diff --git a/release/tools/ec2.conf b/release/tools/ec2.conf
--- a/release/tools/ec2.conf
+++ b/release/tools/ec2.conf
@@ -70,6 +70,10 @@
 	echo 'rtsold_enable="YES"' >> ${DESTDIR}/etc/rc.conf
 	echo 'rtsold_flags="-M /usr/local/libexec/rtsold-M -a"' >> ${DESTDIR}/etc/rc.conf
 
+	# Turn off IPv6 Duplicate Address Detection; the EC2 networking
+	# configuration makes it unnecessary.
+	echo 'net.inet6.ip6.dad_count=0' >> ${DESTDIR}/etc/sysctl.conf
+
 	# Provide a script which rtsold can use to launch DHCPv6
 	mkdir -p ${DESTDIR}/usr/local/libexec
 	cat > ${DESTDIR}/usr/local/libexec/rtsold-M <<'EOF'