From 706a482340141f8edb26fefae993e96b1581b034 Mon Sep 17 00:00:00 2001
From: Nuno Diegues <nuno@cloudflare.com>
Date: Sun, 19 Jun 2022 18:38:34 +0100
Subject: [PATCH] only set DF for sockets that can handle it (#3448)

Fixes #3445
---
 sys_conn.go | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/sys_conn.go b/sys_conn.go
index d73b01d2341..7cc05465808 100644
--- a/sys_conn.go
+++ b/sys_conn.go
@@ -30,9 +30,13 @@ func wrapConn(pc net.PacketConn) (rawConn, error) {
 		if err != nil {
 			return nil, err
 		}
-		err = setDF(rawConn)
-		if err != nil {
-			return nil, err
+
+		if _, ok := pc.LocalAddr().(*net.UDPAddr); ok {
+			// Only set DF on sockets that we expect to be able to handle that configuration.
+			err = setDF(rawConn)
+			if err != nil {
+				return nil, err
+			}
 		}
 	}
 	c, ok := pc.(OOBCapablePacketConn)