[Samba] Re: Unusable performance over WAN (part 2)

[James Lamanna]

On 10/8/07, James Lamanna <jlamanna at gmail.com> wrote:
> On 10/8/07, James Lamanna <jlamanna at gmail.com> wrote:
> > On 10/8/07, James Lamanna <jlamanna at gmail.com> wrote:
> > > On 10/7/07, James Lamanna <jlamanna at gmail.com> wrote:
> > > > On 10/7/07, James Lamanna <jlamanna at gmail.com> wrote:
> > > > > On 10/7/07, Volker Lendecke <Volker.Lendecke at sernet.de> wrote:
> > > > > > On Sun, Oct 07, 2007 at 09:31:23AM -0700, James Lamanna wrote:
> > > > > >
> > > > > > > Server sends 1500 byte packet
> > > > > > > Client sends 52 bye ACK
> > > > > > > Server sends 1500 byte packet
> > > > > > > Client sends 52 byte ACK
> > > > > > > etc..
> > > > > > >
> > > > > > > Can anyone think of a reason for this?
> > > > > >
> > > > > > I did not find a link spontaneously, but Windows sometimes
> > > > > > falls back to something that we call "rabbit pellet"
> > > > > > mode. Maybe google shows up something for you.
> > > > > >
> > > > > > Volker
> > > > > >
> > > > > >
> > > > >
> > > > > I actually see that behavior using smbclient from a linux machine, so
> > > > > its not necessarily Windows related.
> > > > >
> > > > > -- James
> > > > >
> > > >
> > > > I've put some tcpdump logs from my macbook up at:
> > > > http://emagiccards.com/james/tcpdump-vpn-logs.tar.bz2.
> > > > It contains 2 files:
> > > >
> > > > vpn-wan.log - Transferring a file from my macbook over the WAN (logged
> > > > in through VPN)
> > > > vpn-nowan2.log - Transferring a file from my macbook not over the WAN
> > > > (logging through VPN)
> > > > (I have separate VPN servers on each size of the WAN).
> > > >
> > > > Here are the smbclient outputs:
> > > >
> > > > No WAN:
> > > > getting file \Jun07.xls of size 2321920 as Jun07.xls (23.8 kb/s)
> > > > (average 23.8 kb/s)
> > > >
> > > > Using WAN:
> > > > getting file \Jun07.xls of size 2321920 as Jun07.xls Short read when
> > > > getting file \Jun07.xls. Only got 1032192 bytes.
> > > > Error Call timed out: server did not respond after 20000 milliseconds
> > > > closing remote file
> > > > (3.9 kb/s) (average 3.9 kb/s)
> > > >
> > > > -- James
> > > >
> > >
> > > I've put up more logs this morning sans VPN.
> > > They are in:
> > > http://emagiccards.com/james/tcpdump-novpn-logs.tar.bz2
> > >
> > > Both of these logs are from being directly plugged in on either side of the WAN.
> > > The 'nowan' log is the normal, fast transfer, whereas the 'wan' log is
> > > over the WAN and has the unusable throughput.
> > >
> > > -- James
> > >
> >
> > Another point of information:
> >
> > Samba (and only Samba, other protocols work fine) seems to drop a lot
> > of packets.
> > Looking at simultaneous tcpdump traces from both the server and client
> > side, I see that lots of packets are dropped that are going from the
> > samba server to the client.
> > The sequence numbers look like this in some cases:
> >
> > Client Recv                        Server Send
> > 1150                                      1150
> > 1152                                      1152
> >                                              1154
> >                                              1156
> >                                              1158
> >                                              1160
> >                                              1162
> > 1164                                      1164
> > 1166                                      1166
> > 1168                                      1168
> > 1170                                      1170
> >
> > So in that case, a whole 5 packets were missed.
> > I'm going to assume this isn't normal behavior, and other protocols
> > (scp / ftp) don't seem to suffer from this problem.
> >
> > -- James
> >
>
> Of course, it could also be tcpdump dropping packets too :)
>

So as it turns out, apparently it was a window scaling issue.
Turning on an excessively large window size on the routers (thereby
enabling dynamic TCP window scaling) seems to have fixed the issue. I
now get transfer rates around 130-160k/s.

-- James