Unexplained network disconnects can be incredibly frustrating. As a network administrator, troubleshooting these issues quickly is critical to provide users with a reliable connection. This guide will provide an in-depth look at potential causes and solutions for mysterious network outages.
Identify the Scope of the Problem
Before jumping into troubleshooting, it’s important to understand the nature and scope of the disconnects. Here are some key questions to answer:
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Are disconnects widespread or limited to a specific area/group? If the problem is isolated, that points to a more localized issue like faulty cabling or a bad switch port. Widespread problems indicate a problem with core infrastructure like the internet connection, DHCP server, etc.
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How frequent are the disconnects? Frequent, regular disconnects point to an underpowered internet connection or overloaded network equipment. Intermittent issues could be caused by interference or overheating.
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Are wired and wireless networks affected? If wired networks stay online, the problem may be limited to Wi-Fi access points or controllers. Total network failure indicates an issue upstream.
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Can clients reconnect immediately or do connections fail for a prolonged time? The inability to reconnect points to a major outage versus a quick glitch in the network.
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What systems/services are impacted? Disconnects for VoIP phones and access control systems may have different causes than an office PC outage.
Getting clarity on the scope and nature of disconnects focuses troubleshooting efforts.
Check Internet Connectivity
One of the first things to check with widespread connection issues is the internet link itself.
Verify ISP Connection
Log into the core router or firewall and check the status of the external interface connected to the ISP. If the interface status is down or the public IP address is missing, there is an external connectivity problem.
Possible causes include:
- Failed ISP circuit or CPE device
- Loose, damaged, or unplugged cabling
- Power loss to external ISP equipment
- ISP network outage
The ISP line must be repaired or replaced to restore full connectivity.
Confirm DNS Resolution
If the interface status looks normal, test DNS resolution to see if the network can translate domain names to IP addresses:
nslookup example.com
If DNS queries fail, there may be a failure in the recursive DNS servers assigned to the network via DHCP. Work with your ISP to determine the cause of the DNS failure.
Check Internet Routing
Verify that the default route used to send traffic to the internet is present:
show ip route
Missing default routes can occur after router reboots, firmware upgrades, or during network changes. If missing, reconfigure the default route to direct traffic out the ISP-facing interface.
Perform a Path Trace
Run a path tracing utility like traceroute to validate connectivity through the ISP:
traceroute google.com
If the trace completes, routing to the internet is working. Failure indicates a potential ISP or internet backbone issue. Share traceroute results with the ISP to isolate the point of failure.
Review Physical Network
For localized connection problems, inspect the cabling and network ports between devices:
Verify Link Lights
Visually check the link lights on both ends of the network cabling. Solid link lights indicate a functioning cable. No lights or blinking may signify a bad cable, loose connection, or port issue.
Test Cable Continuity
Use a cable tester to confirm that all wires in the cable run have continuity. Look for any open or shorted wire pairs that could cause link failure.
Replace Bad Cables
Replace any damaged cables even if they appear to be working. Intermittent connectivity is hard to troubleshoot and damaged cables often deteriorate over time.
Inspect Network Ports
Closely inspect network ports for any accumulated dust and debris which could cause intermittent contact. Clean ports thoroughly with compressed air. Consider replacing worn or broken port inserts.
Verify Configuration
Ensure port configurations like speed/duplex match on the ends of a link. Auto-negotiation issues can lead to disconnects under load. Hard-code speed/duplex settings if needed.
Evaluate Network Equipment
Network infrastructure like routers, switches, and wireless APs can trigger connectivity problems:
Review Capacity
Adding users, devices, and bandwidth-heavy apps can overload network equipment. Monitor utilization with tools like SolarWinds Bandwidth Analyzer Pack and upgrade capacity before maxing it out.
Verify Power
Loose power cables, faulty power supplies, and switch stack power failures can quickly bring down connectivity. Check power status LEDs and messages on console/SSH.
Update Firmware
Outdated firmware on network devices can cause stability issues leading to disconnects. Check vendor sites for the recommended firmware and upgrade. Schedule regular maintenance windows for firmware updates.
Look for Looping
Switch loops can bring networks down by saturating bandwidth. Check for spikes in traffic between switch ports during disconnect events. Disable redundant links and enable loop protection like Spanning Tree.
Restart Devices
Overloaded network equipment may stop forwarding packets, causing connectivity to drop. Attempt restarting affected devices like routers, switches, and wireless controllers to see if it temporarily restores connectivity.
If rebooting helps, the device requires further troubleshooting when users are offline.
Confirm DHCP Service
DHCP outages can block new devices from joining the network during lease renewal:
Verify Scope Configuration
Log into DHCP servers and validate address pools are adequate for the number of clients. Allocate more addresses if the scope is exhausted.
Monitor DHCP Traffic
Use sniffing tools like Wireshark to check for DHCP requests and responses during a disconnect. Missing DHCP traffic indicates a failure.
Check DHCP Server Status
Monitor DHCP service status and server performance metrics. Restart the DHCP service or service host if issues are detected.
Implement Redundancy
Deploy a backup DHCP server or load balancer so leases can still be handed out if the primary fails. DHCP high availability is crucial to avoid outages.
Inspect Wireless Infrastructure
For Wi-Fi-specific connectivity problems, examine the wireless network:
Scan Available APs
Walk the area with a Wi-Fi scanner tool to spot any missing APs which could explain dead zones. Reset power on downed APs to bring them back online.
Verify AP Channels
APs on overlapping channels can interfere, cutting down wireless bandwidth. Survey channels and adjust to minimize collisions. Leverage 5GHz for additional capacity.
Check Wi-Fi Controller
If APs are online but not forwarding traffic, ping the wireless controller to see if it is reachable. Restart an unresponsive controller.
Validate RF Coverage
Use a wireless survey tool to map RF signal propagation across the facility. Fill any weak coverage zones by adjusting AP placement, power, and antennas.
Upgrade to Latest Standard
Transition older 802.11n/ac networks to Wi-Fi 6 to increase capacity. Support newer client devices and expand network bandwidth.
Leverage Monitoring Tools
Advanced monitoring platforms like SolarWinds Network Performance Monitor provide continuous insight into network health and performance:
Graph Interface Traffic
Chart interface utilization on core routers, switches, and firewalls over time to visualize traffic patterns. Spikes may correlate with disconnect events.
Generate Syslog Alerts
Configure devices to syslog critical events like errors, failures, and redundancy switches that precede outages. Alerts provide real-time notification.
Monitor Ping Latency
Continuously ping internal IPs, DNS servers, and internet sites. Plot latency to show service degradation and outages.
Map Application Traffic
Gain visibility into application traffic flows across the network. Determine the scope of impacted apps during disconnects.
Detect Anomalies
Set dynamic baselines for network traffic. Alert when utilization or errors spike above expected levels as this often indicates trouble.
Conclusion
Troubleshooting network disconnects requires a structured methodology to isolate the root cause. Follow these steps:
- Document the nature and scope of the problem
- Verify internet connectivity and DNS resolution
- Inspect physical cabling and network ports
- Evaluate network devices for faults
- Confirm DHCP services
- Check wireless infrastructure
- Implement monitoring to continuously assess availability
Persistence and process will lead to the source of mysterious network issues. Leverage troubleshooting tools to gain visibility and speed problem identification. With a comprehensive approach, administrators can minimize disruptive disconnections.
