In this video, Tony Fortunato explains how a router can lose its configuration when rebooted.
I was inspired to put together videos that covered basic networking skills last year, while working with an install team as a lead technician. Everyone on the team had a different level of experience, which is always a challenge.
For example, when I asked someone to retrieve a backup router and reconfigure it, I was told that there something "weird" with the replacement router. When I asked what was wrong, the admins explained that even though they configured the router, the router was ignoring it. I understood right away what the problem was; it's a common one that can trip up inexperienced IT admins. When a router is rebooted or loses power, it can lose the configuration you set. In this video, I demonstrate the problem.
I explained to the install team that some people set the configuration registry to ignore the configuration when storing equipment. Using the show version command, I showed them that the registry was set for 0x2142, which tells the router to ignore the startup configuration. I then used the show startup-config command to prove that the configuration was indeed there. I revealed that the solution is to write config-register 0x2102.
When we reloaded the router, the configuration was no longer ignored. Cisco explains this issue in more detail in a troubleshooting tip.
I always try to figure out if equipment I use is susceptible to this problem in case I ever run into it.
As an aside, when it comes to getting familiar with configuration commands in a Cisco environment, you don’t even need to have the physical equipment. You can use Cisco’s Packet Tracer software to run tests on a simulated network without fearing that you may mess something up.