Modem and NIC Gateway

[Zanga Chimombo <z.chimombo@admarc.co.mw>]

i've searched for this topic both online and in the archives but the 
results all seem to have some slight but crucial difference with my 
configuration. e.g. use of firewall

i'm setting up a gateway for use in one of our remote offices. it will 
use a GPRS modem to connect to the outside world and eth0 on the 
internal LAN.

i am connecting to the internet fine using both ppp0 and eth0 interfaces 
_separately_! but setting up the box as a gateway is proving difficult. 
i have set up gateways before but using two NICs, not a NIC and a modem. 
i didn't have to tamper with iptables until later in the configuration. 
i am assuming it is going to be the same in this set up. i want to set 
up routing first.

my ISP is using DHCP and ppp0 gets assigned 172.21.5.136, say and uses 
gateway 172.21.0.1.

i am able to ping 172.21.5.136 but not 172.21.0.1. what do route do i 
need to add?

--

Regards,

Zanga Chimombo
IT Manager
ADMARC
PO Box 5052
Limbe
Malawi

Tel: 01 840 044/500
Fax: 01 840 486