diff --git a/bin/tests/system/digdelv/ans4/ans.py b/bin/tests/system/digdelv/ans4/ans.py
new file mode 100644
index 0000000000..6f5346ff86
--- /dev/null
+++ b/bin/tests/system/digdelv/ans4/ans.py
@@ -0,0 +1,25 @@
+# Copyright (C) Internet Systems Consortium, Inc. ("ISC")
+#
+# SPDX-License-Identifier: MPL-2.0
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0.  If a copy of the MPL was not distributed with this
+# file, you can obtain one at https://mozilla.org/MPL/2.0/.
+#
+# See the COPYRIGHT file distributed with this work for additional
+# information regarding copyright ownership.
+
+from isctest.asyncserver import (
+    AsyncDnsServer,
+    IgnoreAllQueries,
+)
+
+
+def main() -> None:
+    server = AsyncDnsServer()
+    server.install_response_handler(IgnoreAllQueries())
+    server.run()
+
+
+if __name__ == "__main__":
+    main()
diff --git a/bin/tests/system/digdelv/ans4/startme b/bin/tests/system/digdelv/ans4/startme
deleted file mode 100644
index 8b13789179..0000000000
--- a/bin/tests/system/digdelv/ans4/startme
+++ /dev/null
@@ -1 +0,0 @@
-
diff --git a/bin/tests/system/digdelv/ans5/ans.pl b/bin/tests/system/digdelv/ans5/ans.pl
deleted file mode 100644
index 63964060d7..0000000000
--- a/bin/tests/system/digdelv/ans5/ans.pl
+++ /dev/null
@@ -1,176 +0,0 @@
-#!/usr/bin/perl
-
-# Copyright (C) Internet Systems Consortium, Inc. ("ISC")
-#
-# SPDX-License-Identifier: MPL-2.0
-#
-# This Source Code Form is subject to the terms of the Mozilla Public
-# License, v. 2.0.  If a copy of the MPL was not distributed with this
-# file, you can obtain one at https://mozilla.org/MPL/2.0/.
-#
-# See the COPYRIGHT file distributed with this work for additional
-# information regarding copyright ownership.
-
-# This is a TCP-only DNS server whose aim is to facilitate testing how dig
-# copes with prematurely closed TCP connections.
-#
-# This server can be configured (through a separate control socket) with a
-# series of responses to send for subsequent incoming TCP DNS queries.  Only
-# one query is handled before closing each connection.  In order to keep things
-# simple, the server is not equipped with any mechanism for handling malformed
-# queries.
-#
-# Available response types are defined in the %response_types hash in the
-# getAnswerSection() function below.  Each RR returned is generated dynamically
-# based on the QNAME found in the incoming query.
-
-use IO::File;
-use Net::DNS;
-use Net::DNS::Packet;
-
-use strict;
-
-# Ignore SIGPIPE so we won't fail if peer closes a TCP socket early
-local $SIG{PIPE} = 'IGNORE';
-
-# Flush logged output after every line
-local $| = 1;
-
-my $server_addr = "10.53.0.5";
-if (@ARGV > 0) {
-	$server_addr = @ARGV[0];
-}
-
-my $mainport = int($ENV{'PORT'});
-if (!$mainport) { $mainport = 5300; }
-my $ctrlport = int($ENV{'EXTRAPORT1'});
-if (!$ctrlport) { $ctrlport = 5301; }
-
-my $ctlsock = IO::Socket::INET->new(LocalAddr => "$server_addr",
-   LocalPort => $ctrlport, Proto => "tcp", Listen => 5, Reuse => 1) or die "$!";
-
-my $tcpsock = IO::Socket::INET->new(LocalAddr => "$server_addr",
-   LocalPort => $mainport, Proto => "tcp", Listen => 5, Reuse => 1) or die "$!";
-
-my $pidf = new IO::File "ans.pid", "w" or die "cannot open pid file: $!";
-print $pidf "$$\n" or die "cannot write pid file: $!";
-$pidf->close or die "cannot close pid file: $!";;
-sub rmpid { unlink "ans.pid"; exit 1; };
-
-$SIG{INT} = \&rmpid;
-$SIG{TERM} = \&rmpid;
-
-my @response_sequence = ("complete_axfr");
-my $connection_counter = 0;
-
-# Return the next answer type to send, incrementing the connection counter and
-# making sure the latter does not exceed the size of the array holding the
-# configured response sequence.
-sub getNextResponseType {
-	my $response_type = $response_sequence[$connection_counter];
-
-	$connection_counter++;
-	$connection_counter %= scalar(@response_sequence);
-
-	return $response_type;
-}
-
-# Return an array of resource records comprising the answer section of a given
-# response type.
-sub getAnswerSection {
-	my ($response_type, $qname) = @_;
-
-	my %response_types = (
-		no_response => [],
-
-		partial_axfr => [
-			Net::DNS::RR->new("$qname 300 IN SOA . . 0 0 0 0 300"),
-			Net::DNS::RR->new("$qname NS ."),
-		],
-
-		complete_axfr => [
-			Net::DNS::RR->new("$qname 300 IN SOA . . 0 0 0 0 300"),
-			Net::DNS::RR->new("$qname NS ."),
-			Net::DNS::RR->new("$qname 300 IN SOA . . 0 0 0 0 300"),
-		],
-	);
-
-	return $response_types{$response_type};
-}
-
-
-# Generate a Net::DNS::Packet containing the response to send on the current
-# TCP connection.  If the answer section of the response is determined to be
-# empty, no data will be sent on the connection at all (immediate EOF).
-sub generateResponse {
-	my ($buf) = @_;
-	my $request;
-
-	if ($Net::DNS::VERSION > 0.68) {
-		$request = new Net::DNS::Packet(\$buf, 0);
-		$@ and die $@;
-	} else {
-		my $err;
-		($request, $err) = new Net::DNS::Packet(\$buf, 0);
-		$err and die $err;
-	}
-
