diff --git a/bin/delv/delv.c b/bin/delv/delv.c
index e06322de11..5af7c15653 100644
--- a/bin/delv/delv.c
+++ b/bin/delv/delv.c
@@ -2117,12 +2117,13 @@ cleanup:
 
 static isc_result_t
 matchview(isc_netaddr_t *srcaddr, isc_netaddr_t *destaddr,
-	  dns_message_t *message, dns_aclenv_t *env, isc_result_t *sigresultp,
-	  dns_view_t **viewp) {
+	  dns_message_t *message, dns_aclenv_t *env, ns_server_t *lsctx,
+	  isc_result_t *sigresultp, dns_view_t **viewp) {
 	UNUSED(srcaddr);
 	UNUSED(destaddr);
 	UNUSED(message);
 	UNUSED(env);
+	UNUSED(lsctx);
 	UNUSED(sigresultp);
 
 	*viewp = view;
diff --git a/bin/named/config.c b/bin/named/config.c
index 732e28e606..62c05a8314 100644
--- a/bin/named/config.c
+++ b/bin/named/config.c
@@ -109,6 +109,8 @@ options {\n\
 #	session-keyfile \"" NAMED_LOCALSTATEDIR "/run/named/session.key\";\n\
 	session-keyname local-ddns;\n\
 	startup-notify-rate 20;\n\
+	sig0checks-quota 1;\n\
+	sig0checks-quota-maxwait-ms 1500;\n\
 	statistics-file \"named.stats\";\n\
 	tcp-advertised-timeout 300;\n\
 	tcp-clients 150;\n\
diff --git a/bin/named/server.c b/bin/named/server.c
index c41f5d9b24..162b556542 100644
--- a/bin/named/server.c
+++ b/bin/named/server.c
@@ -8412,6 +8412,8 @@ load_configuration(const char *filename, named_server_t *server,
 	configure_server_quota(maps, "recursive-clients",
 			       &server->sctx->recursionquota);
 	configure_server_quota(maps, "update-quota", &server->sctx->updquota);
+	configure_server_quota(maps, "sig0checks-quota",
+			       &server->sctx->sig0checksquota);
 
 	max = isc_quota_getmax(&server->sctx->recursionquota);
 	if (max > 1000) {
@@ -8430,9 +8432,23 @@ load_configuration(const char *filename, named_server_t *server,
 	} else {
 		softquota = (max * 90) / 100;
 	}
-
 	isc_quota_soft(&server->sctx->recursionquota, softquota);
 
+	obj = NULL;
+	result = named_config_get(maps, "sig0checks-quota-exempt", &obj);
+	if (result == ISC_R_SUCCESS) {
+		result = cfg_acl_fromconfig(
+			obj, config, named_g_lctx, named_g_aclconfctx,
+			named_g_mctx, 0, &server->sctx->sig0checksquota_exempt);
+		INSIST(result == ISC_R_SUCCESS);
+	}
+
+	obj = NULL;
+	result = named_config_get(maps, "sig0checks-quota-maxwait-ms", &obj);
+	if (result == ISC_R_SUCCESS) {
+		server->sctx->sig0checksquota_maxwaitms = cfg_obj_asuint32(obj);
+	}
+
 	/*
 	 * Set "blackhole". Only legal at options level; there is
 	 * no default.
@@ -10048,11 +10064,12 @@ shutdown_server(void *arg) {
  */
 static isc_result_t
 get_matching_view(isc_netaddr_t *srcaddr, isc_netaddr_t *destaddr,
-		  dns_message_t *message, dns_aclenv_t *env,
+		  dns_message_t *message, dns_aclenv_t *env, ns_server_t *sctx,
 		  isc_result_t *sigresult, dns_view_t **viewp) {
 	dns_view_t *view;
 
 	REQUIRE(message != NULL);
+	REQUIRE(sctx != NULL);
 	REQUIRE(sigresult != NULL);
 	REQUIRE(viewp != NULL && *viewp == NULL);
 
@@ -10063,13 +10080,49 @@ get_matching_view(isc_netaddr_t *srcaddr, isc_netaddr_t *destaddr,
 		    message->rdclass == dns_rdataclass_any)
 		{
 			const dns_name_t *tsig = NULL;
+			int exempt_match;
+			isc_result_t sig0_qresult = ISC_R_UNSET;
 
