Navigating Common Network Troubleshooting Scenarios

SCENARIO

QUICK FIX

PREVENTIVE MEASURE

Duplicate IP Addresses: When two devices attempt to share a single IP, you see the dreaded "Address Already in Use" Kill — with no ability to access the network.

If you've just introduced a new device or server to your network, it may have its own DHCP server. Simply disable the DHCP server on that device to restore sanity to your network.

Modify your router's configuration to begin assigning DHCP addresses near the top end of your subnet, leaving the lower addresses available for devices that require static IPs.

IP Address Exhaustion: To troubleshoot this issue, use the ipconfig command. If the workstation has assigned itself an IP address that begins with 169.x.x.x, it means that no IP address was available from the DHCP server.

The solution to this is to purchase either a standalone router or WiFi access point with an integrated router. This creates your own local pool of internal addresses, ensuring you won't run out.

It's important that any internet-connected network have a local router in operation with NAT and DHCP, both for security reasons and to prevent IP address exhaustion. The router needs to be the only device connected to the modem, with all other devices connecting through the router.

DNS Problems: Errors such as The Network Path Cannot Be Found, IP Address Could Not Be Found, or DNS Name Does Not Exist, can usually be traced to a DNS configuration issue. 

The command line utility nslookup can be used to quickly show a workstation's DNS settings.

Your local router might be configured to operate as a DNS Server, creating a DNS pass-through to your ISPs servers. On busy networks, this may overload the capabilities of the router. Change your network's DHCP settings to directly access your DNS servers.

Single Workstation Unable to Connect to the Network: If only a single workstation is displaying the "No internet" message when opening a web browser, we can usually assume that the rest of the network is healthy and turn our attention to any hardware and software that is particular to this system.

To resolve this network issue, start by eliminating the obvious communication barriers such as a bad cable, poor WiFi signal, failing network card or incorrect drivers. Ensure that the workstation's network adapter is configured with the correct IP, subnet, and DNS servers.

It's usually best to leave all workstation TCP/IP settings to "Automatically assigned." Use a DHCP server to hand out a uniform configuration to all devices on the network. If a static IP is needed on a particular workstation or server, most DHCP servers allow the ability to create static IP mappings.

Local Network is Unable to Connect to the internet: This situation can either be intermittent or persistent. Oftentimes, the most difficult aspect of dealing with any  external network problem is finding the company responsible. And then tasking them to solve the issue, particularly with intermittent failures that are difficult to trace. It can sometimes be such a problem that organizations will have to switch internet providers in order to solve the issue.

A router and modem reboot is the first order of business. The tracert then utility can be used to identify communication breaks. It will clearly hiccup on the particular router hop that is causing the problem. Contact your ISP with your findings, providing screenshots as necessary.

To avoid the finger-pointing that can prevent rapid resolution of external issues, do some research to ensure that you procure connectivity only from local Tier 1 providers. Other ISPs are more than happy to sell you service, however, they are simply piggybacking the Tier 1 connection, since they don't actually own the infrastructure in your area.