It is said that a client maintains a list of guard nodes for certain time for making a circuit. I want to know how many number of guard nodes they make in a list? How often they change these guard nodes and how do they maintain a list from hundred of nodes available?
You can find your EntryGuards in your data directory. If you are using the Tor Browser Bundle, you have the list in
Data/Tor/state. In other cases there will be a
.tor directory in your home directory or similar.
Currently Tor selects 3 EntryGuards per default. This setting may however be changed using NumEntryGuards. There is another option that is called GuardLifetime. According to the manual it is based of what the network consensus is.