[nas-2000] Slow ftp bin transfer problem

  • From: "Alfred Bruckner" <alf_0001@xxxxxxxxxx>
  • To: <nas-2000@xxxxxxxxxxxxx>
  • Date: Wed, 27 Feb 2008 15:08:20 +0100

  we are trying to find a solution for the "slow ftp bin transfer problem"

There is also a German post at the nas2000 forum:

Many users have the problem that ftp download through an internet connection
from the NAS may be very slow.

Test setup:
PC - Internet - ADSL modem - Router - Switch - NAS
Port forwarding (20,21) is configured for modem and router.
I traced the packets sent/received from NAS (connected sniffer with HUB
between Switch and NAS)

What I know already:
- ascii mode transfer is fast, bin mode may be slow
- on local net ftp is fast
- it is caused from too large packets sent from the nas
  NAS always use packet size like if MTU=1500
  e.g. NAS sends two large and one small packet - the two large ones are
  rejected with "fragmentation needed" and the smaller one passes
  --> retransmission...
- MTU setting of ifconfig is ignored by ftp in bin mode
  In ascii mode packet size is reduced accordingly
- MSS setting of route command is ignored
- MSS setting with SocketOptions in proftpd.conf is ignored
- most PPPoE connections need a setting of MTU=1492 because of 8 bytes
  overhead. That corresponds to MSS=1452.
- same behaviour for Tinky and RS Firmware

What I don't know:
- how to tell proftp or the NAS to reduce the packet size as if MTU=1492

Any ideas?

  HWguru (Alfred)

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  • » [nas-2000] Slow ftp bin transfer problem