I have a dual-homed machine (1 LAN, 1 DMZ) using static IPs on both, with routes configured so that packets coming in on the LAN IP use a LAN gateway and DMZ packets use a DMZ gateway. I am using tcpdump for debugging on the local machine.
When establishing a TCP connection with a source IP on the DMZ subnet, the handshake proceeds normally. When establishing a TCP connection with a source IP outside the DMZ subnet to the DMZ nic, the server never returns an ACK.
I have confirmed that the ACKs are not leaving via the other nic. I have confirmed that no rules are configured in
iptables (primary suspect at this point). Routes look appropriate. SYN packets look normal. I have confirmed that the IP-to-nic mapping is correct (and consistent across boots).
This configuration was working normally. I moved the hardware and changed the LAN and DMZ IPs, and now I am having issues. I updated the new IPs in both
/etc/network/interfaces and in the hosts file (DMZ only).
Where else should I look to see where the traffic is being blocked?
Kernel IP routing table Destination Gateway Genmask Flags MSS Window irtt Iface 10.0.0.0 0.0.0.0 255.255.255.0 U 0 0 0 eth2 10.10.0.0 10.10.0.1 255.255.255.0 UG 0 0 0 eth1 10.10.0.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1 169.254.0.0 0.0.0.0 255.255.0.0 U 0 0 0 eth0 169.254.0.0 0.0.0.0 255.255.0.0 U 0 0 0 eth1 0.0.0.0 10.0.0.1 0.0.0.0 UG 0 0 0 eth2
(eth0 is unconfigured, 10.10.0.0/24 = DMZ, 10.0.0.0/24 = LAN)