Day 1 of CCNA class came to an end and it was simultaneously frustrating and exciting. Our fearless leader is a bit of a soft spoken person and I have lost some of my hearing so it was difficult. I asked him to speak up because there are some folks that cannot hear very well. Fortunately, he was very receptive and did so. We got a crash introduction to Cisco’s Packet Tracer application. It’s something you both simultaneously love and hate. It’s not laid out very intuitively so it is going to take a lot of practice. Fortunately I have a lot of time.
I spent the morning building a small, simple network in packet tracer with 3 routers, 3 switches, and 6 PCs. The entire idea is to simulate a main office with 2 branch offices that are actually connected via leased line because VPN is a more advanced topic. Right now we are looking at a simple network. I built out the LAN and WAN links but initially struggled to figure out how to get everything to “talk” to each other. I understand the basics behind routing but my attempts to get RIP working failed. Well, before you learn to run, you must learn to walk.
I began looking at building static routes and started with one of the branch office routers. I got it to successfully talk to the main office and the PCs on the main and 1st branch offices could talk to each other. Once these two offices were comunicating, I went back to the 1st branch and added routing to try and reach the 2nd branch office – no dice. Puzzling through it for about 15 minutes, I realized something I was fundamentally missing. The realization points to the problem being that the 1st branch office has no way to reach a non-specific route, i.e. no default gateway. This was my “Aha!” moment.
With this moment in mind, I removed all of the routing from the 1st branch office’s router and configured that router with the default gateway so it can reach the non-specific routes. So, essentially every route that the 1st branch office doesn’t know about, simply goes to the nexthop which is the next router. On the main office router, I built static routes to both of the 1st and 2nd branch offices. From there, on the 2nd branch office router, I set a default route pointing to the main office router. Now everything communicates.
Lesson learned! When doing static routing in small, basic networks, always start with the router that has the most specific routes. The main office router is essentially the gateway for 3 networks:
- Network connecting the main and 1st branch
- Network connecting the main and 2nd branch
- Network belonging to the main office
Thus, by simply adding a default gateway on both of the branch office routers, we get connectivity between all three locations. I am really loving CCNA so far. I am going to learn a lot about networks that I never knew. I will become a better OpenBSD admin as a result.