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When I enable the OpenVPN client on my Tomato-based router, port forwarding seems to not work anymore. I have an Asus RT-N16 router with this firmware installed:

Tomato Firmware 1.28.0000 MIPSR2-115 K26 USB VPN (shibby build)

I recently signed up for a VPN service, and followed the guide they provide to set up the VPN on my router: http://www.ipvanish.com/visualguides/OpenVPN/Tomato/

After following the guide, all my traffic is tunneled, which is great. However, I have a ubuntu server connected this router that hosts apache (on ports 80 and 443) that I cannot access externally anymore. I'm new to the VPN world, so please correct me if I have the theory wrong. I was hoping that when WAN requests come in outside the VPN, they would be responded to this way due to the port forwarding. My uneducated guess is that the requests are coming in, but the responses are disappearing into the tunnel.

I've seen multiple postings elsewhere that suggest the need to add additional rules to the router's iptables like this:

iptables -t nat -A PREROUTING -p tcp --dport <your_port_number> -j DNAT --to-destination <your_destination_IP_address>
iptables -A FORWARD -s <your_VPN_IP> -p tcp --dport <your_port_number> -j ACCEPT

However, I've had no success implementing this. Is it possible to do what I'm attempting? If so, what steps am I missing? Below is the output of ifconfig and iptables on my router after the VPN client is enabled. Thanks.

br0        Link encap:Ethernet  HWaddr BC:AE:C5:E8:2B:72
           inet addr:192.168.1.1  Bcast:192.168.1.255  Mask:255.255.255.0
           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
           RX packets:4906280 errors:0 dropped:0 overruns:0 frame:0
           TX packets:6593105 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:0
           RX bytes:3320899619 (3.0 GiB)  TX bytes:3055186673 (2.8 GiB)

eth0       Link encap:Ethernet  HWaddr BC:AE:C5:E8:2B:72
           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
           RX packets:12317339 errors:0 dropped:0 overruns:0 frame:0
           TX packets:11550871 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:1000
           RX bytes:2602762531 (2.4 GiB)  TX bytes:2190393333 (2.0 GiB)
           Interrupt:4 Base address:0x2000

eth1       Link encap:Ethernet  HWaddr BC:AE:C5:E8:2B:74
           UP BROADCAST RUNNING ALLMULTI MULTICAST  MTU:1500  Metric:1
           RX packets:141603 errors:0 dropped:0 overruns:0 frame:12229612
           TX packets:253818 errors:17 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:1000
           RX bytes:11473501 (10.9 MiB)  TX bytes:323350737 (308.3 MiB)
           Interrupt:3 Base address:0x1000

lo         Link encap:Local Loopback
           inet addr:127.0.0.1  Mask:255.0.0.0
           inet6 addr: ::1/128 Scope:Host
           UP LOOPBACK RUNNING MULTICAST  MTU:16436  Metric:1
           RX packets:38 errors:0 dropped:0 overruns:0 frame:0
           TX packets:38 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:0
           RX bytes:3675 (3.5 KiB)  TX bytes:3675 (3.5 KiB)

tun11      Link encap:UNSPEC  HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00
           inet addr:172.20.25.181  P-t-P:172.20.25.181  Mask:255.255.248.0
           UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1500  Metric:1
           RX packets:1649 errors:0 dropped:0 overruns:0 frame:0
           TX packets:1186 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:100
           RX bytes:1808407 (1.7 MiB)  TX bytes:129251 (126.2 KiB)

vlan1      Link encap:Ethernet  HWaddr BC:AE:C5:E8:2B:72
           UP BROADCAST RUNNING ALLMULTI MULTICAST  MTU:1500  Metric:1
           RX packets:5125335 errors:0 dropped:0 overruns:0 frame:0
           TX packets:6732029 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:0
           RX bytes:3654686593 (3.4 GiB)  TX bytes:3092936664 (2.8 GiB)

vlan2      Link encap:Ethernet  HWaddr BC:AE:C5:E8:2B:73
           inet addr:98.228.254.52  Bcast:98.228.255.255  Mask:255.255.248.0
           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
           RX packets:7190398 errors:0 dropped:0 overruns:0 frame:0
           TX packets:4818842 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:0
           RX bytes:3021257256 (2.8 GiB)  TX bytes:3392423965 (3.1 GiB)

