This will be in the new IP MASQ HOWTO that will be
out "any day now"...
--
The typical reason why MASQ users get "failed TCP/UDP checksum"
errors is that somewhere in their upstream network connection,
packets are getting corrupted. Now while most TCP/IP stacks
like Windows95, OS/2, etc will silently drop these packets,
MASQ will report them.
I've found the typical culprit for this corruption is either
a crappy or overloaded terminal server that are performing
VJ-header compression.
Follow these steps (in order) to try fixing your problem:
1) Make sure your COMM port on the Linux box is running at 115200
or better:
/etc/rc.d/rc.local or in /etc/rc.d/rc.serial (when it's
enabled in the /etc/rc.d/rc.S file
--
setserial /dev/ttyS1 spd_vhi
--
- If you have an ISDN connection, you can lose data because
of the serial rate bottleneck (115200 vs. 128000 x 4-times
compression). I would recommend an accelerated serial port
(say a Hayes ESP or something like that) for 230 or 460Kb/s
serial rates.
2) Make sure you have a good connection to your modem (externals)
- If you have one of those ribbon-to-9or25 pin motherboard
adapters, make sure it's in good condition. I personally
have a ferrite coil around each of mine.
- Check your serial cable quality and length.
3) The usual, but unfortunate, fix for the "failed checksum"
error is to disable VJ-header compression. To do this,
edit the /etc/ppp/options file and add:
"-vj"
4) Finally, if you are confident that it's NOT the UART, serial
link, or VJ header compression, try this patch:
--
From: Craig Estey <[EMAIL PROTECTED]>
Newsgroups: comp.os.linux.announce
Subject: IRQTUNE -- A Linux x86 IRQ Priority Optimizer (FAQ 0.2)
Followup-To: comp.os.linux.development.system
Date: Tue, 27 Aug 1996 15:07:44 GMT
Organization: Best Internet Communications
Lines: 62
Approved: [EMAIL PROTECTED] (Lars Wirzenius)
Message-ID: <[EMAIL PROTECTED]>
NNTP-Posting-Host: localhost
-----BEGIN PGP SIGNED MESSAGE-----
Hi, Folks
Announcing IRQTUNE. A Linux x86 IRQ Priority Optimizer.
Many people have recently posted problems with serial/PPP performance to
comp.os.linux.* newsgroups.
I had exactly the same problems. I did some microsecond resolution
performance profiling of the kernel. I found a kernel bug and devised
a fix. I've called it IRQTUNE. The _real_ problem is IRQ priority.
Online documentation (FAQ format) that explains all:
http://www.best.com/~cae/irqtune
The entire package:
ftp://www.best.com/pub/cae/irqtune.tgz
I've been running the patch for over a month and I tripled the
throughput of my 33.6 modem from 700 chars/sec to over 2500 chars/sec.
It also fixes data dropouts.
Please give it a try. I'd greatly appreciate your feedback via email.
Send your configuration data, what performance you got, what you think.
- -----------------------------------------------------------------------
SPECIAL NOTE: To those "alpha" testers that already have irqtune, the
FAQ has been revved to 0.2 to address many of the concerns expressed
in email and subsequent postings. This is a rev to the FAQ _only_.
FAQ 0.2 Changes:
- - Major rewrite and expansion of the problem explanation section
- - More thorough explanation of how and why irqtune works
- - Explanation of why serial devices must be highest priority
- - Impact on other devices
- - Cleaner and better installation instructions
- - Better benchmarking section
- - Problem resolution section
- - Explanation of my prior misread on the EOI thing
- -----------------------------------------------------------------------
.----------------------------------------------------------------------------.
| David A. Ranch - Linux/Networking/PC hardware [EMAIL PROTECTED] |
!---- ----!
`----- For more detailed info, see http://www.ecst.csuchico.edu/~dranch -----'
_______________________________________________
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