nfs and rpc

[Maaz]

Again a stupid questions, plz accept appologies.

http is a tcp based protocol
dns is a udp based protocol
i.e normaly in tcp/ip world, almost all application layer protocols are either udp or tcp, ok, but nfs(also an application layer protocol, is'nt ?) is a RPC based protocol.

I wana know so whats the RPC is ? and why some applications(nfs, nis etc) works/rely on rpc, while other doesnt(like http, dns, ssh etc)

plz help
Regards
Maaz

[Ivan Ferreira · Accepted solution]

RPC is a powerful technique for constructing distributed, client-server based applications.

Normally you use RPC for data exchange between a server and a client. Anyway, this runs under tcp or udp protocols anyway.

A portmapper converts RPC program numbers into port numbers.

The portmap daemon converts RPC program numbers into Internet port numbers.

When an RPC server starts up, it registers with the portmap daemon. The server tells the daemon which port number it is listening to and which RPC program numbers it serves. Thus, the portmap daemon knows the location of every registered port on the host and which programs are available on each of these ports.

A client consults the portmap daemon only once for each program the client tries to call. The portmap daemon tells the client which port to send the call to. The client stores this information for future reference.

[Vitaly Karasik_1]

you may read this article http://www.cs.cf.ac.uk/Dave/C/node33.html for in-depth RPC overview

[john kingsley]

TCP & UDP are Transport Layer protocols.

RPC is a Session Layer protocol. It runs on above TCP & UDP.

NFS does run at the Application Layer. Most implementations of NFS can be configured to use either TCP or UDP. Originally NFS only used UDP, but most UNIX implementations of NFS these days are configured to use TCP. By default, redhat still uses UDP.

RPC are "Remote Procedure Calls". They allow a server to define procedures that can be called by programs running on client machines. RPC was developed by SUN and lot of the services that use RPCs (NIS, NFS) were also developed by SUN.

[Maaz]

Millions of Thanks, Dear Mr Ivan Ferreira, Vitaly Karasik, and john kingsley for such a nice help ;)

Just a little more, plz dont mind ;(

>RPC is a powerful technique for constructing distributed, client-server based >applications

ssh(sshd and ssh client) is also a client-server program/app, but why ssh doesnt use RPC ? i.e sshd is running somewhere, and another part of software/app(ssh client) is running on another machine, so why ssh doesnt use RPC ?
http(http server, and web browser) is also a client-server program/app, but why http doesnt use RPC ?

Regards
Maaz

[Vitaly Karasik_1]

probably it's because NFS is trying to implement local filesystem semantic for remote filesystem.

[Ivan Ferreira]

"Sockets" are a pretty low-level network abstraction. You're required to deal with potentially difficult issues like controlling socket handle lifetime, binding address to sockets, resolving human-readable (?) names into address, connecting, etc. Also, the two most common protocols used by applications on the Internet (TCP and UDP) each have some nasty "gotchas" that can make their use challenging.

"RPC" is a higher level protocol. It's also somewhat protocol neutral -- As long as the client and server have some shared/common network protocol installed (and assuming their RPC implementations play nicely) then the two can communicate.