I have a dual-homed Intranet server that serves 2 different sub-nets. After working just fine, during some re-configuring of some external elements of one of the sub-nets, the accessibility from that sub-net was lost. Of course I thought it was the changed stuff, so I put everything back the way it was. I gradually traced the issue back to the server itself.
Using Wireshark on the server, I can see that clients on the dead sub-net are generating SYN packets, but the server never responds. When I switch to looking at the other (working) interface, I can see all the packets working just like they are supposed to, including full handshakes. This dead interface, just shows incoming SYN packets.
I have verified that Port 80 is LISTENING on all interfaces. The UFW is disabled.
I have seen discussions about intermittent issues of SYN without ACK, that suggest adjusting sysctl parameters, but those solutions haven't done any good here.
I have been beating my head against this wall entirely too long, so I would be very grateful for any assistance.
