On Dec 19, 2004, at 5:04 AM, Alex Tweedly wrote:
This problem happens to me all the time, because I use my laptop connected to an ethernet which connects to the internet through another computer using a dial-up line, and the dial-up is often disconnected. Laptop thinks it has a connection (the ethernet is up) and thinks it has DNS servers it can reach (because the main computer acts as a DNS proxy) - but when it queries a host name, it is blocked until the DNS response times out.
This illustrates that there are several meanings to "is connected to the Internet".
They might be:
A. This computer thinks there is a route to a public IP address.
B. #A and the route works.
C. This computer can modify routing on demand to get to a public IP address.
I have not used a dialup connection in a while so, I don't remember all the problems involved. One problem is that the act of checking can cause dialing to start.
Some ideas:
1 Open TCP to some http port on a reliable server. This does a B check.
2
Open UPD to any port on a public address. This does an A check and is fast. Maybe this is less likely to cause a dial than #1. This is non-intrusive.
3
Parse the results of a command-line utility. Dial-up may take special consideration. This does an A test.
4 External. A test.
Dar
**********************************************
DSC (Dar Scott Consulting & Dar's Lab)
http://www.swcp.com/dsc/
Programming Services and Software
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