The mentoring continues. Here’s the breakdown for each day since I started with the networking training mind meld picking up where we left off Monday in the Launching post.
We talked a little about IP addressing the day before when we statically assigned a couple addresses to our laptops so we could ping one another. He understood that because we were in the same network he would be able to ping me. I waived away the netmask explanation saying we would cover that later. I didn’t want to wait very long, but I took @rickstah‘s suggestion and started with the OSI model.
Please Do Not Throw Sausage Pizza Away = Physical, Datalink, Network, Transport, Session, Presentation, and Application. The 7-layer burrito of computing.
He was amused by the acronym but I’m hoping it’ll make it stick a little easier. He caught on quick when I started throwing scenarios at him – “if I mess up your IP address, will you be able to play WoW? what layer did I mess with?” / “if you can’t ping your gateway, what’s the first thing you check?” / “if you can’t get to a website, how do you troubleshoot it? what layer of the burrito does your web browser run on?”
We talked about classful addressing and the ranges that used to be the A, B, and C networks. I showed him the corresponding netmasks. We dove into some binary. I was tempted to jump into classless addressing, but decided to save that for the next day. We rounded out with some high level DNS discussion (client -> caching server -> web server). I decided to save all the root server talk for the the next day as well.
I’d let classful addressing simmer overnight. Today it was time to jump into VLSM and subnetting with both feet. We wrote down 24 ones and 8 zeros – “here’s the /24 network we’ve been playing with…” We borrowed a bit from the host side, made the analogy of a quarter having only heads and tails, and then parlayed that into subnets that got smaller and smaller by half as we went to a /30.
By the end of the discussion he was able to subnet a /24 for 3 departments. He listened to the requirements (math is a big department, but science and English don’t need as many addresses) and gave one of them a /25 and the other two got /26′s.
We circled back to DNS and covered CNAME and PTR records with a quick tangent to talk about email delivery so the MX record had a little more context. I told him about the good old days when Network Solutions ran the world, took him through the break up of the registrars, and then hooked in with root servers and authoritative vs non-authoritative queries.
We didn’t get any study in yesterday because I had a ton of work to do. Today we dove right in with a discussion about collision domains – why hubs suck and switches rock. We started some talk about how cables are built and how a straight-through differs from a crossover from a rollover. We covered pin-outs and the colors of the wires and he seemed to have a pretty good concept at this point of transmit and receive.
From there we hit low level half-duplex and hubs as dumb electrical devices – transmit frame, loopback frame, collide or not, CSMA/CD or not, etc. Once we he an appreciation of the suck we hit switches and all their glorious full-duplex multi-collision-domain-per-port goodness.
There was new vocabulary throughout – topology, auto-negotiation, and of course NIC. I tested him on his recollection of the 7 layers of the burrito and with the exception of the session & presentation layers he was able to rattle them off pretty easily. Once I got him to stop contracting ‘do not’ he stopped jumping passed the network layer.