diff --git a/Makefile.am b/Makefile.am
index 1f4a8cd..41b9ea7 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -5,7 +5,7 @@ AM_CFLAGS = @GLIB_CFLAGS@ @SLIRP_CFLAGS@ @LIBCAP_CFLAGS@ @LIBSECCOMP_CFLAGS@
 noinst_LIBRARIES = libparson.a
 
 AM_TESTS_ENVIRONMENT = PATH="$(abs_top_builddir):$(PATH)"
-TESTS = tests/test-slirp4netns.sh tests/test-slirp4netns-configure.sh tests/test-slirp4netns-exit-fd.sh tests/test-slirp4netns-ready-fd.sh tests/test-slirp4netns-api-socket.sh tests/test-slirp4netns-disable-host-loopback.sh tests/test-slirp4netns-cidr.sh tests/test-slirp4netns-outbound-addr.sh tests/test-slirp4netns-disable-dns.sh tests/test-slirp4netns-seccomp.sh tests/test-slirp4netns-macaddress.sh
+TESTS = tests/test-slirp4netns.sh tests/test-slirp4netns-configure.sh tests/test-slirp4netns-exit-fd.sh tests/test-slirp4netns-ready-fd.sh tests/test-slirp4netns-api-socket.sh tests/test-slirp4netns-disable-host-loopback.sh tests/test-slirp4netns-cidr.sh tests/test-slirp4netns-outbound-addr.sh tests/test-slirp4netns-disable-dns.sh tests/test-slirp4netns-seccomp.sh tests/test-slirp4netns-macaddress.sh tests/test-slirp4netns-ipv6.sh
 
 EXTRA_DIST = \
 	slirp4netns.1.md \
diff --git a/api.c b/api.c
index 0ba2305..16b306f 100644
--- a/api.c
+++ b/api.c
@@ -207,9 +207,8 @@ static int api_handle_req_add_hostfwd(Slirp *slirp, int fd, struct api_ctx *ctx,
     }
     if (fwd->is_ipv6) {
         if (guest_addr_s == NULL || guest_addr_s[0] == '\0') {
-            guest_addr_s = "fd00::100";
-        }
-        if (inet_pton(AF_INET6, guest_addr_s, &fwd->guest_addr6) != 1) {
+            fwd->guest_addr6 = ctx->cfg->recommended_vguest6;
+        } else if (inet_pton(AF_INET6, guest_addr_s, &fwd->guest_addr6) != 1) {
             const char *err = "{\"error\":{\"desc\":\"bad request: add_hostfwd: "
                               "bad arguments.guest_addr\"}}";
             wrc = write(fd, err, strlen(err));
@@ -270,6 +269,7 @@ static void api_handle_req_list_hostfwd_foreach(gpointer data,
     JSON_Value *entry_value = json_value_init_object();
     JSON_Object *entry_object = json_value_get_object(entry_value);
     char host_addr[INET_ADDRSTRLEN], guest_addr[INET_ADDRSTRLEN];
+    char host_addr6[INET6_ADDRSTRLEN], guest_addr6[INET6_ADDRSTRLEN];
     if (inet_ntop(AF_INET, &fwd->host_addr, host_addr, sizeof(host_addr)) ==
         NULL) {
         perror("fatal: inet_ntop");
@@ -280,11 +280,29 @@ static void api_handle_req_list_hostfwd_foreach(gpointer data,
         perror("fatal: inet_ntop");
         exit(EXIT_FAILURE);
     }
+    if (fwd->is_ipv6) {
+        if (inet_ntop(AF_INET6, &fwd->host_addr6, host_addr6, sizeof(host_addr6)) ==
+            NULL) {
+            perror("fatal: inet_ntop");
+            exit(EXIT_FAILURE);
+        }
+        if (inet_ntop(AF_INET6, &fwd->guest_addr6, guest_addr6, sizeof(guest_addr6)) ==
+            NULL) {
+            perror("fatal: inet_ntop");
+            exit(EXIT_FAILURE);
+        }
+    }
     json_object_set_number(entry_object, "id", fwd->id);
     json_object_set_string(entry_object, "proto", fwd->is_udp ? "udp" : "tcp");
