From bd5146c67eedcfaea054ae569d1621cb511b20da Mon Sep 17 00:00:00 2001
From: Yu Watanabe <watanabe.yu+github@gmail.com>
Date: Wed, 16 Jun 2021 08:33:04 +0900
Subject: [PATCH 1/3] network: IFA_F_NODAD flag is only for IPv6 addresses

---
 src/network/networkd-address.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/network/networkd-address.c b/src/network/networkd-address.c
index b84181892e..afcbb12473 100644
--- a/src/network/networkd-address.c
+++ b/src/network/networkd-address.c
@@ -2111,7 +2111,8 @@ static int address_section_verify(Address *address) {
                 address->scope = RT_SCOPE_HOST;
         }
 
-        if (!FLAGS_SET(address->duplicate_address_detection, ADDRESS_FAMILY_IPV6))
+        if (address->family == AF_INET6 &&
+            !FLAGS_SET(address->duplicate_address_detection, ADDRESS_FAMILY_IPV6))
                 address->flags |= IFA_F_NODAD;
 
         return 0;

From f4c48492fe3dfa268b6d2457c9ae425b685ca4e0 Mon Sep 17 00:00:00 2001
From: Yu Watanabe <watanabe.yu+github@gmail.com>
Date: Wed, 16 Jun 2021 10:32:28 +0900
Subject: [PATCH 2/3] man: fix RFC number and its title

---
 man/systemd.network.xml | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/man/systemd.network.xml b/man/systemd.network.xml
index 8d3d65024c..3e85edec6d 100644
--- a/man/systemd.network.xml
+++ b/man/systemd.network.xml
@@ -1098,8 +1098,8 @@ IPv6Token=prefixstable:2002:da8:1::</programlisting></para>
           <listitem>
             <para>Takes one of <literal>ipv4</literal>, <literal>ipv6</literal>,
             <literal>both</literal>, <literal>none</literal>. When <literal>ipv4</literal>,
-            performs IPv4 Duplicate Address Detection. See
-            <ulink url="https://tools.ietf.org/html/rfc5227">RFC 5224</ulink>.
+            performs IPv4 Address Conflict Detection. See
+            <ulink url="https://tools.ietf.org/html/rfc5227">RFC 5227</ulink>.
             When <literal>ipv6</literal>, performs IPv6 Duplicate Address Detection. See
             <ulink url="https://tools.ietf.org/html/rfc4862">RFC 4862</ulink>.
             Defaults to <literal>ipv6</literal>.</para>

From 1cf4ed142d6c1e2b9dc6a0bc74b6a83ae30b0f8e Mon Sep 17 00:00:00 2001
From: Yu Watanabe <watanabe.yu+github@gmail.com>
Date: Wed, 16 Jun 2021 06:54:47 +0900
Subject: [PATCH 3/3] network: always enable IPv4 ACD for statically configured
 IPv4LL address

---
 src/network/networkd-address.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/network/networkd-address.c b/src/network/networkd-address.c
index afcbb12473..04ad2aa69d 100644
--- a/src/network/networkd-address.c
+++ b/src/network/networkd-address.c
@@ -2115,6 +2115,13 @@ static int address_section_verify(Address *address) {
             !FLAGS_SET(address->duplicate_address_detection, ADDRESS_FAMILY_IPV6))
                 address->flags |= IFA_F_NODAD;
 
+        if (address->family == AF_INET && in4_addr_is_link_local(&address->in_addr.in) &&
+            !FLAGS_SET(address->duplicate_address_detection, ADDRESS_FAMILY_IPV4)) {
+                log_debug("%s: An IPv4 link-local address is specified, enabling IPv4 Address Conflict Detection (ACD).",
+                          address->section->filename);
+                address->duplicate_address_detection |= ADDRESS_FAMILY_IPV4;
+        }
+
         return 0;
 }