From efb381caf102938d24149f38e98881d282ded11a Mon Sep 17 00:00:00 2001
From: Colin Percival <cperciva@FreeBSD.org>
Date: Mon, 22 Nov 2021 20:16:34 -0800
Subject: [PATCH] EC2: Turn off IPv6 DAD

Disable Duplicate Address Detection in EC2 instances.  The networking
configuration in EC2, with IPv6 addresses assigned by DHCPv6 and
host egress filtering, makes "duplicate addresses" impossible.

This speeds up the boot process in EC2 by 2 seconds.

Sponsored by:	https://www.patreon.com/cperciva
Differential Revision:	https://reviews.freebsd.org/D33091

(cherry picked from commit 81075203a057c9ba3467a7f90ea1e9469d7f7723)
---
 release/tools/ec2.conf | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/release/tools/ec2.conf b/release/tools/ec2.conf
index 888a446659a..bb972c456fb 100644
--- a/release/tools/ec2.conf
+++ b/release/tools/ec2.conf
@@ -68,6 +68,10 @@ vm_extra_pre_umount() {
 	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'