[OpenAFS] afs: Lost contact with file server xxx.xxx.xxx.x

[Jeffrey Altman]

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TIARA System Man wrote:
> hi guys,
> 
> can anyone tell what is wrong with "Lost contact with file server " 
> issue? that afs clinet is not in the same domain of afs server. the 
> connection speed is up to 16MB/sec.

Sounds like NAT bouncing to me.  The NAT device keeps timing out the
port mappings and therefore the RX connections in use with the old 
mapping become invalid but neither side of the RX connection is able to 
notice.

Client sends to file server.  File server sees message from an existing 
IP address/port value arrive from a new IP address/port value and 
therefore responds to the original IP address/port value in order to 
prevent hijacking attacks.

The NAT blocks the reply sent to the old port value.

The client thinks the file server is not responding and marks the file 
server as down.

The client later probes the down servers with a new RX connection and 
that succeeds, so the server is marked up.

This was fixed in the Windows cache manager by always retrying RPCs sent 
on an existing RX connection that timed out once with a new RX 
connection.  I am not sure that a similar change was ever made to the 
UNIX cache manager.

Jeffrey Altman



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