-	my @questions = $request->question;
-	my $qname = $questions[0]->qname;
-	my $qtype = $questions[0]->qtype;
-	my $qclass = $questions[0]->qclass;
-	my $id = $request->header->id;
-
-	my $packet = new Net::DNS::Packet($qname, $qtype, $qclass);
-	$packet->header->qr(1);
-	$packet->header->aa(1);
-	$packet->header->id($id);
-
-	my $response_type = getNextResponseType();
-	my $answers = getAnswerSection($response_type, $qname);
-	for my $rr (@$answers) {
-		$packet->push("answer", $rr);
-	}
-
-	print "    Sending \"$response_type\" response\n";
-
-	return $packet->data if @$answers;
-}
-
-my $rin;
-my $rout;
-for (;;) {
-	$rin = '';
-	vec($rin, fileno($ctlsock), 1) = 1;
-	vec($rin, fileno($tcpsock), 1) = 1;
-
-	select($rout = $rin, undef, undef, undef);
-
-	if (vec($rout, fileno($ctlsock), 1)) {
-		my $conn = $ctlsock->accept;
-		@response_sequence = split(' ', $conn->getline);
-		$connection_counter = 0;
-		print "Response sequence set to: @response_sequence\n";
-		$conn->close;
-	} elsif (vec($rout, fileno($tcpsock), 1)) {
-		my $buf;
-		my $lenbuf;
-		my $conn = $tcpsock->accept;
-		my $n = $conn->sysread($lenbuf, 2);
-		die unless $n == 2;
-		my $len = unpack("n", $lenbuf);
-		$n = $conn->sysread($buf, $len);
-		die unless $n == $len;
-		print "TCP request\n";
-		my $response = generateResponse($buf);
-		if ($response) {
-			$len = length($response);
-			$n = $conn->syswrite(pack("n", $len), 2);
-			$n = $conn->syswrite($response, $len);
-			print "    Sent: $n chars via TCP\n";
-		} else {
-			print "    No response sent\n";
-		}
-		$conn->close;
-	}
-}
diff --git a/bin/tests/system/digdelv/ans5/ans.py b/bin/tests/system/digdelv/ans5/ans.py
new file mode 100644
index 0000000000..a53045305d
--- /dev/null
+++ b/bin/tests/system/digdelv/ans5/ans.py
@@ -0,0 +1,104 @@
+# Copyright (C) Internet Systems Consortium, Inc. ("ISC")
+#
+# SPDX-License-Identifier: MPL-2.0
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0.  If a copy of the MPL was not distributed with this
+# file, you can obtain one at https://mozilla.org/MPL/2.0/.
+#
+# See the COPYRIGHT file distributed with this work for additional
+# information regarding copyright ownership.
+
+import logging
+from typing import AsyncGenerator, List, Optional
+
+import dns.rcode
+import dns.rdatatype
+import dns.rrset
+
+from isctest.asyncserver import (
+    CloseConnection,
+    ControlCommand,
+    ControllableAsyncDnsServer,
+    DnsResponseSend,
+    QueryContext,
+    ResponseAction,
+    ResponseHandler,
+)
+
+
+class ErraticAxfrHandler(ResponseHandler):
+    allowed_actions = ["no-response", "partial-axfr", "complete-axfr"]
+
+    def __init__(self, actions: List[str]) -> None:
+        self.actions = actions
+        self.counter = 0
+        for action in actions:
+            assert action in self.allowed_actions
+
+    async def get_responses(
+        self, qctx: QueryContext
+    ) -> AsyncGenerator[ResponseAction, None]:
+        action = self.actions[self.counter % len(self.actions)]
+        self.counter += 1
+
+        logging.info("current response action: %s", action)
+
+        if action == "no-response":
+            yield CloseConnection()
+            return
+
+        soa_rr = dns.rrset.from_text(
+            qctx.qname, 300, qctx.qclass, dns.rdatatype.SOA, ". . 0 0 0 0 300"
+        )
+        ns_rr = dns.rrset.from_text(qctx.qname, 300, qctx.qclass, dns.rdatatype.NS, ".")
+
+        qctx.response.answer.append(soa_rr)
+        qctx.response.answer.append(ns_rr)
+
+        if action == "partial-axfr":
+            yield DnsResponseSend(qctx.response)
+        elif action == "complete-axfr":
+            qctx.response.answer.append(soa_rr)
+            yield DnsResponseSend(qctx.response)
+        yield CloseConnection()
+
+
+class ResponseSequenceCommand(ControlCommand):
+    control_subdomain = "response-sequence"
+
+    def __init__(self) -> None:
+        self._current_handler: Optional[ResponseHandler] = None
+
+    def handle(
+        self, args: List[str], server: ControllableAsyncDnsServer, qctx: QueryContext
+    ) -> str:
+        for action in args:
+            if action not in ErraticAxfrHandler.allowed_actions:
+                logging.error("invalid %s action '%s'", self, action)
+                qctx.response.set_rcode(dns.rcode.SERVFAIL)
+                return f"invalid action '{action}'; must be one of {ErraticAxfrHandler.allowed_actions}"
+
+        actions = args
+
+        if self._current_handler is not None:
+            server.uninstall_response_handler(self._current_handler)
+
+        self._current_handler = ErraticAxfrHandler(actions)
+        server.install_response_handler(self._current_handler)
+
+        msg = f"reponse sequence set to {actions}"
+        logging.info(msg)
+        return msg
+
+
+def main() -> None:
+    server = ControllableAsyncDnsServer(
+        default_aa=True, default_rcode=dns.rcode.NOERROR
+    )
+    server.install_control_command(ResponseSequenceCommand())
