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iptables - Server behind DMZ firewall won't respond

I have a DMZ server set up to forward specific ports to a
couple of machines. The intended behavior is for me to send a request to the DMZ on a
specific port, and have the machine that's inaccessible publicly respond with data. In
this example, I'm forwarding port 10001 to the non-pub server on port
80.



I can see that the forward is working,
because I can see the packets come in via tcpdump on the server. For whatever reason,
the packets it responds with aren't making it back to my terminal (I'm
curling).




iptables-save:



#
            Generated by iptables-save v1.4.10 on Fri Dec 23 17:36:10
            2011
*nat
:PREROUTING ACCEPT [5609:332934]
:INPUT ACCEPT
            [5609:332934]
:OUTPUT ACCEPT [5231:376507]
:POSTROUTING ACCEPT
            [5248:377595]
-A PREROUTING -i eth0 -p tcp -m tcp --dport 10001 -j DNAT
            --to-destination 192.168.1.11:80
COMMIT

# Completed on
            Fri Dec 23 17:36:10 2011
# Generated by iptables-save v1.4.10 on Fri Dec 23
            17:36:10 2011
*filter
:INPUT ACCEPT
            [119300:24294441]
:FORWARD ACCEPT [183:10688]
:OUTPUT ACCEPT
            [118926:28442933]
-A INPUT -i eth0 -p tcp -m state --state NEW -m tcp --dport
            10001 -j ACCEPT
COMMIT
# Completed on Fri Dec 23 17:36:10
            2011



Note:
I took my ip out and replaced it with 10.10.10.10
Legend:




  • 192.168.1.3 =
    DMZ

  • 192.168.1.11 = Non-public
    server

  • 10.10.10.10 = me from a remote
    network.




tcpdump
from the DMZ:



17:44:45.039273 IP
            10.10.10.10.64090 > 192.168.1.3.10001: Flags [S], seq 2710805211, win 65535, options
            [mss 1460,nop,wscale 3,nop,nop,TS val 1211306586 ecr 0,sackOK,eol], length
            0
17:44:45.039365 IP 10.10.10.10.64090 > 192.168.1.11.www: Flags [S], seq
            2710805211, win 65535, options [mss 1460,nop,wscale 3,nop,nop,TS val 1211306586 ecr
            0,sackOK,eol], length
            0


Based on the above,
the forwarding appears to be working.



tcpdump
from the non-public
server:




17:51:14.260134
            IP 10.10.10.10.64110 > 192.168.1.11.www: Flags [S], seq 722619659, win 65535, options
            [mss 1460,nop,wscale 3,nop,nop,TS val 1211694763 ecr 0,sackOK,eol], length
            0
17:51:14.260378 IP 192.168.1.11.www > 10.10.10.10.64110: Flags [S.], seq
            3171485713, ack 722619660, win 14480, options [mss 1460,sackOK,TS val 4294937443 ecr
            1211694763,nop,wscale 3], length 0
17:51:14.260470 IP 10.10.10.10.64111 >
            192.168.1.11.www: Flags [S], seq 483447265, win 65535, options [mss 1460,nop,wscale
            3,nop,nop,TS val 1211694763 ecr 0,sackOK,eol], length
            0


My curl from a
remote network (obfuscated IP):



$
            curl -vv remote-unit:10001
* About to connect() to remote-unit port 10001
            (#0)
* Trying 99.99.99.99... Operation timed out

*
            couldn't connect to host
* Closing connection #0
curl: (7) couldn't
            connect to host

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