[OpenAFS] Network becomes terribly slow when cache manager flushes updates over xDSL

Simon Wilkinson sxw@inf.ed.ac.uk
Wed, 8 Jul 2009 13:12:47 +0100

One interesting project, for someone who's looking to write something  
really useful for OpenAFS, would be to implement path MTU discovery.  
This was original an idea for this year's Summer of Code, and it's  
description there read ...

OpenAFS uses a UDP based RPC transport called Rx. RX uses the endpoint  
maximum transfer units (MTUs) to determine how large a packet may be  
transmitted without requiring the packet to be broken into fragments  
on its journey. The prevalence of IP tunnelling, typically with  
reduced MTUs, on modern internet topographies, means this is often not  
an accurate way to determine true maximum packet size. This project  
would develop and integrate into Rx a mechanism to discover the MTU of  
the path rather than merely the endpoints, resultingly tuning packet  
sizes accordingly.