Port based routing

After i came on new work i found that can not send email thru SMTPS, because port 465 closed on router. At this point i already had configured VPN access on my home router, so i think that it is good idea to route SMTPS traffic thru VPN, let’s start.

For this purposes i needed iproute2 and iptables. First i created new route table and add default route:

$ echo "1    VPN" >> /etc/iproute2/rt_tables
$ ip route add default via 192.168.107.5 src 192.168.107.6 dev tun_vpn table VPN
$ ip route show table VPN
default via 192.168.107.5 dev tun_vpn src 192.168.107.6

Where 192.168.107.5 – ip of my router into VPN and tun_vpn – VPN interface.
After that i created rule, that route marked packets thru VPN route table:

$ ip rule add from all fwmark 0x16 lookup VPN
$ ip  ru sh
0:      from all lookup local
32765:  from all fwmark 0x16 lookup VPN
32766:  from all lookup main
32767:  from all lookup default

There is time to mark SMTPS packets:

$ iptables -t mangle -I PREROUTING -p tcp --dport 465 -j MARK --set-mark 0x16
$ iptables -t mangle -I OUTPUT -p tcp --dport 465 -j MARK --set-mark 0x16

Let’s check:

$ traceroute -n -T -p 993 imap.gmail.com
traceroute to imap.gmail.com (173.194.69.109), 30 hops max, 60 byte packets
1  192.168.130.1  0.217 ms  0.233 ms  0.201 ms
2  *  2.318 ms  2.377 ms  2.503 ms
3  *  1.411 ms  1.714 ms  1.947 ms
4  *  1.486 ms  1.733 ms  1.796 ms
5  * 12.762 ms 72.14.212.22  12.791 ms  12.836 ms
6  * 65.528 ms  61.534 ms  67.431 ms
7  216.239.43.250  66.606 ms 209.85.248.132  61.808 ms 216.239.43.250  60.219 ms
8  216.239.48.53  66.225 ms 209.85.254.153  61.190 ms 64.233.174.55  66.038 ms
9  66.249.95.67  60.271 ms 66.249.95.175  60.510 ms  60.956 ms
10  64.233.174.55  65.304 ms  65.610 ms 64.233.174.29  76.697 ms
11  173.194.69.109  66.954 ms  65.824 ms  61.563 ms
$ traceroute -n -T -p 465 imap.gmail.com
traceroute to imap.gmail.com (173.194.69.108), 30 hops max, 60 byte packets
1  192.168.107.1  26.088 ms  42.767 ms  42.748 ms
2  *  42.813 ms  42.799 ms  68.297 ms
3  *  42.668 ms  42.665 ms  42.619 ms
4  * 42.539 ms  42.521 ms  42.504 ms
5  *  42.522 ms  68.071 ms  68.039 ms
6  *  68.015 ms  76.070 ms  85.085 ms
7  * 136.618 ms  136.634 ms  136.555 ms
8  216.239.43.250  110.732 ms  110.744 ms  110.712 ms
9  64.233.174.55  136.549 ms 209.85.254.153  136.506 ms  136.463 ms
10  * 66.249.95.67  137.978 ms 66.249.95.175  137.887 ms
11  173.194.69.108  137.893 ms 216.239.48.53  137.846 ms 64.233.174.55  130.177 ms

Profit!
PS
In my situation i observed strange effect, although that i set src ip, my host trying to send packets with src ip of local ethernet interface, so i just add masquerade rule into iptables.

$ iptables -A POSTROUTING -o tun_vpn -J MASQUERADE

Another way to fix it, set route to local work network on router, but i too lazy to do it.

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