diff --git a/CHANGES b/CHANGES
index e62e9e7..19006c7 100644
--- a/CHANGES
+++ b/CHANGES
@@ -75,6 +75,9 @@ Features:
 	Tests: TRY_ADDRS_4 TRY_ADDRS_4_6
 	Feature recommended by Anand Buddhdev.
 
+	configure option --with-default-ipv allows to specify at build time if
+	IPv4, IPv6, or none of these is the preferred default.
+
 Corrections:
 	When a sub process (EXEC, SYSTEM) terminated with exit code other than
 	0, its last sent data might have been lost depending on timing of read/
diff --git a/config.h.in b/config.h.in
index 5535e9b..6342635 100644
--- a/config.h.in
+++ b/config.h.in
@@ -723,6 +723,8 @@
 
 #undef WITH_MSGLEVEL
 
+#undef WITH_DEFAULT_IPV 		/* default IP version: undef, "4", "6" */
+
 #define BUILD_DATE __DATE__ " " __TIME__
 
 #endif /* !defined(__config_h_included) */
diff --git a/configure.ac b/configure.ac
index eaad7b4..f5fae83 100644
--- a/configure.ac
+++ b/configure.ac
@@ -820,6 +820,16 @@ AC_ARG_ENABLE(msglevel, [  --enable-msglevel=N     set max verbosity to debug,in
 	       esac],
 	       [AC_DEFINE(WITH_MSGLEVEL,0) AC_MSG_RESULT(debug)])
 
+AC_MSG_CHECKING(default IP version)
+AC_ARG_ENABLE(ip-version, [  --enable-ip-version=N     set default IP version to undef, "4", "6"],
+	      [case "$enableval" in
+	       "") AC_DEFINE(WITH_DEFAULT_IPV, 0) AC_MSG_RESULT("0");;
+	       4) AC_DEFINE(WITH_DEFAULT_IPV, '4') AC_MSG_RESULT("4");;
+	       6) AC_DEFINE(WITH_DEFAULT_IPV, '6') AC_MSG_RESULT("6");;
+	       *) AC_DEFINE(WITH_DEFAULT_IPV, 0) AC_MSG_RESULT("0");;
+	       esac],
+	       [AC_DEFINE(WITH_DEFAULT_IPV, '0') AC_MSG_RESULT("0")])
+
 #AC_SUBST(V_INCL)
 
 dnl Checks for typedefs, structures, and compiler characteristics.
diff --git a/socat.c b/socat.c
index 4e0e618..c61fc21 100644
--- a/socat.c
+++ b/socat.c
@@ -676,6 +676,15 @@ void socat_version(FILE *fd) {
 #else
    fputs("  #undef WITH_MSGLEVEL\n", fd);
 #endif
+#ifdef WITH_DEFAULT_IPV
+#  if WITH_DEFAULT_IPV
+   fprintf(fd, "  #define WITH_DEFAULT_IPV %c\n", WITH_DEFAULT_IPV);
+#  else
+   fprintf(fd, "  #define WITH_DEFAULT_IPV '\\0'\n");
+#  endif
+#else
+   fputs("  #undef WITH_DEFAULT_IPV\n", fd);
+#endif
 }
 
 
diff --git a/test.sh b/test.sh
index 193fbe7..439a2c2 100755
--- a/test.sh
+++ b/test.sh
@@ -44,7 +44,7 @@ usage() {
     $ECHO "\t-foreign \tAllow tests that send packets to Internet"
     $ECHO "\t-expect-fail N1,N2,... \tIgnore failure of these tests"
     $ECHO "\ttest-spec \Number of test or name of test"
-    $ECHO "Contents of environment variable OPTS are passed to Socat invokations, e.'g:"
+    $ECHO "Contents of environment variable OPTS are passed to Socat invocations, e.'g:"
     $ECHO "OPTS=\"-d -d -d -d -lu\" ./test.sh"
     $ECHO "TRACE=\"strace -tt -v\" 	Use trace,valgrind etc.on socat"
     $ECHO "SOCAT=/path/to/socat \tselect socat executable for test"
@@ -155,7 +155,7 @@ MCINTERFACE=$INTERFACE
 [ -z "$MCINTERFACE" ] && MCINTERFACE=lo	# !!! Linux only - and not always
 #LOCALHOST=192.168.58.1
 LOCALHOST=localhost 	# attention: on FreeBSD-10 localhost resolves primarily to IPv6
-#LOCALHOST=127.0.0.1
+LOCALHOST4=127.0.0.1
 LOCALHOST6="[::1]"
 #PROTO=$(awk '{print($2);}' /etc/protocols |sort -n |tail -n 1)
 #PROTO=$(($PROTO+1))
@@ -972,17 +972,11 @@ runssctp4 () {
 # check if SCTP on IPv6 is available on host
 runssctp6 () {
     runsip6 >/dev/null || { echo SCTP6; return 1; }
-    $SOCAT -h |grep ' SCTP6-' >/dev/null || return 1
+    $SOCAT -h |grep -i ' SCTP6-' >/dev/null || return 1
     $SOCAT /dev/null SCTP6-L:0,accept-timeout=0.001 2>/dev/null || return 1;
     return 0;
 }
 
