iptables; still can't get out from DNAT'ed servers... help please?! :)

Thu Feb 19 15:38:06 UTC 2004

Hi all,

   A few days ago I posted a problem I had with 'iptables' (Fedora Core 
1, 2.4.2166 kernel) and NAT'ed servers. I never got a reply but I also 
found some big problems so I re-wrote a good chunk of my script but the 
problem remains. I hope no one minds me asking again for help with the 
new info in 'iptables-save' :)

   I have my network setup like this:
LAN clients - 192.168.1.0/24, eth0
SRV clients - 192.168.2.0/24, eth1
Public IPs - 111.222.33.32/27, eth2

eth0 - 192.168.1.1
eth1 - 192.168.2.1
eth2 - 111.222.33.34
eth2:0 - 111.222.33.46
eth2:1 - 111.222.33.47
eth2:2 - 111.222.33.48

   I have all of my LAN SNAT'ed behind the firewall's IP address and 
that network is working great.

   I have each Server client DNAT/SNAT'ed behind a single public IP 
address. For example, the machine I am currently testing from is DNAT to 
192.168.2.12 and SNAT'ed to 111.222.33.47. I have a test web server up 
and 'sshd' running and I specifically allowed ports 22 and 80 into that 
server. Internet and LAN clients -can- connect to the server just fine. 
The problem lies in that the server -cannot- connect out to the Internet.

   I think it has something to do with the DNAT because when I simply 
SNAT the 192.168.2.0/24 subnet behind the firewall (as though it too 
where a LAN subnet) then I can connect out fine.

   Does anyone have any suggestions as to what I could be doing wrong? I 
admit the script is still being debug'ed so there may still be unrelated 
problems, too.

   Thanks again for any potential help!

Madison

  PS - Watch the answer end up being one that was staring me in the face! :)

