BIND 9.9.4 (and higher) provides support for Response Rate Limiting (RRL). However, it is not enabled by default when building BIND. The reason for this is that BIND 9.9 is an Extended Support Version of BIND and per our policy on mangement of ESVs, we do not introduce any new features or functionality to a stable ESV version.
Therefore the activation of RRL as a new feature must be selected when building BIND via the new configure option --enable-rrl:
$ ./configure --enable-rrl
In the BIND 9.9 subscription-only releases (for example, 9.9.4-S3), RRL is always available, and there is no configure option to enable it. This will also be the case in BIND 9.10.