Day 2: Not My Job

Two months have passed since Day 1. You close about forty tickets a week now.

When a ticket has the word network in it, people send it to you.

Figure 1 – Your desk, two months in

Dave, the Helpdesk manager, has seen your numbers: "You are good at tickets. Stay on tickets."

Marcus, your friend, still reads the same book every lunch break, at the desk next to yours.

But... incidents can happen at any time.

At 10:20 AM, every PC in Warehouse A loses the network at the same time.
The network team is already busy on another incident, and a message from Sarah opens on your screen.

Figure 2 – The message that changes your day

You take the console kit from the drawer and cross the parking lot. Dave does not ask where you are going.

You open the switch and look at the ports.

Everything looks good, all the ports are plugged in and there are no errors.

So you go and look at one of the dock PCs. Its address starts with 169.254, and you have never seen an address like that on this network.

Where a PC Gets Its Address

A PC does not choose its own address. When it starts, it asks the network for one, and a server answers. That exchange is called DHCP, in four steps:

Figure 3 – DORA: Discover, Offer, Request, Acknowledge

When Nobody Answers

A PC that asks and gets no answer does not stay without an address. It gives itself one, and that address always starts with 169.254.
It's an APIPA address.

The PC cannot reach anything with that address, but it tells you the PC asked and nobody answered.

So the PC is fine and its cable is fine. The problem is somewhere between the PC and the server.

Figure 4 – The path a Discover must travel

You call Sarah and tell her about the 169.254 address.

"That's APIPA. Check the VLANs on the ports."

You ask her what a VLAN is.

"A separate network inside the switch. Two ports in different VLANs can't talk to each other."

Lab Instructions

The dock PCs are on ports 1 to 4. The printer is on port 5, and it still prints.

• From a dock PC, ping the gateway 10.20.30.1

• On SW-WH1, compare the dock ports with the printer port

• Put the four dock ports back where the printer is

• Ask for an address again (dhcp command on windows), and ping the gateway

Finish the lab, then type the flag below.

The four PCs get an address again and the labels start printing.

That evening, a message from Sarah opens on your screen.

Figure 5 - Sarah's last message of the day

You fill in the form before you go home.

Sarah replies a minute later.

"Come find me in the server room tomorrow morning."