  -= 'iptables-save' =-
# Generated by iptables-save v1.2.9 on Thu Feb 19 10:20:06 2004
*mangle
:PREROUTING ACCEPT [39:3516]
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [39:3516]
:OUTPUT ACCEPT [0:0]
:POSTROUTING ACCEPT [36:3216]
COMMIT
# Completed on Thu Feb 19 10:20:06 2004
# Generated by iptables-save v1.2.9 on Thu Feb 19 10:20:06 2004
*nat
:PREROUTING ACCEPT [4:400]
:POSTROUTING ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
-A PREROUTING -d 111.222.33.47 -j DNAT --to-destination 192.168.2.12
-A PREROUTING -d 111.222.33.48 -j DNAT --to-destination 192.168.2.11
-A PREROUTING -d 111.222.33.46 -j DNAT --to-destination 192.168.2.15
-A POSTROUTING -s 192.168.1.0/255.255.255.0 -o eth2 -j SNAT --to-source 
111.222.33.34
-A POSTROUTING -s 192.168.2.12 -j SNAT --to-source 111.222.33.47
-A POSTROUTING -s 192.168.2.11 -j SNAT --to-source 111.222.33.48
-A POSTROUTING -s 192.168.2.15 -j SNAT --to-source 111.222.33.46
COMMIT
# Completed on Thu Feb 19 10:20:06 2004
# Generated by iptables-save v1.2.9 on Thu Feb 19 10:20:06 2004
*filter
:INPUT DROP [0:0]
:FORWARD DROP [3:300]
:OUTPUT ACCEPT [0:0]
:FWIN - [0:0]
:FWOUT - [0:0]
:LANIN - [0:0]
:LANOUT - [0:0]
:LDROP - [0:0]
:LREJECT - [0:0]
:LTREJECT - [0:0]
:SRVIN - [0:0]
:SRVOUT - [0:0]
:TCPACCEPT - [0:0]
:TREJECT - [0:0]
:UDPACCEPT - [0:0]
:ULDROP - [0:0]
:ULREJECT - [0:0]
:ULTREJECT - [0:0]
-A INPUT -i eth2 -j FWIN
-A INPUT -i eth0 -j FWIN
-A INPUT -i eth1 -j FWIN
-A INPUT -i lo -j ACCEPT
-A INPUT -i eth0 -p udp -m udp --dport 67 -j ACCEPT
-A FORWARD -i eth2 -o eth0 -j LANIN
-A FORWARD -i eth0 -o eth2 -j LANOUT
-A FORWARD -i eth2 -o eth1 -j SRVIN
-A FORWARD -i eth1 -o eth2 -j SRVOUT
-A FORWARD -i eth1 -o eth0 -j LANIN
-A FORWARD -i eth0 -o eth1 -j LANOUT
-A OUTPUT -o eth2 -j FWOUT
-A OUTPUT -o eth0 -j FWOUT
-A OUTPUT -o eth1 -j FWOUT
-A FWIN -m state --state INVALID -j TREJECT
-A FWIN -p tcp -m mac --mac-source 00:50:BA:D2:31:0F -m tcp --dport 22 
-j TCPACCEPT
-A FWIN -p tcp -m mac --mac-source 00:02:B3:07:F6:1A -m tcp --dport 22 
-j TCPACCEPT
-A FWIN -p tcp -m mac --mac-source 00:60:97:6D:A1:0E -m tcp --dport 22 
-j TCPACCEPT
-A FWIN -p udp -m mac --mac-source 00:50:BA:D2:31:0F -m udp --dport 22 
-j UDPACCEPT
-A FWIN -p udp -m mac --mac-source 00:02:B3:07:F6:1A -m udp --dport 22 
-j UDPACCEPT
-A FWIN -p udp -m mac --mac-source 00:60:97:6D:A1:0E -m udp --dport 22 
-j UDPACCEPT
-A FWIN -i eth0 -p tcp -m tcp --dport 53 -j TCPACCEPT
-A FWIN -i eth0 -p udp -m udp --dport 53 -j UDPACCEPT
-A FWIN -i eth1 -p tcp -m tcp --dport 53 -j TCPACCEPT
-A FWIN -i eth1 -p udp -m udp --dport 53 -j UDPACCEPT
-A FWIN -p icmp -m icmp --icmp-type 5 -j TREJECT
-A FWIN -p icmp -m icmp --icmp-type 9 -j TREJECT
-A FWIN -p icmp -m icmp --icmp-type 10 -j TREJECT
-A FWIN -p icmp -m icmp --icmp-type 15 -j TREJECT
-A FWIN -p icmp -m icmp --icmp-type 16 -j TREJECT
-A FWIN -p icmp -m icmp --icmp-type 17 -j TREJECT
-A FWIN -p icmp -m icmp --icmp-type 18 -j TREJECT
-A FWIN -p icmp -m icmp --icmp-type 8 -m limit --limit 1/sec -j ACCEPT
-A FWIN -p icmp -m icmp --icmp-type 8 -j TREJECT
-A FWIN -p icmp -m icmp ! --icmp-type 8 -j ACCEPT
-A FWIN -m state --state ESTABLISHED -j ACCEPT
-A FWIN -p tcp -m tcp --dport 1024:65535 -m state --state RELATED -j 
TCPACCEPT
-A FWIN -p udp -m udp --dport 1024:65535 -m state --state RELATED -j 
UDPACCEPT
