Re: [gentoo-user] OT: default route dependent on dest port?

[Dragostin Yanev <gentoo+user@netixen.com>]

On Fri, 4 Oct 2013 20:55:25 +0000 (UTC)
Grant Edwards <grant.b.edwards@gmail.com> wrote:

> Let's posit two network interfaces net1 (192.168.x.y/16) and net2
> (172.16.a.b/16).  There's a NAT/gateway available on each of the
> networks. I want to use the 172.16 gateway for TCP connections to port
> 80 and the 192.168 gateway for everything else.
> 
> I'm primarily following this example:
> 
>   http://www.tldp.org/HOWTO/Adv-Routing-HOWTO/lartc.netfilter.html
> 
> My "main" routing table contains all directly accessible subnets plus
> a default route via the 192.168 gateway.
>   
> I created a second route table named "pmain" which is identical to
> "main" except it has a different default route via the 172.16 gateway.
> 
> My ip rules are:
> 
>   0:      from all lookup local 
>   10000:  from all fwmark 0x1 lookup pmain 
>   32766:  from all lookup main 
>   32767:  from all lookup default 
> 
> I then add an iptables rule like this:
> 
>   iptables -A OUTPUT -t mangle -p tcp --dport 80 -j MARK --set-mark 1
> 
> Now all TCP packets destined for port 80 are sent to the 172.16
> gateway, _but_ they're being sent with a 192.168 source address. The
> TCP stack is apparently unaware of the advanced routing tricks and
> thinks that the packets are going out via the 192.168 gateway.
> 
> IOW I've succesfully re-routed TCP _packets_ but not the TCP
> _connection_.
> 
> How do I tell the TCP stack that it's supposed to use the 172.16
> inteface/gateway for connections to port 80?
> 

Hi,
It's been a while but i believe you want to route via interface not
gateway. Providing more info will make it easier to help you.