+    server.run()
+
+
+if __name__ == "__main__":
+    main()
diff --git a/bin/tests/system/digdelv/ans6/ans.pl b/bin/tests/system/digdelv/ans6/ans.pl
deleted file mode 100755
index 39d02b2c69..0000000000
--- a/bin/tests/system/digdelv/ans6/ans.pl
+++ /dev/null
@@ -1,84 +0,0 @@
-#!/usr/bin/perl -w
-
-# Copyright (C) Internet Systems Consortium, Inc. ("ISC")
-#
-# SPDX-License-Identifier: MPL-2.0
-#
-# This Source Code Form is subject to the terms of the Mozilla Public
-# License, v. 2.0.  If a copy of the MPL was not distributed with this
-# file, you can obtain one at https://mozilla.org/MPL/2.0/.
-#
-# See the COPYRIGHT file distributed with this work for additional
-# information regarding copyright ownership.
-
-use IO::File;
-use IO::Socket;
-use Net::DNS;
-use Net::DNS::Packet;
-
-my $localport = int($ENV{'PORT'});
-if (!$localport) { $localport = 5300; }
-
-my $sock = IO::Socket::INET->new(LocalAddr => "10.53.0.6",
-   LocalPort => $localport, Proto => "udp") or die "$!";
-
-my $pidf = new IO::File "ans.pid", "w" or die "cannot open pid file: $!";
-print $pidf "$$\n" or die "cannot write pid file: $!";
-$pidf->close or die "cannot close pid file: $!";
-sub rmpid { unlink "ans.pid"; exit 1; };
-
-$SIG{INT} = \&rmpid;
-$SIG{TERM} = \&rmpid;
-
-for (;;) {
-	$sock->recv($buf, 512);
-
-	print "**** request from " , $sock->peerhost, " port ", $sock->peerport, "\n";
-
-	my $packet;
-
-	if ($Net::DNS::VERSION > 0.68) {
-		$packet = new Net::DNS::Packet(\$buf, 0);
-		$@ and die $@;
-	} else {
-		my $err;
-		($packet, $err) = new Net::DNS::Packet(\$buf, 0);
-		$err and die $err;
-	}
-
-	print "REQUEST:\n";
-	$packet->print;
-
-	$packet->header->qr(1);
-
-	my @questions = $packet->question;
-	my $qname = $questions[0]->qname;
-	my $qtype = $questions[0]->qtype;
-
-	my $donotrespond = 0;
-
-	$packet->header->aa(1);
-	if ($qtype eq "A") {
-		$packet->push("answer",
-			      new Net::DNS::RR($qname .  " 300 A 10.53.0.5"));
-	} else {
-		$donotrespond = 1;
-	}
-
-	if ($donotrespond == 0) {
-                my $sendsock =
-                        IO::Socket::INET->new(LocalAddr => "10.53.1.2",
-                                              PeerAddr => $sock->peerhost,
-                                              PeerPort => $sock->peerport,
-                                              Proto => "udp") or die "$!";
-                print "**** response from ", $sendsock->sockhost, " to " ,
-                      $sendsock->peerhost, " port ", $sendsock->peerport, "\n";
-		$sendsock->send($packet->data);
-                $sendsock->close;
-		print "RESPONSE:\n";
-		$packet->print;
-		print "\n";
-	} else {
-		print "DROP:\n";
-	}
-}
diff --git a/bin/tests/system/digdelv/ans6/ans.py b/bin/tests/system/digdelv/ans6/ans.py
new file mode 100644
index 0000000000..77e7141590
--- /dev/null
+++ b/bin/tests/system/digdelv/ans6/ans.py
@@ -0,0 +1,40 @@
+# Copyright (C) Internet Systems Consortium, Inc. ("ISC")
+#
+# SPDX-License-Identifier: MPL-2.0
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0.  If a copy of the MPL was not distributed with this
+# file, you can obtain one at https://mozilla.org/MPL/2.0/.
+#
+# See the COPYRIGHT file distributed with this work for additional
+# information regarding copyright ownership.
+
+from typing import AsyncGenerator
+
+import dns.opcode
+import dns.rcode
+
+from isctest.asyncserver import (
+    AsyncDnsServer,
+    DnsResponseSend,
+    ResponseHandler,
+    QueryContext,
+)
+
+
+class ReplyUpdateHandler(ResponseHandler):
+    async def get_responses(
+        self, qctx: QueryContext
+    ) -> AsyncGenerator[DnsResponseSend, None]:
+        qctx.response.set_opcode(dns.opcode.UPDATE)
+        yield DnsResponseSend(qctx.response)
+
+
+def main() -> None:
+    server = AsyncDnsServer(default_aa=True, default_rcode=dns.rcode.NOERROR)
+    server.install_response_handler(ReplyUpdateHandler())
+    server.run()
+
+
+if __name__ == "__main__":
+    main()
diff --git a/bin/tests/system/digdelv/ans7/ans.pl b/bin/tests/system/digdelv/ans7/ans.pl
deleted file mode 100755
index a7aa60eb9d..0000000000
--- a/bin/tests/system/digdelv/ans7/ans.pl
+++ /dev/null
@@ -1,68 +0,0 @@
-#!/usr/bin/perl -w
-
-# Copyright (C) Internet Systems Consortium, Inc. ("ISC")
-#
-# SPDX-License-Identifier: MPL-2.0
-#
-# This Source Code Form is subject to the terms of the Mozilla Public
-# License, v. 2.0.  If a copy of the MPL was not distributed with this
-# file, you can obtain one at https://mozilla.org/MPL/2.0/.
-#
-# See the COPYRIGHT file distributed with this work for additional
-# information regarding copyright ownership.
-
-use IO::File;
-use IO::Socket;
-use Net::DNS;
-use Net::DNS::Packet;
-
-my $localport = int($ENV{'PORT'});
-if (!$localport) { $localport = 5300; }
-
-my $sock = IO::Socket::INET->new(LocalAddr => "10.53.0.7",
-   LocalPort => $localport, Proto => "udp") or die "$!";
-
-my $pidf = new IO::File "ans.pid", "w" or die "cannot open pid file: $!";
