Packet loss in IP/UDP Stack?

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?

Quoted 19 lines · Martin Rauh

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).

Quoted 2 lines

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.

(quoted diff) +0 -2

-Andi
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