     json_object_set_string(entry_object, "host_addr", host_addr);
+    if (fwd->is_ipv6) {
+        json_object_set_string(entry_object, "host_addr6", host_addr6);
+    }
     json_object_set_number(entry_object, "host_port", fwd->host_port);
     json_object_set_string(entry_object, "guest_addr", guest_addr);
+    if (fwd->is_ipv6) {
+        json_object_set_string(entry_object, "guest_addr6", guest_addr6);
+    }
     json_object_set_number(entry_object, "guest_port", fwd->guest_port);
     /* json_array_append_value does not copy passed value */
     if (json_array_append_value(entries_array, entry_value) != JSONSuccess) {
diff --git a/main.c b/main.c
index de49394..c7cc343 100644
--- a/main.c
+++ b/main.c
@@ -524,6 +524,9 @@ static void usage(const char *argv0)
     printf(
         "--cidr=CIDR              specify network address CIDR (default=%s)\n",
         DEFAULT_CIDR);
+    printf(
+        "--cidr6=CIDR             specify network address CIDR (default=%s)\n",
+        DEFAULT_CIDR6);
     printf("--disable-host-loopback  prohibit connecting to 127.0.0.1:* on the "
            "host namespace\n");
     /* v0.4.0 */
@@ -611,6 +614,10 @@ static void options_destroy(struct options *options)
         free(options->cidr);
         options->cidr = NULL;
     }
+    if (options->cidr6 != NULL) {
+        free(options->cidr6);
+        options->cidr6 = NULL;
+    }
     if (options->api_socket != NULL) {
         free(options->api_socket);
         options->api_socket = NULL;
@@ -649,13 +656,15 @@ static void parse_args(int argc, char *const argv[], struct options *options)
     int opt;
     char *strtol_e = NULL;
     char *optarg_cidr = NULL;
+    char *optarg_cidr6 = NULL;
     char *optarg_netns_type = NULL;
     char *optarg_userns_path = NULL;
     char *optarg_api_socket = NULL;
     char *optarg_outbound_addr = NULL;
     char *optarg_outbound_addr6 = NULL;
     char *optarg_macaddress = NULL;
-#define CIDR -42
+#define CIDR -41
+#define CIDR6 -42
 #define DISABLE_HOST_LOOPBACK -43
 #define NETNS_TYPE -44
 #define USERNS_PATH -45
@@ -675,6 +684,7 @@ static void parse_args(int argc, char *const argv[], struct options *options)
         { "ready-fd", required_argument, NULL, 'r' },
         { "mtu", required_argument, NULL, 'm' },
         { "cidr", required_argument, NULL, CIDR },
+        { "cidr6", required_argument, NULL, CIDR6 },
         { "disable-host-loopback", no_argument, NULL, DISABLE_HOST_LOOPBACK },
         { "no-host-loopback", no_argument, NULL, _DEPRECATED_NO_HOST_LOOPBACK },
         { "netns-type", required_argument, NULL, NETNS_TYPE },
@@ -728,6 +738,9 @@ static void parse_args(int argc, char *const argv[], struct options *options)
         case CIDR:
             optarg_cidr = optarg;
             break;
+        case CIDR6:
+            optarg_cidr6 = optarg;
+            break;
         case _DEPRECATED_NO_HOST_LOOPBACK:
             // There was no tagged release with support for --no-host-loopback.
             // So no one will be affected by removal of --no-host-loopback.
