Over the weekend, I was establishing a dedicated server on Ubuntu. Although I was able to view my server within the network, I was unable to access the server from outside the web.
Figuring this was a port issue, I decided to investigate on my Linksys WRT54G router.
Unfortunately, this did not resolve my issue. Since I have ruled out that port-forwarding was not the issue, I decided to try something else. The Linksys WRT54G router is capable of establishing a "DMZ" (in reference to Demilitarized Zone) which allows you to expose a specific IP directly to the internet.
1.) Unchecking "Block Anonymous Internet Requests" from Security -> "Firewall"
The real issue was due to the modem provided by my ISP was configured in NAT mode (Network Address Translation) and subsequently blocked outside connections from properly resolving to the IP address of my server. The customer support representative remotely switched my modem from NAT mode to Bridge mode. Bridge Mode forwards the traffic to my router for decision-making as opposed to my modem deciding which traffic was appropriate to pass on to my router.
For example, "18.104.22.168" is an example of an external IP address. "192.168.1.1" is an example of an internal/private IP address. There are specific IP ranges that Internet Service Providers are unavailable to use for public/external IP addresses.
For example, these are the following private IP reservations:
10.0.0.0 to 10.255.255.255 - Class A
172.16.0.0 to 172.31.255.255 - Class B
192.168.0.0 to 192.168.255.255 - Class C
If you are having issues with port-forwarding / external access to your router, check to see if your router displays an IP address that is different from your public IP address. If the IP addresses are inconsistent, call your ISP support to resolve the issue.