Forwarding to a secondary router

icedown · 07-26-2013, 12:27 PM

At my house I have 2 internet connections. The primary one is satellite, high speed, very high pings. The second one is a 3G connection, relatively low speed but good ping. My router is an ubuntu machine with 2 nics. One nic is connected to the satellite, the other to the internal network. The 3G gateways is connected to the internal network as well. I'm wanting certain traffic, eg dns, ssh, games, etc, that need low latency to be routed to the 3G gateway from the main router. what kind of iptables rules will I need?

Ser Olmy · 07-26-2013, 01:27 PM

iptables rules do not affect packet routing. However, iptables can be used to "mark" packets of a certain kind, and it is possible to route packets based on these "marks".

What you want to do is called policy routing, and you need to have the iproute2 tools installed to be able to do it. Basically, you will need to do this:

create one or more alternative routing tables with the ip route add table command
create iptables rules that match certain types of packets and "mark" them using the MARK target
create at least one rule with the ip rule add command to direct marked packets to a certain routing table

Are you using your Linux system as a router, or do you want to do this just for local traffic from the Linux PC?

icedown · 07-26-2013, 01:50 PM

It's a router for the network. What iptable should I use to mark? Prerouting in nat?

Ser Olmy · 07-26-2013, 02:33 PM

Quote:

Originally Posted by icedown

It's a router for the network. What iptable should I use to mark? Prerouting in nat?

Prerouting in mangle. Use the MARK target and specify a value with the --set-mark option. The MARK value is just a number you can refer to in an ip rule later.