+			if (message->sig0 != NULL) {
+				/*
+				 * If the message has a SIG0 signature and the
+				 * client is not exempt from the quota, then
+				 * acquire a quota. If quota is reached, then
+				 * return early.
+				 */
+				if (sctx->sig0checksquota_exempt != NULL) {
+					isc_result_t result = dns_acl_match(
+						srcaddr, NULL,
+						sctx->sig0checksquota_exempt,
+						env, &exempt_match, NULL);
+					if (result == ISC_R_SUCCESS &&
+					    exempt_match > 0)
+					{
+						sig0_qresult = ISC_R_EXISTS;
+					}
+				}
+				if (sig0_qresult == ISC_R_UNSET) {
+					sig0_qresult = isc_quota_acquire(
+						&sctx->sig0checksquota);
+				}
+				if (sig0_qresult == ISC_R_SOFTQUOTA) {
+					isc_quota_release(
+						&sctx->sig0checksquota);
+				}
+				if (sig0_qresult != ISC_R_SUCCESS &&
+				    sig0_qresult != ISC_R_EXISTS)
+				{
+					return (ISC_R_QUOTA);
+				}
+			}
+
+			/* Check the signature, then release the quota  */
 			*sigresult = dns_message_rechecksig(message, view);
+			if (sig0_qresult == ISC_R_SUCCESS) {
+				isc_quota_release(&sctx->sig0checksquota);
+			}
 			if (*sigresult == ISC_R_SUCCESS) {
-				dns_tsigkey_t *tsigkey;
-
-				tsigkey = message->tsigkey;
-				tsig = dns_tsigkey_identity(tsigkey);
+				tsig = dns_tsigkey_identity(message->tsigkey);
 			}
 
 			if (dns_acl_allowed(srcaddr, tsig, view->matchclients,
diff --git a/bin/tests/system/checkconf/bad-sig0checks-quota-exempt.conf b/bin/tests/system/checkconf/bad-sig0checks-quota-exempt.conf
new file mode 100644
index 0000000000..c54227dd91
--- /dev/null
+++ b/bin/tests/system/checkconf/bad-sig0checks-quota-exempt.conf
@@ -0,0 +1,16 @@
+/*
+ * 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.
+ */
+
+options {
+	sig0checks-quota-exempt { unknownacl; };
+};
diff --git a/bin/tests/system/checkconf/good-sig0checks-quota-exempt.conf b/bin/tests/system/checkconf/good-sig0checks-quota-exempt.conf
new file mode 100644
index 0000000000..2968ebefe0
--- /dev/null
+++ b/bin/tests/system/checkconf/good-sig0checks-quota-exempt.conf
@@ -0,0 +1,20 @@
+/*
+ * 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.
+ */
+
+acl goodacl {
+	192.168.0.1;
+};
+
+options {
+	sig0checks-quota-exempt { 10.0.0.0/8; 2001:db8::100; goodacl; };
+};
diff --git a/doc/misc/options b/doc/misc/options
index de24eef2c2..d003e9e741 100644
--- a/doc/misc/options
+++ b/doc/misc/options
@@ -277,6 +277,9 @@ options {
 	sig-signing-signatures <integer>;
 	sig-signing-type <integer>;
 	sig-validity-interval <integer> [ <integer> ]; // obsolete
+	sig0checks-quota <integer>;
+	sig0checks-quota-exempt { <address_match_element>; ... };
+	sig0checks-quota-maxwait-ms <integer>;
 	sortlist { <address_match_element>; ... }; // deprecated
 	stale-answer-client-timeout ( disabled | off | <integer> );
 	stale-answer-enable <boolean>;
diff --git a/lib/isccfg/check.c b/lib/isccfg/check.c
index e0c4bdc5b8..8dd8efa934 100644
--- a/lib/isccfg/check.c
+++ b/lib/isccfg/check.c
@@ -2073,6 +2073,21 @@ check_options(const cfg_obj_t *options, const cfg_obj_t *config,
 
 	cfg_aclconfctx_create(mctx, &actx);
 
