mtufinder tests several different sized HTTP requests to a web server. I wrote this after discovering I couldn't use my yahoo mail account. I was able to login fine, however whenever I tried to send mail or view my folders nothing happened. I'd seen this before and learnt the hard way that it can be an MTU size problem. So I changed my MTU on my external network interface from 1500 to 576 and yes, my yahoo mail now worked fine. That got me thinking it would be nice to have a program that could attempt several different sized HTTP requests and report which worked. I called the program "mtufinder". Here I use mtufinder while my network inferface has a 1500 MTU, $ mtufinder f122.mail.yahoo.com website, f122.mail.yahoo.com trying 16 bytes... connected ok trying 516 bytes... connected ok trying 1016 bytes... connected ok trying 1516 bytes... failed Since only the last attempt fails, it strongly suggests an MTU problem. Now after changing my network interface to a 576 MTU, $ mtufinder f122.mail.yahoo.com website, f122.mail.yahoo.com trying 16 bytes... connected ok trying 516 bytes... connected ok trying 1016 bytes... connected ok trying 1516 bytes... connected ok