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Any Questions?. Chapter 10-Ethernet Switch Troubleshooting. Perspectives on Network Verification and Troubleshooting Verifying the Network Topology with Cisco Discovery Protocol Analyzing Layer 1 and 2 Interface Status Analyzing the Layer 2 Forwarding Path with the MAC Address Table.

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  1. Any Questions?

  2. Chapter 10-Ethernet Switch Troubleshooting • Perspectives on Network Verification and Troubleshooting • Verifying the Network Topology with Cisco Discovery Protocol • Analyzing Layer 1 and 2 Interface Status • Analyzing the Layer 2 Forwarding Path with the MAC Address Table

  3. Do I know this? Go through the Quiz- 5 minutes

  4. Imagine that a switch connects via an Ethernet cable to a router, and the router’s hostname is Hannah. Which of the following commands could tell you information about the IOS version on Hannah without establishing a Telnet connection to Hannah? a. show neighbor Hannah b. show cdp c. show cdp neighbor d. show cdp neighbor Hannah e. show cdp entry Hannah f. show cdp neighbor detail

  5. Imagine that a switch connects via an Ethernet cable to a router, and the router’s hostname is Hannah. Which of the following commands could tell you information about the IOS version on Hannah without establishing a Telnet connection to Hannah? a. show neighbor Hannah b. show cdp c. show cdp neighbor d. show cdp neighbor Hannah e. show cdp entry Hannah f. show cdp neighbor detail Answer: E& F

  6. 2. Which of the following CDP commands could identify a neighbor’s model of hardware? a. show neighbors b. show neighbors Hannah c. show cdp d. show cdp interface e. show cdp neighbors f. show cdp entry hannah

  7. 2. Which of the following CDP commands could identify a neighbor’s model of hardware? a. show neighbors b. show neighbors Hannah c. show cdp d. show cdp interface e. show cdp neighbors f. show cdp entry hannah Answer: E & F

  8. 3. The output of the show interfaces status command on a 2960 switch shows interface Fa0/1 in a “disabled” state. Which of the following is true about interface Fa0/1? a. The interface is configured with the shutdown command. b. The show interfaces fa0/1 command will list the interface with two status codes of administratively down and down. c. The show interfaces fa0/1 command will list the interface with two status codes of up and down. d. The interface cannot currently be used to forward frames. e. The interface can currently be used to forward frames.

  9. 3. The output of the show interfaces status command on a 2960 switch shows interface Fa0/1 in a “disabled” state. Which of the following is true about interface Fa0/1? a. The interface is configured with the shutdown command. b. The show interfaces fa0/1 command will list the interface with two status codes of administratively down and down. c. The show interfaces fa0/1 command will list the interface with two status codes of up and down. d. The interface cannot currently be used to forward frames. e. The interface can currently be used to forward frames. Answer: A, B & D

  10. 4. Switch SW1 uses its gigabit 0/1 interface to connect to switch SW2’s gigabit 0/2 interface. SW2’s Gi0/2 interface is configured with the speed 1000 and duplex full commands. SW1 uses all defaults for interface configuration commands on its Gi0/1 interface. Which of the following is true about the link after it comes up? a. The link works at 1000 Mbps (1 Gbps). b. SW1 attempts to run at 10 Mbps because SW2 has effectively disabled IEEE standard autonegotiation. c. The link runs at 1 Gbps, but SW1 uses half duplex, and SW2 uses full duplex. d. Both switches use full duplex.

  11. 4. Switch SW1 uses its gigabit 0/1 interface to connect to switch SW2’s gigabit 0/2 interface. SW2’s Gi0/2 interface is configured with the speed 1000 and duplex full commands. SW1 uses all defaults for interface configuration commands on its Gi0/1 interface. Which of the following is true about the link after it comes up? a. The link works at 1000 Mbps (1 Gbps). b. SW1 attempts to run at 10 Mbps because SW2 has effectively disabled IEEE standard autonegotiation. c. The link runs at 1 Gbps, but SW1 uses half duplex, and SW2 uses full duplex. d. Both switches use full duplex. Answer: A & D

  12. 5. The following line of output was taken from a show interfaces fa0/1 command: Full-duplex, 100Mbps, media type is 10/100BaseTX Which of the following is/are true about the interface? a. The speed was definitely configured with the speed 100 interface subcommand. b. The speed may have been configured with the speed 100 interface subcommand. c. The duplex was definitely configured with the duplex full interface subcommand. d. The duplex may have been configured with the duplex full interface subcommand.

