diff --git a/Vagrantfile b/Vagrantfile
index 861f276c..9576c27e 100644
--- a/Vagrantfile
+++ b/Vagrantfile
@@ -19,6 +19,7 @@ Vagrant.configure("2") do |config|
 	# subdomain on our justtesting.email domain so we can get
 	# started quickly.
     export PUBLIC_IP=auto
+    export PUBLIC_IPV6=auto
     export PUBLIC_HOSTNAME=auto-easy
     export CSR_COUNTRY=US
 
diff --git a/management/dns_update.py b/management/dns_update.py
index 7ac9fb2f..66a2bf6c 100755
--- a/management/dns_update.py
+++ b/management/dns_update.py
@@ -60,9 +60,13 @@ def build_zone(domain, env):
 	records.append((None,  "NS",  "ns1.%s." % env["PUBLIC_HOSTNAME"]))
 	records.append((None,  "NS",  "ns2.%s." % env["PUBLIC_HOSTNAME"]))
 	records.append((None,  "A",   env["PUBLIC_IP"]))
+	if env.get('PUBLIC_IPV6'):
+		records.append((None, "AAAA", env["PUBLIC_IPV6"]))
 	records.append((None,  "MX",  "10 %s." % env["PUBLIC_HOSTNAME"]))
 	records.append((None,  "TXT", '"v=spf1 mx -all"'))
 	records.append(("www", "A",   env["PUBLIC_IP"]))
+	if env.get('PUBLIC_IPV6'):
+		records.append(("www", "AAAA", env["PUBLIC_IPV6"]))
 
 	# In PUBLIC_HOSTNAME, also define ns1 and ns2.
 	if domain == env["PUBLIC_HOSTNAME"]:
diff --git a/setup/functions.sh b/setup/functions.sh
index 1a18b28d..210113ac 100644
--- a/setup/functions.sh
+++ b/setup/functions.sh
@@ -39,11 +39,19 @@ function get_default_publicip {
 	get_publicip_from_web_service || get_publicip_fallback
 }
 
+function get_default_publicipv6 {
+	get_publicipv6_from_web_service || get_publicipv6_fallback
+}
+
 function get_publicip_from_web_service {
 	# This seems to be the most reliable way to determine the
 	# machine's public IP address: asking a very nice web API
 	# for how they see us. Thanks go out to icanhazip.com.
-	curl --fail --silent icanhazip.com 2>/dev/null
+	curl -4 --fail --silent icanhazip.com 2>/dev/null
+}
+
+function get_publicipv6_from_web_service {
+	curl -6 --fail --silent icanhazip.com 2>/dev/null
 }
 
 function get_publicip_fallback {
@@ -53,17 +61,39 @@ function get_publicip_fallback {
 	# have multiple addresses if it has multiple network adapters.
 	set -- $(hostname --ip-address       2>/dev/null) \
 	       $(hostname --all-ip-addresses 2>/dev/null)
-	while (( $# )) && is_loopback_ip "$1"; do
+	while (( $# )) && { ! is_ipv4 "$1" || is_loopback_ip "$1"; }; do
 		shift
 	done
 	printf '%s\n' "$1" # return this value
 }
 
+function get_publicipv6_fallback {
+	set -- $(hostname --ip-address       2>/dev/null) \
+	       $(hostname --all-ip-addresses 2>/dev/null)
+	while (( $# )) && { ! is_ipv6 "$1" || is_loopback_ipv6 "$1"; }; do
+		shift
+	done
+	printf '%s\n' "$1" # return this value
+}
+
+function is_ipv4 {
+	# helper for get_publicip_fallback
+	[[ "$1" == *.*.*.* ]]
+}
+
+function is_ipv6 {
+	[[ "$1" == *:*:* ]]
+}
+
 function is_loopback_ip {
 	# helper for get_publicip_fallback
 	[[ "$1" == 127.* ]]
 }
 
