We have monowall installed with four interfaces one of them is the WAN interface
the other three manage 14 different tagged vlans. Users (about 300) browse the
web without a problem. connectivity between vlans works at a basic level
meaning that pinging any host works well but moving files between vlans is
impossible. I have tested in many different ways, and proved that moving an 8
bytes empty text file works flawlessly but anything bigger gets the network
hang. However I can move the same big file outside monowall into another public
IP without a problem.
This is not a rules problem, the logs do not show anything being blocked.

I have collected network traffic going out of my work station and noticed that
big files get divided and sent in chunks of 1514 bytes which is greater that
the configured MTU, I am ready to assume this is the problem however why does
it only affect traffic between internal VLANs???

BTW, I did change the MTU on my machine to 1450 and that got the file moving,
slowly but it moved. I also changed the MTU on the VLAN interface but that
didn't help.

Thanks in advance for your help!!
eric.