diff --git a/blockcheck.sh b/blockcheck.sh
new file mode 100644
index 0000000..be09619
--- /dev/null
+++ b/blockcheck.sh
@@ -0,0 +1,452 @@
+#!/bin/sh
+
+EXEDIR="$(dirname "$0")"
+EXEDIR="$(cd "$EXEDIR"; pwd)"
+ZAPRET_BASE="$EXEDIR"
+
+[ -n "$QNUM" ] || QNUM=59780
+[ -n "$NFQWS" ] || NFQWS="$ZAPRET_BASE/nfq/nfqws"
+[ -n "$MDIG" ] || MDIG="$ZAPRET_BASE/mdig/mdig"
+[ -n "$DESYNC_MARK" ] || DESYNC_MARK=0x40000000
+DOMAIN=rutracker.org
+CURL_MAX_TIME=5
+MIN_TTL=1
+MAX_TTL=12
+HDRTEMP=/tmp/zapret-hdr.txt
+ECHON="echo -n"
+
+DNSCHECK_DNS="8.8.8.8 1.1.1.1 77.88.8.8"
+DNSCHECK_DOM="pornhub.com putinhuylo.com rutracker.org nnmclub.to protonmail.com"
+DNSCHECK_DIG1=/tmp/dig1.txt
+DNSCHECK_DIG2=/tmp/dig2.txt
+DNSCHECK_DIGS=/tmp/digs.txt
+
+
+exists()
+{
+	which $1 >/dev/null 2>/dev/null
+}
+killwait()
+{
+	# $1 - signal (-9, -2, ...)
+	# $2 - pid
+	kill $1 $2
+	# suppress job kill message
+	wait $2 2>/dev/null
+}
+
+exitp()
+{
+	local A
+
+	echo
+	echo press enter to continue
+	read A
+	exit $1
+}
+
+read_yes_no()
+{
+	# $1 - default (Y/N)
+	local A
+	read A
+	[ -z "$A" ] || ([ "$A" != "Y" ] && [ "$A" != "y" ] && [ "$A" != "N" ] && [ "$A" != "n" ]) && A=$1
+	[ "$A" = "Y" ] || [ "$A" = "y" ] || [ "$A" = "1" ]
+}
+ask_yes_no()
+{
+	# $1 - default (Y/N or 0/1)
+	# $2 - text
+	local DEFAULT=$1
+	[ "$1" = "1" ] && DEFAULT=Y
+	[ "$1" = "0" ] && DEFAULT=N
+	[ -z "$DEFAULT" ] && DEFAULT=N
+	$ECHON "$2 (default : $DEFAULT) (Y/N) ? "
+	read_yes_no $DEFAULT
+}
+ask_yes_no_var()
+{
+	# $1 - variable name for answer : 0/1
+	# $2 - text
+	local DEFAULT
+	eval DEFAULT="\$$1"
+	if ask_yes_no "$DEFAULT" "$2"; then
+		eval $1=1
+	else
+		eval $1=0
+	fi
+}
+
+
+require_root()
+{
+	echo \* checking privileges
+	[ $(id -u) -ne "0" ] && {
+		echo root is required
+		exists sudo && exec sudo "$0"
+		exists su && exec su -c "$0"
+		echo su or sudo not found
+		exitp 2
+	}
+}
+
+IPT()
+{
+	$IPTABLES -C "$@" >/dev/null 2>/dev/null || $IPTABLES -I "$@"
+}
+IPT_DEL()
+{
+	$IPTABLES -C "$@" >/dev/null 2>/dev/null && $IPTABLES -D "$@"
+}
+
+
+check_system()
+{
+	echo \* checking system
+
+	local UNAME=$(uname)
+	[ "$UNAME" = "Linux" ] || {
+		echo not supported
+		exitp 5
+	}
+}
+
+check_prerequisites()
+{
+	echo \* checking prerequisites
+
+	[ -x "$NFQWS" ] && [ -x "$MDIG" ] || {
+		echo $NFQWS or $MDIG is not available. run $ZAPRET_BASE/install_bin.sh
+		exitp 6
+	}
+
+	for prog in iptables ip6tables curl; do
+		exists $prog || {
+			echo $prog does not exist. please install
+			exitp 6
+		}
+	done
+}
+
+
+hdrfile_http_code()
+{
+	# $1 - hdr file
+	sed -nre '1,1 s/^HTTP\/1\.[0,1] ([0-9]+) .*$/\1/p' "$1"
+}
+hdrfile_location()
+{
+	# $1 - hdr file
+
+	# some DPIs return CRLF line ending
+	tr -d '\015' <"$1" | sed -nre 's/^[L|l][O|o][C|c][A|a][T|t][I|i][O|o][N|n]:[ \t]*([^ \t]*)[ \t]*$/\1/p'
+}
+curl_test_http()
+{
+	# $1 - ip version : 4/6
+	# $2 - domain name
+	local code loc
+	curl -${1}SsD "$HDRTEMP" --max-time $CURL_MAX_TIME $CURL_OPT "http://$2" -o /dev/null 2>&1 || {
+		code=$?
