Subject: Re: NFS problem.
To: Michael van Elst <>
From: Garrett D'Amore <>
List: current-users
Date: 12/10/2005 10:35:22
Michael van Elst wrote:

> (Matthias Scheler) writes:
>>Yes, but it hasn't changed and never will. Large UDP packets are sent
>>as IP fragments. If you lose one of the IP fragments the whole UDP
>>packet is lost because there is no selective retransmit. When a machine
>>e.g. loses 5% of incoming packets at least one of the IP fragments
>>of a 32KB UDP packet will always get lost. Retries will not help because
>>another single lost packet will prevent the reception of the UDP packet.
>On the other hand, TCP isn't exactly fast with 5% packet loss either.
No, but it still functions.  UDP functions fine in this environment --
if the UDP packets are small.  If the UDP packets are large, you're toast.

>The problem with some older machines however was not some arbitrary
>packet loss but a very specific packet loss caused by back-to-back
>sending of IP fragments. By using TCP or by reducing rsize/wsize to 1k
>the problem goes away.

Garrett D'Amore                
Sr. Staff Engineer          Extending the Power of 64-bit UNIX Computing
Tadpole Computer, Inc.                             Phone: (951) 325-2134