NAME

bufsize - sizes EDNS0 buffer size to prevent IP fragmentation.

DESCRIPTION

bufsize limits a requester's UDP payload size. It prevents IP fragmentation, mitigating certain DNS vulnerabilities.

SYNTAX

bufsize [SIZE]

[SIZE] is an int value for setting the buffer size. The default value is 512, and the value must be within 512 - 4096. Only one argument is acceptable, and it covers both IPv4 and IPv6.

EXAMPLES

Enable limiting the buffer size of outgoing query to the resolver (172.31.0.10):

. {
    bufsize 512
    forward . 172.31.0.10
    log
}

Enable limiting the buffer size as an authoritative nameserver:

. {
    bufsize 512
    file db.example.org
    log
}

CONSIDERATIONS

Setting 1232 bytes to bufsize may avoid fragmentation on the majority of networks in use today, but it depends on the MTU of the physical network links.
For now, if a client does not use EDNS, this plugin adds OPT RR.