Chain INPUT (policy DROP 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination
  119 10231 ACCEPT     all  --  tun11  *       0.0.0.0/0            0.0.0.0/0
   14  1470 DROP       all  --  br0    *       0.0.0.0/0            98.228.254.52
  393  163K DROP       all  --  *      *       0.0.0.0/0            0.0.0.0/0           state INVALID
19219 6264K ACCEPT     all  --  *      *       0.0.0.0/0            0.0.0.0/0           state RELATED,ESTABLISHED
   11   861 ACCEPT     all  --  lo     *       0.0.0.0/0            0.0.0.0/0
42101 2556K ACCEPT     all  --  br0    *       0.0.0.0/0            0.0.0.0/0
 4974 1716K ACCEPT     udp  --  *      *       0.0.0.0/0            0.0.0.0/0           udp spt:67 dpt:68

Chain FORWARD (policy DROP 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination
 3269 2974K ACCEPT     all  --  tun11  *       0.0.0.0/0            0.0.0.0/0
  11M   11G            all  --  *      *       0.0.0.0/0            0.0.0.0/0           account: network/netmask: 192.168.1.0/255.255.255.0 name: lan
13009 5871K ACCEPT     all  --  br0    br0     0.0.0.0/0            0.0.0.0/0
  122  5288 DROP       all  --  *      *       0.0.0.0/0            0.0.0.0/0           state INVALID
37051 2152K TCPMSS     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp flags:0x06/0x02 TCPMSS clamp to PMTU
  11M   11G ACCEPT     all  --  *      *       0.0.0.0/0            0.0.0.0/0           state RELATED,ESTABLISHED
 5081  302K wanin      all  --  vlan2  *       0.0.0.0/0            0.0.0.0/0
20195 1208K wanout     all  --  *      vlan2   0.0.0.0/0            0.0.0.0/0
20300 1216K ACCEPT     all  --  br0    *       0.0.0.0/0            0.0.0.0/0

Chain OUTPUT (policy ACCEPT 3994 packets, 1258K bytes)
 pkts bytes target     prot opt in     out     source               destination

Chain wanin (1 references)
 pkts bytes target     prot opt in     out     source               destination
 2186  125K ACCEPT     tcp  --  *      *       0.0.0.0/0            192.168.1.132       tcp dpt:49151
 1054 79129 ACCEPT     udp  --  *      *       0.0.0.0/0            192.168.1.132       udp dpt:49151
    0     0 ACCEPT     tcp  --  *      *       0.0.0.0/0            192.168.1.132       tcp dpt:8112
  172 10288 ACCEPT     tcp  --  *      *       0.0.0.0/0            192.168.1.132       tcp dpt:443
    5   358 ACCEPT     tcp  --  *      *       0.0.0.0/0            192.168.1.132       tcp dpt:993
    1    52 ACCEPT     tcp  --  *      *       0.0.0.0/0            192.168.1.132       tcp dpt:5222
    2   120 ACCEPT     tcp  --  *      *       0.0.0.0/0            192.168.1.132       tcp dpt:5269
    0     0 ACCEPT     tcp  --  *      *       0.0.0.0/0            192.168.1.132       tcp dpt:25
    0     0 ACCEPT     tcp  --  *      *       0.0.0.0/0            192.168.1.132       tcp dpt:110
    4   240 ACCEPT     tcp  --  *      *       0.0.0.0/0            192.168.1.132       tcp dpt:26
    0     0 ACCEPT     tcp  --  *      *       0.0.0.0/0            192.168.1.115       tcp dpt:49491
    0     0 ACCEPT     udp  --  *      *       0.0.0.0/0            192.168.1.115       udp dpt:49491
 1610 83944 ACCEPT     tcp  --  *      *       0.0.0.0/0            192.168.1.132       tcp dpt:32400
    0     0 ACCEPT     tcp  --  *      *       0.0.0.0/0            192.168.1.132       tcp dpt:465
    0     0 ACCEPT     tcp  --  *      *       0.0.0.0/0            192.168.1.132       tcp dpt:587
    3   168 ACCEPT     tcp  --  *      *       0.0.0.0/0            192.168.1.132       tcp dpt:22
   29  1704 ACCEPT     tcp  --  *      *       0.0.0.0/0            192.168.1.132       tcp dpt:80
    0     0 ACCEPT     udp  --  *      *       0.0.0.0/0            192.168.1.136       udp dpt:88
    0     0 ACCEPT     tcp  --  *      *       0.0.0.0/0            192.168.1.136       tcp dpt:3074
    0     0 ACCEPT     udp  --  *      *       0.0.0.0/0            192.168.1.136       udp dpt:3074
    1    44 ACCEPT     tcp  --  *      *       0.0.0.0/0            192.168.1.136       tcp dpt:53
   14  1143 ACCEPT     udp  --  *      *       0.0.0.0/0            192.168.1.136       udp dpt:53

