accf_dns(9) buffer incoming DNS requests until the whole first request is present


options INET
kldload accf_dns


This is a filter to be placed on a socket that will be using Fn accept to receive incoming connections.

It prevents the application from receiving the connected descriptor via Fn accept until a whole DNS request is available on the socket. It does this by reading the first two bytes of the request, to determine its size, and waiting until the required amount of data is available to be read.

The Fa ACCEPT_FILTER_DNS kernel option is also a module that can be enabled at runtime via kldload(8) if the INET option has been compiled into the kernel.


If the options INET module is available in the kernel, the following code will enable the DNS accept filter on a socket Fa sok .
        struct accept_filter_arg afa;
        bzero(&afa, sizeof(afa));
        strcpy(afa.af_name, "dnsready");
        setsockopt(sok, SOL_SOCKET, SO_ACCEPTFILTER, &afa, sizeof(afa));


The accept filter mechanism was introduced in Fx 4.0 .


This manual page and the filter were written by An David Malone .