COREDNS-DNSTAP(7)

NAME

dnstap - enables logging to dnstap.

DESCRIPTION

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

Every message is sent to the socket as soon as it comes in, the dnstap plugin has a buffer of 10000 messages, above that number dnstap messages will be dropped (this is logged).

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 ⟨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 ⟨https://dnstap.info⟩ has info on the dnstap protocol. The forward plugin's dnstap.go uses dnstap to tap messages sent to an upstream.