Arlon's CSUMB Intro to Computer Networks CST-311 Module 7 Learning Journal #7/#39 for the week Wed 10/12-Tues 10/19, year 2021

Arlon's CSUMB Intro to Computer Networks CST-311 Module 7 Learning Journal #7/#39 for the week Wed 10/12-Tues 10/19, year 2021

The topics this week are ARP, DHCP, subnetting, CRC calculations for error checking, layer 2, link layer, frames, wireshark, python, mininet, arp tables, subnet addresses, and the subnetting in particular I've been waiting for, so although I'm currently a hair stuck getting out group project to work, I'm super excited about that simultaneously because then once I get it hopefully I'll have something new figured out - it's something with adding routes, I'm not doing that right (yet).

Group work is going great and we are trucking through out second week of designing a dhcp network with multiple subnets, routing table additions, python scripted mininet topology and plenty of built-in puzzles to figure out to make it all super fun. CodeAnywhere is working out as a decent team-online-IDE. It's not perfect (we observe you have to manually hit save because it usually saves, but doesn't always, and the official auto-save feature also activates auto-type-whatever-it-wants-all-by-itself simultaneously, obviously not helping, so we just hit save often. Story of my life, right?) but is the best we know of, being like a Google Docs form of what I've been told Visual Studio looks like. In other words it's like Google Docs in that documents can be simultaneously edited by multiple people on the internet and like VS in that it's an IDE with code hiliting, code folding, AND you get a console, you can actually run stuff in it.

Family stuff got really heavy this week, with a 97 year old bed ridden dad, but I've been dying to understand subnetting and that's what we're working on in class, so as always I feel like the material is gold and super excited to be finally digging in to these super applicable topics. I'm going to have to cut this journal a hair short because I'm a little stuck on add route in the python mininet network script adding routes so pingall works so I'm doing a minimal journal here and then I'm going to hit that until I figure it out, short length of journal to be made up for, next week.

Update - Wednesday, day after: I nailed it - a few hours of doing, redoing, doing again, doing smaller, doing differently, checking examples, and I finally found one thing I was completely missing that brought it all together - when you link routers you link two interfaces and two interface labels and two ip addresses, unlike when you link switches you just add one interface. For at least one of the routers, when you link more than one, depending. I found in one place I could add the second interface or not, it worked either way. But for at least one, you need to add a link with two ends to it, not shown in any examples, you have to extrapolate or find an obscure example to figure it out. A stack overflow page I found had that on it, which was how I found out eventually. Google search '(mininet) How to create a topology with two routers and their respective hosts' and that is the page that had the missing peice to the puzzle that made everything click and get everything connected, specifically the line right below where it says ' # Add router-router link in a new subnet for the router-router connection'.... Once I saw that was the missing peice the entire puzzle fell together and we got it all figured out. Adding routes isn't too tricky, a few other tricks I used to figure it all out was running [device] ifconfig to see if the right interfaces had the right ip addresses and also [device] ip route show to make sure the routes were all in place. After hours of working on it, these two tools really showed themself. You can just stare at it and run pingall over and over again to see it isn't working, or you can get additional clues with ifconfig and ip route show. When it's not working you can see there's missing ip addresses or missing routes, and normally that leads you to an inconsistency in the python script you can fix and that process made it work 100%. Very exciting. Now I can create software defined networks, and my next question is, how do I actually....I want to use that as a tool for something but I'm not exactly sure what to do with it yet - but it 's super awesome, for learning network testing, if nothing else.

Thanks for reading!