-print $pidf "$$\n" or die "cannot write pid file: $!";
-$pidf->close or die "cannot close pid file: $!";
-sub rmpid { unlink "ans.pid"; exit 1; };
-
-$SIG{INT} = \&rmpid;
-$SIG{TERM} = \&rmpid;
-
-STDOUT->autoflush(1);
-
-print "Net::DNS::VERSION => $Net::DNS::VERSION\n";
-
-for (;;) {
-	$sock->recv($buf, 512);
-
-	print "**** request from " , $sock->peerhost, " port ", $sock->peerport, "\n";
-
-	my $packet;
-
-	if ($Net::DNS::VERSION > 0.68) {
-		$packet = new Net::DNS::Packet(\$buf, 0);
-		$@ and die $@;
-	} else {
-		my $err;
-		($packet, $err) = new Net::DNS::Packet(\$buf, 0);
-		$err and die $err;
-	}
-
-	print "REQUEST:\n";
-	$packet->print;
-
-	$packet->header->qr(1);
-	$packet->header->opcode(5);
-
-	my @questions = $packet->question;
-	my $qname = $questions[0]->qname;
-	my $qtype = $questions[0]->qtype;
-	$packet->push("update", rr_del("$qname SOA"));
-
-	print "RESPONSE:\n";
-	$packet->print;
-
-	$sock->send($packet->data);
-}
diff --git a/bin/tests/system/digdelv/ans7/ans.py b/bin/tests/system/digdelv/ans7/ans.py
new file mode 100644
index 0000000000..d959b597e2
--- /dev/null
+++ b/bin/tests/system/digdelv/ans7/ans.py
@@ -0,0 +1,76 @@
+# Copyright (C) Internet Systems Consortium, Inc. ("ISC")
+#
+# SPDX-License-Identifier: MPL-2.0
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0.  If a copy of the MPL was not distributed with this
+# file, you can obtain one at https://mozilla.org/MPL/2.0/.
+#
+# See the COPYRIGHT file distributed with this work for additional
+# information regarding copyright ownership.
+
+from typing import AsyncGenerator
+
+import dns
+import dns.rcode
+
+from isctest.asyncserver import (
+    AsyncDnsServer,
+    CloseConnection,
+    DnsResponseSend,
+    DomainHandler,
+    IgnoreAllQueries,
+    QueryContext,
+    ResponseAction,
+    ResponseDrop,
+)
+
+
+class SilentHandler(DomainHandler, IgnoreAllQueries):
+    """Handler that doesn't respond."""
+
+    domains = ["silent.example"]
+
+
+class CloseHandler(DomainHandler):
+    """Handler that doesn't respond and closes TCP connection."""
+
+    domains = ["close.example"]
+
+    async def get_responses(
+        self, qctx: QueryContext
+    ) -> AsyncGenerator[ResponseAction, None]:
+        yield CloseConnection()
+
+
+class SilentThenServfailHandler(DomainHandler):
+    """Handler that drops one query and response to the next one with SERVFAIL."""
+
+    domains = ["silent-then-servfail.example"]
+    counter = 0
+
+    async def get_responses(
+        self, qctx: QueryContext
+    ) -> AsyncGenerator[ResponseAction, None]:
+        if self.counter % 2 == 0:
+            yield ResponseDrop()
+        else:
+            qctx.response.set_rcode(dns.rcode.SERVFAIL)
+            yield DnsResponseSend(qctx.response, authoritative=False)
+        self.counter += 1
+
+
+def main() -> None:
+    server = AsyncDnsServer()
+    server.install_response_handlers(
+        [
+            CloseHandler(),
+            SilentHandler(),
+            SilentThenServfailHandler(),
+        ]
+    )
+    server.run()
+
+
+if __name__ == "__main__":
+    main()
diff --git a/bin/tests/system/digdelv/ans8/ans.py b/bin/tests/system/digdelv/ans8/ans.py
deleted file mode 100644
index 3e18edc1cc..0000000000
--- a/bin/tests/system/digdelv/ans8/ans.py
+++ /dev/null
@@ -1,202 +0,0 @@
-# Copyright (C) Internet Systems Consortium, Inc. ("ISC")
-#
-# SPDX-License-Identifier: MPL-2.0
-#
-# This Source Code Form is subject to the terms of the Mozilla Public
-# License, v. 2.0.  If a copy of the MPL was not distributed with this
-# file, you can obtain one at https://mozilla.org/MPL/2.0/.
-#
-# See the COPYRIGHT file distributed with this work for additional
-# information regarding copyright ownership.
-
-from __future__ import print_function
-import os
-import sys
-import signal
-import socket
-import select
-import struct
-
-import dns, dns.message
-from dns.rcode import *
-
-modes = [
-    b"silent",  # Do not respond
-    b"close",  # UDP: same as silent; TCP: also close the connection
-    b"servfail",  # Always respond with SERVFAIL
-    b"unstable",  # Constantly switch between "silent" and "servfail"
-]
-mode = modes[0]
-n = 0
-
-
-def ctrl_channel(msg):
-    global modes, mode, n
-
-    msg = msg.splitlines().pop(0)
-    print("Received control message: %s" % msg)
-
-    if msg in modes:
-        mode = msg
-        n = 0
-        print("New mode: %s" % str(mode))
-
-
-def create_servfail(msg):
-    m = dns.message.from_wire(msg)
-    qname = m.question[0].name.to_text()
-    rrtype = m.question[0].rdtype
-    typename = dns.rdatatype.to_text(rrtype)
-
-    with open("query.log", "a") as f:
-        f.write("%s %s\n" % (typename, qname))
-        print("%s %s" % (typename, qname), end=" ")
-
-    r = dns.message.make_response(m)
-    r.set_rcode(SERVFAIL)
-    return r
-
-
-def sigterm(signum, frame):
-    print("Shutting down now...")
-    os.remove("ans.pid")
-    running = False
-    sys.exit(0)
-
-
-ip4 = "10.53.0.8"
-
-try:
-    port = int(os.environ["PORT"])
