Problem configuring asterisk with 2 interfaces

Iam actually new to this forum.Excuse me for my poor english.

I have been facing Problem configuring asterisk with 2 interfaces.

I built a system with 2 NIC’s.Now I tried to configure the Asterisk with

2 ip’s one public ip and another private ip.This is because,I want remote

office calls to use public ip bandwidth as there are ports blocked in my

LAN.I configured eth0 with public ip and eth1 with private ip.

Iam listening on bind address in sip.conf.Sometimes after reboot

the eth1 ip is not getting up.So the phones registered with that IP are

getting unregistered.

Is my setup correct.Wht could be the ideal setup.

Say If eth0 is down due to maintainence how the traffic will be routed from