Fifteen questions on the whole course, each with an explanation.
Intermediate · 12 min read
Technical definition
Redundant links are additional links between switches that give traffic an alternative path when a cable or switch fails. Because Ethernet frames have no TTL, redundant Layer 2 paths form loops, so switches must either block the extra paths with Spanning Tree or bundle parallel links into one logical link with EtherChannel.
Fifteen questions on the whole course, using the two lab networks: the distribution switch DS1 (Gi1/0/1–2) joined to the access switch AS1 (Gi1/0/23–24) by two uplinks bundled into Port-channel 1, a trunk for VLANs 10 and 20; and router R1 (Gi0/0) on a trunk to SW1 (Gi0/1), routing between PC10 (VLAN 10, 192.168.10.10) and PC20 (VLAN 20, 192.168.20.10) with gateways 192.168.10.1 and 192.168.20.1. If you get one wrong, the explanation names the lesson to go back to.
Predict · scenario 1
1. A loop between three switches has started a broadcast storm on a live network. What is usually the quickest way out?
Predict · scenario 2
2. DS1 and AS1 now form Po1 from both uplinks. What does show spanning-tree vlan 10 show between them?
Predict · scenario 3
3. DS1 uses channel-group 1 mode on and AS1 uses channel-group 1 mode active. What do you expect?
Predict · scenario 4
4. On AS1, show etherchannel summary shows '1 Po1(SD) LACP Gi1/0/23(I) Gi1/0/24(I)'. What is the most likely cause?
Predict · scenario 5
5. AS1 shows 'Po1(SU) LACP Gi1/0/23(P) Gi1/0/24(s)'. Someone typed switchport trunk allowed vlan 10 on Gi1/0/24 only. How do you fix it?
Predict · scenario 6
6. Po1 is made of two 1 Gbps links. One large file transfer runs between two hosts across it. What is the most that transfer can get?
Predict · scenario 7
7. This Catalyst platform allows up to eight active LACP members. A ten-member group shows eight (P) and two (H). Why?
Predict · scenario 8
8. You need to bundle two links from a Catalyst switch to a server from another vendor. Which choice suits it best?
Predict · scenario 9
9. A server behind a data-centre switch running cut-through shows CRC errors, but its own cable tests fine. What is a likely explanation?
Predict · scenario 10
10. show power inline shows 'Gi1/0/4 auto off 0.0 n/a n/a 30.0'. What does it mean?
Predict · scenario 11
11. A PTZ camera needs about 50 W at the device. Which is the lowest power level that can supply it?
Predict · scenario 12
12. PC20 can't ping its gateway; PC10 works. R1's show running-config interface GigabitEthernet0/0.20 shows 'encapsulation dot1Q 21'. What is wrong?
Predict · scenario 13
13. After moving the routing to SW1's SVIs, both SVIs are up/up and each PC can ping its own gateway, but PC10 can't reach PC20. What is missing?
Predict · scenario 14
14. With router-on-a-stick in place, PC10 pings PC20 for the first time. Whose MAC address does PC10 ask for in its ARP request?
Predict · scenario 15
15. An old lab switch in client mode, in the same VTP domain, with revision 50 and only VLAN 1, is connected to a production network at revision 5 (VTP version 2). What happens?