Inbound TCP Circuits over PPP Stall; MTUs and Kppp
Randall R Schulz
rrschulz at cris.com
Tue Sep 28 02:35:53 EST 1999
Thanks to Paul and all the others who responded with information and
At Paul M.'s suggestion, I tried using the "novj" option (only) in my
~/.ppprc file. I made several tests against a few files on a couple
of different servers.
The good news (at least as far as it offers a work-around): It does
appear that disabling Van Jacobsen compression alleviates the symptom.
However, I did also discover that even with VJ compression left
enabled, not all remote hosts experience this problem. As one of my
tests, I transferred a 2.2 Mbyte file from my private ISP's personal
web page site (via the FTP interface to that file area). Two attempts
to transfer that file both succeeded flawlessly even with VJ
compression turned on. That server is "ftp.cris.com." I don't know
for a fact, but I'm guessing that host does *not* run Linux.
On the other hand, transferring files from "ftp.xemacs.org" (a.k.a.
"gwyn.tux.org") is virtually impossible while VJ compression is
enabled but works just fine with VJ disabled. In this case, my guess
is that this host *does* run Linux.
It does also appear to be data related (not surprising if it's a
problem with the implementation of the compression algorithm, whether
in LinuxPPC 2.2.6 or whatever's running on ftp.xemacs.org). In
particular this file:
will stall the TCP circuit after just a few K have been transferred.
I repeated this twice and (like every file I tried) and it does
transfer fine with VJ off.
So, it may be the case that the LinuxPPC code in my kernel is OK (as
evidenced by the fact that connecting to ftp.cris.com works OK) but
that the implementation on ftp.xemacs.org is not correct or fully
compliant with the VJ specification. It's also possible that my
kernel's VJ code has a bug that is somehow tolerated by
ftp.cris.com's VJ code.
Right now, I'm content that I can successfully access the net.
Naturally, the maximum throughput I can get is reduced without VJ
compression, but that's far better than dealing with constantly
One last question: Can I turn VJ compression on and off while a PPP
link is active, or must I choose before connecting?
Thanks again. If there's anything else I can do for people wishing to
investigate further, please just let me know.
Mountain View, CA USA
At 10:14 +1000 9/27/99, Paul Mackerras wrote:
>Randall R Schulz <rrschulz at cris.com> wrote:
>This sounds like the remote system isn't getting the ACKs (or they are
>getting corrupted). Try putting the `novj' option in your ~/.ppprc
>file and see if that makes any difference.
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