange phenomenon with PCs connected to the network through 3com 2948 switches. All of these PCs fail to configure DHCP addresses during the PXE boot process of network boot, prior to launching WDS. If I connect a pre-installed PC to the same switch and boot windows all works fine, no problems with DHCP, no problems connecting to network. Only an issue with PXE booting, and across the whole network, only a problem with the 3com 2948 switches.
I cannot find anything in the switch config to enable or disable anything relating to PXE booting. The problem applies whether configured with VLANs or at factory default settings.
Has anyone else had a similar problem with these switches, and does anyone know a fix?
The switch is now discontinued but I have flashed the firmware to the latest available from 3com's website

[morganw]

I've got one of these as well and have the same issue, I use FOG and I can't PXE boot through this switch. I've also tried the latest firmware. I guess I'll have to call 3com support at some point but haven't got around to it yet.

[CyberNerd]

get a command line on the switch, turn on igmp-snooping
show us the config:

display running-config

? not sure about that model

[nrobb28]

Ran into same problem, did you guys ever resolve this issue?

[morganw]

Ran into same problem, did you guys ever resolve this issue?

I've changed jobs since this, but try disabling Spanning Tree Protocol.

[psydii]

Make sure you are on the latest firmware.

Also try Port Link Type Static, with RSTP enabled, power save disabled and if your PXE/DHCP server is on another subnet check that the UDP helper is reachable listening on the correct interface.