Re: Packet loss in IP/UDP Stack?

[Andi Kleen]

On Fri, Jan 26, 2001 at 07:01:12PM +0100, Martin Rauh wrote:
> Hi folks,
> 
> It seems that we are loosing packets in the UDP stack.
> Somebody might think that this is not astonishing, but
> the packets are not lost at the network layer. They seem to get
> lost in the IP/UDP Layer of the receiving box.
> 
> We have got the following configuration:
> Two linux boxes (P4, 733 MHz, 256 MB RAM, kernel 2.4.0)
> are directly connected with two syskonnect sk98xx
> gigabit ethernet cards. We are sending a file from one host to the other
> 
> with UDP. About half of the file is lost in the receiving application.
> But according to the statistics in /proc/net/dev no errors (fifo, frame,
> dropped...)
> occured in the network layer. Even the transmitted and received
> data at the network layer (tx-bytes, -packets) are identical
> to the amount of the transfered file (plus network overhead).
> 
> Doas anybody know where the loss occurs? Is there a loss at the
> network layer or in the higher protocol layers?
 
UDP by default has 64K buffer and drops packets when it overflows.
You can check that using netstat -s. 
You can increase it use the SO_{SND,RCV}BUF socket options and/or the 
net/core/[rw]mem_* sysctls.

-Andi