Day 3: The Server Room

Yesterday, after you fixed the warehouse, Sarah sent you a Network Technician job on her team.

You applied, and two weeks later you had the interview.

This morning, you signed.

Figure 1 - Your new title

Sarah is waiting on the third floor, right by that door you keep looking at.
The door of the network room.

Her badge opens it.

Figure 2 - Behind the door

The room is cold, and forty fans make it very loud.

One rack goes from the floor to the ceiling. Hundreds of cables run into the back of it.

Sarah points at a port near the top: "That cable goes to the warehouse switch you worked on in the first two days."

You ask her how she knows what is connected to what?

"There is a command that tells you what is on the other end of every port. Come and sit down."

Asking the Switch

A switch knows what is plugged into it. Every Cisco device sends its own name and port to its direct neighbours.

That protocol is called CDP.

She runs it on the warehouse switch.

SW-WH1# show cdp neighbors
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
                  S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone,
                  D - Remote, C - CVTA, M - Two-port Mac Relay

Device ID        Local Intrfce     Holdtme    Capability  Platform  Port ID
SW-CORE1         Gig 0/24          142              R S I PMN-L3-24T Gig 1/0/24

Port Gig 0/24 on this switch goes to port Gig 1/0/24 on SW-CORE1.

When a Neighbor Is Missing

Cisco devices send CDP messages every 60 seconds to discover connected neighbors.
Non-Cisco devices or interfaces with CDP disabled won't send messages, stopping network discovery on that port.

An interface where CDP was turned off shows no cdp enable in its configuration.
In the interface configuration, cdp enable turns it back on.

SW-WH1# show running-config interface GigabitEthernet0/6
interface GigabitEthernet0/6
 description OLD-SCALE DECOMMISSIONED
 switchport mode access
 switchport access vlan 30
 no cdp enable
 shutdown

SW-WH1# configure terminal
SW-WH1(config)# interface GigabitEthernet0/6
SW-WH1(config-if)# cdp enable

Figure 3 - The path out of the building

Lab Instructions

Sarah hands you the keyboard: "Start on the third floor switch. Reach every device in the building."

You have one console, on SW-3F-ACC1. You reach everything else over SSH, with the user tech and the password cisco123.

show cdp neighbors detail also prints the IP address of the neighbor. That is the address you connect to: ssh -l tech <ip>.

Sarah gives you the address plan of the building. Every switch has an address in VLAN 99, the management VLAN.

Table 1 - The address plan of the building

The lab:

• Open an SSH session, as tech, on SW-CORE1, R-HQ1, SW-3F-SRV1 and SW-WH1

• One switch is missing from CDP. Find it. And put it back.

• From R-HQ1, ping the management address of the four switches

• Save the configuration on the switch you changed

Finish the lab, then type the flag below.

(PS: there are some hidden routers with a complex architecture behind them, have you found them? Not required to complete the lab.)

Sarah, about the warehouse switch:

"A contractor installed it. He turned CDP off on the uplink, and nobody put it back until today."

She locks the door behind you.

"Six people start on Monday, on the east side of this floor. The desks and the cables are already there, and nothing is connected to the switch."

"I will send you the change tomorrow morning."