+	obj = NULL;
+	(void)cfg_map_get(options, "sig0checks-quota-exempt", &obj);
+	if (obj != NULL) {
+		dns_acl_t *acl = NULL;
+
+		tresult = cfg_acl_fromconfig(obj, config, logctx, actx, mctx, 0,
+					     &acl);
+		if (acl != NULL) {
+			dns_acl_detach(&acl);
+		}
+		if (result == ISC_R_SUCCESS) {
+			result = tresult;
+		}
+	}
+
 	obj = NULL;
 	(void)cfg_map_get(options, "listen-on", &obj);
 	if (obj != NULL) {
diff --git a/lib/isccfg/namedconf.c b/lib/isccfg/namedconf.c
index 18b40fab7f..3a27432f7e 100644
--- a/lib/isccfg/namedconf.c
+++ b/lib/isccfg/namedconf.c
@@ -1361,6 +1361,9 @@ static cfg_clausedef_t options_clauses[] = {
 	{ "session-keyalg", &cfg_type_astring, 0 },
 	{ "session-keyfile", &cfg_type_qstringornone, 0 },
 	{ "session-keyname", &cfg_type_astring, 0 },
+	{ "sig0checks-quota", &cfg_type_uint32, 0 },
+	{ "sig0checks-quota-maxwait-ms", &cfg_type_uint32, 0 },
+	{ "sig0checks-quota-exempt", &cfg_type_bracketed_aml, 0 },
 	{ "sit-secret", NULL, CFG_CLAUSEFLAG_ANCIENT },
 	{ "stacksize", &cfg_type_size, CFG_CLAUSEFLAG_ANCIENT },
 	{ "startup-notify-rate", &cfg_type_uint32, 0 },
diff --git a/lib/ns/client.c b/lib/ns/client.c
index c1341be828..03afc4d25c 100644
--- a/lib/ns/client.c
+++ b/lib/ns/client.c
@@ -118,11 +118,27 @@
 
 atomic_uint_fast64_t ns_client_requests = 0;
 
+static atomic_uint_fast32_t last_sigchecks_quota_log = 0;
+
+static bool
+can_log_sigchecks_quota(void) {
+	isc_stdtime_t last;
+	isc_stdtime_t now = isc_stdtime_now();
+	last = atomic_exchange_relaxed(&last_sigchecks_quota_log, now);
+	if (now != last) {
+		return (true);
+	}
+
+	return (false);
+}
+
 static void
 clientmgr_destroy_cb(void *arg);
 static void
 ns_client_dumpmessage(ns_client_t *client, const char *reason);
 static void
+ns_client_request_continue(void *arg);
+static void
 compute_cookie(ns_client_t *client, uint32_t when, const unsigned char *secret,
 	       isc_buffer_t *buf);
 
@@ -1739,6 +1755,53 @@ ns__client_put_cb(void *client0) {
 	ns_clientmgr_detach(&manager);
 }
 
+static isc_result_t
+ns_client_setup_view(ns_client_t *client, isc_netaddr_t *netaddr) {
+	isc_result_t result;
+
+	result = client->manager->sctx->matchingview(
+		netaddr, &client->destaddr, client->message,
+		client->manager->aclenv, client->manager->sctx,
+		&client->sigresult, &client->view);
+	if (result != ISC_R_SUCCESS) {
+		if (result == ISC_R_QUOTA) {
+			if (can_log_sigchecks_quota()) {
+				ns_client_log(client, NS_LOGCATEGORY_CLIENT,
+					      NS_LOGMODULE_CLIENT, ISC_LOG_INFO,
+					      "SIG(0) checks quota reached");
+				ns_client_dumpmessage(
+					client, "SIG(0) checks quota reached");
+			}
+		} else {
+			char classname[DNS_RDATACLASS_FORMATSIZE];
+			isc_buffer_t b;
+			isc_region_t *r;
+
+			/*
+			 * Do a dummy TSIG verification attempt so that the
+			 * response will have a TSIG if the query did, as
+			 * required by RFC2845.
+			 */
+			dns_message_resetsig(client->message);
+			r = dns_message_getrawmessage(client->message);
+			isc_buffer_init(&b, r->base, r->length);
+			isc_buffer_add(&b, r->length);
+			(void)dns_tsig_verify(&b, client->message, NULL, NULL);
+
+			dns_rdataclass_format(client->message->rdclass,
+					      classname, sizeof(classname));
+			ns_client_log(client, NS_LOGCATEGORY_CLIENT,
+				      NS_LOGMODULE_CLIENT, ISC_LOG_DEBUG(1),
+				      "no matching view in class '%s'",
+				      classname);
+			ns_client_dumpmessage(client,
+					      "no matching view in class");
+		}
+	}
+
+	return (result);
+}
+
 /*
  * Handle an incoming request event from the socket (UDP case)
  * or tcpmsg (TCP case).
@@ -1748,12 +1811,7 @@ ns_client_request(isc_nmhandle_t *handle, isc_result_t eresult,
 		  isc_region_t *region, void *arg) {
 	ns_client_t *client = NULL;
 	isc_result_t result;
-	isc_result_t sigresult = ISC_R_SUCCESS;
-	isc_buffer_t *buffer = NULL;
-	isc_buffer_t tbuffer;
 	dns_rdataset_t *opt = NULL;
-	const dns_name_t *signame = NULL;
-	bool ra; /* Recursion available. */
 	isc_netaddr_t netaddr;
 	int match;
 	dns_messageid_t id;
@@ -1761,28 +1819,6 @@ ns_client_request(isc_nmhandle_t *handle, isc_result_t eresult,
 	bool notimp;
 	size_t reqsize;
 	dns_aclenv_t *env = NULL;
-#ifdef HAVE_DNSTAP
-	dns_transport_type_t transport_type;
-	dns_dtmsgtype_t dtmsgtype;
-#endif /* ifdef HAVE_DNSTAP */
-	static const char *ra_reasons[] = {
-		"ACLs not processed yet",
-		"no resolver in view",
-		"recursion not enabled for view",
-		"allow-recursion did not match",
-		"allow-query-cache did not match",
-		"allow-recursion-on did not match",
-		"allow-query-cache-on did not match",
-	};
-	enum refusal_reasons {
-		INVALID,
-		NO_RESOLVER,
-		RECURSION_DISABLED,
-		ALLOW_RECURSION,
-		ALLOW_QUERY_CACHE,
-		ALLOW_RECURSION_ON,
-		ALLOW_QUERY_CACHE_ON
-	} ra_refusal_reason = INVALID;
 
