We have a network with a few switches. One of these is a 3com 4500, where there are many computers connected, a custom linux firewall and a wireless bridge. The port where the wireless bridge and the firewall are connected are in a separate VLAN, let's call it VLAN4. Port is in access mode, untagged. Everything else is in VLAN1, untagged.
When we disconnect the wireless bridge from the switch, connectivity is lost for a few seconds between random computers connected to the switch in VLAN1, then everything goes back to normal. During that period, our Nagios monitor displays many alerts regarding "DUPLICATE PACKETS FOUND".
We have isolated the firewall completely and it happens anyway, so it isn't the firewall.
Any ideas on why this happens?