I have been studying SNMP for a while. I understood SNMP manager can query a particular OID within the managed device's MIB. In order to do that the SNMP manager must know the MIB of the managed device first. I read MIBs are stored in files. Now how does Manager know about the MIB of each devices of the network. Does the manager send a request to the snmp agent for sharing the MIB or it has to be loaded manually?
You have to install and load relevant MIBs to the manager manually. A number of MIBs are standard and come preinstalled with many SNMP solutions, but vendor MIBs for specific devices are often hard or impossible to get, outdated, difficult to find, with the requirements to sign NDAs and whatnot else.
Just downloading the MIB from the device would be a dream that would make working with SNMP actually sufferable...
But: Strictly speaking, you don't need MIBs at all, you can just walk the OID tree and download everything or a specific OID, but of course then you have to play the guessing game what the data actually means.