  13. 5. The following line of output was taken from a show interfaces fa0/1 command: Full-duplex, 100Mbps, media type is 10/100BaseTX Which of the following is/are true about the interface? a. The speed was definitely configured with the speed 100 interface subcommand. b. The speed may have been configured with the speed 100 interface subcommand. c. The duplex was definitely configured with the duplex full interface subcommand. d. The duplex may have been configured with the duplex full interface subcommand. Answer: B & D

  14. 6. Switch SW1, a Cisco 2960 switch, has all default settings on interface Fa0/1, the speed 100 command configured on Fa0/2, and both the speed 100 and duplex half commands on Fa0/3. Each interface is cabled to a 10/100 port on different Cisco 2960 switches, with those switches using all default settings. Which of the following is true about the interfaces on the other 2960 switches? a. The interface connected to SW1’s Fa0/1 runs at 100 Mbps and full duplex. b. The interface connected to SW1’s Fa0/2 runs at 100 Mbps and full duplex. c. The interface connected to SW1’s Fa0/3 runs at 100 Mbps and full duplex. d. The interface connected to SW1’s Fa0/3 runs at 100 Mbps and half duplex. e. The interface connected to SW1’s Fa0/2 runs at 100 Mbps and half duplex.

  15. 6. Switch SW1, a Cisco 2960 switch, has all default settings on interface Fa0/1, the speed 100 command configured on Fa0/2, and both the speed 100 and duplex half commands on Fa0/3. Each interface is cabled to a 10/100 port on different Cisco 2960 switches, with those switches using all default settings. Which of the following is true about the interfaces on the other 2960 switches? a. The interface connected to SW1’s Fa0/1 runs at 100 Mbps and full duplex. b. The interface connected to SW1’s Fa0/2 runs at 100 Mbps and full duplex. c. The interface connected to SW1’s Fa0/3 runs at 100 Mbps and full duplex. d. The interface connected to SW1’s Fa0/3 runs at 100 Mbps and half duplex. e. The interface connected to SW1’s Fa0/2 runs at 100 Mbps and half duplex. Answer: A, B & D

  16. 7. A frame just arrived on interface Fa0/2, source MAC address 0200.2222.2222, destination MAC address 0200.2222.2222. (The frame was created as part of a security attack; it is not normal to see frames with the same source and destination MAC address.) Interface Fa0/2 is assigned to VLAN 2. Consider the following command output: SW2#show mac address-table dynamic Mac Address Table ------------------------------------------- Vlan Mac Address Type Ports ---- ----------- -------- ----- 1 0200.1111.1111 DYNAMIC Gi0/2 1 0200.2222.2222 DYNAMIC Fa0/13 Total Mac Addresses for this criterion: 2 Which of the following describes how the switch will forward the frame if the destination address is 0200.2222.2222? a. The frame will likely be flooded on all other interfaces in VLAN 2, unless the switch has a static entry for 0200.2222.2222, VLAN 2, in the MAC address table. b. The frame will be flooded out all other interfaces in VLAN 2. c. The switch will add an entry to its MAC address table for MAC address 0200.2222.2222, interface Fa0/2, and VLAN 2. d. The switch will replace the existing entry for 0200.2222.2222 with an entry for address 0200.2222.2222, interface Fa0/2, and VLAN 2.

  17. 7. A frame just arrived on interface Fa0/2, source MAC address 0200.2222.2222, destination MAC address 0200.2222.2222. (The frame was created as part of a security attack; it is not normal to see frames with the same source and destination MAC address.) Interface Fa0/2 is assigned to VLAN 2. Consider the following command output: SW2#show mac address-table dynamic Mac Address Table ------------------------------------------- Vlan Mac Address Type Ports ---- ----------- -------- ----- 1 0200.1111.1111 DYNAMIC Gi0/2 1 0200.2222.2222 DYNAMIC Fa0/13 Total Mac Addresses for this criterion: 2 Which of the following describes how the switch will forward the frame if the destination address is 0200.2222.2222? a. The frame will likely be flooded on all other interfaces in VLAN 2, unless the switch has a static entry for 0200.2222.2222, VLAN 2, in the MAC address table. b. The frame will be flooded out all other interfaces in VLAN 2. c. The switch will add an entry to its MAC address table for MAC address 0200.2222.2222, interface Fa0/2, and VLAN 2. d. The switch will replace the existing entry for 0200.2222.2222 with an entry for address 0200.2222.2222, interface Fa0/2, and VLAN 2. Answer: A & C

