Thank you for mentioning extension headers. IMHO, they are the worst mistake in IPv6, because they are unbounded. If you design your hardware to handle extens

Thank you for mentioning extension headers. IMHO, they are the worst mistake in IPv6, because they are unbounded. If you design your hardware to handle extension headers, there are all kinds of edge cases to worry about, and regression testing the different combination of headers is nearly impossible. So lots of hardware vendors just don't handle them (or handle just one), which means they might as well not exist.