Read a switch port's status line to find a shut port, a dead NIC, a duplex mismatch and a speed mismatch

Steps

1. Place two 2960-24TT switches and two PC-PT hosts, and name them S1, S2, PC1 and PC2 on their labels. Cable them as the Links table lists. Use a Copper Straight-Through cable from each PC to its switch: a PC and a switch are unlike devices, so the PC's transmit pins (1 and 2) already land on the switch's receive pins. Use a Copper Cross-Over cable between S1 Fa0/24 and S2 Fa0/24: two switches are like devices, so the crossover swaps pins 1 and 2 with 3 and 6. Leave the light blue Console cable alone: that is the rollover cable for a terminal, not an Ethernet link.

The link lights start amber and turn green after about 30 seconds while spanning tree settles. Click Fast Forward Time at the bottom of the window to skip the wait. 2. Name the switches. On S1's CLI tab:

Switch> enable
Switch# configure terminal
Switch(config)# hostname S1
S1(config)# end

Do the same on S2 with hostname S2. Then on each PC open Desktop > IP Configuration, choose Static, and enter the address and mask from the Addressing table (no gateway is needed: both PCs share one subnet). On PC1, open Desktop > Command Prompt and test:

C:\> ping 192.168.1.12

Expect four Reply from 192.168.1.12 lines (the first may time out while ARP resolves). 3. Take a baseline before you break anything. Read the whole switch, then the inter-switch port in detail:

S1# show interfaces status
S1# show interfaces fa0/24

In the first output, Fa0/1 and Fa0/24 read connected and every other port reads notconnect. In the second, find the status line (FastEthernet0/24 is up, line protocol is up (connected)), the duplex and speed line (Full-duplex, 100Mb/s), and the counter lines: input errors, CRC, runts, giants, collisions and late collision. Write down what each counter would point to if it were rising (lesson 1's list). Then zero them so that new errors would stand out, and press Enter at the confirm prompt:

S1# clear counters fa0/24

4. Fault 1, a shut port. Shut PC1's port:

S1# configure terminal
S1(config)# interface fa0/1
S1(config-if)# shutdown

The ping from PC1 now fails. Read the evidence:

S1(config-if)# do show interfaces status
S1(config-if)# do show interfaces fa0/1

Fa0/1 reads disabled in the status table, and the detail reads FastEthernet0/1 is administratively down, line protocol is down (disabled). Administratively down only ever comes from the shutdown command, so the fix is configuration, not cabling:

S1(config-if)# no shutdown
S1(config-if)# end

5. Fault 2, a far-end NIC that is off. On PC2, open Config > FastEthernet0 and clear the On box next to Port Status. The link light goes red. Read S2:

S2# show interfaces status
S2# show interfaces fa0/1

Fa0/1 now reads notconnect, and the detail reads FastEthernet0/1 is down, line protocol is down (notconnect). Compare it with fault 1: the word administratively is missing, because nothing in S2's configuration changed. notconnect means no link signal, so you check the cable, the jack and the device at the far end. Tick On again and wait for the light to turn green. 6. Fault 3, a duplex mismatch. Hard-code the two ends of the inter-switch link so that they disagree on duplex but agree on speed:

S1# configure terminal
S1(config)# interface fa0/24
S1(config-if)# speed 100
S1(config-if)# duplex full
S1(config-if)# end
S2# configure terminal
S2(config)# interface fa0/24
S2(config-if)# speed 100
S2(config-if)# duplex half
S2(config-if)# end

The link stays up and PC1 can still ping PC2: that is what makes a duplex mismatch hard to spot. Click Fast Forward Time a few times; within a minute CDP prints a %CDP-4-DUPLEX_MISMATCH message on the switch consoles naming Fa0/24. Then read both sides:

S1# show interfaces status
S2# show interfaces status

S1's Fa0/24 shows full and 100, S2's shows half and 100, with no a- prefix on either because both were typed by hand. Say which side would count late collisions (the half-duplex side, S2) and which would count CRC errors and runts (the full-duplex side, S1). Fix it the best-practice way, with auto on both ends (enter configure terminal on each switch first, because the fault block ended with end):

S1(config)# interface fa0/24
S1(config-if)# duplex auto
S1(config-if)# speed auto
S2(config)# interface fa0/24
S2(config-if)# duplex auto
S2(config-if)# speed auto

7. Fault 4, a speed mismatch. Now fix the two ends at different speeds:

S1(config)# interface fa0/24
S1(config-if)# speed 10
S2(config)# interface fa0/24
S2(config-if)# speed 100

This time the link light goes red and the ping between the PCs fails. Read it:

S1(config-if)# do show interfaces fa0/24

The status line reads FastEthernet0/24 is down, line protocol is down (notconnect). Two fixed, different speeds cannot form a link at all, unlike the duplex mismatch, which linked up and misbehaved. Put both ends back to speed auto and wait for the light to turn green. 8. Run the baseline from step 3 again on S1 and S2 and confirm every port you used reads connected with matching duplex and speed on both ends of Fa0/24. Then ping PC2 from PC1 once more.