 	if (eresult != ISC_R_SUCCESS) {
 		return;
@@ -1830,14 +1866,14 @@ ns_client_request(isc_nmhandle_t *handle, isc_result_t eresult,
 
 	(void)atomic_fetch_add_relaxed(&ns_client_requests, 1);
 
-	isc_buffer_init(&tbuffer, region->base, region->length);
-	isc_buffer_add(&tbuffer, region->length);
-	buffer = &tbuffer;
+	isc_buffer_init(&client->tbuffer, region->base, region->length);
+	isc_buffer_add(&client->tbuffer, region->length);
+	client->buffer = &client->tbuffer;
 
 	client->peeraddr = isc_nmhandle_peeraddr(handle);
 	client->peeraddr_valid = true;
 
-	reqsize = isc_buffer_usedlength(buffer);
+	reqsize = isc_buffer_usedlength(client->buffer);
 
 	client->state = NS_CLIENTSTATE_WORKING;
 
@@ -1876,7 +1912,7 @@ ns_client_request(isc_nmhandle_t *handle, isc_result_t eresult,
 		      ISC_LOG_DEBUG(3), "%s request",
 		      TCP_CLIENT(client) ? "TCP" : "UDP");
 
-	result = dns_message_peekheader(buffer, &id, &flags);
+	result = dns_message_peekheader(client->buffer, &id, &flags);
 	if (result != ISC_R_SUCCESS) {
 		/*
 		 * There isn't enough header to determine whether
@@ -1951,7 +1987,7 @@ ns_client_request(isc_nmhandle_t *handle, isc_result_t eresult,
 	/*
 	 * It's a request.  Parse it.
 	 */
-	result = dns_message_parse(client->message, buffer, 0);
+	result = dns_message_parse(client->message, client->buffer, 0);
 	if (result != ISC_R_SUCCESS) {
 		/*
 		 * Parsing the request failed.  Send a response
@@ -2080,38 +2116,119 @@ ns_client_request(isc_nmhandle_t *handle, isc_result_t eresult,
 	client->destsockaddr = isc_nmhandle_localaddr(handle);
 	isc_netaddr_fromsockaddr(&client->destaddr, &client->destsockaddr);
 
