The Server Message Block (SMB) protocol (which explains the "smb" part of mrxsmb.sys). Two kernel mode components initiate and manage remote connections, mrxsmb.sys and rdbss.sys. Together, these components create a remote session, perform the file system operations you request (e.g., open, close, read, or write a file or spool a print job), and terminate the session when you no longer need the resource. When a system encounters a problem connecting to or accessing a remote resource, you see event log warnings and error messages from mrxsmb.sys. In severe cases, mrxmb.sys crashes with a veritable smorgasbord of stop codes.
Mrxsmb writes event log messages when a network is alive