-# check if UNIX domain sockets work - see above
-#runsunix () {
-#    # for now...
-#    return 0;
-#}
-
 routesip6 () {
     runsip6 >/dev/null || { echo route6; return 1; }
     ping -c 1 -s 0 -6 2606:4700:4700::1111 >/dev/null 2>&1 || { echo route6; return 1; }
@@ -3457,6 +3451,8 @@ esac
 N=$((N+1))
 
 
+newport $RUNS 	# in case it has not yet been invoked
+
 while read NAMEKEYW FEAT RUNS TESTTMPL PEERTMPL WAITTMPL; do
 if [ -z "$NAMEKEYW" ] || [[ "$NAMEKEYW" == \#* ]]; then continue; fi
 
@@ -11398,8 +11394,9 @@ if [ $RLIMIT_NOFILE -gt 1024 ]; then
 fi
 newport tcp4
 CMD0="$TRACE $SOCAT $opt_d0 $opts TCP4-LISTEN:$PORT,$REUSEADDR,range=$LOCALHOST:255.255.255.255 PIPE"
+#CMD0="$TRACE $SOCAT $opts TCP-LISTEN:$PORT,pf=ip4,$REUSEADDR,range=$LOCALHOST4:255.255.255.255 PIPE"
 CMD1="$TRACE $SOCAT $opts -t 0 /dev/null TCP4:$SECONDADDR:$PORT,bind=$SECONDADDR"
-CMD2="$TRACE $SOCAT $opts - TCP4:$LOCALHOST:$PORT,bind=$LOCALHOST"
+CMD2="$TRACE $SOCAT $opts - TCP:$LOCALHOST4:$PORT,bind=$LOCALHOST4"
 printf "test $F_n $TEST... " $N
 $CMD0 >/dev/null 2>"${te}0" &
 pid0=$!
@@ -11414,7 +11411,11 @@ kill $pid0 2>/dev/null; wait
 echo -e "$da" |diff "${tf}2" - >$tdiff
 if [ $rc2 -ne 0 ]; then
     $PRINTF "$FAILED (rc2=$rc2)\n"
-    echo "$CMD2 &"
+    echo "$CMD0 &"
+    cat "${te}0" >&2
+    echo "$CMD1"
+    cat "${te}1" >&2
+    echo "$CMD2"
     cat "${te}2" >&2
     numFAIL=$((numFAIL+1))
     listFAIL="$listFAIL $N"
@@ -11690,20 +11691,20 @@ gentestcert testcli
 test_proto=tcp4
 case "$MODE" in
     SERVER)
-	CMD0="$SOCAT $opts -u $TESTADDRESS system:\"echo SOCAT_${SSLDIST}_${MODULE}_${FIELD}=\\\$SOCAT_${SSLDIST}_${MODULE}_${FIELD}; sleep 1\""
+	CMD0="$SOCAT $opts -u -lp socat $TESTADDRESS SYSTEM:\"echo SOCAT_${SSLDIST}_${MODULE}_${FIELD}=\\\$SOCAT_${SSLDIST}_${MODULE}_${FIELD}; sleep 1\""
 	CMD1="$SOCAT $opts -u /dev/null $PEERADDRESS"
 	printf "test $F_n $TEST... " $N
 	eval "$CMD0 2>\"${te}0\" >\"$tf\" &"
 	pid0=$!
 	wait${test_proto}port $PORT 1
-	$CMD1 2>"${te}1"
+	{ $CMD1 2>"${te}1"; sleep 1; }
 	rc1=$?
 	waitfile "$tf" 2
 	kill $pid0 2>/dev/null; wait
 	;;
     CLIENT)
 	CMD0="$SOCAT $opts -u /dev/null $PEERADDRESS"
-	CMD1="$SOCAT $opts -u $TESTADDRESS system:\"echo SOCAT_${SSLDIST}_${MODULE}_${FIELD}=\\\$SOCAT_${SSLDIST}_${MODULE}_${FIELD}; sleep 1\""
+	CMD1="$SOCAT $opts -u -lp socat $TESTADDRESS SYSTEM:\"echo SOCAT_${SSLDIST}_${MODULE}_${FIELD}=\\\$SOCAT_${SSLDIST}_${MODULE}_${FIELD}; sleep 1\""
 	printf "test $F_n $TEST... " $N
 	$CMD0 2>"${te}0" &
 	pid0=$!
@@ -14663,7 +14664,7 @@ CMD="$TRACE $SOCAT $opts -d -d -d -d /dev/null UDP4-SENDTO:$LOCALHOST:$PORT,lowp
 printf "test $F_n $TEST... " $N
 $CMD >/dev/null 2>"${te}"
 rc1=$?
-LOWPORT=$(grep '[DE] bind(.*:' $te |sed 's/.*:\([0-9][0-9]*\),.*/\1/')
+LOWPORT=$(grep '[DE] bind(.*:' $te |sed 's/.*:\([0-9][0-9]*\)[}]*,.*/\1/' |head -n 1)
 #echo "LOWPORT=\"$LOWPORT\"" >&2
 #type socat >&2
 if  [[ $LOWPORT =~ [0-9][0-9]* ]] && [ "$LOWPORT" -ge 640 -a "$LOWPORT" -le 1023 ]; then
@@ -15937,10 +15938,12 @@ tf="$td/test$N.stdout"
 te="$td/test$N.stderr"
 tdiff="$td/test$N.diff"
 da="test$N $(date) $RANDOM"
+printf "test $F_n $TEST... " $N
 newport tcp6
 # Yup, it seems that with OpenSSL the side that begins with shutdown does NOT
 # begin shutdown of the TCP connection
 # therefore we let the client timeout
+# result is not reliable (OK seen even without any SO_REUSEADDR)
 CMD0a="$TRACE $SOCAT $opts -lp server1 -6 OPENSSL-LISTEN:$PORT,cert=testsrv.crt,key=testsrv.key,verify=0 PIPE"
 CMD0b="$TRACE $SOCAT $opts -lp server2 -6 OPENSSL-LISTEN:$PORT,accept-timeout=.01,cert=testsrv.crt,key=testsrv.key,verify=0 PIPE"