-	result = client->manager->sctx->matchingview(
-		&netaddr, &client->destaddr, client->message, env, &sigresult,
-		&client->view);
-	if (result != ISC_R_SUCCESS) {
-		char classname[DNS_RDATACLASS_FORMATSIZE];
-
-		/*
-		 * Do a dummy TSIG verification attempt so that the
-		 * response will have a TSIG if the query did, as
-		 * required by RFC2845.
-		 */
-		isc_buffer_t b;
-		isc_region_t *r;
-
-		dns_message_resetsig(client->message);
-
-		r = dns_message_getrawmessage(client->message);
-		isc_buffer_init(&b, r->base, r->length);
-		isc_buffer_add(&b, r->length);
-		(void)dns_tsig_verify(&b, client->message, NULL, NULL);
-
-		dns_rdataclass_format(client->message->rdclass, classname,
-				      sizeof(classname));
+	result = ns_client_setup_view(client, &netaddr);
+	if (result == ISC_R_QUOTA) {
 		ns_client_log(client, NS_LOGCATEGORY_CLIENT,
-			      NS_LOGMODULE_CLIENT, ISC_LOG_DEBUG(1),
-			      "no matching view in class '%s'", classname);
-		ns_client_dumpmessage(client, "no matching view in class");
+			      NS_LOGMODULE_CLIENT, ISC_LOG_DEBUG(5),
+			      "client is starting to wait for quota");
+		client->async = true;
+		isc_nmhandle_ref(client->handle);
+		isc_async_run(client->manager->loop, ns_client_request_continue,
+			      client);
+		return;
+	} else if (result != ISC_R_SUCCESS) {
 		ns_client_extendederror(client, DNS_EDE_PROHIBITED, NULL);
 		ns_client_error(client, notimp ? DNS_R_NOTIMP : DNS_R_REFUSED);
 		return;
 	}
 
+	ns_client_request_continue(client);
+}
+
+static void
+ns_client_request_continue(void *arg) {
+	ns_client_t *client = arg;
+	isc_netaddr_t netaddr;
+	const dns_name_t *signame = NULL;
+	bool ra; /* Recursion available. */
+	isc_result_t result;
+	static const char *ra_reasons[] = {
+		"ACLs not processed yet",
+		"no resolver in view",
+		"recursion not enabled for view",
+		"allow-recursion did not match",
+		"allow-query-cache did not match",
+		"allow-recursion-on did not match",
+		"allow-query-cache-on did not match",
+	};
+	enum refusal_reasons {
+		INVALID,
+		NO_RESOLVER,
+		RECURSION_DISABLED,
+		ALLOW_RECURSION,
+		ALLOW_QUERY_CACHE,
+		ALLOW_RECURSION_ON,
+		ALLOW_QUERY_CACHE_ON
+	} ra_refusal_reason = INVALID;
+#ifdef HAVE_DNSTAP
+	dns_transport_type_t transport_type;
+	dns_dtmsgtype_t dtmsgtype;
+#endif /* ifdef HAVE_DNSTAP */
+
+	/*
+	 * This function could be running asynchronously if a quota was reached
+	 * before, and named was waiting for available quota. In that case we
+	 * need to update the current 'now', and check that named doesn't wait
+	 * for too long.
+	 */
+	if (client->async) {
+		uint64_t wait_us;
+		uint64_t maxwait_us;
+
+		client->tnow = isc_time_now();
+		client->now = isc_time_seconds(&client->tnow);
+
+		wait_us = isc_time_microdiff(&client->tnow,
+					     &client->requesttime);
+		maxwait_us = US_PER_MS *
+			     client->manager->sctx->sig0checksquota_maxwaitms;
+		if (wait_us > maxwait_us) {
+			isc_buffer_t b;
+			isc_region_t *r;
+
+			ns_client_log(client, NS_LOGCATEGORY_CLIENT,
+				      NS_LOGMODULE_CLIENT, ISC_LOG_DEBUG(5),
+				      "client reached max wait time for quota");
+
+			/*
+			 * Do a dummy TSIG verification attempt so that the
+			 * response will have a TSIG if the query did, as
+			 * required by RFC2845.
+			 */
+			dns_message_resetsig(client->message);
+			r = dns_message_getrawmessage(client->message);
+			isc_buffer_init(&b, r->base, r->length);
+			isc_buffer_add(&b, r->length);
+			(void)dns_tsig_verify(&b, client->message, NULL, NULL);
+
+			ns_client_extendederror(client, DNS_EDE_PROHIBITED,
+						NULL);
+			ns_client_error(client, DNS_R_REFUSED);
+			goto cleanup;
+		}
+	}
+
+	isc_netaddr_fromsockaddr(&netaddr, &client->peeraddr);
+
+	if (client->view == NULL) {
+		result = ns_client_setup_view(client, &netaddr);
+		if (result == ISC_R_QUOTA) {
+			ns_client_log(client, NS_LOGCATEGORY_CLIENT,
+				      NS_LOGMODULE_CLIENT, ISC_LOG_DEBUG(5),
+				      "client continues waiting for quota");
+			client->async = true;
+			isc_nmhandle_ref(client->handle);
+			isc_async_run(client->manager->loop,
+				      ns_client_request_continue, client);
+			goto cleanup;
+		} else if (result != ISC_R_SUCCESS) {
+			ns_client_extendederror(client, DNS_EDE_PROHIBITED,
+						NULL);
+			ns_client_error(client, DNS_R_REFUSED);
+			goto cleanup;
+		}
+	}
+
 	if (isc_nm_is_proxy_handle(client->handle)) {
 		char fmtbuf[ISC_SOCKADDR_FORMATSIZE] = { 0 };
 		isc_netaddr_t real_local_addr, real_peer_addr;
@@ -2140,8 +2257,8 @@ ns_client_request(isc_nmhandle_t *handle, isc_result_t eresult,
 					"ACL",
 					fmtbuf);
 			}
-			isc_nm_bad_request(handle);
-			return;
+			isc_nm_bad_request(client->handle);
+			goto cleanup;
 		}
 
