From f5c256affdecc50ecf485b7ad54986ebb17e783a Mon Sep 17 00:00:00 2001
From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: Fri, 20 Apr 2018 05:30:22 +0200
Subject: [PATCH] Check for correct first nibble

The code before assumed that the flow label was always zero.
---
 tun_linux.go | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tun_linux.go b/tun_linux.go
index a37b727..1abc86f 100644
--- a/tun_linux.go
+++ b/tun_linux.go
@@ -273,7 +273,7 @@ func (tun *NativeTun) Write(buff []byte, offset int) (int, error) {
 		buff[0] = 0x00
 		buff[1] = 0x00
 
-		if buff[4] == ipv6.Version<<4 {
+		if buff[4]>>4 == ipv6.Version {
 			buff[2] = 0x86
 			buff[3] = 0xdd
 		} else {