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SubjectRe: UDP ports 800-n used by NFS client in 2.2.17
On Friday December 29, Roy.Hills@nta-monitor.com wrote:
> Does anyone know what causes netstat to show UDP port 800
> as active on a Linux NFS client with 2.2.17 kernel when an NFS filesystem
> is mounted?
>
> Using Debian Linux 2.2 with Kernel 2.2.17 with one NFS filesystem mounted,
> I see
> the following:
>
> rsh@lithium [3]$ netstat -n -a -u
> Active Internet connections (servers and established)
> Proto Recv-Q Send-Q Local Address Foreign Address
> udp 0 0 0.0.0.0:800 0.0.0.0:*
>
> If I unmount the NFS Filesystem, the UDP port disappears.

That will be the local port that is used to talk to the NFS server.

>
> It appears that each NFS mounted filesystem uses a separate UDP
> port, and that they count down from port 800. I.e. the first
> mount uses UDP port 800, the second UDP port 799.
>
> "lsof -i" doesn't show this port belonging to any process, and the "-p"
> option to netstat
> doesn't show any process info either. I assume that this means that it's a
> kernel thing
> rather than a process level thing.
>
> A network sniff while mounting and umounting the NFS filesystem
> doesn't show any traffic on UDP port 800 - I just see portmapper, mountd
> and nfs
> traffic.

While mounting and unmounting you might not (I'm not sure) but while
accessing the filesystem you definately should.
You say that you see "nfs" traffic. Each packet has a source port and
a destintation port. For an NFS request, the destination port will be 2049
on the server, the source port will be 800 (or 799 ...) on the client.

>
> Does anyone know what this is or where I can look in the source for more info?
> I've searched /usr/src/linux/fs/nfs/*.c for 800 and 320 (800 in hex)
> without success.

Check out net/sunrpc/xprt.c:xprt_bindresvport

NeilBrown

>
> Roy Hills
> --
> Roy Hills Tel: +44 1634 721855
> NTA Monitor Ltd FAX: +44 1634 721844
> 14 Ashford House, Beaufort Court,
> Medway City Estate, Email: Roy.Hills@nta-monitor.com
> Rochester, Kent ME2 4FA, UK WWW: http://www.nta-monitor.com/
>
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