 		/* allow by default */
@@ -2161,8 +2278,8 @@ ns_client_request(isc_nmhandle_t *handle, isc_result_t eresult,
 					"'allow-proxy-on' ACL",
 					fmtbuf);
 			}
-			isc_nm_bad_request(handle);
-			return;
+			isc_nm_bad_request(client->handle);
+			goto cleanup;
 		}
 	}
 
@@ -2255,8 +2372,8 @@ ns_client_request(isc_nmhandle_t *handle, isc_result_t eresult,
 		if (!(client->message->tsigstatus == dns_tsigerror_badkey &&
 		      client->message->opcode == dns_opcode_update))
 		{
-			ns_client_error(client, sigresult);
-			return;
+			ns_client_error(client, client->sigresult);
+			goto cleanup;
 		}
 	}
 
@@ -2340,25 +2457,25 @@ ns_client_request(isc_nmhandle_t *handle, isc_result_t eresult,
 
 		dns_dt_send(client->view, dtmsgtype, &client->peeraddr,
 			    &client->destsockaddr, transport_type, NULL,
-			    &client->requesttime, NULL, buffer);
+			    &client->requesttime, NULL, client->buffer);
 #endif /* HAVE_DNSTAP */
 
-		ns_query_start(client, handle);
+		ns_query_start(client, client->handle);
 		break;
 	case dns_opcode_update:
 		CTRACE("update");
 #ifdef HAVE_DNSTAP
 		dns_dt_send(client->view, DNS_DTTYPE_UQ, &client->peeraddr,
 			    &client->destsockaddr, transport_type, NULL,
-			    &client->requesttime, NULL, buffer);
+			    &client->requesttime, NULL, client->buffer);
 #endif /* HAVE_DNSTAP */
 		ns_client_settimeout(client, 60);
-		ns_update_start(client, handle, sigresult);
+		ns_update_start(client, client->handle, client->sigresult);
 		break;
 	case dns_opcode_notify:
 		CTRACE("notify");
 		ns_client_settimeout(client, 60);
-		ns_notify_start(client, handle);
+		ns_notify_start(client, client->handle);
 		break;
 	case dns_opcode_iquery:
 		CTRACE("iquery");
@@ -2368,6 +2485,15 @@ ns_client_request(isc_nmhandle_t *handle, isc_result_t eresult,
 		CTRACE("unknown opcode");
 		ns_client_error(client, DNS_R_NOTIMP);
 	}
+
+cleanup:
+	if (client->async) {
+		/*
+		 * Do not detach, only 'unref' the corresponding 'ref' when
+		 * async was used, because the client can still be reused.
+		 */
+		isc_nmhandle_unref(client->handle);
+	}
 }
 