Chain wanout (1 references)
 pkts bytes target     prot opt in     out     source               destination

Chain PREROUTING (policy ACCEPT 625 packets, 97194 bytes)
 pkts bytes target     prot opt in     out     source               destination
 5625  364K WANPREROUTING  all  --  *      *       0.0.0.0/0            98.228.254.52
    0     0 DROP       all  --  vlan2  *       0.0.0.0/0            192.168.1.0/24

Chain POSTROUTING (policy ACCEPT 174 packets, 10820 bytes)
 pkts bytes target     prot opt in     out     source               destination
  142  9572 MASQUERADE  all  --  *      tun11   192.168.1.0/24       0.0.0.0/0
    0     0 SNAT       tcp  --  *      *       192.168.1.0/24       192.168.1.132       tcp dpt:49151 to:98.228.254.52
    0     0 SNAT       udp  --  *      *       192.168.1.0/24       192.168.1.132       udp dpt:49151 to:98.228.254.52
    0     0 SNAT       tcp  --  *      *       192.168.1.0/24       192.168.1.132       tcp dpt:8112 to:98.228.254.52
  333 17356 SNAT       tcp  --  *      *       192.168.1.0/24       192.168.1.132       tcp dpt:443 to:98.228.254.52
   63  5305 SNAT       tcp  --  *      *       192.168.1.0/24       192.168.1.132       tcp dpt:993 to:98.228.254.52
    2   230 SNAT       tcp  --  *      *       192.168.1.0/24       192.168.1.132       tcp dpt:5222 to:98.228.254.52
    0     0 SNAT       tcp  --  *      *       192.168.1.0/24       192.168.1.132       tcp dpt:5269 to:98.228.254.52
    0     0 SNAT       tcp  --  *      *       192.168.1.0/24       192.168.1.132       tcp dpt:25 to:98.228.254.52
    0     0 SNAT       tcp  --  *      *       192.168.1.0/24       192.168.1.132       tcp dpt:110 to:98.228.254.52
    0     0 SNAT       tcp  --  *      *       192.168.1.0/24       192.168.1.132       tcp dpt:26 to:98.228.254.52
    0     0 SNAT       tcp  --  *      *       192.168.1.0/24       192.168.1.115       tcp dpt:49491 to:98.228.254.52
    0     0 SNAT       udp  --  *      *       192.168.1.0/24       192.168.1.115       udp dpt:49491 to:98.228.254.52
   10   600 SNAT       tcp  --  *      *       192.168.1.0/24       192.168.1.132       tcp dpt:32400 to:98.228.254.52
    0     0 SNAT       tcp  --  *      *       192.168.1.0/24       192.168.1.132       tcp dpt:465 to:98.228.254.52
    0     0 SNAT       tcp  --  *      *       192.168.1.0/24       192.168.1.132       tcp dpt:587 to:98.228.254.52
    0     0 SNAT       tcp  --  *      *       192.168.1.0/24       192.168.1.132       tcp dpt:22 to:98.228.254.52
  111  6084 SNAT       tcp  --  *      *       192.168.1.0/24       192.168.1.132       tcp dpt:80 to:98.228.254.52
    0     0 SNAT       udp  --  *      *       192.168.1.0/24       192.168.1.136       udp dpt:88 to:98.228.254.52
    0     0 SNAT       tcp  --  *      *       192.168.1.0/24       192.168.1.136       tcp dpt:3074 to:98.228.254.52
    0     0 SNAT       udp  --  *      *       192.168.1.0/24       192.168.1.136       udp dpt:3074 to:98.228.254.52
    0     0 SNAT       tcp  --  *      *       192.168.1.0/24       192.168.1.136       tcp dpt:53 to:98.228.254.52
    0     0 SNAT       udp  --  *      *       192.168.1.0/24       192.168.1.136       udp dpt:53 to:98.228.254.52
29907 1817K MASQUERADE  all  --  *      vlan2   0.0.0.0/0            0.0.0.0/0

