Re: NFSv4 guest opens random ports

[Trond Myklebust <trond.myklebust@primarydata.com>]

On Jan 19, 2014, at 13:27, Justus Ranvier <justusranvier@gmail.com> wrote:

> I have systems running Gentoo Linux mounting shares hosted on a Gentoo
> Linux server. All are running 3.12.8 kernels and using NFS 4.
> 
> I've followed all instructions I can find for fixing everything to a
> static port, but I still see one instance ofrandom port behavior.
> 
> A kernel process (does not display a PID in netstat) on the guests is
> opening listening sockets on random high-numbered ports. The server is
> attempting to contact those guests via random low-numbered ports, which
> my firewall is blocking.
> 
> Despite these packets being blocked, I haven't noticed any adverse
> effects - everything appears to work normally except for my system logs
> on the server being spammed with blocked outgoing connection attempts.
> 
> What is this random port the client is trying to accept connections on,
> and how do I make it listen on a fixed port instead of a random one so
> that I can write useful firewall rules?
> 

That’s probably the NFSv4 callback port. Please see your kernel Documentation/kernel-parameters.txt for how to set the nfs.callback_tcpport kernel/module option.

--
Trond Myklebust
Linux NFS client maintainer