Cisco® Router Configuration & Troubleshooting, Second Edition

Conclusion

The physical layer is probably the easiest to troubleshoot. It is often not, however, the easiest to diagnose. Cabling problems and hardware degradation can cause bizarre problems that are manifested in the upper layers of the OSI model. It is always a good idea to verify all aspects of the physical layer before moving on to the layers above. It is also a good idea to keep spare hardware onsite to make the troubleshooting process move faster. Cisco will often ask that you swap interface cards when trying to determine the cause of an interface failure. Having Cisco supply replacement hardware usually takes at least a day and sometimes longer. If you have your own spare equipment onsite, you can verify that the existing hardware is ...