-except:
-    port = 5300
-
-try:
-    ctrlport = int(os.environ["EXTRAPORT1"])
-except:
-    ctrlport = 5300
-
-query4_udp = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
-query4_udp.bind((ip4, port))
-
-query4_tcp = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
-query4_tcp.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
-query4_tcp.bind((ip4, port))
-query4_tcp.listen(100)
-
-ctrl4_tcp = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
-ctrl4_tcp.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
-ctrl4_tcp.bind((ip4, ctrlport))
-ctrl4_tcp.listen(100)
-
-signal.signal(signal.SIGTERM, sigterm)
-
-f = open("ans.pid", "w")
-pid = os.getpid()
-print(pid, file=f)
-f.close()
-
-running = True
-
-print("Listening on %s port %d" % (ip4, port))
-print("Listening on %s port %d" % (ip4, ctrlport))
-print("Ctrl-c to quit")
-
-input = [query4_udp, query4_tcp, ctrl4_tcp]
-
-hung_conns = []
-
-while running:
-    try:
-        inputready, outputready, exceptready = select.select(input, [], [])
-    except select.error as e:
-        break
-    except socket.error as e:
-        break
-    except KeyboardInterrupt:
-        break
-
-    for s in inputready:
-        if s == query4_udp:
-            n = n + 1
-            print("UDP query received on %s" % ip4, end=" ")
-            msg = s.recvfrom(65535)
-            if (
-                mode == b"silent"
-                or mode == b"close"
-                or (mode == b"unstable" and n % 2 == 1)
-            ):
-                # Do not respond.
-                print("NO RESPONSE (%s)" % str(mode))
-                continue
-            elif mode == b"servfail" or (mode == b"unstable" and n % 2 == 0):
-                rsp = create_servfail(msg[0])
-                if rsp:
-                    print(dns.rcode.to_text(rsp.rcode()))
-                    s.sendto(rsp.to_wire(), msg[1])
-                else:
-                    print("NO RESPONSE (can not create a response)")
-            else:
-                raise (Exception("unsupported mode: %s" % mode))
-        elif s == query4_tcp:
-            n = n + 1
-            print("TCP query received on %s" % ip4, end=" ")
-            conn = None
-            try:
-                if mode == b"silent" or (mode == b"unstable" and n % 2 == 1):
-                    conn, addr = s.accept()
-                    # Do not respond and hang the connection.
-                    print("NO RESPONSE (%s)" % str(mode))
-                    hung_conns.append(conn)
-                    continue
-                elif mode == b"close":
-                    conn, addr = s.accept()
-                    # Do not respond and close the connection.
-                    print("NO RESPONSE (%s)" % str(mode))
-                    conn.close()
-                    continue
-                elif mode == b"servfail" or (mode == b"unstable" and n % 2 == 0):
-                    conn, addr = s.accept()
-                    # get TCP message length
-                    msg = conn.recv(2)
-                    if len(msg) != 2:
-                        print("NO RESPONSE (can not read the message length)")
-                        conn.close()
-                        continue
-                    length = struct.unpack(">H", msg[:2])[0]
-                    msg = conn.recv(length)
-                    if len(msg) != length:
-                        print("NO RESPONSE (can not read the message)")
-                        conn.close()
-                        continue
-                    rsp = create_servfail(msg)
-                    if rsp:
-                        print(dns.rcode.to_text(rsp.rcode()))
-                        wire = rsp.to_wire()
-                        conn.send(struct.pack(">H", len(wire)))
-                        conn.send(wire)
-                    else:
-                        print("NO RESPONSE (can not create a response)")
-                else:
-                    raise (Exception("unsupported mode: %s" % mode))
-            except socket.error as e:
-                print("NO RESPONSE (error: %s)" % str(e))
-            if conn:
-                conn.close()
-        elif s == ctrl4_tcp:
-            print("Control channel connected")
-            conn = None
-            try:
-                # Handle control channel input
-                conn, addr = s.accept()
-                msg = conn.recv(1024)
-                if msg:
-                    ctrl_channel(msg)
-                conn.close()
-            except s.timeout:
-                pass
-            if conn:
-                conn.close()
-
-    if not running:
-        break
diff --git a/bin/tests/system/digdelv/ns2/example.db.in b/bin/tests/system/digdelv/ns2/example.db.in
index 8a88e038cf..9f938873f5 100644
--- a/bin/tests/system/digdelv/ns2/example.db.in
+++ b/bin/tests/system/digdelv/ns2/example.db.in
@@ -33,6 +33,9 @@ c			AAAA	fd92:7065:b8e:ffff::3
 d			A	10.0.0.0
 d			AAAA	fd92:7065:b8e:ffff::
 
