So I did a little search here on the forums and haven't found anything solid solution to my problem yet.

Here goes, the situation. I want a Gateway-to-Gateway (or as IPCop calls Site-to-Site) VPN installation.

RV042 Linksys Gateway
WAN IP: 112.202.70.X (THIS IS IN A DYNAMIC IP)
Local IP: 172.16.0.0/24
Gateway IP: 172.16.0.1
Additional Info: THE FIREWALL OF THE NETWORK (DIRECT INTERFACE TO INERNET)

IPCop v1.4.21
WAN IP: 222.127.117.X (THIS IS A STATIC IP)
Local IP: 192.168.100.0/24
Gateway IP: 192.168.100.254
Additional Info: Same as Above. The FIREWALL of entire NETWORK


TIMELINE
First, I tried OpenVPN ROADWARRIOR (Host-to-Net) following this guide OpenVPN Guide. It worked but the problem is I can't ping from RV042 --> IPCop network BUT ping works in IPCop --> RV042. So I tried to re-read the instructions and found I missed a step from the guide. You can see below that the IP is "192.168.101.0/24". This is the OpenVPN IP I use for the RV042. But I wont explain that since the problem is not that one. eth0 by the way is my LAN Interface for my IPCop network.

/etc/rc.d/rc.firewall.local file
Code:
#!/bin/sh
# Used for private firewall rules

# See how we were called.
case "$1" in
  start)
        ## add your 'start' rules here
    #Added for zerina start - BEGIN
    /usr/local/bin/openvpnctrl --create-chains-and-rules
    #Added for zerina start - END
    #
    # Line below is added to allow Windows PC's access thru the VPN
    iptables -t nat -A CUSTOMPOSTROUTING -s 192.168.101.0/24 -o eth0 -j MASQUERADE
After I did this step it worked. The OpenVPN was a SUCCESS. So from translating the above RED code. I am to translate the RV042 IP that can be understood by my IPCop.

Day 2. SWITCH FROM OPENVpn to ACTUAL VPN
So you might wonder why get VPN when you already got OpenVPN working. Again, my MAIN goal is a SITE-to-SITE VPN. So here goes VPN.

I found numerous sources for this and they were one-way successful just like above issue of OpenVPN. I can't ping from RV042 --> IPCop network BUT ping works in IPCop --> RV042.

so I tried to add a second line for the code above hoping it would work. You may notice below in GREEN (VPN) and RED (OpenVPN). Also notice how I set SOURCE as the ACTUAL IP SUBNET of RV042.

/etc/rc.d/rc.firewall.local file
Code:
#!/bin/sh
# Used for private firewall rules

# See how we were called.
case "$1" in
  start)
        ## add your 'start' rules here
    #Added for zerina start - BEGIN
    /usr/local/bin/openvpnctrl --create-chains-and-rules
    #Added for zerina start - END
    #
    # Line below is added to allow Windows PC's access thru the VPN
    iptables -t nat -A CUSTOMPOSTROUTING -s 192.168.101.0/24 -o eth0 -j MASQUERADE

    iptables -t nat -A CUSTOMPOSTROUTING -s 172.16.0.0/24 -o eth0 -j MASQUERADE
This did not work. I researched more and found many sources.

(1) My most concrete source. But I was not satisfied because he was making rules in the INPUT Chain. I prefer the NAT way. So I research more. (2) Not IPCop but an IDEA nevertheless. So If I understand it right, its the code below.

Code:
iptables -t nat -I REDNAT -j ACCEPT -s 192.168.100.0/24 -d 172.16.0.0/24
NOTE: I HAVENT TRIED THIS YET. I just posted this so I know what you guys think.

(3) I need help explaining this SOURCE

Any help/advice/suggestion is helpful. :cheers: