iChat, Bonjour, RB751G-2HnD

I have a network of Macintosh only machines connected behind a Mikrotik RB751G-2HnD. These group of people use iChat internally which works for chat but not for transferring files and/or video chat.

All machines have the firewall disabled. I have test with two machines connected to another router (linksys) and ichat does work correctly.

I have tried several firewall rules at the router with no luck.

Does anyone have any experience with it ? I search and google it with no luck.