 CMD1="$TRACE $SOCAT $opts -lp client -6 -T 0.1 PIPE OPENSSL-CONNECT:$LOCALHOST6:$PORT,verify=0"
@@ -16078,6 +16081,10 @@ elif [ -z "$FOREIGN" ]; then
     $PRINTF "test $F_n $TEST... ${YELLOW}use test.sh option -foreign${NORMAL}\n" $N
     numCANT=$((numCANT+1))
     listCANT="$listCANT $N"
+#elif ! $(type nslookup >/dev/null 2>&1) && ! $(type host >/dev/null 2>&1); then
+#    $PRINTF "test $F_n $TEST... ${YELLOW}nslookup and host not available${NORMAL}\n" $N
+#    numCANT=$((numCANT+1))
+#    listCANT="$listCANT $N"
 elif ! F=$(testfeats IP4 TCP GOPEN); then
     $PRINTF "test $F_n $TEST... ${YELLOW}Feature $F not available${NORMAL}\n" $N
     numCANT=$((numCANT+1))
@@ -16095,7 +16102,11 @@ tf="$td/test$N.stdout"
 te="$td/test$N.stderr"
 tdiff="$td/test$N.diff"
 da="test$N $(date) $RANDOM"
-ADDRS=$(nslookup server-4.dest-unreach.net. |sed -n '/^$/,$ p' |grep ^Address |awk '{print($2);}')
+if type nslookup >/dev/null 2>&1; then
+    ADDRS=$(nslookup server-4.dest-unreach.net. |sed -n '/^$/,$ p' |grep ^Address |awk '{print($2);}')
+elif type host >/dev/null 2>&1; then
+    ADDRS=$(host server-4.dest-unreach.net. |sed 's/.*address //')
+fi
 while true; do
     newport tcp4
     OPEN=
@@ -16115,7 +16126,7 @@ CMD="$TRACE $SOCAT $opts -d -d /dev/null TCP4:server-4.dest-unreach.net:$PORT"
 printf "test $F_n $TEST... " $N
 $CMD >/dev/null 2>"${te}"
 rc=$?
-if [ $(grep " N opening connection to AF=2 " ${te} |wc -l) -eq 2 ]; then
+if [ $(grep " N opening connection to .*AF=2 " ${te} |wc -l) -eq 2 ]; then
     $PRINTF "$OK\n"
     if [ "$VERBOSE" ]; then echo "$CMD"; fi
     if [ "$DEBUG" ];   then cat "${te}" >&2; fi
@@ -16143,8 +16154,12 @@ TEST="$NAME: for TCP try all available IPv4 and IPv6 addresses"
 # neither IPv4 nor IPv6
 # Check the log if Socat tried both addresses
 if ! eval $NUMCOND; then :;
-#elif [ -z "$FOREIGN" ]; then	# only needs Internet DNS
-#    $PRINTF "test $F_n $TEST... ${YELLOW}use test.sh option -foreign${NORMAL}\n" $N
+elif [ -z "$FOREIGN" ]; then	# only needs Internet DNS
+    $PRINTF "test $F_n $TEST... ${YELLOW}use test.sh option -foreign${NORMAL}\n" $N
+    numCANT=$((numCANT+1))
+    listCANT="$listCANT $N"
+#elif ! $(type nslookup >/dev/null 2>&1) && ! $(type host >/dev/null 2>&1); then
+#    $PRINTF "test $F_n $TEST... ${YELLOW}nslookup and host not available${NORMAL}\n" $N
 #    numCANT=$((numCANT+1))
 #    listCANT="$listCANT $N"
 elif ! F=$(testfeats ip4 ip6 tcp); then
@@ -16169,7 +16184,11 @@ te="$td/test$N.stderr"
 tdiff="$td/test$N.diff"
 da="test$N $(date) $RANDOM"
 LOCALHOST_4_6=localhost-4-6.dest-unreach.net
-ADDRS=$(nslookup . |sed -n '/^$/,$ p' |grep ^Address |awk '{print($2);}')
+if type nslookup >/dev/null 2>&1; then
+    ADDRS=$(nslookup server-4.dest-unreach.net. |sed -n '/^$/,$ p' |grep ^Address |awk '{print($2);}')
+elif type host >/dev/null 2>&1; then
+    ADDRS=$(host server-4.dest-unreach.net. |sed 's/.*address //')
+fi
 while true; do
     OPEN=
     for addr in $ADDRS; do
@@ -16192,7 +16211,7 @@ CMD="$TRACE $SOCAT $opts -d -d /dev/null TCP:localhost-4-6.dest-unreach.net:$POR
 printf "test $F_n $TEST... " $N
 $CMD >/dev/null 2>"${te}"
 rc=$?
-if [ $(grep " N opening connection to AF=\(2\|10\) " ${te} |wc -l) -eq 2 ]; then
+if [ $(grep " N opening connection to .*AF=[0-9]" ${te} |wc -l) -eq 2 ]; then
     $PRINTF "$OK\n"
     if [ "$VERBOSE" ]; then echo "$CMD"; fi
     if [ "$DEBUG" ];   then cat "${te}" >&2; fi
diff --git a/xio-ip.c b/xio-ip.c
index 5e3a6c8..0d68338 100644
--- a/xio-ip.c
+++ b/xio-ip.c
@@ -104,6 +104,24 @@ const struct optdesc opt_res_dnsrch   = { "res-dnsrch",   "dnsrch",   OPT_RES_DN
 #endif /* WITH_IP4 || WITH_IP6 */
 
