Network troubleshooting entails recognizing and diagnosing network problems with the objective of keeping your network running at peak performance. It requires a technique that begins with the cabling and works through the OSI (Open System Interconnection) reference model to the application layer. Network devices have cables that terminate at wired switches and cabling is a major source of network issues, so they're a perfect place to focus on at the start.
When troubleshooting, the trick is to figure out what's changed just before the problem began. Often it's simply hardware that isn't functioning or some modification was made like a new software installation, a change in equipment configuration or the addition of new employees that's putting added stress on the network.
The problem could be a single issue or several problems that have arisen simultaneously. Begin at the client adapter, ascertain specific symptoms and proceed with troubleshooting from there.
Questions:
Below is a sequence of questions that should be used as guidelines during your troubleshooting procedures:
- 1. Are you able to ping the switch IP address?
- 2. Are you able to ping the router?
- 3. Are you able to ping the DHCP server?
- 4. Can the client obtain an IP address?
- 5. WAN circuit available?
- 6. Any new software recently installed on the client or server?
- 7. Do ALL clients have this problem?
- 8. Is the pattern random or specific?
- 9. Is it a server specific or application specific issue?
- 10. Is the DNS server IP address setting correct?
- 11. Is a firewall filtering traffic?
- 12. Have you ran traceroute and examined routing behavior?
TOOLS:
- A) Windows control panel shows network adapter settings, firewall configuration etc.
- B) Ping and traceroute verify that network routing is working.
- C) Look at the ARP table on the desktop, switch and router confirming the device MAC address is there.
- D) Network packet sniffers examine packet information such as protocols, filtered programs or errors with applications.
- E) Verify change management activities and determine what if any device was changed and how.
- F) Show interfaces at the router will reveal any interface errors pointing to a cable or hardware problem.
- G) Examine router interface utilization patterns.
Check Cables:
Determine if the network problem is affecting a single user, a department, building or city wide by working at the cable level first. A city-wide problem sometimes means a data center outage. An on-site issue often points to a circuit, router or primary switch. A department level issue can mean a problem with their network switch or fiber cabling.
The single user problem might be a plethora of issues from a bad cable to network permissions. It might not be something you do all the time, but having the equipment, supplies and know-how to whip up a network cable on the spot can be very useful.
Because companies often use hundreds of applications, network switches and routers the problem becomes much more complicated when it's a cross department issue. Not all employees have the same network permissions and use a variety of software applications across departments, cities and countries.
Determining who is being affected by the problem can be a critical factor in solving the issue. The ping is a popular tool because it verifies that at the network layer, all is working as it should. In this case, you should then be focusing on application issues. This is not always the case though. Traceroute verifies how packets are traveling between source and destination. You could have packets using non-optimal routing paths and this could be causing performance problems.
Final Note:
Understanding basic network troubleshooting methods in various situations will help you recover quickly on work networks and in the home. By recognizing how network troubleshooting fits into the framework of the OSI model, you can identify at what layer problems are located and which type of troubleshooting tools you need to employ. Using proven strategies for network troubleshooting and following the steps outlined here, you can approach a network problem methodically and resolve it with minimal interference with network users.