Inbound TCP Circuits over PPP Stall; MTUs and Kppp
mlan at cpu.lu
Tue Sep 28 05:57:52 EST 1999
On 27 Sep, this message from Randall R Schulz echoed through cyberspace:
> 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.
> 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.
OK, I saw similar things as well. I had more trouble with the
ftp.linuxppc.org server at that time (running some 2.1.x kernel), than
with my provider's HP server...
> 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.
EEeeeepppp.... wrong conclusion here ;-). VJ compression is only active
on your PPP link, not end-to-end. So the remote server knows nothing of
the VJ copmpression your machine negotiates with the access server at
Which brings us to another variable in the connection chain: the access
server at your provider. In my case, it was a Cisco 2509 with
USRobotics modems. You might want to check with your provider, just in
case... If it really is a VJ problem, then the provider's box could
have an influence, too.
> One last question: Can I turn VJ compression on and off while a PPP
> link is active, or must I choose before connecting?
I don't think Linux's PPP can renegotiate link parameters. In any case,
the remote end must then be prepared to renegotiate as well...
Michel Lanners | " Read Philosophy. Study Art.
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email mlan at cpu.lu |
http://www.cpu.lu/~mlan | Learn Always. "
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