Administrative distance – Which route is the best?
Administrative distance is the measure used by Cisco routers to help them decide how to select the best path when there’s more that one route to the same destination from different routing protocols. We can say that in this manner administrative distance shows the real reliability of a routing protocol in one system. It shows which routes are more important based on the routing protocol from which they derived. Each routing protocol is prioritized in order of most to least reliable using an administrative distance value. Don’t get confused, a lower numerical value is preferred. For example, an EIGRP with an administrative distance of 90 will be chosen over a RIP route with an administrative distance of 120 and over OSPF route with an administrative distance of 110 to.
Here is a table with all default administrative distances used by Cisco routers:

Sometimes it can happen to you that the VLAN Database is lost when the switch is restarted. This is especially often when working in the lab environment. To help cross this issue you can tell the switch to save the VLAN.dat file to NVRAM instead of storing it to Flash. By default on Cisco switches that are running Cisco IOS the Flash memory is a default place to store VLAN.dat