In the thread published two weeks ago a serious , causing the exhaustion of the limit on the number of TCP connections. A new network subsystem was proposed in BIND 9.16, transitioned to an asynchronous request processing mechanism based on the library . Due to an error in this subsystem, the counter for active TCP connections does not decrease under certain conditions, leading to an increasing discrepancy between its value and the actual number of connections. After a while, the counter value may reach the established limit on client connections, resulting in new TCP requests being refused (UDP requests will continue to be processed).
The problem mainly manifests on servers accepting TCP connections from clients on multiple network interfaces.
An update for BIND 9.16 has not yet been released, but a has been published to fix the error. As a temporary solution, a limit on the number of connections (tcp-clients option) can be set to a very high value. Besides BIND 9.16, the problem affects the experimental branch 9.15 starting with version 9.15.6, but this branch is initially used only for development and is not intended for deployment on production servers.
Source: opennet.ru
