dnstap

Source

dnstap enables logging to dnstap.

Description

dnstap is a flexible, structured binary log format for DNS software; see https://dnstap.info. With this plugin you make CoreDNS output dnstap logging.

Note that there is an internal buffer, so expect at least 13 requests before the server sends its dnstap messages to the socket.

Syntax

dnstap SOCKET [full]
  • SOCKET is the socket path supplied to the dnstap command line tool.
  • full to include the wire-format DNS message.

Examples

Log information about client requests and responses to /tmp/dnstap.sock.

dnstap /tmp/dnstap.sock

Log information including the wire-format DNS message about client requests and responses to /tmp/dnstap.sock.

dnstap unix:///tmp/dnstap.sock full

Log to a remote endpoint.

dnstap tcp://127.0.0.1:6000 full

Command Line Tool

Dnstap has a command line tool that can be used to inspect the logging. The tool can be found at Github: https://github.com/dnstap/golang-dnstap. It’s written in Go.

The following command listens on the given socket and decodes messages to stdout.

$ dnstap -u /tmp/dnstap.sock

The following command listens on the given socket and saves message payloads to a binary dnstap-format log file.

$ dnstap -u /tmp/dnstap.sock -w /tmp/test.dnstap

Listen for dnstap messages on port 6000.

$ dnstap -l 127.0.0.1:6000

Using Dnstap in your plugin

In your setup function, check to see if the dnstap plugin is loaded:

c.OnStartup(func() error {
    if taph := dnsserver.GetConfig(c).Handler("dnstap"); taph != nil {
        if tapPlugin, ok := taph.(dnstap.Dnstap); ok {
            f.tapPlugin = &tapPlugin
        }
    }
    return nil
})

And then in your plugin:

func (x RandomPlugin) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
    if tapPlugin != nil {
        q := new(msg.Msg)
        msg.SetQueryTime(q, time.Now())
        msg.SetQueryAddress(q, w.RemoteAddr())
        if tapPlugin.IncludeRawMessage {
            buf, _ := r.Pack() // r has been seen packed/unpacked before, this should not fail
            q.QueryMessage = buf
        }
        msg.SetType(q, tap.Message_CLIENT_QUERY)
        tapPlugin.TapMessage(q)
    }
    // ...
}

See Also

The website dnstap.info has info on the dnstap protocol. The forward plugin’s dnstap.go uses dnstap to tap messages sent to an upstream.