pls help on 3 interfaces

[John Nielsen]

On Wednesday 18 March 2009 10:36:15 pm Lin Zhao wrote:
> hi all, wish my english is enough :-)
> my freebsd has 3 interfaces, like this,
>
>      ----                               ----switch1
>
>          |         ----------  fxp0    |
>          |
>          |        |          |---------
>
> internal |--------|freebsd71 |
>
>          |    rl0 |          |---------
>          |         ----------  fxp1    |
>
>      ----                               ----switch2
>
> we're in the internal and want to visit outside
> we use fxp0 for default outside address and it works well
> but for some reason, i want to use fxp1 for some special outside
> address how can i do for it?
> thanks a lot.

Is the FreeBSD box performing network address translation (NAT)? I'm going 
to assume that it is and everything is being aliased through fxp0. I'm 
also assuming you're using ipfw since you wrote to the ipfw list.

If the IP addresses which you'd like to reach via fxp1 are static, you 
should be able to do something like the following:

Configure static routes on the FreeBSD machine for the the special outside 
addresses using the gateway of fxp1's network as the router.
Configure an additional NAT rule (if still using natd now might be a good 
time to switch to in-kernel ipfw NAT..) to alias through fxp1.
Configure ipfw to direct traffic to/from the special outside addresses to 
the new NAT instance instead of the default.

I actually used a similar setup recently. If you care to confirm my 
assumptions above I can give you a more step-by-step guide.

JN