Chain OUTPUT (policy ACCEPT 180 packets, 11182 bytes)
 pkts bytes target     prot opt in     out     source               destination

Chain WANPREROUTING (1 references)
 pkts bytes target     prot opt in     out     source               destination
    4   172 DNAT       icmp --  *      *       0.0.0.0/0            0.0.0.0/0           to:192.168.1.1
 2103  120K DNAT       tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp dpt:49151 to:192.168.1.132
  834 57491 DNAT       udp  --  *      *       0.0.0.0/0            0.0.0.0/0           udp dpt:49151 to:192.168.1.132
    0     0 DNAT       tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp dpt:8112 to:192.168.1.132
  505 27636 DNAT       tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp dpt:443 to:192.168.1.132
   68  5663 DNAT       tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp dpt:993 to:192.168.1.132
    3   282 DNAT       tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp dpt:5222 to:192.168.1.132
    2   120 DNAT       tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp dpt:5269 to:192.168.1.132
    0     0 DNAT       tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp dpt:25 to:192.168.1.132
    0     0 DNAT       tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp dpt:110 to:192.168.1.132
    4   240 DNAT       tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp dpt:26 to:192.168.1.132
    0     0 DNAT       tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp dpt:49491 to:192.168.1.115
    0     0 DNAT       udp  --  *      *       0.0.0.0/0            0.0.0.0/0           udp dpt:49491 to:192.168.1.115
 1633 85204 DNAT       tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp dpt:32400 to:192.168.1.132
    0     0 DNAT       tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp dpt:465 to:192.168.1.132
    0     0 DNAT       tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp dpt:587 to:192.168.1.132
    3   168 DNAT       tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp dpt:22 to:192.168.1.132
  140  7788 DNAT       tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp dpt:80 to:192.168.1.132
    0     0 DNAT       udp  --  *      *       0.0.0.0/0            0.0.0.0/0           udp dpt:88 to:192.168.1.136
    0     0 DNAT       tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp dpt:3074 to:192.168.1.136
    0     0 DNAT       udp  --  *      *       0.0.0.0/0            0.0.0.0/0           udp dpt:3074 to:192.168.1.136
    1    40 DNAT       tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp dpt:53 to:192.168.1.136
   14  1143 DNAT       udp  --  *      *       0.0.0.0/0            0.0.0.0/0           udp dpt:53 to:192.168.1.136
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migrated from serverfault.com Feb 17 at 17:33

This question came from our site for professional system and network administrators.

2 Answers 2

up vote 0 down vote accepted

It's not true that port forwarding does not work any more. Rather, what is happenng is that the reply from your Ubuntu server is routed through the VPN, so that, when it reaches the pc that was trying to contact the Ubuntu server, it will be coming from a different IP address than the one the initial message was written to. All pcs, for obvious questions of security, are instructed to drop these fake (?) reply packets.

So that the basic idea is to oblige your LAN to allow replies (from the Ubuntu server) outside the VPN. That requires policy routing, i.e., the simultaneous use of two routing tables according to the source (not the destination!) IP address. Policy routing is sometimes referred to as source routing.