 
+int xioinit_ip(
+	struct single *sfd,
+	int *pf)
+{
+	if (*pf == PF_UNSPEC) {
+		switch (xioparms.preferred_ip) {
+		case '0': *pf = PF_UNSPEC; break;
+#if WITH_IP4
+		case '4': *pf = PF_INET; break;
+#endif
+#if WITH_IP6
+		case '6': *pf = PF_INET6; break;
+#endif
+		}
+	}
+	return 0;
+}
+
 #if HAVE_RESOLV_H
 int Res_init(void) {
    int result;
@@ -274,7 +292,11 @@ int xiogetaddrinfo(const char *node, const char *service,
       /* first fallback is getipnodebyname() */
       if (family == PF_UNSPEC) {
 #if WITH_IP4 && WITH_IP6
-	 family = xioparms.default_ip=='6'?PF_INET6:PF_INET;
+      switch (xioparms.default_ip) {
+      case '4': pf = PF_INET; break;
+      case '6': pf = PF_INET6; break;
+      default: break;		/* includes \0 */
+      }
 #elif WITH_IP6
 	 family = PF_INET6;
 #else
@@ -325,7 +347,11 @@ int xiogetaddrinfo(const char *node, const char *service,
 	 be useful somewhere sometimes in a future even for IP6 */
       if (family == PF_UNSPEC) {
 #if WITH_IP4 && WITH_IP6
-	 family = xioparms.default_ip=='6'?PF_INET6:PF_INET;
+      switch (xioparms.default_ip) {
+      case '4': pf = PF_INET; break;
+      case '6': pf = PF_INET6; break;
+      default: break;		/* includes \0 */
+      }
 #elif WITH_IP6
 	 family = PF_INET6;
 #else
diff --git a/xio-ip4.c b/xio-ip4.c
index e6338d2..264a00d 100644
--- a/xio-ip4.c
+++ b/xio-ip4.c
@@ -33,10 +33,10 @@ int xioparsenetwork_ip4(const char *rangename, struct xiorange *range) {
       char *endptr;
       bits = strtoul(delimpos+1, &endptr, 10);
       if (! ((*(delimpos+1) != '\0') && (*endptr == '\0'))) {
-	 Error1("not a valid netmask in \"%s\"", rangename);
+	 Error1("not a valid IPv4 netmask in \"%s\"", rangename);
 	 bits = 32;	/* most secure selection */
       } else if (bits > 32) {
-	 Error1("netmask \"%s\" is too large", rangename);
+	 Error1("IPv4 netmask \"%s\" is too large", rangename);
 	 bits = 32;
       }
       if (bits <= 0) {
diff --git a/xio-ipapp.c b/xio-ipapp.c
index 3fc3370..c0a6b59 100644
--- a/xio-ipapp.c
+++ b/xio-ipapp.c
@@ -284,7 +284,11 @@ int xioopen_ipapp_listen(int argc, const char *argv[], struct opt *opts,
 
