An attempt to generate a large number of session IDs and have a server process them as part of a session hijack attempt is known as what type of attack

An attempt to generate a large number of session IDs and have a server process them as part of a session hijack attempt is known as

TCP Session Hijacking.

Explanation:

TCP Session Hijacking is a cyber-attack in which illegitimate access is acquired to a client's server in the network.  The attacker then hijacks the TCP/IP session by reading and modifying transmitted data packets and also sending requests to the addressee's server.  To achieve this attack effectively, the hacker generates a large number of session IDs, thereby confusing the client's server to process them as a part of the users' sessions. Sessions (a series of interactions between two communication end points) are used by applications to store user parameters and, they remain alive until the user logs off.

that would be my answer.