Network Troubleshooting and Configuration Management

Key Steps in Network Troubleshooting

1. Initial Assessment:

   • Identify affected devices.
   • Understand the network configuration before making changes.

2. Accessing Device Configurations:

   • Log into switches, routers, or other devices via web-based console or command line (SSH).
   • Review current configurations and settings.
   • Useful to document configurations before making changes, especially if involved in change control or upgrades.

3. Example Scenario:

   • Accessed a switch's web-based front end, also possible through SSH.
   • Device is in Layer 3 mode (acts as switch and router).
   • Firmware version: 1.3.7.18 (upgraded from 1.3.0.62).
   • Ability to revert to previous firmware if issues arise.

Understanding Routing Tables

1. Role of Routing Tables:

   • Determine where traffic is sent based on destination IP address.
   • Compare incoming traffic against the routing table.
   • Traffic is either forwarded to the next hop or dropped if no match is found.

2. Mapping Network Routes:

   • Create a network map to track packet destinations.
   • Routes can be dynamically created or manually configured.
   • Ensure accuracy in both outbound and inbound routing tables.
   • Avoid routing loops (e.g., Router A sending to Router B and vice versa).

3. Configuration Example:

   • Static routes configuration:
     • Network 10.1.10.0 and 10.1.20.0 are locally connected.
     • Default route (0.0.0.0) to 10.1.10.1.
   • Example: Traffic to 10.10.10.1 follows default route to 10.1.10.1.
   • Examine next hops to trace packet paths effectively.

Troubleshooting Individual Device Interfaces

1. Initial Checks:

   • Check for physical connectivity (link lights, traffic flow).
   • Review interface configurations (duplex settings, speed mismatches).

2. Configuration Verification:

   • Confirm interface settings (SNMP, auto-negotiation, flow control, etc.) match between device and switch.

3. VLAN Configuration Issues:

   • Verify VLAN configurations on the switch per interface.
   • Differentiate between access and trunk interfaces.
   • Ensure devices are connected to correct interfaces or correctly configured VLANs.

Long-Term Analysis and Monitoring

1. Trend Analysis:

   • Monitor network usage trends and baselines over time.
   • Identify patterns and potential problem areas.

2. Utilizing Logs and Data Collection:

   • Use SIM, NetFlow, or other collection mechanisms to gather long-term statistics.
   • Analyze data for errors and anomalies based on time and protocols.