[Beowulf] automount on high ports

Perry E. Metzger perry at piermont.com
Tue Jul 1 07:53:06 PDT 2008

Henning Fehrmann <henning.fehrmann at aei.mpg.de> writes:
> we need to automount NFS directories on high ports to increase the
> number of possible mounts. Currently, we are limited up to ca 360 mounts.

A TCP socket is a 4-tuple of localhost:localport:remotehost:remoteport

A given localhost:localport pair can speak to an unlimted array of
remotehost:remoteport sets. For example, in theory, your SMTP port can
get connections from up to 2^32 different hosts on each of 2^16
different sockets from each, for a total space of 2^48 connections to
a single local socket number. This in no way restricts how many
connections can come in to another port, either, because a given
socket is again the full 4-tuple -- if you have an SSH port, it too
can get 2^48 connections.

Now, there is this (odd) convention that only root can open a socket
below 1024, so hosts "trust" (what a bad idea) sockets under that
number. You can still, however, get up to 1023 connections from any
given remote host to a given local host's port.

Thus, your problem sounds rather odd. There is no obvious reason you
should be limited to 360 connections.

Perhaps your problem is not what you think it is at all. Could you
explain it in more detail?

Perry E. Metzger		perry at piermont.com

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