@@ -800,6 +813,9 @@ static void parse_args(int argc, char *const argv[], struct options *options)
     if (optarg_cidr != NULL) {
         options->cidr = strdup(optarg_cidr);
     }
+    if (optarg_cidr6 != NULL) {
+        options->cidr6 = strdup(optarg_cidr6);
+    }
     if (optarg_netns_type != NULL) {
         options->netns_type = strdup(optarg_netns_type);
     }
@@ -825,6 +841,7 @@ static void parse_args(int argc, char *const argv[], struct options *options)
         }
     }
 #undef CIDR
+#undef CIDR6
 #undef DISABLE_HOST_LOOPBACK
 #undef NETNS_TYPE
 #undef USERNS_PATH
@@ -940,10 +957,12 @@ static int parse_cidr6(struct in6_addr *network, struct in6_addr *netmask,
 {
     int rc = 0;
     regex_t r;
-    regmatch_t matches[4];
+    regmatch_t matches[5];
     size_t nmatch = sizeof(matches) / sizeof(matches[0]);
-    const char *cidr_regex = "^(([a-fA-F0-9]{1,4}):){1,4}:/([0-9]{1,3})";
-    char snetwork[INET6_ADDRSTRLEN], sprefix[INET6_ADDRSTRLEN];
+    const char *cidr_regex = "^((([a-fA-F0-9]{1,4}):){1,4}):/([0-9]{1,3})";
+    char snetwork[INET6_ADDRSTRLEN],
+         snetwork_end[INET6_ADDRSTRLEN],
+         sprefix[INET6_ADDRSTRLEN];
     int prefix;
     const char *random;
     rc = regcomp(&r, cidr_regex, REG_EXTENDED);
@@ -963,19 +982,28 @@ static int parse_cidr6(struct in6_addr *network, struct in6_addr *netmask,
         fprintf(stderr, "invalid CIDR: %s\n", cidr);
         goto finish;
     }
-    rc = from_regmatch(sprefix, sizeof(sprefix), matches[3], cidr);
+    rc = from_regmatch(snetwork_end, sizeof(snetwork_end), matches[2], cidr);
     if (rc < 0) {
         fprintf(stderr, "invalid CIDR: %s\n", cidr);
         goto finish;
     }
-    random = pseudo_random_global_id(NULL);
-    if (random == NULL) {
-        fprintf(stderr, "cannot create pseudo random global id\n");
-        rc = -1;
+    rc = from_regmatch(sprefix, sizeof(sprefix), matches[4], cidr);
+    if (rc < 0) {
+        fprintf(stderr, "invalid CIDR: %s\n", cidr);
         goto finish;
     }
-    strcpy(snetwork, random);
-    strcat(snetwork, "0");
+    if (strcmp(snetwork, snetwork_end) == 0) {
+        random = pseudo_random_global_id(NULL);
+        if (random == NULL) {
+            fprintf(stderr, "cannot create pseudo random global id\n");
+            rc = -1;
+            goto finish;
+        }
+        strcpy(snetwork, random);
+        strcat(snetwork, "0");
+    } else {
+        strcat(snetwork, ":0");
+    }
 
     if (inet_pton(AF_INET6, snetwork, network) != 1) {
         fprintf(stderr, "invalid network address: %s\n", snetwork);
diff --git a/tests/test-slirp4netns-api-socket.sh b/tests/test-slirp4netns-api-socket.sh
index 8de0c21..c73592f 100755
--- a/tests/test-slirp4netns-api-socket.sh
+++ b/tests/test-slirp4netns-api-socket.sh
@@ -47,6 +47,7 @@ result=$(cat /dev/zero | ncat -U $apisocket || true)
 set set -e
 echo $result | jq .error.desc | grep "bad request: too large message"
 
+set -e
 result=$(echo '{"execute": "add_hostfwd", "arguments":{"proto": "tcp","host_port":8080,"guest_port":80}}' | ncat -U $apisocket)
