Re: Nfs over tcp retries
- From: Peter Staubach <staubach@xxxxxxxxxx>
- Date: Mon, 05 Mar 2007 11:31:29 -0500
Andy Chittenden wrote:
Here's a sequence of packets captured at the end of a NFS connection and
the start of the next for a RH Fedora Core 6 client:
# cat ~/tmp/28852a.txt
...
As you can see in packet 3, the nfs server's sent a FIN-ACK which is
acknowledged in packet 6 by the client. So by packet 8, the connection's
closed. The client attempts to reconnect to the server in packet 8 which
is refused by the server in packet 9 as the client is using the same
port number as the previous session: the server's in TIME WAIT from the
previous connection and the initial send sequence number of this new
connection is below the highest sequence number of the previous
connection. The client's attempts to reconnect continue unsuccessfully
until 2MSL is exceeded.
So, a few questions:
* why does the NFS client reuse the same source port number (894 in the
example above)?
* if the socket's being reused, why is the ISS being chosen such that
it's within the same range as the last successful connection?
* why does the ISS seem to go up by only 3 since the last attempt to
connect?
If the linux NFS client had used a different source port number or
chosen an out-of-range ISS, then its reconnection attempts would have
been successful in a more timely manner.
I suspect that the NFS client attempts to reuse the same port number
for the new connection so that it does not invalidate the duplicate
request cache on the server. NFS servers typically use the entire
IP address of the client, including the port number, when performing
the tests to check to see if the current request is the duplicate of
a previous request.
ps
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- Nfs over tcp retries
- From: Andy Chittenden
- Nfs over tcp retries
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