+function is_loopback_ipv6 {
+	[[ "$1" == ::1 ]]
+}
+
 function ufw_allow {
 	if [ -z "$DISABLE_FIREWALL" ]; then
 		# ufw has completely unhelpful output
diff --git a/setup/start.sh b/setup/start.sh
index 51a1ebdd..301adead 100755
--- a/setup/start.sh
+++ b/setup/start.sh
@@ -24,6 +24,11 @@ fi
 # Gather information from the user about the hostname and public IP
 # address of this host.
 if [ -z "$PUBLIC_HOSTNAME" ]; then
+	if [ -z "$DEFAULT_PUBLIC_HOSTNAME" ]; then
+		# set a default on first run
+		DEFAULT_PUBLIC_HOSTNAME=`get_default_hostname`
+	fi
+
 	echo
 	echo "Enter the hostname you want to assign to this machine."
 	echo "We've guessed a value. Just backspace it if it's wrong."
@@ -31,27 +36,35 @@ if [ -z "$PUBLIC_HOSTNAME" ]; then
 	echo "be similar."
 	echo
 
-	if [ -z "$DEFAULT_PUBLIC_HOSTNAME" ]; then
-		# set a default on first run
-		DEFAULT_PUBLIC_HOSTNAME=`get_default_hostname`
-	fi
-
 	read -e -i "$DEFAULT_PUBLIC_HOSTNAME" -p "Hostname: " PUBLIC_HOSTNAME
 fi
 
 if [ -z "$PUBLIC_IP" ]; then
+	if [ -z "$DEFAULT_PUBLIC_IP" ]; then
+		# set a default on first run
+		DEFAULT_PUBLIC_IP=`get_default_publicip`
+	fi
+
 	echo
 	echo "Enter the public IP address of this machine, as given to"
 	echo "you by your ISP. We've guessed a value, but just backspace"
 	echo "it if it's wrong."
 	echo
 
-	if [ -z "$DEFAULT_PUBLIC_IP" ]; then
+	read -e -i "$DEFAULT_PUBLIC_IP" -p "Public IP: " PUBLIC_IP
+fi
+
+if [ -z "$PUBLIC_IPV6" ]; then
+	if [ -z "$DEFAULT_PUBLIC_IPV6" ]; then
 		# set a default on first run
-		DEFAULT_PUBLIC_IP=`get_default_publicip`
+		DEFAULT_PUBLIC_IPV6=`get_default_publicipv6`
 	fi
 
-	read -e -i "$DEFAULT_PUBLIC_IP" -p "Public IP: " PUBLIC_IP
+	echo
+	echo "(Optional) Enter the IPv6 address of this machine. Leave blank"
+	echo "           if the machine does not have an IPv6 address."
+
+	read -e -i "$DEFAULT_PUBLIC_IPV6" -p "Public IPv6: " PUBLIC_IPV6
 fi
 
 if [ -z "$CSR_COUNTRY" ]; then
@@ -70,12 +83,17 @@ if [ -z "$CSR_COUNTRY" ]; then
 fi
 
 # Automatic configuration, e.g. as used in our Vagrant configuration.
-if [ "$PUBLIC_IP" == "auto" ]; then
+if [ "$PUBLIC_IP" = "auto" ]; then
 	# Use a public API to get our public IP address.
 	PUBLIC_IP=`get_default_publicip`
 	echo "IP Address: $PUBLIC_IP"
 fi
-if [ "$PUBLIC_HOSTNAME" == "auto-easy" ]; then
+if [ "$PUBLIC_IPV6" = "auto" ]; then
+	# Use a public API to get our public IP address.
+	PUBLIC_IPV6=`get_default_publicipv6`
+	echo "IPv6 Address: $PUBLIC_IPV6"
+fi
+if [ "$PUBLIC_HOSTNAME" = "auto-easy" ]; then
 	# Generate a probably-unique subdomain under our justtesting.email domain.
 	PUBLIC_HOSTNAME=m`get_default_publicip | sha1sum | cut -c1-5`.justtesting.email
 	echo "Public Hostname: $PUBLIC_HOSTNAME"
@@ -97,6 +115,7 @@ cat > /etc/mailinabox.conf << EOF;
 STORAGE_ROOT=$STORAGE_ROOT
 PUBLIC_HOSTNAME=$PUBLIC_HOSTNAME
 PUBLIC_IP=$PUBLIC_IP
+PUBLIC_IPV6=$PUBLIC_IPV6
 CSR_COUNTRY=$CSR_COUNTRY
 EOF