Chap 35 Remote Procedure Calls RPC allows one host to make a procedure call that appears to be part of a local process (fig 35.1), but is really executed on another machine on the network(fig 35.2).(fig 35.1)(fig 35.2) The host on which the procedure call is executed has resources that are not available on the calling host.

RPC Architecture Client/server relationship between the two hosts Arguments and parameters are passed from local procedure to client stub which passes info to server stub. Arguments are unpacked and passed to server process on server. Results are sent back in reverse(fig 35.3).(fig 35.3)

RPC Examples Sun NFS, mount, and NIS all use remote procedure calls(rpc) and XDR The server resource might be a centralized configuration file (NIS) or a shared file system(NFS) RPC is the session protocol used by both NFS and NIS. RPC may be built on top of TCP or UDP transports. Both NFS and NIS use connection UDP transport. /etc/rpc file contains list of RPC servers (eg.NFS) and their program numbers. Each program may contain many procedures( eg. NFS read block, write block, create file …).

RPC Implementation Each RPC server registers its service with the portmapper (port 111) by informing the portmapper which ports it will listen on for incoming client requests. Ypbind is NIS client; ypserv is NIS rpc server nfs client contacts portmapper(port 111) to find the ports on which mountd(port 33003) and nfsd (port 2049) rpc servers are listening