Help needed in understanding port allocation in NFS

Help needed in understanding port allocation in NFS

[naveen a]

Hi,

I wanted some info related to port selection in NFS.

What happens when the port number is not specified in the command line swit=
ch or configuration=20

file for mountd and statd?

In man pages it is mentioned as statd/mountd will select the port from port=
mapper.=20

Can you please let me know how a port is allotted and the code path in sour=
ce.

What is the criteria for allocation of ports by portmapper ?

Please educate me on this.

Thanks
Naveen
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Re: Help needed in understanding port allocation in NFS

[Neil Horman]

naveen a wrote:
> Hi,
> 
> I wanted some info related to port selection in NFS.
> 
> What happens when the port number is not specified in the command line switch or configuration 
> 
> file for mountd and statd?
> 
> In man pages it is mentioned as statd/mountd will select the port from portmapper. 
> 
> Can you please let me know how a port is allotted and the code path in source.
> 
Thats really the entire point of the portmapper.  When userspace service 
are started up, there is not preset port which is allocated.  The new 
rpc service opens a socket and binds to a system selected port (using 
bindresvport IIRC).  That port value is then registered witht he 
portmapper.  The portmapper always listens on the sunrpc port (port 111 
I think), so that remote clients can query the portmapper daemon for 
which port to connect to to get a specific service.

HTH
Neil


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  *Software Engineer
  *Red Hat, Inc.
  *nhorman@redhat.com
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