dnstcpbench man page

dnstcpbench — tool to perform TCP benchmarking of nameservers




dnstcpbench reads DNS queries (by default from standard input) and sends them out in parallel to a remote nameserver. By default TCP/IP is used, but optionally, UDP is tried first, which allows for the benchmarking of TCP/IP fallback.

The program reports both mean and median numbers for queries per second and UDP and TCP latency. Each query only counts once, even if it is tried over UDP first. This effectively means that passing '-u' can lower query rates if many queries get shunted to TCP.

The input format is one query per line: qname single-space qtype. An example:

www.powerdns.com ANY

When benchmarking extended runs, it may be necessary to enable TIME_WAIT recycling, as TCP/IP port tuples may otherwise run out. On Linux this is performed by running:

echo 1 > /proc/sys/net/ipv4/tcp_tw_recycle

The equivalent for IPv6 is not known.


-f | --file FILENAME
FILENAME from which to read queries. Defaults to standard input if unspecified.
-h | --help
Provide a helpful message.
--timeout-msec MSEC
MSEC milliseconds to wait for an answer.
-u | --udp-first
Attempt resolution via UDP first, only do TCP if truncated answer is received.
-v | --verbose
Be wordy on what the program is doing.
--workers NUM
Use NUM parallel worker threads.
IPv4 or IPv6 to test against.
Port to test against, defaults to 53.


Currently the timeout code does not actually perform non-blocking connects or writes. So a slow connect or slow writes will still cause low performance and delays.

Median queries per second statistics are reported as 0 for sub-second runs.




July 2013