Troubleshooting Network

Question 1

In order to troubleshoot network issues, you should troubleshoot using:

Answer 1

OSI Model in reverse order

Question 2

OSI Layer 1 (Physical) may refer to network problems that involve:

Answer 2

• Network cable issues
• Wireless signal issues

Question 3

OSI Layer 2 (Network) may refer to network problems that involve:

Answer 3

• NIC - User has Network connectivity issues
• Switch/Router - All users have Network connectivity issues

Question 4

OSI Layer 3 (Data) may refer to network problems that includes:

Answer 4

• All users complaining of no internet access
• Website being down

Question 5

OSI Layer 4 (Transport) may refer to network problems that involve:

Answer 5

• Firewall issues

Question 6

OSI Layers 5, 6, 7 may refer to network problems that include:

Answer 6

• Operating System (OS) Application issues

Question 7

What 4 steps for troubleshooting a network issue?

Answer 7

1. Check network cable or Wifi signal
2. Check NIC for Link lights
3. IPConfig to confirm settings
4. Ping gateway and other workstations/servers

Question 8

The IPConfig command is used for

Answer 8

• Checking if Default Gateway is correct
• Checking if DHCP is working
• Chekcing if device has APIPA address

Question 9

User complains that “I don’t have Internet but everyone else does”

• What can we safely assume?
• What can be checked and what OSI layer does it belong to?

Answer 9

• Problem is the user PC, not the switch or router
• Check cables/wifi (L1), Check NIC (L2)

Question 10

Some Users (not all) complain that “I don’t have Network access”

• What are 2 possible causes?

Answer 10

• If we have multiple routers/switches, one may be down
• DHCP may have ran out of IPs

Question 11

ALL Users complain that “I don’t have Network access” Assume that WAN access is available, LAN is the problem

• What Layers can we safely assume are NOT the problem and why?

Answer 11

• Layer 1 - Because it is unlikely that all cables and all wireless signals are down
• Layer 3 - LAN access is the problem, not WAN
• Layer 4 - Ports are not suddenly being blocked for everyone

Question 12

ALL Users complain that “I don’t have Network access” Assume that WAN access is available, LAN is the problem

• What Layers can we safely assume COULD be the problem and why?

Answer 12

• Layer 2 - Perhaps the Switch(es) is/are down
• Layer 7 - DNS could be down

Question 13

All users are complaining about Intermittent Internet Issues. What are two possible issues?

Answer 13

• Bad Internet Connection from ISP
• Traffic Congestion on Network

Question 14

What terminal command is used to get DNS information?

Answer 14

nslookup