I battled for a while, but eventually got Internet Connection Sharing to work with Sentech's MyWireless system. There were two important things I had to do.
1. The TCP/IP settings on the network adapter of the client machines need to specify a Maximum Transmission Unit (MTU) size of 576 instead of the probable default value somewhere around 1400 to 1500. This is set in the registry of the client machine. As I learned, the MTU is the maximum size of a packet of data that can be transferred in one frame over a network. Recommended values are in the region of 1400 to 1500 for different varieties of physical network connections (e.g. Ethernet). However, a number of systems on the Internet, including dial-up connections (and Sentech MyWireless so it appears), only work properly if this value is set to 576.
When a user requests a web site, a client/server negotiation occurs between the PC and the web server that is hosting the web site. During the negotiation, a maximum MTU size is negotiated, but is basically set by the client PC. If the packets are too large, they can become fragmented and get dropped. This generates a message to the web server that sent the oversized packet. The message informs the web server that it sent an oversized packet and that it needs to resend the packet with a smaller MTU. However, many web servers block such messages, which causes the server to continue sending oversize packets. These packets are dropped, and as a result, the requested web site doesn't load. A partially loaded page occurs when the initial data packets sent from the web server are under the maximum size. However, a packet is then sent that exceeds this maximum. The server continues to retransmit this oversized packet resulting in a partially loaded page and a "waiting for reply..." message in the status bar.
See http://www.cisco.com/warp/public/794/router_mtu.html for a better version (albeit for a different context) of the explanation above, and for more information on how to change the MTU setting in the registry of the client machine.
One additional piece of information that seems to prove the diagnosis above can be obtained by setting the buffer size in a Ping (from a command prompt). Try the following:
ping -f -l 548 www.sentech.co.za
ping -f -l 549 www.sentech.co.za
The first line works (for any number between 68 and 548), but the second line (for any number greater than 548) does not. (More information about 'ping' can be found by typing the word Ping on its own at a command prompt.) For some obscure reason, the correct maximum MTU size is 28 more than the 548 number above. That is, the correct value to use for the maximum MTU setting is 576.
My experience has been that, by changing the maximum MTU size in the registry, the shared (client) connection has gone from not working to fully working. I have done this for a wired Ethernet connection to a Windows 98SE client at home, and to a wireless connection to a Windows 2000 client at work.
2. The second item applies if you are attempting to run Microsoft's Internet Connection Sharing together with Zone Alarm personal firewall software (on the host and/or client computers). Internet Zone Security must be set to Medium, otherwise the sharing does not work. This leaves your computer secure, although slightly visible to the outside world.
I hope this information is helpful to others trying to set up a shared connection.
Regards,
Rodney Jones, Mintek, Randburg