-A FWIN -j TREJECT
-A FWOUT -j ACCEPT
-A LANIN -m state --state INVALID -j TREJECT
-A LANIN -p icmp -m icmp --icmp-type 5 -j TREJECT
-A LANIN -p icmp -m icmp --icmp-type 9 -j TREJECT
-A LANIN -p icmp -m icmp --icmp-type 10 -j TREJECT
-A LANIN -p icmp -m icmp --icmp-type 15 -j TREJECT
-A LANIN -p icmp -m icmp --icmp-type 16 -j TREJECT
-A LANIN -p icmp -m icmp --icmp-type 17 -j TREJECT
-A LANIN -p icmp -m icmp --icmp-type 18 -j TREJECT
-A LANIN -p icmp -m icmp --icmp-type 8 -m limit --limit 1/sec -j ACCEPT
-A LANIN -p icmp -m icmp --icmp-type 8 -j TREJECT
-A LANIN -p icmp -m icmp ! --icmp-type 8 -j ACCEPT
-A LANIN -m state --state ESTABLISHED -j ACCEPT
-A LANIN -p tcp -m tcp --dport 1024:65535 -m state --state RELATED -j 
TCPACCEPT
-A LANIN -p udp -m udp --dport 1024:65535 -m state --state RELATED -j 
UDPACCEPT
-A LANIN -s 192.168.2.12 -d 192.168.1.100 -p tcp -m tcp --dport 22 -j 
TCPACCEPT
-A LANIN -s 192.168.2.12 -d 192.168.1.100 -p udp -m udp --dport 22 -j 
UDPACCEPT
-A LANIN -j TREJECT
-A LANOUT -s 192.168.1.0/255.255.255.0 -o eth2 -j ACCEPT
-A LANOUT -j ACCEPT
-A LDROP -p tcp -m limit --limit 2/sec -j LOG --log-prefix "TCP Dropped 
" --log-level 6
-A LDROP -p udp -m limit --limit 2/sec -j LOG --log-prefix "UDP Dropped 
" --log-level 6
-A LDROP -p icmp -m limit --limit 2/sec -j LOG --log-prefix "ICMP 
Dropped " --log-level 6
-A LDROP -f -m limit --limit 2/sec -j LOG --log-prefix "FRAGMENT Dropped "
-A LDROP -j DROP
-A LREJECT -p tcp -m limit --limit 2/sec -j LOG --log-prefix "TCP 
Rejected " --log-level 6
-A LREJECT -p udp -m limit --limit 2/sec -j LOG --log-prefix "UDP 
Rejected " --log-level 6
-A LREJECT -p icmp -m limit --limit 2/sec -j LOG --log-prefix "ICMP 
Rejected " --log-level 6
-A LREJECT -f -m limit --limit 2/sec -j LOG --log-prefix "FRAGMENT 
Rejected "
-A LREJECT -j REJECT --reject-with icmp-port-unreachable
-A LTREJECT -p tcp -m limit --limit 2/sec -j LOG --log-prefix "TCP 
Rejected " --log-level 6
-A LTREJECT -p udp -m limit --limit 2/sec -j LOG --log-prefix "UDP 
Rejected " --log-level 6
-A LTREJECT -p icmp -m limit --limit 2/sec -j LOG --log-prefix "ICMP 
Rejected " --log-level 6
-A LTREJECT -f -m limit --limit 2/sec -j LOG --log-prefix "FRAGMENT 
Rejected "
-A LTREJECT -j TREJECT
-A SRVIN -m state --state INVALID -j TREJECT
-A SRVIN -p icmp -m icmp --icmp-type 5 -j TREJECT
-A SRVIN -p icmp -m icmp --icmp-type 9 -j TREJECT
-A SRVIN -p icmp -m icmp --icmp-type 10 -j TREJECT
-A SRVIN -p icmp -m icmp --icmp-type 15 -j TREJECT
-A SRVIN -p icmp -m icmp --icmp-type 16 -j TREJECT
-A SRVIN -p icmp -m icmp --icmp-type 17 -j TREJECT
-A SRVIN -p icmp -m icmp --icmp-type 18 -j TREJECT
-A SRVIN -p icmp -m icmp --icmp-type 8 -m limit --limit 1/sec -j ACCEPT
-A SRVIN -p icmp -m icmp --icmp-type 8 -j TREJECT
-A SRVIN -p icmp -m icmp ! --icmp-type 8 -j ACCEPT
-A SRVIN -m state --state ESTABLISHED -j ACCEPT
-A SRVIN -p tcp -m tcp --dport 1024:65535 -m state --state RELATED -j 
TCPACCEPT
-A SRVIN -p udp -m udp --dport 1024:65535 -m state --state RELATED -j 
UDPACCEPT
-A SRVIN -d 192.168.2.12 -p tcp -m tcp --dport 22 -j TCPACCEPT
-A SRVIN -d 192.168.2.12 -p tcp -m tcp --dport 53 -j TCPACCEPT
-A SRVIN -d 192.168.2.12 -p tcp -m tcp --dport 80 -j TCPACCEPT
-A SRVIN -d 192.168.2.12 -p udp -m udp --dport 22 -j UDPACCEPT
-A SRVIN -d 192.168.2.12 -p udp -m udp --dport 53 -j UDPACCEPT
