how to force packets to go out on a specific interface

[Julian Elischer]

if you use ipfw then the 'fwd' command CAN be used to force this if you
set up the routes correctly.. you send the packets to addresses that can
only reached through the different interfaces according to the routes
that you have installed..


On Thu, 4 Dec 2003, Maksim Yevmenkin wrote:

> Dear Hackers,
> 
> is there a way to force packets to go out on a specific interface
> based on a source IP address? 
> 
> here is what we want: for testing purposes we have a FreeBSD box with
> two 100Mbit NICs (em0 and em1). both NICs are on the the same subnet
> 172.1.1.x/23. both NICs are connected to the ServerIron. the purpose
> of the setup is to get 200Mbit link between FreeBSD and ServerIron.
> 
> ethernet trunking is NOT an option. it seems ServerIron uses algorithm
> that selects physical port in the trunk based on source and destination
> IP. IPs do not change during the test, so one NIC gets more traffic then
> another (we only have few clients that talk to the FreeBSD box).
> 
> so what is really required is: if a process was bound to 172.1.1.1 (em0)
> then the packets should go out on em0 and if process was bound to
> 172.1.1.2 (em1) then packets should go out on em1. we tried ipfw(8)
> "forward" and it did not do what we want. Linux can handle this via
> "ip route foo bar" thing where we can specify which local source address
> should go out on which interface.
> 
> one more thing: the solution must be compatible with dummynet(4).
> 
> thanks,
> max
> 
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