If I didn't mention it before, I tended to skip around in the lessons I went through as it relates to my 1841 Router(s). It's crucial to first understand the Cisco Command Line Interface and the fact that commands you enter will only be recognized if they are entered in the correct user mode. Cisco themselves have provided a brief rundown that can help you get started: https://www.cisco.com/c/en/us/td/docs/switches/wan/mgx/mgx_8850/software/mgx_r3/rpm/rpm_r1-1/configuration/guide/appc.htmlWhile I certainly picked up some skills and was able to get two of my Cisco 1841 routers to ping each other, something was still off. Although they could communicate with each other, I could not reach the web when plugging my laptop into Router 1. Surely, the end-goal of most routers is to connect subnetworks so that users can reach the internet, not just to be able to talk to other devices in the same location. I spent about a week scratching my head over this. I had a straight through cable running from a free port in my ISP router to my Cisco 1841 router. The port lit up green on the ISP router, the port lit up green on it's connecting port to my 1841 (FastEthernet Fe0/0), as I had made sure to enable the interface. Why could I still not reach the internet when plugging my laptop into port Fe0/1 on my 1841??
This is the part of my blog where I absolutely have to give a huge shoutout to the Cisco forum community. If you are serious about truly learning this stuff, you are going to run into issues that you may not be able to figure out, even with the help of Google.
I strongly suggest creating a free account with the Cisco community using the link below:
https://community.cisco.com/t5/technology-and-support/ct-p/technology-support
The Cisco community was able to help me get my 1841 router to work in conjunction with my ISP router and fully connect to the internet (you can see that thread here for the exact commands that needed to be entered). Looking back, this should have been the first thing I figured out how to do. The main issue I was running into was that my ISP router had Network Address Translation set up (which is common for most ISP routers). A VERY in-depth guide to NAT can be found here: https://computer.howstuffworks.com/nat.htm , but just know that my ISP router has a public IP address unique to the entire world and a private IP address that is unique only to the other devices in my home. Because of the fact that NAT was already at play on the ISP router, this required double NATing to be set up via my 1841 router, meaning that yet another private IP address range/subnet (172.16.0.x in my case ) needed to be configured on the Fe0/1 port of which my host computer was plugged into. Fe0/0 needed only to be given an IP address within the already-present private range that my ISP router was giving out. My ISP router (the default gateway) has a private IP address of 192.168.1.1. Because it is directly connected to my 1841 router via Fe0/0, that Fe0/0 port needed only to be assigned the address of 192.168.1.2 to be linked to the default gateway/ISP router. And now, SUCCESS! My laptop plugged in to Fe0/1 can finally reach that little old thing known as the world wide web!
Immediately upon getting online with my home lab, I decided it was a good time to display all my configurations so that I could familiarize myself with what I now know to be the correct configurations to do so. This has helped me immensely in understanding how routers connect networks and in hindsight, should have been among the first things learned. Below, I am going to show you several readouts of my Router config that will hopefully help you understand why it is configured the way it is and how it is reaching the web. I will also provide you with some command prompt information from my host laptop with hope that it will help solidify things further. I have included show running-config, show ip route, show ARP, as well as an ipconfig and a traceroute to google.com ran from my laptop connected to Fe0/1, just to help bring it all home. I've separated each by color to help make it easier to differentiate them. Click the link below to view the pdf of all readouts:
https://drive.google.com/file/d/1FNx7nJTLRjJeHAGw7QfMlWEPrsjMzXYm/view?usp=sharing
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