[Beowulf] automount on high ports

Bogdan Costescu Bogdan.Costescu at iwr.uni-heidelberg.de
Wed Jul 2 07:12:09 PDT 2008

On Wed, 2 Jul 2008, Perry E. Metzger wrote:

> A given client would need to be forming over 1000 connections to a 
> given server NFS port for that to be a problem.

Not quite. The reserved ports that are free for use (512 and up) are 
not all free to be taken by NFS as it pleases - there are many daemons 
that have to use those well-known ports. F.e. some years ago a common 
complaint was that the CUPS daemon (port 631) was often conflicting 
with NFS client mounts; I think that what was chosen by various 
distributions was the easy way out - make the NFS client only allocate 
ports starting at 650 or so.

> 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). 
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. 
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 

I do encourage you to subscribe to the Linux NFS list if you want to 
learn more; I've been there for a long time (unfortunately not 
anymore...) and the people, especially the developers, were very 

Bogdan Costescu

IWR, University of Heidelberg, INF 368, D-69120 Heidelberg, Germany
Phone: +49 6221 54 8869/8240, Fax: +49 6221 54 8868/8850
E-mail: bogdan.costescu at iwr.uni-heidelberg.de

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