  18. 8. Which of the following commands list the MAC address table entries for MAC addresses configured by port security? a. show mac address-table dynamic b. show mac address-table c. show mac address-table static d. show mac address-table port-security

  19. 8. Which of the following commands list the MAC address table entries for MAC addresses configured by port security? a. show mac address-table dynamic b. show mac address-table c. show mac address-table static d. show mac address-table port-security Answer: B & C

  20. Any Questions?

  21. Perspective on Verification and Troubleshooting • Finding configuration problems • Look at configs • Use show commands • Check status • Simlets • Show and debug commands

  22. Organizaed Troubleshooting • What would be normal • IP, subnet, gateways • Routing • Switch ports • Speed, duplex, security • Isolate Problem • Root Cause • What could cause this problem

  23. Going down the layers

  24. Layer 3, 2, 1 • Check IPs • Check gateway • Check MAC addresses

  25. Any Questions?

  26. Troubleshooting topics • CDP • Interface Status • Analyzing where frames will go

  27. Cisco Discovery Protocol • Critical Troubleshooting tool • Device identifier: Typically the hostname • Address list: Network and data-link addresses • Local interface: The interface on the router or switch issuing the show cdp command with which the neighbor was discovered • Port identifier: Text that identifies the port used by the neighboring device to send CDP messages to the local device • Capabilities list: Information on what type of device it is (for instance, a router or a switch) • Platform: The model and OS level running in the device

  28. CDP • Broadcast or multicast at layer 2 • Commands • Sh cdp neighbors [type number] • Sh cdp neighbors detail • Show cdp entry name

  29. CDP • On by default • Disable on interface of globally • No cdp enable • Interface • No cdp run • global

  30. Check CDP status • Sh cdp • Is it on • Sh cdp interface [type number] • Up and holdtime on that interface • Sh cdp traffic • List stats about cdp

  31. Any Questions?

  32. Layer 1 and 2 status • Show interfaces command • See details about the interfaces • Protocol status and line status

  33. Speeds and Duplex • Can autoconfigure or manual • Show interfaces status • Show the speed, duplex and connection status • If speed and duplex are auto • a-full is the duplex column • a-100 in the speed column

  34. Switchport default behaviors • If the speed is not known, use 10 Mbps, half duplex. • If the speed is somehow known to be 10 or 100 Mbps, default to use half duplex. • If the speed is somehow known to be 1000 Mbps, default to use full duplex.

  35. Any Questions?

  36. Common Error causes • EMI or physical cable damage • Can see errors-CRC/FCS errors • Show interfaces will show the details of errors and collisions

  37. Common Errors SW1#show interfaces fa0/13 ! lines omitted for brevity Received 284 broadcasts (0 multicast) 0 runts, 0 giants, 0 throttles 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored 0 watchdog, 281 multicast, 0 pause input 0 input packets with dribble condition detected 95226 packets output, 10849674 bytes, 0 underruns 0 output errors, 0 collisions, 1 interface resets 0 babbles, 0 late collision, 0 deferred 0 lost carrier, 0 no carrier, 0 PAUSE output 0 output buffer failures, 0 output buffers swapped out

  38. Layer 2 forwarding path • Show mac address-table • See what is in the table • Can also limit to just dynamic entries

  39. Any Questions?

  40. Understanding what should happen • Step 1 Determine the VLAN in which the frame should be forwarded. On access interfaces this is based on the access VLAN associated with the incoming interface. • Step 2 Look for the frame’s destination MAC address in the MAC address table, but only for entries in the VLAN identified in Step 1. If the destination MAC is... • A. Found (unicast), forward the frame out the only interface listed in the matched address table entry. • B. Not found (unicast), flood the frame out all other access ports (except the incoming port) in that same VLAN. • C. Broadcast or multicast, flood the frame out all other access ports (except the incoming port) in that same VLAN.

  41. Port Security • As from last chapter • Port security behaviors

  42. Any Questions?

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