[Beowulf] automount on high ports

Perry E. Metzger perry at piermont.com
Wed Jul 2 07:35:45 PDT 2008

Bogdan Costescu <Bogdan.Costescu at iwr.uni-heidelberg.de> writes:
>> Every machine might get 1341 connections from clients, and every
>> machine might make 1341 client connections going out to other
>> machines None of this should cause you to run out of ports, period.
> With all due respect, I think that you are not quite familiar with the
> NFS implementation on Linux (and maybe other NFS
> implementations).

I'm plenty familiar with the implementations on other OSes. I only
looked at the code on Linux this morning for the first time (never had
call before)...

> What you describe is the theoretical use of TCP
> connections; the way NFS on Linux uses TCP is not quite as you
> imagine: there is one port taken on the client for each NFS mount and
> that port is not reused.

That's not an NFS implementation issue. It is a TCP implementation
issue. (Actually, I'm currently looking at the code and it may be an
issue in the rpc code, but never mind that.)

In general, the OS should let you use a given port to connect to as
many remote hosts as you like. The only thing it should prevent is
having you talk to a single remote host/port combination from one
local port (because you can't -- that would be the same 4-tuple.)

> Also mounting 2 different mount points from
> the same NFS server to the same NFS client uses 2 TCP ports on the
> client side - at least with NFS v2 and v3; for v4 I think that there
> is only one connection between a client and a server independent on
> the number of mount points.

That is indeed correct. (Actually, linux can burn more than 2 ports,

Perry E. Metzger		perry at piermont.com

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