MTU settings with pppoe
I have Pfsense 2.0.1 on a mini PC with 2 nics. One interface on my LAN and the other connecting to my ISP via pppoe with a modem in bridge mode.
Recently I setup a new mailserver which has a webmail component, the webserver runs on port 3000. So I have a port forwarding rule set to forward webmail traffic to the mail server on port 3000.
Webmail works perfectly on my LAN.
I'm gussing I may have a blackhole router problem. Using wireshark on the mail server and pfsense packet capture I can see a TCP handshake take place, but then after a while I see [TCP Retransmission] packets.
ifconfig on my interfaces
LAN = 1500 mtu
pppoe = 1492 mtu
I do not have the MTU or MSS set on either interface.
I have tried disableing PF scrubbing with no change.
The packets that are retransmitted have a 1506 byte frame size and TCP len is 1452. Don't fragment is set!
I guess these will be dropped. But shouldnt the firewall instruct the mail server to send smaller packets? Any ideas?