+		rm -f "$HDRTEMP"
+		return $code
+	}
+	code=$(hdrfile_http_code "$HDRTEMP")
+	[ "$code" = 301 -o "$code" = 302 -o "$code" = 307 -o "$code" = 308 ] && {
+		loc=$(hdrfile_location "$HDRTEMP")
+		[ "${loc#*$2}" = "$loc" ] && {
+			echo suspicious redirection to : $loc
+			rm -f "$HDRTEMP"
+			return 254
+		}
+	}
+	rm -f "$HDRTEMP"
+	return 0
+}
+curl_test_https()
+{
+	# $1 - ip version : 4/6
+	# $2 - domain name
+
+	# prevent using QUIC if available in curl
+	curl -${1}Ss --max-time $CURL_MAX_TIME $CURL_OPT --http1.1 "https://$2" -o /dev/null 2>&1 
+}
+
+nfqws_ipt_prepare()
+{
+	# $1 - port
+	IPT POSTROUTING -t mangle -p tcp --dport $1 -m mark ! --mark $DESYNC_MARK/$DESYNC_MARK -j NFQUEUE --queue-num $QNUM
+}
+nfqws_ipt_unprepare()
+{
+	# $1 - port
+	IPT_DEL POSTROUTING -t mangle -p tcp --dport $1 -m mark ! --mark $DESYNC_MARK/$DESYNC_MARK -j NFQUEUE --queue-num $QNUM
+}
+nfqws_start()
+{
+	"$NFQWS" --dpi-desync-fwmark=$DESYNC_MARK --qnum=$QNUM "$@" >/dev/null &
+}
+
+curl_test()
+{
+	# $1 - test function
+	# $2 - domain
+	$1 $IPV $2 && {
+		echo '!!!!! AVAILABLE !!!!!'
+		return 0
+	}
+	local code=$?
+	if [ $code = 254 ]; then
+		echo UNAVAILABLE
+	else
+		echo UNAVAILABLE code=$code
+	fi
+	return $code
+}
+nfqws_curl_test()
+{
+	# $1 - test function
+	# $2 - domain
+	# $3,$4,$5, ... - nfqws params
+	local code pid testf=$1 dom=$2
+	shift
+	shift
+	echo - checking nfqws "$@"
+	nfqws_start "$@"
+	pid=$!
+	curl_test $testf $dom
+	code=$?
+	killwait -9 $pid
+	return $code
+}
+check_domain_bypass()
+{
+	# $1 - test function
+	# $2 - domain
+
+	local pid strategy tests='fake'
+
+	if nfqws_curl_test $1 $2 --dpi-desync=split2; then
+		strategy='--dpi-desync=split2'
+	else
+		tests="$tests split fake,split"
+	fi
+	if nfqws_curl_test $1 $2 --dpi-desync=disorder2; then
+		[ -n "$strategy" ] || strategy='--dpi-desync=disorder2'
+	else
+		tests="$tests disorder fake,disorder"
+	fi
+
+	local ttls=$(seq -s ' ' $MIN_TTL $MAX_TTL)
+	for desync in $tests; do
+		for ttl in $ttls; do
+			nfqws_curl_test $1 $2 --dpi-desync=$desync --dpi-desync-ttl=$ttl && {
+				[ -n "$strategy" ] || strategy="--dpi-desync=$desync --dpi-desync-ttl=$ttl"
+				break
+			}
+		done
+	done
+
+	echo
+	if [ -n "$strategy" ]; then
+		echo "!!!!! working strategy found : nfqws $strategy !!!!!"
