I recently tried to configure my Linux box to be the router (with NAT) for my internal network to the ISP and failed, situation:

1.) dual homed Linux box (eth0, eth1)
2.) eth1 connected to TV cable modem (ISP connection via PPTP)
3.) eth0 connected to internal network (and properly configured, i.e. my internal network is: 192.168.76.0, 255.255.255.0, internal default gw: 192.168.76.1=eth0)

I'm using:
a) pppd 2.4.1
b) pptp 1.4.0
c) dhcpcd 1.3.22

My ISP requests me to use DHCP to get a local IP (+name servers+def.gw), which is my biggest problem using pppd.

Question #1: How do I configure pppd to perform the following steps:

step 1) issue a DHCP request to configure eth1 with a local IP, get name servers, establish default routing
step 2) force pppd to get p-t-p IP and to establish link eth1 <-> ppp0 using the 'pty' option to execute pptp for authentication
step 3) [already solved]: netfilter configuration (done in /etc/ppp/ip-up)

Question #2: What happens to ppp0 when DHCP lease (1 day) expires?
Question #3: Is is possible for pppd to issue a new DHCP request when DHCP lease expires?

Thanks in advance for your help.