As others have pointed out, that's not the case. Something you do have to be careful of is the compile options for libwebsockets and what version you're using. Recent-ish version of libwebsockets in particular disable by default some features Mosquitto relies on, so some installations may suffer.

Version 2.1 of Mosquitto will no longer need libwebsockets (although it can still be selected at compile time) and so websockets support will be less dependant on how other libraries are compiled.

> Unfortunately the websockets implementation only allows IPv6

Huh? Pretty sure that's not true.

>socket_domain [ ipv4 | ipv6 ]

>By default, a listener will attempt to listen on all supported IP protocol versions.

>If you do not have an IPv4 or IPv6 interface you may wish to disable support for either of those protocol versions. In particular, note that due to the limitations of the websockets library, it will only ever attempt to open IPv6 sockets if IPv6 support is compiled in, and so will fail if IPv6 is not available.

From the manual. Huh, seems like I might’ve misunderstood this paragraph. But I was only ever able to access the broker if the browser was using an ipv6 address. I’ll have to test again I suppose. Still, the performance and reliability was not good.

Right, that just says if you don't have IPv6 support compiled in, you can't use IPv6. IPv4 is always available, and has worked wonderfully well in my experience.

Thanks for pointing that out. I’ll have to try again. Maybe ipv4 got disabled in the configuration somehow by accident.