+		return 0
+	else
+		echo 'working strategy not found'
+		return 1
+	fi
+}
+
+check_domain()
+{
+	# $1 - test function
+	# $2 - port
+	# $3 - domain
+
+	echo
+	echo \* $1 $3
+
+	# in case was interrupted before
+	nfqws_ipt_unprepare $2
+	killall nfqws 2>/dev/null
+
+	echo "- checking without DPI bypass"
+	curl_test $1 $3 && return 0
+
+	echo preparing nfqws redirection
+	nfqws_ipt_prepare $2
+
+	check_domain_bypass $1 $3
+
+	echo clearing nfqws redirection
+	nfqws_ipt_unprepare $2
+}
+check_domain_http()
+{
+	# $1 - domain
+	check_domain curl_test_http 80 $1
+}
+check_domain_https()
+{
+	# $1 - domain
+	check_domain curl_test_https 443 $1
+}
+
+ask_params()
+{
+	echo
+	echo NOTE ! this test should be run with zapret or any other bypass software disabled, without VPN
+	echo NOTE ! this test will kill all nfqws processes. if you have already set up zapret you will need to restart it after test is complete.
+
+	$ECHON "test this domain [ $DOMAIN ] : "
+	local dom
+	read dom
+	[ -n "$dom" ] && DOMAIN=$dom
+
+	$ECHON "ip protocol version [ 4 ] : "
+	read IPV
+	[ -n "$IPV" ] || IPV=4
+	[ "$IPV" = 4 -o "$IPV" = 6 ] || {
+		echo invalid ip version. should be 4 or 6.
+		exitp 1
+	}
+	IPTABLES=iptables
+	[ "$IPV" = 6 ] && IPTABLES=ip6tables
+
+	ENABLE_HTTP=1
+	ask_yes_no_var ENABLE_HTTP "check http"
+
+	ENABLE_HTTPS=1
+	ask_yes_no_var ENABLE_HTTPS "check https"
+
+	IGNORE_CA=0
+	CURL_OPT=
+	[ "$ENABLE_HTTPS" = "1" ] && {
+		echo on limited systems like openwrt CA certificates might not be installed to preserve space
+		echo in such a case curl cannot verify server certificate and you should either install ca-bundle or disable verification
+		echo however disabling verification will break https check if ISP does MitM attack and substitutes server certificate
+		ask_yes_no_var IGNORE_CA "do not verify server certificate"
+		[ "$IGNORE_CA" = 1 ] && CURL_OPT=-k
+	}
+}
+
+
+
+pingtest()
+{
+	ping -c 1 -W 1 $1 >/dev/null
+}
+dnstest()
+{
+	# $1 - dns server. empty for system resolver
+	nslookup w3.org $1 >/dev/null 2>/dev/null
+}
+find_working_public_dns()
+{
+	for dns in $DNSCHECK_DNS; do
+		pingtest $dns && dnstest $dns && {
+			PUBDNS=$dns
+			return 0
+		}
+	done
+	return 1
+}
+check_dns_spoof()
+{
+	# $1 - domain
+	# $2 - public DNS
+	echo $1 | "$EXEDIR/mdig/mdig" --family=4 >"$DNSCHECK_DIG1"
+	nslookup $1 $2 | sed -n '/Name:/,$p' | grep ^Address | grep -oE '([0-9]{1,3}\.){3}[0-9]{1,3}' >"$DNSCHECK_DIG2"
+	# check whether system resolver returns anything other than public DNS
+	grep -qvFf "$DNSCHECK_DIG2" "$DNSCHECK_DIG1"
+}
+check_dns_cleanup()
+{
+	rm -f "$DNSCHECK_DIG1" "$DNSCHECK_DIG2" "$DNSCHECK_DIGS" 2>/dev/null
+}
+check_dns()
+{
+	local C1 C2
+
+	echo \* checking DNS
+
+	[ -f "$DNSCHECK_DIGS" ] && rm -f "$DNSCHECK_DIGS"
+
+	dnstest || {
+		echo -- DNS is not working. It's either misconfigured or blocked or you don't have inet access.
+		return 1
+	}
+	echo system DNS is working
+
+	if find_working_public_dns ; then
+		echo comparing system resolver to public DNS : $PUBDNS
+		for dom in $DNSCHECK_DOM; do
+			if check_dns_spoof $dom $PUBDNS ; then
+				echo $dom : MISMATCH
+				echo -- system resolver :
+				cat "$DNSCHECK_DIG1"
+				echo -- $PUBDNS :
+				cat "$DNSCHECK_DIG2"
+				check_dns_cleanup
+				echo -- POSSIBLE DNS HIJACK DETECTED. ZAPRET WILL NOT HELP YOU IN CASE DNS IS SPOOFED !!!