 [[ $(echo $result | jq .error) == null ]]
 id=$(echo $result | jq .return.id)
@@ -54,12 +55,12 @@ id=$(echo $result | jq .return.id)
 
 result=$(echo '{"execute": "list_hostfwd"}' | ncat -U $apisocket)
 [[ $(echo $result | jq .error) == null ]]
-[[ $(echo $result | jq .return.entries[0].id) == $id ]]
-[[ $(echo $result | jq .return.entries[0].proto) == '"tcp"' ]]
-[[ $(echo $result | jq .return.entries[0].host_addr) == '"0.0.0.0"' ]]
-[[ $(echo $result | jq .return.entries[0].host_port) == 8080 ]]
-[[ $(echo $result | jq .return.entries[0].guest_addr) == '"10.0.2.100"' ]]
-[[ $(echo $result | jq .return.entries[0].guest_port) == 80 ]]
+[[ $(echo $result | jq .entries[0].id) == $id ]]
+[[ $(echo $result | jq .entries[0].proto) == '"tcp"' ]]
+[[ $(echo $result | jq .entries[0].host_addr) == '"0.0.0.0"' ]]
+[[ $(echo $result | jq .entries[0].host_port) == 8080 ]]
+[[ $(echo $result | jq .entries[0].guest_addr) == '"10.0.2.100"' ]]
+[[ $(echo $result | jq .entries[0].guest_port) == 80 ]]
 
 result=$(echo '{"execute": "remove_hostfwd", "arguments":{"id": 1}}' | ncat -U $apisocket)
 [[ $(echo $result | jq .error) == null ]]
diff --git a/tests/test-slirp4netns-ipv6.sh b/tests/test-slirp4netns-ipv6.sh
new file mode 100755
index 0000000..60f6af3
--- /dev/null
+++ b/tests/test-slirp4netns-ipv6.sh
@@ -0,0 +1,50 @@
+#!/bin/bash
+set -xeuo pipefail
+
+. $(dirname $0)/common.sh
+
+unshare -r -n sleep infinity &
+child=$!
+
+wait_for_network_namespace $child
+
+tmpdir=$(mktemp -d /tmp/slirp4netns-bench.XXXXXXXXXX)
+apisocket=${tmpdir}/slirp4netns.sock
+
+slirp4netns -c $child --enable-ipv6 --cidr6=fd00:fb14:63ee:b::/64 --api-socket $apisocket tun11 &
+slirp_pid=$!
+
+wait_for_network_device $child tun11
+
+function cleanup() {
+	kill -9 $child $slirp_pid
+	rm -rf $tmpdir
+}
+trap cleanup EXIT
+
+set +e
+result=$(cat /dev/zero | ncat -U $apisocket || true)
+set set -e
+echo $result | jq .error.desc | grep "bad request: too large message"
+
+set -e
+result=$(echo '{"execute": "add_hostfwd", "arguments":{"proto": "tcp","host_port":8080,"guest_port":80}}' | ncat -U $apisocket)
+[[ $(echo $result | jq .error) == null ]]
+id=$(echo $result | jq .return.id)
+[[ $id == 1 ]]
+
+result=$(echo '{"execute": "list_hostfwd"}' | ncat -U $apisocket)
+[[ $(echo $result | jq .error) == null ]]
+[[ $(echo $result | jq .entries[0].id) == $id ]]
+[[ $(echo $result | jq .entries[0].proto) == '"tcp"' ]]
+[[ $(echo $result | jq .entries[0].host_addr) == '"0.0.0.0"' ]]
+[[ $(echo $result | jq .entries[0].host_addr6) == '"::"' ]]
+[[ $(echo $result | jq .entries[0].host_port) == 8080 ]]
+[[ $(echo $result | jq .entries[0].guest_addr) == '"10.0.2.100"' ]]
+[[ $(echo $result | jq .entries[0].guest_addr6) == '"fd00:fb14:63ee:b::100"' ]]
+[[ $(echo $result | jq .entries[0].guest_port) == 80 ]]
+
+result=$(echo '{"execute": "remove_hostfwd", "arguments":{"id": 1}}' | ncat -U $apisocket)
+[[ $(echo $result | jq .error) == null ]]
+
+# see also: benchmarks/benchmark-iperf3-reverse.sh