Setup routing and iptables for new VPN connection to redirect **only** ports 80 and 443
- by Steve
I have a new VPN connection (using openvpn) to allow me to route around some ISP restrictions. Whilst it is working fine, it is taking all the traffic over the vpn. This is causing me issues for downloading (my internet connection is a lot faster than the vpn allows), and for remote access. I run an ssh server, and have a daemon running that allows me to schdule downloads via my phone.
I have my existing ethernet connection on eth0, and the new VPN connection on tun0.
I believe I need to setup the default route to use my existing eth0 connection on the 192.168.0.0/24 network, and set the default gateway to 192.168.0.1 (my knowledge is shaky as I haven't done this for a number of years). If that is correct, then I'm not exactly sure how to do it!. My current routing table is:
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface MSS Window irtt
0.0.0.0 10.51.0.169 0.0.0.0 UG 0 0 0 tun0 0 0 0
10.51.0.1 10.51.0.169 255.255.255.255 UGH 0 0 0 tun0 0 0 0
10.51.0.169 0.0.0.0 255.255.255.255 UH 0 0 0 tun0 0 0 0
85.25.147.49 192.168.0.1 255.255.255.255 UGH 0 0 0 eth0 0 0 0
169.254.0.0 0.0.0.0 255.255.0.0 U 1000 0 0 eth0 0 0 0
192.168.0.0 0.0.0.0 255.255.255.0 U 1 0 0 eth0 0 0 0
After fixing the routing, I believe I need to use iptables to configure prerouting or masquerading to force everything for destination port 80 or 443 over tun0. Again, I'm not exactly sure how to do this!
Everything I've found on the internet is trying to do something far more complicated, and trying to sort the wood from the trees is proving difficult.
Any help would be much appreciated.
UPDATE
So far, from the various sources, I've cobbled together the following:
#!/bin/sh
DEV1=eth0
IP1=`ifconfig|perl -nE'/dr:(\S+)/&&say$1'|grep 192.`
GW1=192.168.0.1
TABLE1=internet
TABLE2=vpn
DEV2=tun0
IP2=`ifconfig|perl -nE'/dr:(\S+)/&&say$1'|grep 10.`
GW2=`route -n | grep 'UG[ \t]' | awk '{print $2}'`
ip route flush table $TABLE1
ip route flush table $TABLE2
ip route show table main | grep -Ev ^default | while read ROUTE ; do
ip route add table $TABLE1 $ROUTE
ip route add table $TABLE2 $ROUTE
done
ip route add table $TABLE1 $GW1 dev $DEV1 src $IP1
ip route add table $TABLE2 $GW2 dev $DEV2 src $IP2
ip route add table $TABLE1 default via $GW1
ip route add table $TABLE2 default via $GW2
echo "1" > /proc/sys/net/ipv4/ip_forward
echo "1" > /proc/sys/net/ipv4/ip_dynaddr
ip rule add from $IP1 lookup $TABLE1
ip rule add from $IP2 lookup $TABLE2
ip rule add fwmark 1 lookup $TABLE1
ip rule add fwmark 2 lookup $TABLE2
iptables -t nat -A POSTROUTING -o $DEV1 -j SNAT --to-source $IP1
iptables -t nat -A POSTROUTING -o $DEV2 -j SNAT --to-source $IP2
iptables -t nat -A PREROUTING -m state --state ESTABLISHED,RELATED -j CONNMARK --restore-mark
iptables -A OUTPUT -m state --state ESTABLISHED,RELATED -j CONNMARK --restore-mark
iptables -t nat -A PREROUTING -i $DEV1 -m state --state NEW -j CONNMARK --set-mark 1
iptables -t nat -A PREROUTING -i $DEV2 -m state --state NEW -j CONNMARK --set-mark 2
iptables -t nat -A PREROUTING -m connmark --mark 1 -j MARK --set-mark 1
iptables -t nat -A PREROUTING -m connmark --mark 2 -j MARK --set-mark 2
iptables -t nat -A PREROUTING -m state --state NEW -m connmark ! --mark 0 -j CONNMARK --save-mark
iptables -t mangle -A PREROUTING -i $DEV2 -m state --state NEW -p tcp --dport 80 -j CONNMARK --set-mark 2
iptables -t mangle -A PREROUTING -i $DEV2 -m state --state NEW -p tcp --dport 443 -j CONNMARK --set-mark 2
route del default
route add default gw 192.168.0.1 eth0
Now this seems to be working. Except it isn't!
Connections to the blocked websites are going through, connections not on ports 80 and 443 are using the non-VPN connection.
However port 80 and 443 connections that aren't to the blocked websites are using the non-VPN connection too!
As the general goal has been reached, I'm relatively happy, but it would be nice to know why it isn't working exactly right.
Any ideas?
For reference, I now have 3 routing tables, main, internet, and vpn. The listing of them is as follows...
Main:
default via 192.168.0.1 dev eth0
10.38.0.1 via 10.38.0.205 dev tun0
10.38.0.205 dev tun0 proto kernel scope link src 10.38.0.206
85.removed via 192.168.0.1 dev eth0
169.254.0.0/16 dev eth0 scope link metric 1000
192.168.0.0/24 dev eth0 proto kernel scope link src 192.168.0.73 metric 1
Internet:
default via 192.168.0.1 dev eth0
10.38.0.1 via 10.38.0.205 dev tun0
10.38.0.205 dev tun0 proto kernel scope link src 10.38.0.206
85.removed via 192.168.0.1 dev eth0
169.254.0.0/16 dev eth0 scope link metric 1000
192.168.0.0/24 dev eth0 proto kernel scope link src 192.168.0.73 metric 1
192.168.0.1 dev eth0 scope link src 192.168.0.73
VPN:
default via 10.38.0.205 dev tun0
10.38.0.1 via 10.38.0.205 dev tun0
10.38.0.205 dev tun0 proto kernel scope link src 10.38.0.206
85.removed via 192.168.0.1 dev eth0
169.254.0.0/16 dev eth0 scope link metric 1000
192.168.0.0/24 dev eth0 proto kernel scope link src 192.168.0.73 metric 1
