datagram queue length

[Jonathan Ellis <jonathan@berkeleydata.net>]

(Posted a few days ago to c.os.l.networking; no replies there.)

I seem to be running into a limit of 64 queued datagrams.  This isn't a
data buffer size; varying the size of the datagram makes no difference
in the observed queue size.  If more datagrams are sent before some are
read, they are silently dropped.  (By "silently," I mean, "tcpdump
doesn't record these as dropped packets.")

This only happens when the sending and receiving processes are on
different machines, btw.

Can anyone tell me where this magic 64 number comes from, so I can
increase it?

Python demo attached.

-Jonathan

# <receive udp requests>
# start this, then immediately start the other
# _on another machine_
import socket, time

sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
sock.bind(('', 3001))

time.sleep(5)

while True:
     data, client_addr = sock.recvfrom(8192)
     print data

# <separate process to send stuff>
import socket

for i in range(200):
     sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
     sock.sendto('a' * 100, 0, ('***other machine ip***', 3001))
     sock.close()