+				echo -- DNS CHANGE OR DNSCRYPT MAY BE REQUIRED
+				return 1
+			else
+				echo $dom : OK
+				cat "$DNSCHECK_DIG1" >>"$DNSCHECK_DIGS"
+			fi
+		done
+	else
+		echo no working public DNS was found. looks like public DNS blocked.
+		for dom in $DNSCHECK_DOM; do echo $dom; done | "$EXEDIR/mdig/mdig" --threads=10 --family=4 >"$DNSCHECK_DIGS"
+	fi
+
+	echo checking resolved IP uniqueness for : $DNSCHECK_DOM
+	echo censor\'s DNS can return equal result for multiple blocked domains.
+	C1=$(wc -l <"$DNSCHECK_DIGS")
+	C2=$(sort -u "$DNSCHECK_DIGS" | wc -l)
+	[ "$C1" -eq 0 ] &&
+	{
+		echo -- DNS is not working. It's either misconfigured or blocked or you don't have inet access.
+		check_dns_cleanup
+		return 1
+	}
+	[ "$C1" = "$C2" ] ||
+	{
+		echo system dns resolver has returned equal IPs for some domains checked above \($C1 total, $C2 unique\)
+		echo non-unique IPs :
+		sort "$DNSCHECK_DIGS" | uniq -d
+		echo -- POSSIBLE DNS HIJACK DETECTED. ZAPRET WILL NOT HELP YOU IN CASE DNS IS SPOOFED !!!
+		echo -- DNSCRYPT MAY BE REQUIRED
+		check_dns_cleanup
+		return 1
+	}
+	echo all resolved IPs are unique
+	echo -- DNS looks good
+	echo -- NOTE this check is Russia targeted. In your country other domains may be blocked.
+	check_dns_cleanup
+	return 0
+}
+
+
+sigint()
+{
+	# make sure we are not in a middle state that impacts connectivity
+	echo
+	echo terminating...
+	nfqws_ipt_unprepare 80
+	nfqws_ipt_unprepare 443
+	killall nfqws 2>/dev/null
+	exit 1
+}
+
+trap 'sigint' 2
+
+check_system
+check_prerequisites
+require_root
+check_dns
+ask_params
+
+[ "$ENABLE_HTTP" = 1 ] && check_domain_http $DOMAIN
+[ "$ENABLE_HTTPS" = 1 ] && check_domain_https $DOMAIN
diff --git a/docs/changes.txt b/docs/changes.txt
index fa7f2cd..202f983 100644
--- a/docs/changes.txt
+++ b/docs/changes.txt
@@ -202,3 +202,7 @@ init scripts : openwrt uses now OPENWRT_LAN parameter to override incoming inter
 v41
 
 install_easy : openrc support
+
+v42
+
+blockcheck.sh
diff --git a/docs/readme.txt b/docs/readme.txt
index c77a989..95c42de 100644
--- a/docs/readme.txt
+++ b/docs/readme.txt
@@ -1,4 +1,4 @@
-zapret v.41
+zapret v.42
 
 English
 -------
@@ -711,14 +711,12 @@ tpws и nfqws решают нужно ли применять дурение в
 Перед настройкой нужно провести исследование какую бяку устроил вам ваш провайдер.
 
 Нужно выяснить не подменяет ли он DNS и какой метод обхода DPI работает.
-В этом вам поможет скрипт https://github.com/ValdikSS/blockcheck.
+В этом вам поможет скрипт blockcheck.sh.
 
 Если DNS подменяется, но провайдер не перехватывает обращения к сторонним DNS, поменяйте DNS на публичный.
 Например : 8.8.8.8, 8.8.4.4, 1.1.1.1, 1.0.0.1, 9.9.9.9
 Если DNS подменяется и провайдер перехватывает обращения к сторонним DNS, настройте dnscrypt.
 
-Если blockcheck не определил рабочие методы обхода, попробуйте атаку десинхронизации с различными параметрами.
-
 Проанализируйте какие методы дурения DPI работают, в соответствии с ними настройте /opt/zapret/config.