5.3 Given a scenario, troubleshoot common issues with network services.

Question 1

What is a network loop?

Answer 1

• STP is not enabled (&)
• More traffic is allowed into the network but does not have a clear destination.

Question 2

What is a root bridge selection?

Answer 2

• When starting STP, the bridges elect a root bridge (all other bridges choose the best connection to the root)
• All bridges/switches are assigned a bridge ID between 0 and 61440 (the lowest ID is the root)

Question 3

What is a port role?

Answer 3

• Each bridge assigns a port role to each interface
• (3) role choices:
  – 1. Root
  – 2. Designated
  – 3. Blocked

Question 4

What is port state?

Answer 4

1. Blocking/discarding state (not forwarding to prevent a loop)
2. Listening (not forwarding and cleaning the MAC table)
3. Learning (not forwarding and adding to the MAC table)
4. Forwarding (data passes through and is fully operational)
5. Disabled (administrator has turned off the port)

Question 5

What is the easiest way to determine if you have a route selection issue?

Answer 5

• If packet gets dropped because the route to the destination network does not exist, you will receive “ICMP host unreachable message.” This should be a good indication that you need to check your routes.

Question 6

What is a simple way to resolve a route selection issue?

Answer 6

Default Routes: Adding a static route like this can simplify your routing table as a “gateway of last resort” if the address does not match any other entries.

Question 7

How would you resolve an “Address Pool exhaustion” issue?

Answer 7

1. You would want to check your DHCP server and add more addresses if possible.
2. You may need to decrease the lease time to free up some IP addresses.

Question 8

What is an indication that you have exhausted the address pool on your network?

Answer 8

• The client received an APIPA address (This only uses local subnet communication).

Question 9

What STP issues could arise for switching on a network?

Answer 9

1. STP enabled has NOT be enabled, creating a switching loop on your network.
2. Broadcasts and multicasts are sent to all
3. Nothing at the MAC address level to identify loops.
4. BPDU- Bridge Protocol Data Unit: this interval is every 2 seconds; if (3) of those are missed the link is considered down.

Question 10

What could happen if there is an incorrect VLAN issue with a switch?

Answer 10

• This situation arises when network link is active and IP address is assigned but you do not have access to resources or limited functionality.
• Confirm the specific switch interface has the correct VLAN assignment based on its configuration.

Question 11

How could ACLs affect a switch’s ability to function?

Answer 11

• This situation arises when you have already checked that Clients are working properly, DHCP is assigning correct IP addresses and routing tables look correct, but packets are still getting dropped.
• ACLs would still break the traffic flow

Question 12

When troubleshooting IP configurations, what issues may arise?

Answer 12

1. Incorrect default gateway
2. Incorrect/duplicate IP address
3. Incorrect subnet mask

Question 13

What commands might you use to troubleshoot your IP configuration?

Answer 13

• traceroute/tracert or ping
  1. Ping local IP
  2. Ping default gateway
  3. Ping outside IP address

Question 14

How would you troubleshoot a duplicate IP address?

Answer 14

1. Check your IP addressing (Did you misconfigure?)
2. Ping an IP address before static addressing (Does it respond?)
3. Determine the IP addrss
   - Ping the IP address, check your ARP table and get the MAC address in your switch.