Cisco troubleshooting follows many of the basic principles of any type of detective work. You need to be predictive, detect anomalies and source out why anomalies occurred. The easiest way through it for many admins is an analysis of the network's Layer 3 path. The goal here is to:
- Cross the network hop by hop.
- Isolate the issue.
- Determine which hop the issues is located in.
- Conduct further analysis for patching the problem.
Cisco devices often repeat the same common issues. While predictability can expedite a diagnosis, the reality is that there are many nuances nested within common Cisco problems that often lengthen the process. The list of common Cisco errors includes:
- Interface speed/duplex issues.
- Incorrect MAC address table predictions.
- Port security and filtering.
- Alignment between access interfaces and VLANs.
- Undefined access VLANs.
- Disabled access VLANs.
- Mismatched trunking operational states.
Of course, troubleshooting requires tools. Cisco has a whole trove of them waiting to help you detect, diagnosis and fix your network infrastructure problem. Look at what's in your kit when troubleshooting a Cisco issue:
- Cisco Discovery Protocol CDP: The Cisco Discovery Protocol CDP sources information from surrounding routers and switches without password access using the self-announcing CDP messages sent between Cisco routers. CPD allows you to discover the device identifier, address list, port identifier, capabilities list and platform. Use the "show cdp command" to see each device listed by line.
- Show Version: Cisco IOS version and release number for IOS software can be fished out while in "privileged exec mode." This reveals the software version, switch uptime, switch platform and processor ID board/serial number.
- Ping: This gives you access to info on reachability, round trip time (RTT) and packet loss using a specific device IP address.
- Traceroute: This tool traces paths between networks to detect issues by triggering timeout messages until the packet hits a "port unreachable" signal.
- Telnet: This is for connecting to remote devices to detect if a remote device is listening to a port.
- Show Interface Command and Interface Status Codes: These status codes determine if interfaces are functioning. While "show interfaces" and "show interfaces description" list line and protocol statuses, "show interfaces status" reports on interface status based on different combinations of line and protocol statuses.
- Cisco Shutdown Command: The "no shutdown command" is used in terminal mode to allow IOS software on the interface. Problematic or maintenance-ready interfaces can be disabled to isolate them from the network.
- Show IP Route: The "IP route command" verifies static routes to differentiate between static and dynamic routes.
Cisco troubleshooting requires a library of mapping and information. Fortunately, getting your Cisco errors handled is simple with DynaSis. Reach out today for network support that lets you streamline a library's worth of troubleshooting required for a smooth, secure network.