+silent			A	10.0.0.1
+close			A	10.0.0.1
+
 xn--caf-dma		A	10.1.2.3
 
 foo			TXT	"testing"
diff --git a/bin/tests/system/digdelv/tests.sh b/bin/tests/system/digdelv/tests.sh
index 265366a247..c688c5a999 100644
--- a/bin/tests/system/digdelv/tests.sh
+++ b/bin/tests/system/digdelv/tests.sh
@@ -19,10 +19,6 @@ set -e
 status=0
 n=0
 
-sendcmd() {
-  send "${1}" "$EXTRAPORT1"
-}
-
 dig_with_opts() {
   "$DIG" -p "$PORT" "$@"
 }
@@ -31,6 +27,12 @@ mdig_with_opts() {
   "$MDIG" -p "$PORT" "$@"
 }
 
+set_response_sequence() {
+  SEQUENCE="${1}"
+  LOGID="${2}"
+  dig_with_opts @10.53.0.5 "${SEQUENCE}.response-sequence._control" TXT >dig.out.control${LOGID} 2>&1 || ret=1
+}
+
 # Check if response in file $1 has the correct TTL range.
 # The response record must have RRtype $2 and class IN (CLASS1).
 # Maximum TTL is given by $3.  This works in most cases where TTL is
@@ -71,72 +73,44 @@ NOSPLIT="$(sed <ns2/keydata -e 's/+/[+]/g' -e 's/ //g')"
 HAS_PYYAML=0
 $PYTHON -c "import yaml" 2>/dev/null && HAS_PYYAML=1
 
-#
-# test whether ans7/ans.pl will be able to send a UPDATE response.
-# if it can't, we will log that below.
-#
-if "$PERL" -e 'use Net::DNS; use Net::DNS::Packet; my $p = new Net::DNS::Packet; $p->header->opcode(5);' >/dev/null 2>&1; then
-  checkupdate=1
-else
-  checkupdate=0
-fi
+n=$((n + 1))
+echo_i "check nslookup handles UPDATE response ($n)"
+ret=0
+"$NSLOOKUP" -q=CNAME -timeout=1 "-port=$PORT" foo.bar 10.53.0.6 >nslookup.out.test$n 2>&1 && ret=1
+grep "Opcode mismatch" nslookup.out.test$n >/dev/null || ret=1
+if [ $ret -ne 0 ]; then echo_i "failed"; fi
+status=$((status + ret))
 
-if [ -x "$NSLOOKUP" -a $checkupdate -eq 1 ]; then
+n=$((n + 1))
+echo_i "check host handles UPDATE response ($n)"
+ret=0
+"$HOST" -W 1 -t CNAME -p $PORT foo.bar 10.53.0.6 >host.out.test$n 2>&1 && ret=1
+grep "Opcode mismatch" host.out.test$n >/dev/null || ret=1
+if [ $ret -ne 0 ]; then echo_i "failed"; fi
+status=$((status + ret))
 
-  n=$((n + 1))
-  echo_i "check nslookup handles UPDATE response ($n)"
-  ret=0
-  "$NSLOOKUP" -q=CNAME -timeout=1 "-port=$PORT" foo.bar 10.53.0.7 >nslookup.out.test$n 2>&1 && ret=1
-  grep "Opcode mismatch" nslookup.out.test$n >/dev/null || ret=1
-  if [ $ret -ne 0 ]; then echo_i "failed"; fi
-  status=$((status + ret))
-
-fi
-
-if [ -x "$HOST" -a $checkupdate -eq 1 ]; then
-
-  n=$((n + 1))
-  echo_i "check host handles UPDATE response ($n)"
-  ret=0
-  "$HOST" -W 1 -t CNAME -p $PORT foo.bar 10.53.0.7 >host.out.test$n 2>&1 && ret=1
-  grep "Opcode mismatch" host.out.test$n >/dev/null || ret=1
-  if [ $ret -ne 0 ]; then echo_i "failed"; fi
-  status=$((status + ret))
-
-fi
-
-if [ -x "$NSUPDATE" -a $checkupdate -eq 1 ]; then
-
-  n=$((n + 1))
-  echo_i "check nsupdate handles UPDATE response to QUERY ($n)"
-  ret=0
-  res=0
-  $NSUPDATE <<EOF >nsupdate.out.test$n 2>&1 || res=$?
-server 10.53.0.7 ${PORT}
+n=$((n + 1))
+echo_i "check nsupdate handles UPDATE response to QUERY ($n)"
+ret=0
+res=0
+$NSUPDATE <<EOF >nsupdate.out.test$n 2>&1 || res=$?
+server 10.53.0.6 ${PORT}
 add x.example.com 300 in a 1.2.3.4
 send
 EOF
-  test $res -eq 1 || ret=1
-  grep "invalid OPCODE in response to SOA query" nsupdate.out.test$n >/dev/null || ret=1
-  if [ $ret -ne 0 ]; then echo_i "failed"; fi
-  status=$((status + ret))
-
-fi
+test $res -eq 1 || ret=1
+grep "invalid OPCODE in response to SOA query" nsupdate.out.test$n >/dev/null || ret=1
+if [ $ret -ne 0 ]; then echo_i "failed"; fi
+status=$((status + ret))
 
 if [ -x "$DIG" ]; then
-
-  if [ $checkupdate -eq 1 ]; then
-
-    n=$((n + 1))
-    echo_i "check dig handles UPDATE response ($n)"
-    ret=0
-    dig_with_opts @10.53.0.7 +tries=1 +timeout=1 cname foo.bar >dig.out.test$n 2>&1 && ret=1
-    grep "Opcode mismatch" dig.out.test$n >/dev/null || ret=1
-    if [ $ret -ne 0 ]; then echo_i "failed"; fi
-    status=$((status + ret))
-  else
-    echo_i "Skipped UPDATE handling test"
-  fi
+  n=$((n + 1))
+  echo_i "check dig handles UPDATE response ($n)"
+  ret=0
+  dig_with_opts @10.53.0.6 +tries=1 +timeout=1 cname foo.bar >dig.out.test$n 2>&1 && ret=1
+  grep "Opcode mismatch" dig.out.test$n >/dev/null || ret=1
+  if [ $ret -ne 0 ]; then echo_i "failed"; fi
+  status=$((status + ret))
 
