Several websites inaccessible through HTTPS proxy using IPv6
I've noticed several websites over the last few months are not accessible through the HTTPS proxy. Just today a user mentioned that a sharepoint.com link sent from a client wouldn't open. I tested and confirmed the behavior. Later I came across this link as well...
These are just a couple of examples but I've noticed probably a dozen or so. About the same time this started I enabled IPv6 on the network. After some more testing with the two problematic links above from a different Watchguard site without IPv6, it seems IPv6 may be the culprit. Or rather, the HTTPS proxy isn't fully compatible with IPv6.
The workaround is to use an HTTPS packet filter instead however it appears that some work needs to be done to improve the current HTTPS proxy.