From be6f856840979cbeb43fb1f3364e5131aae395c1 Mon Sep 17 00:00:00 2001
From: Cameron Gutman <aicommander@gmail.com>
Date: Sat, 3 Feb 2024 16:06:31 -0600
Subject: [PATCH] Fix DSCP tagging for dual-stack sockets on Linux

---
 src/platform/linux/misc.cpp | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/platform/linux/misc.cpp b/src/platform/linux/misc.cpp
index 7bd38d6d..6cfa9e49 100644
--- a/src/platform/linux/misc.cpp
+++ b/src/platform/linux/misc.cpp
@@ -628,7 +628,10 @@ namespace platf {
     if (dscp_tagging) {
       int level;
       int option;
-      if (address.is_v6()) {
+
+      // With dual-stack sockets, Linux uses IPV6_TCLASS for IPv6 traffic
+      // and IP_TOS for IPv4 traffic.
+      if (address.is_v6() && !address.to_v6().is_v4_mapped()) {
         level = SOL_IPV6;
         option = IPV6_TCLASS;
       }