You can find clear instructions on how to do that on a Tomato route on the serverfault site, here. It is the contribution starting with: I finally did it. I believe that thread was unjustly closed, the contribution is instead quite useful. Come back if you have specific problems with following the instructions.

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Thanks to MariusMatutiae's answer above, I was able to solve this problem using an answer from the link provided. All the credit for the script I'll include goes to grdnkln from his serverfault answer. I tweaked his script to suit my needs better, as he wanted to exclude all traffic by default from the VPN, and I wanted to do the opposite. So my final solution, includes all traffic in the VPN by default, and adds exclusions for the port 80/443 responses coming from my server.

Additionally, I added some exceptions at the bottom for DynDns's IP lookup tool (checkip.dyndns.com). I was stymied for a while because my dynamic IP resolver tool (ddclient) was picking up the new VPN IP and setting all my domain host records to resolve to that.

# This code goes in the WAN UP section of the Tomato GUI.
#
# This script configures "selective" VPN routing. Normally Tomato will route ALL traffic out
# the OpenVPN tunnel. These changes to iptables allow some outbound traffic to use the VPN, and some
# traffic to bypass the VPN and use the regular Internet instead.
#
#  To list the current rules on the router, issue the command:
#      iptables -t mangle -L PREROUTING
#
#  Flush/reset all the rules to default by issuing the command:
#      iptables -t mangle -F PREROUTING
#

#
# First it is necessary to disable Reverse Path Filtering on all
# current and future network interfaces:
#
for i in /proc/sys/net/ipv4/conf/*/rp_filter ; do
      echo 0 > $i
done

#
# Delete and table 100 and flush any existing rules if they exist.
#
ip route flush table 100
ip route del default table 100
ip rule del fwmark 1 table 100
ip route flush cache
iptables -t mangle -F PREROUTING

#
# Copy all non-default and non-VPN related routes from the main table into table 100.
# Then configure table 100 to route all traffic out the WAN gateway and assign it mark "1"
#
# NOTE: Here I assume the OpenVPN tunnel is named "tun11".
#
#
ip route show table main | grep -Ev ^default | grep -Ev tun11 \
  | while read ROUTE ; do
      ip route add table 100 $ROUTE
done
ip route add default table 100 via $(nvram get wan_gateway)
ip rule add fwmark 1 table 100
ip route flush cache

#
# Define the routing policies for the traffic. The rules will be applied in the order that they
# are listed. In the end, packets with MARK set to "0" will pass through the VPN. If MARK is set
# to "1" it will bypass the VPN.
#
# EXAMPLES:
#
#  All LAN traffic will bypass the VPN (Useful to put this rule first, so all traffic bypasses the VPN and you can configure exceptions afterwards)
#    iptables -t mangle -A PREROUTING -i br0 -j MARK --set-mark 1
#  Ports 80 and 443 will bypass the VPN
#    iptables -t mangle -A PREROUTING -i br0 -p tcp -m multiport --dport 80,443 -j MARK --set-mark 1
#  All traffic from a particular computer on the LAN will use the VPN
#    iptables -t mangle -A PREROUTING -i br0 -m iprange --src-range 192.168.1.2 -j MARK --set-mark 0
#  All traffic to a specific Internet IP address will use the VPN
#    iptables -t mangle -A PREROUTING -i br0 -m iprange --dst-range 216.146.38.70 -j MARK --set-mark 0
#  All UDP and ICMP traffic will bypass the VPN
#    iptables -t mangle -A PREROUTING -i br0 -p udp -j MARK --set-mark 1
#    iptables -t mangle -A PREROUTING -i br0 -p icmp -j MARK --set-mark 1

# Whitelist ports for server
iptables -t mangle -A PREROUTING -i br0 -p tcp -m multiport --sport 80,443 -s 192.168.1.132 -j MARK --set-mark 1
# DynDNS lockup IPs
iptables -t mangle -A PREROUTING -i br0 -m iprange --dst-range 216.146.38.1-216.146.43.254 -j MARK --set-mark 1
iptables -t mangle -A PREROUTING -i br0 -m iprange --dst-range 91.198.22.1-91.198.22.254 -j MARK --set-mark 1
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