I've never had much difficulty with ESP (protocol 50), 6in4 (Protocol 41), or GRE (protocol 47). By and large, if it's IP, your packet will get to the destination without too much filtering in North America with most of the major ISPs (Comcast, AT&T, etc...)
As someone who just set up IPv6 tunnels to both home and the office, I had no issues with 6in4 (proto-41) traffic with both ISPs I used. This is in The Netherlands.
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I've never had much difficulty with ESP (protocol 50), 6in4 (Protocol 41), or GRE (protocol 47). By and large, if it's IP, your packet will get to the destination without too much filtering in North America with most of the major ISPs (Comcast, AT&T, etc...)
I can't speak for other countries.
GRE tends to bugger off down a hole in a lot of ISPs in the UK from experience. Very annoying.
Is that a routing issue, or a fragmentation problem? Reducing your MTU on a GRE link greatly improves performance.
I'd be interested in hearing if there were any ISPs that didn't just forward GRE packets using normal IP routing conventions.
Absolutely no idea. AFAIK they just disappear into a void.
Used to be like this on Demon, Virgin Media and Easynet. The latter fixed their stuff circa 2007 however.
As someone who just set up IPv6 tunnels to both home and the office, I had no issues with 6in4 (proto-41) traffic with both ISPs I used. This is in The Netherlands.