   n=$((n + 1))
   echo_i "checking dig short form works ($n)"
@@ -382,8 +356,6 @@ if [ -x "$DIG" ]; then
   n=$((n + 1))
   echo_i "checking dig preserves origin on TCP retries ($n)"
   ret=0
-  # Ask ans4 to still accept TCP connections, but not respond to queries
-  echo "//" | sendcmd 10.53.0.4
   dig_with_opts -d +tcp @10.53.0.4 +retry=1 +time=1 +domain=bar foo >dig.out.test$n 2>&1 && ret=1
   test "$(grep -c "trying origin bar" dig.out.test$n)" -eq 2 || ret=1
   grep "using root origin" <dig.out.test$n >/dev/null && ret=1
@@ -1042,7 +1014,7 @@ if [ -x "$DIG" ]; then
   n=$((n + 1))
   echo_i "checking exit code for a retry upon TCP EOF (immediate -> immediate) ($n)"
   ret=0
-  echo "no_response no_response" | sendcmd 10.53.0.5
+  set_response_sequence no-response $n
   dig_with_opts @10.53.0.5 example AXFR +tries=2 >dig.out.test$n 2>&1 && ret=1
   # Sanity check: ensure ans5 behaves as expected.
   [ $(grep "communications error.*end of file" dig.out.test$n | wc -l) -eq 2 ] || ret=1
@@ -1052,7 +1024,7 @@ if [ -x "$DIG" ]; then
   n=$((n + 1))
   echo_i "checking exit code for a retry upon TCP EOF (partial AXFR -> partial AXFR) ($n)"
   ret=0
-  echo "partial_axfr partial_axfr" | sendcmd 10.53.0.5
+  set_response_sequence partial-axfr $n
   dig_with_opts @10.53.0.5 example AXFR +tries=2 >dig.out.test$n 2>&1 && ret=1
   # Sanity check: ensure ans5 behaves as expected.
   [ $(grep "communications error.*end of file" dig.out.test$n | wc -l) -eq 2 ] || ret=1
@@ -1062,7 +1034,7 @@ if [ -x "$DIG" ]; then
   n=$((n + 1))
   echo_i "checking exit code for a retry upon TCP EOF (immediate -> partial AXFR) ($n)"
   ret=0
-  echo "no_response partial_axfr" | sendcmd 10.53.0.5
+  set_response_sequence no-response.partial-axfr $n
   dig_with_opts @10.53.0.5 example AXFR +tries=2 >dig.out.test$n 2>&1 && ret=1
   # Sanity check: ensure ans5 behaves as expected.
   [ $(grep "communications error.*end of file" dig.out.test$n | wc -l) -eq 2 ] || ret=1
@@ -1072,7 +1044,7 @@ if [ -x "$DIG" ]; then
   n=$((n + 1))
   echo_i "checking exit code for a retry upon TCP EOF (partial AXFR -> immediate) ($n)"
   ret=0
-  echo "partial_axfr no_response" | sendcmd 10.53.0.5
+  set_response_sequence partial-axfr.no-response $n
   dig_with_opts @10.53.0.5 example AXFR +tries=2 >dig.out.test$n 2>&1 && ret=1
   # Sanity check: ensure ans5 behaves as expected.
   [ $(grep "communications error.*end of file" dig.out.test$n | wc -l) -eq 2 ] || ret=1
@@ -1082,7 +1054,7 @@ if [ -x "$DIG" ]; then
   n=$((n + 1))
   echo_i "checking exit code for a retry upon TCP EOF (immediate -> complete AXFR) ($n)"
   ret=0
-  echo "no_response complete_axfr" | sendcmd 10.53.0.5
+  set_response_sequence no-response.complete-axfr $n
   dig_with_opts @10.53.0.5 example AXFR +tries=2 >dig.out.test$n 2>&1 || ret=1
   # Sanity check: ensure ans5 behaves as expected.
   [ $(grep "communications error.*end of file" dig.out.test$n | wc -l) -eq 1 ] || ret=1
@@ -1092,7 +1064,7 @@ if [ -x "$DIG" ]; then
   n=$((n + 1))
   echo_i "checking exit code for a retry upon TCP EOF (partial AXFR -> complete AXFR) ($n)"
   ret=0
-  echo "partial_axfr complete_axfr" | sendcmd 10.53.0.5
+  set_response_sequence partial-axfr.complete-axfr $n
   dig_with_opts @10.53.0.5 example AXFR +tries=2 >dig.out.test$n 2>&1 || ret=1
   # Sanity check: ensure ans5 behaves as expected.
   [ $(grep "communications error.*end of file" dig.out.test$n | wc -l) -eq 1 ] || ret=1
@@ -1102,7 +1074,7 @@ if [ -x "$DIG" ]; then
   n=$((n + 1))
   echo_i "checking +tries=1 won't retry twice upon TCP EOF ($n)"
   ret=0
-  echo "no_response no_response" | sendcmd 10.53.0.5
+  set_response_sequence no-response $n
   dig_with_opts @10.53.0.5 example AXFR +tries=1 >dig.out.test$n 2>&1 && ret=1
   # Sanity check: ensure ans5 behaves as expected.
   [ $(grep "communications error.*end of file" dig.out.test$n | wc -l) -eq 1 ] || ret=1
@@ -1236,20 +1208,16 @@ if [ -x "$DIG" ]; then
   # See [GL #3020] for more information
   n=$((n + 1))
   echo_i "check that dig handles UDP timeout followed by a SERVFAIL correctly ($n)"
-  # Ask ans8 to be in "unstable" mode (switching between "silent" and "servfail" modes)
-  echo "unstable" | sendcmd 10.53.0.8
   ret=0
-  dig_with_opts +timeout=1 +nofail @10.53.0.8 a.example >dig.out.test$n 2>&1 || ret=1
+  dig_with_opts +timeout=1 +nofail @10.53.0.7 silent-then-servfail.example >dig.out.test$n 2>&1 || ret=1
   grep -F "status: SERVFAIL" dig.out.test$n >/dev/null || ret=1
   if [ $ret -ne 0 ]; then echo_i "failed"; fi
   status=$((status + ret))
 
