One NIC for LAN, another NIC for SIP

What is the best way for me to setup my Asterisk PBX using one network card for the internal network and another network card for the SIP gateway.

I’m using a Cisco 878 SHDSL router. One port on it is configured to connect to my SIP provider.

Anyone using this kind of setup?

[Asterisk will be running on Debian 4.0]

my asterisk server runs with dual NICs… basicilly I have it set up where 1 NIC is a public IP and is used for my SIP provider and the other NICis for the LAN… the main thing is making sure the WAN NIC is on a different subnet than the LAN NIC if you are wanting all SIP traffic to go out the WAN NIC… and then the default gateway of your machine should be the WAN NIC and not the LAN NIC…

I have a similar setup asterisk w/ 2 nic: 1 lan and 1 wan.

LAN ( - computers and ip phones register to this IP so that it doesnt have to go out of the wan and comes back again in WAN.

WAN (public ip) - if we’re outside the office and at the same time registers to the service provider.

im really sure if this is working the way i want it to work. somebody told me to check the routing as well. It might be sending the calls to the default gateway of the LAN instead of the WAN nic.