-A SRVIN -d 192.168.2.12 -p udp -m udp --dport 80 -j UDPACCEPT
-A SRVIN -d 192.168.2.11 -p tcp -m tcp --dport 22 -j TCPACCEPT
-A SRVIN -d 192.168.2.11 -p tcp -m tcp --dport 25 -j TCPACCEPT
-A SRVIN -d 192.168.2.11 -p tcp -m tcp --dport 53 -j TCPACCEPT
-A SRVIN -d 192.168.2.11 -p tcp -m tcp --dport 80 -j TCPACCEPT
-A SRVIN -d 192.168.2.11 -p tcp -m tcp --dport 110 -j TCPACCEPT
-A SRVIN -d 192.168.2.11 -p udp -m udp --dport 22 -j UDPACCEPT
-A SRVIN -d 192.168.2.11 -p udp -m udp --dport 25 -j UDPACCEPT
-A SRVIN -d 192.168.2.11 -p udp -m udp --dport 53 -j UDPACCEPT
-A SRVIN -d 192.168.2.11 -p udp -m udp --dport 80 -j UDPACCEPT
-A SRVIN -d 192.168.2.11 -p udp -m udp --dport 110 -j UDPACCEPT
-A SRVIN -d 192.168.2.15 -p tcp -m tcp --dport 22 -j TCPACCEPT
-A SRVIN -d 192.168.2.15 -p tcp -m tcp --dport 53 -j TCPACCEPT
-A SRVIN -d 192.168.2.15 -p tcp -m tcp --dport 80 -j TCPACCEPT
-A SRVIN -d 192.168.2.15 -p udp -m udp --dport 22 -j UDPACCEPT
-A SRVIN -d 192.168.2.15 -p udp -m udp --dport 53 -j UDPACCEPT
-A SRVIN -d 192.168.2.15 -p udp -m udp --dport 80 -j UDPACCEPT
-A SRVIN -j TREJECT
-A SRVOUT -s 192.168.2.0/255.255.255.0 -o eth2 -j ACCEPT
-A SRVOUT -j ACCEPT
-A TCPACCEPT -p tcp -m tcp --tcp-flags SYN,RST,ACK SYN -m limit --limit 
20/sec -j ACCEPT
-A TCPACCEPT -p tcp -m tcp --tcp-flags SYN,RST,ACK SYN -m limit --limit 
2/sec -j LOG --log-prefix "Possible SynFlood "
-A TCPACCEPT -p tcp -m tcp --tcp-flags SYN,RST,ACK SYN -j TREJECT
-A TCPACCEPT -p tcp -m tcp ! --tcp-flags SYN,RST,ACK SYN -j ACCEPT
-A TCPACCEPT -m limit --limit 2/sec -j LOG --log-prefix "Mismatch in 
TCPACCEPT "
-A TCPACCEPT -j TREJECT
-A TREJECT -p tcp -j REJECT --reject-with tcp-reset
-A TREJECT -p udp -j REJECT --reject-with icmp-port-unreachable
-A TREJECT -p icmp -j DROP
-A TREJECT -j REJECT --reject-with icmp-port-unreachable
-A UDPACCEPT -p udp -j ACCEPT
-A UDPACCEPT -m limit --limit 2/sec -j LOG --log-prefix "Mismatch on 
UDPACCEPT "
-A UDPACCEPT -j TREJECT
-A ULDROP -p tcp -m limit --limit 2/sec -j ULOG --ulog-prefix "LDROP_TCP"
-A ULDROP -p udp -m limit --limit 2/sec -j ULOG --ulog-prefix "LDROP_UDP"
-A ULDROP -p icmp -m limit --limit 2/sec -j ULOG --ulog-prefix "LDROP_ICMP"
-A ULDROP -f -m limit --limit 2/sec -j ULOG --ulog-prefix "LDROP_FRAG"
-A ULDROP -j DROP
-A ULREJECT -p tcp -m limit --limit 2/sec -j ULOG --ulog-prefix 
"LREJECT_TCP"
-A ULREJECT -p udp -m limit --limit 2/sec -j ULOG --ulog-prefix 
"LREJECT_UDP"
-A ULREJECT -p icmp -m limit --limit 2/sec -j ULOG --ulog-prefix 
"LREJECT_UDP"
-A ULREJECT -f -m limit --limit 2/sec -j ULOG --ulog-prefix "LREJECT_FRAG"
-A ULREJECT -j REJECT --reject-with icmp-port-unreachable
-A ULTREJECT -p tcp -m limit --limit 2/sec -j ULOG --ulog-prefix 
"LTREJECT_TCP"
-A ULTREJECT -p udp -m limit --limit 2/sec -j ULOG --ulog-prefix 
"LTREJECT_UDP"
-A ULTREJECT -p icmp -m limit --limit 2/sec -j ULOG --ulog-prefix 
"LTREJECT_ICMP"
-A ULTREJECT -f -m limit --limit 2/sec -j ULOG --ulog-prefix "LTREJECT_FRAG"
-A ULTREJECT -p tcp -j REJECT --reject-with tcp-reset
-A ULTREJECT -p udp -j REJECT --reject-with icmp-port-unreachable
-A ULTREJECT -p icmp -j DROP
-A ULTREJECT -j REJECT --reject-with icmp-port-unreachable
COMMIT
# Completed on Thu Feb 19 10:20:06 2004
  -= 'iptables-save' =-

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