Windows XP Some PC on Network can't open all web sites

[tjm4fun]

Is there an email tech support link at the us robotics site? email them, there is something really wrong with this that you can;t just make it work.
If it were me, I'd return the POS and get a different unit, linksys, dlink, netgear, or something. but that doesn;t help you much.

 

[Humperandjumper]

Hi,

Sent an e-mail to US Robotics and got an automated response telling me they'll be in touch. I wonder how good their support is? I'll let you know.

 

[Humperandjumper]

Two days later and no reponse! Does not look good!

 

[Humperandjumper]

Well, I still have not had a response. Has anyone else experianced US Robotics support or, to be more precise, the lack of it?

 

[Mantheren]

Hey,

I read thourgh the thread and if some sites work and some do not (hotmail is a good example) it sounds like it could be a fragmentation issue perhaps?

Also since you have an ADSL modem this will add a few bytes to your ip packets when transfering and if these ip packets are then too big they will get broken up or fragmented, and not all sites seem to like this.

You can test this by pinging google for example with packes of a predefined lenght like so:

ping [url="http://www.google.com/"]www.google.com[/url] -l 1500
 
Pinging [url="http://www.l.google.com/"]www.l.google.com[/url] [66.249.93.99] with 1500 bytes of data:
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Ping statistics for 66.249.93.99:
	Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),
 
ping [url="http://www.google.com/"]www.google.com[/url] -l 1300
 
Pinging [url="http://www.l.google.com/"]www.l.google.com[/url] [66.249.93.99] with 1300 bytes of data:
Reply from 66.249.93.99: bytes=56 (sent 1300) time=50ms TTL=244
Reply from 66.249.93.99: bytes=56 (sent 1300) time=70ms TTL=244
Reply from 66.249.93.99: bytes=56 (sent 1300) time=50ms TTL=244
Reply from 66.249.93.99: bytes=56 (sent 1300) time=49ms TTL=244
Ping statistics for 66.249.93.99:
	Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
	Minimum = 49ms, Maximum = 70ms, Average = 54ms

As you can see when pinging with packets that are too large the host www.google.com is just not reachable. But when pinging with smaller packets it is...
btw 1500 is the default size for packets in windows and max you should use on a lan. however ping normally uses 32 bytes to ping so that is why it works under normal conditions.

if this is the problem you can change the MTU (Maximum Transmission Unit) on the system that does not contact the sites. This must be done in the registry so be carefull..

In registry key

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces

there are one or more entries ( one for each network interface ). Here find the one you need by checking the ip numbers in the keys. And in the correct key add a DWORD value called "MTU".
Give it a value of 1300 decimal ( 0x514 hex ).
Reboot and if this was the problem, it should now work for all sites. because the packets are no longer sent at the default value of 1500 but at 1300 thus leaving room for the extra bytes that the ADSL modem will add to the packets.

I Hope this works for you because it worked for me...

Kind Regards,
Mantheren

Ps. If it doesn't work, undo everything again...

 

[Humperandjumper]

Thanks Mantheren
RESULT!!!!!
Well spotted and sorted now. All machines can connect to all sites!
THANK YOU VERY MUCH.
This worked on AOL that already has an MTU of 1400.
I really hope this helps others and BTW still no response from Support at US Robotics! Buyers Beware
Thanks again Mantheren

 

[tjm4fun]

Wow, now that;s one I never would have thought of.
MTU size..... sounds more like the isp is out of spec, there is no reason you should need to adjust this. All requests are split up if over a certain size, and that is a transparent issue when all is working properly.
Well, a moot point, it works, and the imapct of a change from 1500 to 1300 will be minimal if any on internet performance.
Even local file xfer should'nt be impacted enough to notice.

Definately filing this away for future reference !

 

[Mantheren]

Hey Again,

I'm glad to hear it all works now... because this really is the kind of thing that takes ages to figure out. I think it took me a pretty long time to fix when I started getting complaints on our network. Much to everyones enoyance.

I looked up the exact reason cuz of course I could not remember, and was kinda curious again myself. In short I think it is a problem with the webpage host and the fact that they block ICMP packets that normally are sent from the router back to the host to tell the host to retransmit the packets with a smaller MTU. Or something like that... Here is a webpage with the precice reason if anyone is interested...
http://www.cisco.com/en/US/tech/tk175/tk15/technologies_tech_note09186a0080093bc7.shtml

Specifically the part called "Why the MTU Size Must Be Changed", the rest is just cisco specific i think.

Anyways good to hear it all works again...

Kind Regards,
Mantheren