 isc_result_t
diff --git a/lib/ns/include/ns/client.h b/lib/ns/include/ns/client.h
index 67126b01f7..39c1fa0a86 100644
--- a/lib/ns/include/ns/client.h
+++ b/lib/ns/include/ns/client.h
@@ -167,6 +167,7 @@ struct ns_client {
 	ns_clientmgr_t	*manager;
 	ns_clientstate_t state;
 	bool		 nodetach;
+	bool		 async;
 	unsigned int	 attributes;
 	dns_view_t	*view;
 	dns_dispatch_t	*dispatch;
@@ -192,6 +193,9 @@ struct ns_client {
 	isc_time_t    tnow;
 	dns_name_t    signername; /*%< [T]SIG key name */
 	dns_name_t   *signer;	  /*%< NULL if not valid sig */
+	isc_result_t  sigresult;
+	isc_buffer_t *buffer;
+	isc_buffer_t  tbuffer;
 
 	isc_sockaddr_t peeraddr;
 	bool	       peeraddr_valid;
diff --git a/lib/ns/include/ns/server.h b/lib/ns/include/ns/server.h
index 84003bf57f..fae2040b74 100644
--- a/lib/ns/include/ns/server.h
+++ b/lib/ns/include/ns/server.h
@@ -64,9 +64,12 @@ typedef void (*ns_fuzzcb_t)(void);
 /*%
  * Type for callback function to get the view that can answer a query.
  */
-typedef isc_result_t (*ns_matchview_t)(
-	isc_netaddr_t *srcaddr, isc_netaddr_t *destaddr, dns_message_t *message,
-	dns_aclenv_t *env, isc_result_t *sigresultp, dns_view_t **viewp);
+typedef isc_result_t (*ns_matchview_t)(isc_netaddr_t *srcaddr,
+				       isc_netaddr_t *destaddr,
+				       dns_message_t *message,
+				       dns_aclenv_t *env, ns_server_t *sctx,
+				       isc_result_t *sigresultp,
+				       dns_view_t  **viewp);
 
 /*%
  * Server context.
@@ -88,6 +91,9 @@ struct ns_server {
 	isc_quota_t tcpquota;
 	isc_quota_t xfroutquota;
 	isc_quota_t updquota;
+	isc_quota_t sig0checksquota;
+	uint32_t    sig0checksquota_maxwaitms;
+	dns_acl_t  *sig0checksquota_exempt;
 	ISC_LIST(isc_quota_t) http_quotas;
 	isc_mutex_t http_quotas_lock;
 
diff --git a/lib/ns/server.c b/lib/ns/server.c
index d853848a76..ea4a588c18 100644
--- a/lib/ns/server.c
+++ b/lib/ns/server.c
@@ -66,6 +66,7 @@ ns_server_create(isc_mem_t *mctx, ns_matchview_t matchingview,
 	isc_quota_init(&sctx->tcpquota, 10);
 	isc_quota_init(&sctx->recursionquota, 100);
 	isc_quota_init(&sctx->updquota, 100);
+	isc_quota_init(&sctx->sig0checksquota, 1);
 	ISC_LIST_INIT(sctx->http_quotas);
 	isc_mutex_init(&sctx->http_quotas_lock);
 
@@ -134,6 +135,11 @@ ns_server_detach(ns_server_t **sctxp) {
 			isc_mem_put(sctx->mctx, altsecret, sizeof(*altsecret));
 		}
 
+		if (sctx->sig0checksquota_exempt != NULL) {
+			dns_acl_detach(&sctx->sig0checksquota_exempt);
+		}
+
+		isc_quota_destroy(&sctx->sig0checksquota);
 		isc_quota_destroy(&sctx->updquota);
 		isc_quota_destroy(&sctx->recursionquota);
 		isc_quota_destroy(&sctx->tcpquota);
diff --git a/tests/libtest/ns.c b/tests/libtest/ns.c
index 91799a774c..f09b20045c 100644
--- a/tests/libtest/ns.c
+++ b/tests/libtest/ns.c
@@ -57,12 +57,13 @@ ns_server_t *sctx = NULL;
 
 static isc_result_t
 matchview(isc_netaddr_t *srcaddr, isc_netaddr_t *destaddr,
-	  dns_message_t *message, dns_aclenv_t *env, isc_result_t *sigresultp,
-	  dns_view_t **viewp) {
+	  dns_message_t *message, dns_aclenv_t *env, ns_server_t *lsctx,
+	  isc_result_t *sigresultp, dns_view_t **viewp) {
 	UNUSED(srcaddr);
 	UNUSED(destaddr);
 	UNUSED(message);
 	UNUSED(env);
+	UNUSED(lsctx);
 	UNUSED(sigresultp);
 	UNUSED(viewp);