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unreliable "big" packets puzzle

Okay, I'm going nuts with this one. (I joined OSNN just to see if someone could help with this! :) )

A client's WinXP SP2 Home machine suddenly stopped working on theirhome LAN network/internet, everything. (They do all kinds ofthings to their system when I'm not there; I don't "own" the system....)

[Some stats: Only has TCP/IP networking, all wired, NICs are defaultedto auto-determine connection type/speed (although I've tried forcing10Mb half&full with no better luck), no Net Address set, and 64kbuffer (have tried 8k with no diff, too. System has video, audio,and NIC add-on cards/MB options only, and there is no IRQ sharing goingon. No viruses found, and Spybot & HiJackThis areclean. Problem was occuring before update to SP2 (which I didfrom CD, BTW, hoping it might solve the problem. Have done arepair on XP, as well, with no diff....]

When I went to diagnose it, pings worked fine, as well as DNS lookups, but I couldn't get a browser to download a web page. (Specifically download,as the browser would report that it found the page, connected and wastrying to get it....) Once connected the browser would just spinfor hours trying to download the page.

Ok, "bad NIC" says I, and replaces the NIC. Twice. Now havesystem on bench using totally different network/wiring, and have triedvarious NICs in different PCI slots, all with same results.

"Looks like a funky software setting problem" says I....

So I installed and checked network settings with iSpeed/DrTCP (takeyour pick) and found that as packet size increases (above ping'sdefault of 32 bytes) they fail more, and do not get through at all whenpacket size (data portion) get over 512B! Furthermore, oncerejecting happens, even 32B packets aren't reliable again until after aminute of "cool down"! (Sometimes even 16B packets don't reliablyget through. And FYI: all this is local to the bench network, say20' total to my "lab" gateway....)

I think that something is set somewhere in WinXP that has trashed thebuffer management or something, but am at a loss as to how to find/fixthat.

As always, I'd prefer to not have to re-install WinXP if at all possible.

I've solved their immediate needs with a replacement machine, but Idon't like being beat by a networking problem! I need to figurethis out! (Guess it sounds like I belong in this forum, eh? :))

Okay folks, prove to me that it's going to be worth the outrageous cost of membership :yowch: to have joined this elite and austere group!
Well if you can ping out it sounds like it is connecting. Try going into the command prompt and trace route somthing. such as tracert www.yahoo.com
That will tell you where your timing out at if at all. So you can see if it stops after your clients ISP or at the nic. Now the DNS is still at the ISP so you can't just yet assume you have an alright connection. You could have an issue with the ISP. If it is able to start a session with the DNS then every thing on your end is probely fine. I bet the ISP is to blame. Also make sure you have the correct DNS numbers. They may have changed.
Just thought of another idea. XP has that rollback/restore feature. You can set it back to the settings of like a month ago or such, and you dont loose your data. It has saved my ass once or twice.

Thanks for your kind offer of help! WRT the details of what you said:

1) RE: tracert/traceroute as a diag: Checked that: No dice.
Sometimes I can't even trace to my own gwy/rtr or DNS server,
(usu works tho) other times I can trace anywhere I try (rare, but
happens.) No, I'm positive it's nothing beyond the card itself;
it has to be from the connector inward.

2) RE: DNS prob's: I'm pinging internal IP addresses and it's failing.
'Rules out any DNS prob's, eh?! :)

3) RE: Rollback to a previous Restore Point: You gave me an idea
with this suggestion, tho. (Rollbacks aren't all they're cracked up
to be, BTW....) I'm going to swap out the HDD and do a clean
XP Home install on the clean HDD and see if I can get it to work!
That will point a definite finger at HW vs. SW vs. SW config.

FYI: I sold the client a NEW COMPUTER as a fix! That one's working
fine! :laugh: . (I still gotta figure this one out, tho!)

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