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NNTP-Posting-Date: Mon, 09 Jan 2006 03:09:35 -0600
Newsgroups: fidonet.os2
From: Peter_Knapper@p10.f1.n772.z3
Date: Mon, 09 Jan 2006 03:20:49 -0500
Subject: Networking issue
Message-ID: 
Organization: Another Good Point About OS/2
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Hi Alan,

 AH> On an unrelated issue, I'm still having trouble connecting to some sites, 
 AH> among them cnn.com, gmail.com, and maps.google.com when 
 AH> I'm booted to eCS (1.21 or 1.15.) The sites simply 
 AH> won't load, no matter which browser I try (Firefox 1.5, 
 AH> Mozilla 1.7.1.2, Opera 5.1.2, Netscape 4.61.)  
 AH> Sometimes, right after a reboot, they will load, but 
 AH> after eCS has run for a few hours, no more. 

This sounds like what one might see if there is an MTU size issue.

 AH> They load fine in Mozilla or Firefox under Win98, with no time 
 AH> limitation.   Clearing the browser cache in eCS makes 
 AH> no difference.  The cable modem is a D-Link DCM202 with 
 AH> the Comcast firmware.  

Cable services usually (although they can be different), run using an MTU of
1492 or even possibly down at 1480 (if PPPoE is being used). Standard Ethernet is
1500, so this means packet fragmentation is always happening. This is not
normally a problem as long as a service called PathMTUDiscovery is being used to
determine the MTU size availiable on each segment for packets. If PMTUD is
disabled anywhere you most often see this as a, first time work, with eventual
subsequent packets usually failing, IE for small amounts of data things often
work fine, for larger amounts you get incomplete transmissions. 

False PMTUD data was a favourite hacker tool a few years ago, they could bring
an ISP's operation to its knees if the ISP H/W was listenng to erroneous PMTUD
packets and adjusting sizes when it shouldn't. This issue should be long gone
now...

Try setting your MTU size of your local LAN segment to 1492 (or even try 1480)
and see if that works better. 

Run "INETCFG -g all" to get the current values for TCP/IP and look in your
x:\MPTN\ETC directory for the INETCFG.INI file. Its a plain text file that lists
current TCP/IP settings and one of the paremeters reported should be MTUDISCOVER.
Make sure that is turned ON or set to 1. You can change settings using INETCFG as
well as display them so record the current settigns before alter them...

Also run "NETSTAT -n" to list your interface settings. You should get something
like this -
==================================================
[E:\Z]netstat -n
Interface 0  Ethernet-Csmacd
physical address    00105a735f58      MTU 1500
                                      ^^^^^^^^  <=== This is the main bit.
speed 100000000 bits/sec
unicast packets received 159756
broadcast packets received 2380
total bytes received 133968624
unicast packets sent 92598
broadcast packets sent 628
total bytes sent 10134648
packets discarded on transmission 0
packets discarded on reception 0
received packets in error 0
errors trying to send 0
packets received in unsupported protocols 0
==================================================
It shows you the current MTU value. Note that if you are using a ROUTER between
your Cable modem and your PC then the MTU value you see is only for the PC to
Router segment, you need to find the MTU being used on the other side of the
Router, in which case the Router should be handling MTU size changes (if they are
even required).

Cheers..........pk.