From c11a52d60c51f104ff60fed47e60d66aa77f6fef Mon Sep 17 00:00:00 2001
From: Eugene Burkov <e.burkov@adguard.com>
Date: Tue, 7 Mar 2023 15:49:47 +0300
Subject: [PATCH] Pull request: 5281-dhcp-mtu-opt

Merge in DNS/adguard-home from 5281-dhcp-mtu-opt to master

Updates #5281.

Squashed commit of the following:

commit fd97ab7ca4745c7ac2f82261dce42d377dede8b7
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Tue Mar 7 15:40:33 2023 +0300

    all: fix docs

commit eb4ecc12efab1acb3755e4ff2708a490adf6855d
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Tue Mar 7 15:37:07 2023 +0300

    all: imp docs, log changes

commit 887a28af8590da454763725b298baee2d022ce38
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Tue Mar 7 14:35:12 2023 +0300

    dhcpd: rm default mtu
---
 CHANGELOG.md                   |  2 ++
 internal/dhcpd/options_unix.go | 13 +++++--------
 2 files changed, 7 insertions(+), 8 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7107748f..2eb59ef4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -64,6 +64,7 @@ In this release, the schema version has changed from 16 to 17.
 
 ### Fixed
 
+- Obsolete value of the Interface MTU DHCP option is now omitted ([#5281]).
 - Various dark theme bugs ([#5439], [#5441], [#5442], [#5515]).
 - Automatic update on MIPS64 and little-endian 32-bit MIPS architectures
   ([#5270], [#5373]).
@@ -74,6 +75,7 @@ In this release, the schema version has changed from 16 to 17.
 [#1472]: https://github.com/AdguardTeam/AdGuardHome/issues/1472
 [#4884]: https://github.com/AdguardTeam/AdGuardHome/issues/4884
 [#5270]: https://github.com/AdguardTeam/AdGuardHome/issues/5270
+[#5281]: https://github.com/AdguardTeam/AdGuardHome/issues/5281
 [#5373]: https://github.com/AdguardTeam/AdGuardHome/issues/5373
 [#5431]: https://github.com/AdguardTeam/AdGuardHome/issues/5431
 [#5439]: https://github.com/AdguardTeam/AdGuardHome/issues/5439
diff --git a/internal/dhcpd/options_unix.go b/internal/dhcpd/options_unix.go
index 082826d5..6881d942 100644
--- a/internal/dhcpd/options_unix.go
+++ b/internal/dhcpd/options_unix.go
@@ -263,15 +263,12 @@ func (s *v4Server) prepareOptions() {
 
 		// IP-Layer Per Interface
 
-		// Since nearly all networks in the Internet currently support an MTU of
-		// 576 or greater, we strongly recommend the use of 576 for datagrams
-		// sent to non-local networks.
+		// Don't set the Interface MTU because client may choose the value on
+		// their own since it's listed in the [Host Requirements RFC].  It also
+		// seems the values listed there sometimes appear obsolete, see
+		// https://github.com/AdguardTeam/AdGuardHome/issues/5281.
 		//
-		// See https://datatracker.ietf.org/doc/html/rfc1122#section-3.3.3.
-		dhcpv4.Option{
-			Code:  dhcpv4.OptionInterfaceMTU,
-			Value: dhcpv4.Uint16(576),
-		},
+		// [Host Requirements RFC]: https://datatracker.ietf.org/doc/html/rfc1122#section-3.3.3.
 
 		// Set the All Subnets Are Local Option to false since commonly the
 		// connected hosts aren't expected to be multihomed.