Member Avatar for Calzone

I have the following problem, and would appreciate some advice on how to go about fixing it!!

My PC at home (WinXP SP2) has a decent internet connection, but for the last few weeks I have been unable to access the microsoft.com website, first noticed due to failure of the windows update service to connect. It turns out I cannot access the site using IE6 or Mozilla Firefox either.

There are various other websites I cannot access either, one being my online bank, another being the BBC weather website......

My PC is connected to a wireless router by cable. However, when I connect to my netwrok wirelessly through my other laptop, it can access all of these sites no problem.

From this I am guessing that there is no problem with my router or my internet connection or ISP, nor is it a browser problem. I suspect either my firewall, a virus of some type, or some problem with Java/activeX used by both browsers....

Firewall is Norton IS 2006. When i turn off the firewall protection, I still can't access the websites. Virus scan doesn't turn up much. Heard the worm can screw things up a bit like this but don't know if that isthe problem.

Anyone have any suggestions?

Cheers, Calzone

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  • Latest Post Latest Post by nanosani

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Useful summary and a compact how-to based on the thread (and the steps that finally fixed it for ). This is a common, solvable networking issue that typically shows up as: some sites load fine, others fail; pings either time out or show fragmentation errors; a second machine on the same LAN works. Check the cheap/quick things first (hosts file, DNS, duplicate firewalls) as suggested, then follow the diagnostic sequence below.

Run these diagnostics from a Command Prompt and compare results with the working laptop:

ipconfig /all
ping -n 4 -f -l 1472 www.example.com
tracert www.example.com
telnet www.example.com 80   (requires Telnet client)

If the ping with -f/-l fails at a certain size, reduce the payload until it succeeds. Add ~28 to the payload that succeeded to get the MTU to use. That pinpoints a Path MTU/fragmentation problem (often caused by PPPoE or mismatched router/modem vs. PC MTU and by intermediate devices blocking ICMP "fragmentation needed" messages).

Fixes to try (safe sequence):

ipconfig /flushdns
netsh winsock reset
netsh int ip reset resetlog.txt
(reboot)

# to change MTU on Windows XP (replace connection name)
netsh interface ip set subinterface "Local Area Connection" mtu=1492 store=persistent

Also check the router/modem MTU and align it with the client, or set the card’s MTU in Device Manager if the driver exposes it. After changes, re-run the ping fragmentation test.

Notes and cautions: some servers block ICMP echo (so a ping timeout doesn't necessarily mean the site is unreachable over HTTP). PMTU blackholes occur when "fragmentation needed" ICMP is filtered; that causes selective failures. If everything above fails, test the PC directly on the modem (bypass the router), boot into Safe Mode with Networking, update/reinstall the NIC driver, and watch for multiple security products or LSP/Winsock hooks that may interfere. Credit to for finding the MTU root cause and to earlier posters for the initial troubleshooting pointers.

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Member Avatar for Calzone

Just to add - when I ping www.microsoft.com on my wireless laptop it gets request timed out (i.e. no reply), and yet I can access the website itself no problem.

Maybe it is a problem with the connection......

Member Avatar for cereal

Check your hosts file. You can find it in c:\windows\system32\drivers\etc. Open it with notepad, and check if there is any of the websites you can't access.

Bye :)

Member Avatar for Calzone

cereal,

Nothing in the hosts file other than localhost.

Various websites don't load, not sure I can see a consistent theme with them. Norton firewall has no obvious issues I can see.

Member Avatar for Calzone

When I try to load , the tab does show the titles of the website (though this could come from temp files or a cookie?), and when I ping it I get a quick response. but the site wont' load. Mozilla shows its trying to load from image.com.com, I can ping that fine too, but still nothing comes up.

Have tried running LSP fix and changing host files but no joy. Norton finds nothing. All security restrictions that I can find appear to be fine. As said before my wireless laptop has no problems connecting to these sites. Suggests something is up on my machine, but am struggling to find it at this point.....

Member Avatar for gabimartinescu

you can also try to add those sites in the trusted list (in internet explorer internet settings->security->trusted sited , unmark "https...blah blah" and add there "microsoft.com" and others)

Are you sure there are no other firewalls/viruses on your pc? You can try to boot from a bootable cd with knoppix linux or erd commander(windows xp modified) for a short test (if it works you can reinstall windows :) )

PS Please share with us your progres and solution in this metter :)

Member Avatar for Calzone

I solved this problem eventually - turned out to be a problem with the MTU settings on my computer and new laptop being set at 1500, while the modem was at 1492. This can lead to problems where websites end up sending the wrong packet size to the router and it doesn't get through.

www.kitz.co.uk provides a goodguide to resovling this issue.

Member Avatar for santana69

I solved this problem eventually - turned out to be a problem with the MTU settings on my computer and new laptop being set at 1500, while the modem was at 1492. This can lead to problems where websites end up sending the wrong packet size to the router and it doesn't get through.

www.kitz.co.uk provides a goodguide to resovling this issue.

I'm having the same problem. How do you change the MTU Settings?

Member Avatar for Calzone

I'm having the same problem. How do you change the MTU Settings?

Basically you need to make sure your windows MTU settings match those in your Router / modem. See the link below for more detailed guide.

http://www.kitz.co.uk/adsl/MTU.htm

MTU settings should be somewhere in the main configuration page of your router, don't remember where they are in Windows, but remember it being non trivial to find.

Calzone

Member Avatar for nanosani

Wow .. this was the fix I was also looking for .. thanks for sharing dude.

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