    if (pf == PF_UNSPEC) {
 #if WITH_IP4 && WITH_IP6
-      pf = xioparms.default_ip=='6'?PF_INET6:PF_INET;
+      switch (xioparms.default_ip) {
+      case '4': pf = PF_INET; break;
+      case '6': pf = PF_INET6; break;
+      default: break;		/* includes \0 */
+      }
 #elif WITH_IP6
       pf = PF_INET6;
 #else
diff --git a/xio-openssl.c b/xio-openssl.c
index 24b6285..479cd67 100644
--- a/xio-openssl.c
+++ b/xio-openssl.c
@@ -548,7 +548,7 @@ static int
    struct opt *opts0 = NULL;
    union sockaddr_union us_sa, *us = &us_sa;
    socklen_t uslen = sizeof(us_sa);
-   int pf;
+   int pf = PF_UNSPEC;
    bool use_dtls = (protogrp != 0);
    int socktype = SOCK_STREAM;
    int ipproto = IPPROTO_TCP;
@@ -572,7 +572,11 @@ static int
    }
 
 #if WITH_IP4 && WITH_IP6
-   pf = xioparms.default_ip=='6'?PF_INET6:PF_INET;
+   switch (xioparms.default_ip) {
+   case '4': pf = PF_INET; break;
+   case '6': pf = PF_INET6; break;
+   default: break;		/* includes \0 */
+   }
 #elif WITH_IP6
    pf = PF_INET6;
 #else
@@ -612,6 +616,8 @@ static int
        != STAT_OK) {
       return STAT_NORETRY;
    }
+   if (pf == 0)
+      pf = us->soa.sa_family;
 
    xfd->dtype = XIODATA_OPENSSL;
 
diff --git a/xio-rawip.c b/xio-rawip.c
index 6d60d77..76984f9 100644
--- a/xio-rawip.c
+++ b/xio-rawip.c
@@ -226,7 +226,11 @@ int xioopen_rawip_recvfrom(int argc, const char *argv[], struct opt *opts,
    retropt_socket_pf(opts, &pf);
    if (pf == PF_UNSPEC) {
 #if WITH_IP4 && WITH_IP6
-      pf = xioparms.default_ip=='6'?PF_INET6:PF_INET;
+      switch (xioparms.default_ip) {
+      case '4': pf = PF_INET; break;
+      case '6': pf = PF_INET6; break;
+      default: break;		/* includes \0 */
+      }
 #elif WITH_IP6
       pf = PF_INET6;
 #else
diff --git a/xio-udp.c b/xio-udp.c
index ee6af64..5a3215f 100644
--- a/xio-udp.c
+++ b/xio-udp.c
@@ -296,7 +296,11 @@ int xioopen_ipdgram_listen(int argc, const char *argv[], struct opt *opts,
 
