Sorry, "it did work" was not enough for me to understand that you saw the diagnostic from tcpdump and then fixed it yourself ;-) I thought you were saying tcpdump made it work directly. I'm really glad that it helped.
Tcpdump is really useful to be your eyes on the network cable. There is a filtering language that is important to know, it works like this
tcpdump not port 22
will show you everything except udp or tcp port 22 - important if you plan to use it over a ssh link, otherwise what you want is hidden in a spew of entries showing the packets making the ssh display.... You can append filters with "and" and "or", but a wise person would not restrict like this
tcpdump port 80
because often your troubles are visible outside the obvious channel, eg, ICMP like you just experienced, and such a filter will hide it.