diff --git a/src/tun.c b/src/tun.c
index 44bb220..c05a591 100644
--- a/src/tun.c
+++ b/src/tun.c
@@ -521,11 +521,15 @@ write_tun(int tun_fd, char *data, size_t len)
 		len -= 4;
 	} else {
 #ifdef LINUX
+		// Linux prefixes with 32 bits ethertype
+		// 0x0800 for IPv4, 0x86DD for IPv6
 		data[0] = 0x00;
 		data[1] = 0x00;
 		data[2] = 0x08;
 		data[3] = 0x00;
 #else /* OPENBSD and DARWIN(utun) */
+		// BSDs prefix with 32 bits address family
+		// AF_INET for IPv4, AF_INET6 for IPv6
 		data[0] = 0x00;
 		data[1] = 0x00;
 		data[2] = 0x00;