    if (pf == PF_UNSPEC) {
 #if WITH_IP4 && WITH_IP6
-      pf = xioparms.default_ip=='6'?PF_INET6:PF_INET;
+      switch (xioparms.default_ip) {
+      case '4': pf = PF_INET; break;
+      case '6': pf = PF_INET6; break;
+      default: break;		/* includes \0 */
+      }
 #elif WITH_IP6
       pf = PF_INET6;
 #else
@@ -506,7 +510,11 @@ int xioopen_udp_recvfrom(int argc, const char *argv[], struct opt *opts,
    retropt_socket_pf(opts, &pf);
    if (pf == PF_UNSPEC) {
 #if WITH_IP4 && WITH_IP6
-      pf = xioparms.default_ip=='6'?PF_INET6:PF_INET;
+      switch (xioparms.default_ip) {
+      case '4': pf = PF_INET; break;
+      case '6': pf = PF_INET6; break;
+      default: break;		/* includes \0 */
+      }
 #elif WITH_IP6
       pf = PF_INET6;
 #else
@@ -579,7 +587,11 @@ int xioopen_udp_recv(int argc, const char *argv[], struct opt *opts,
    retropt_socket_pf(opts, &pf);
    if (pf == PF_UNSPEC) {
 #if WITH_IP4 && WITH_IP6
-      pf = xioparms.default_ip=='6'?PF_INET6:PF_INET;
+      switch (xioparms.default_ip) {
+      case '4': pf = PF_INET; break;
+      case '6': pf = PF_INET6; break;
+      default: break;		/* includes \0 */
+      }
 #elif WITH_IP6
       pf = PF_INET6;
 #else
diff --git a/xio.h b/xio.h
index 596d101..910909c 100644
--- a/xio.h
+++ b/xio.h
@@ -109,7 +109,7 @@ typedef struct {
    char ip6portsep;	/* do not change, might be hardcoded somewhere! */
    char logopt;	/* 'm' means "switch to syslog when entering daemon mode" */
    const char *syslogfac;	/* syslog facility (only with mixed mode) */
-   char default_ip;	/* default prot.fam for IP based listen ('4' or '6') */
+   char default_ip;	/* default prot.fam for IP based listen ('4' '6' or '\0') */
    char preferred_ip;	/* preferred prot.fam. for name resolution ('0' for
 			   unspecified, '4', or '6') */
    bool experimental;	/* enable some features */
diff --git a/xioinitialize.c b/xioinitialize.c
index 880f828..ec06c7b 100644
--- a/xioinitialize.c
+++ b/xioinitialize.c
@@ -71,17 +71,25 @@ int xioinitialize(void) {
 
    {
       const char *default_ip;
+
+      // xioparms.default_ip = WITH_DEFAULT_IPV;
       default_ip = getenv("SOCAT_DEFAULT_LISTEN_IP");
       if (default_ip != NULL) {
 	 switch (default_ip[0]) {
 	 case '4':
 	 case '6':
-	    xioparms.default_ip = default_ip[0]; break;
+	    xioparms.default_ip = default_ip[0];
+	    break;
+	 default:
+	    xioparms.default_ip = '0';
+	    break;
 	 }
       }
    }
    {
       const char *preferred_ip;
+
+      // xioparms.preferred_ip = WITH_DEFAULT_IPV;
       preferred_ip = getenv("SOCAT_PREFERRED_RESOLVE_IP");
       if (preferred_ip != NULL) {
 	 switch (preferred_ip[0]) {
diff --git a/xioparam.c b/xioparam.c
index 5a4d3da..11830c5 100644
--- a/xioparam.c
+++ b/xioparam.c
@@ -19,8 +19,8 @@ xioparms_t xioparms = {
    ':',		/* ip6portsep */
    '\0',	/* logopt */
    NULL,	/* syslogfac */
-   '4',		/* default_ip */
-   '4',		/* preferred_ip */
+   WITH_DEFAULT_IPV, 	/* default_ip */
+   WITH_DEFAULT_IPV, 	/* preferred_ip */
    false, 	/* experimental */
    NULL, 	/* sniffleft_name */
    NULL 	/* sniffright_name */