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SubjectUDP ports 800-n used by NFS client in 2.2.17
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.

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.

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.

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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