   n=$((n + 1))
   echo_i "check that dig handles TCP timeout followed by a SERVFAIL correctly ($n)"
-  # Ask ans8 to be in "unstable" mode (switching between "silent" and "servfail" modes)
-  echo "unstable" | sendcmd 10.53.0.8
   ret=0
-  dig_with_opts +timeout=1 +nofail +tcp @10.53.0.8 a.example >dig.out.test$n 2>&1 || ret=1
+  dig_with_opts +timeout=1 +nofail +tcp @10.53.0.7 silent-then-servfail.example >dig.out.test$n 2>&1 || ret=1
   grep -F "status: SERVFAIL" dig.out.test$n >/dev/null || ret=1
   if [ $ret -ne 0 ]; then echo_i "failed"; fi
   status=$((status + ret))
@@ -1282,10 +1250,8 @@ if [ -x "$DIG" ]; then
 
   n=$((n + 1))
   echo_i "check that dig tries the next server after a TCP socket read error ($n)"
-  # Ask ans8 to be in "close" mode, which closes the connection after accepting it
-  echo "close" | sendcmd 10.53.0.8
   ret=0
-  dig_with_opts +tcp @10.53.0.8 @10.53.0.3 a.example >dig.out.test$n 2>&1 || ret=1
+  dig_with_opts +tcp @10.53.0.7 @10.53.0.3 close.example >dig.out.test$n 2>&1 || ret=1
   grep -F "status: NOERROR" dig.out.test$n >/dev/null || ret=1
   if [ $ret -ne 0 ]; then echo_i "failed"; fi
   status=$((status + ret))
@@ -1307,20 +1273,16 @@ if [ -x "$DIG" ]; then
 
   n=$((n + 1))
   echo_i "check that dig tries the next server after UDP socket read timeouts ($n)"
-  # Ask ans8 to be in "silent" mode
-  echo "silent" | sendcmd 10.53.0.8
   ret=0
-  dig_with_opts +timeout=1 @10.53.0.8 @10.53.0.3 a.example >dig.out.test$n 2>&1 || ret=1
+  dig_with_opts +timeout=1 @10.53.0.7 @10.53.0.3 silent.example >dig.out.test$n 2>&1 || ret=1
   grep -F "status: NOERROR" dig.out.test$n >/dev/null || ret=1
   if [ $ret -ne 0 ]; then echo_i "failed"; fi
   status=$((status + ret))
 
   n=$((n + 1))
   echo_i "check that dig tries the next server after TCP socket read timeouts ($n)"
-  # Ask ans8 to be in "silent" mode
-  echo "silent" | sendcmd 10.53.0.8
   ret=0
-  dig_with_opts +timeout=1 +tcp @10.53.0.8 @10.53.0.3 a.example >dig.out.test$n 2>&1 || ret=1
+  dig_with_opts +timeout=1 +tcp @10.53.0.7 @10.53.0.3 silent.example >dig.out.test$n 2>&1 || ret=1
   grep -F "status: NOERROR" dig.out.test$n >/dev/null || ret=1
   if [ $ret -ne 0 ]; then echo_i "failed"; fi
   status=$((status + ret))
@@ -1329,7 +1291,7 @@ if [ -x "$DIG" ]; then
   n=$((n + 1))
   echo_i "check that dig correctly refuses to use a server with a IPv4 mapped IPv6 address after failing with a regular IP address ($n)"
   ret=0
-  dig_with_opts @10.53.0.8 @::ffff:10.53.0.8 a.example >dig.out.test$n 2>&1 || ret=1
+  dig_with_opts @10.53.0.7 @::ffff:10.53.0.7 silent.example >dig.out.test$n 2>&1 || ret=1
   grep -F ";; Skipping mapped address" dig.out.test$n >/dev/null || ret=1
   grep -F ";; No acceptable nameservers" dig.out.test$n >/dev/null || ret=1
   if [ $ret -ne 0 ]; then echo_i "failed"; fi
diff --git a/bin/tests/system/digdelv/tests_sh_digdelv.py b/bin/tests/system/digdelv/tests_sh_digdelv.py
index 5767bc1a6e..3ed7811c1c 100644
--- a/bin/tests/system/digdelv/tests_sh_digdelv.py
+++ b/bin/tests/system/digdelv/tests_sh_digdelv.py
@@ -11,6 +11,9 @@
 
 import pytest
 
+# isctest.asyncserver requires dnspython >= 2.0.0
+pytest.importorskip("dns", minversion="2.0.0")
+
 pytestmark = pytest.mark.extra_artifacts(
     [
         "delv.out.*",
@@ -20,7 +23,6 @@ pytestmark = pytest.mark.extra_artifacts(
         "nsupdate.out.*",
         "yamlget.out.*",
         "ans*/ans.run",
-        "ans*/query.log",
         "ns*/anchor.*",
         "ns*/dsset-*",
         "ns*/keydata",
diff --git a/bin/tests/system/isctest/asyncserver.py b/bin/tests/system/isctest/asyncserver.py
index eaf9ded26c..86de57cf71 100644
--- a/bin/tests/system/isctest/asyncserver.py
+++ b/bin/tests/system/isctest/asyncserver.py
@@ -429,10 +429,9 @@ class _ConnectionTeardownRequested(Exception):
 
 
 @dataclass
-class ResponseDropAndCloseConnection(ResponseAction):
+class CloseConnection(ResponseAction):
     """
-    Action which makes the server close the connection after the DNS query is
-    received by the server (TCP only).
+    Action which makes the server close the connection (TCP only).
 
     The connection may be closed with a delay if requested.
     """
@@ -555,8 +554,8 @@ class ConnectionReset(ConnectionHandler):
     make the server send an RST segment; this happens when the server closes a
     client's socket while there is still unread data in that socket's buffer.
     If closing the connection _after_ the query is read by the server is enough
-    for a given use case, the ResponseDropAndCloseConnection response handler
-    should be used instead.
+    for a given use case, the CloseConnection response handler should be used
+    instead.
     """
 
     delay: float = 0.0