X-Git-Url: https://git.tcpdump.org/tcpdump/blobdiff_plain/272333b0ed149132aa39b4a53a6a1105fcff6976..58ed5c2fc8227f64624e55d832c1785c22efbb5a:/print-mpls.c

diff --git a/print-mpls.c b/print-mpls.c
index fe15a86e..d97cce52 100644
--- a/print-mpls.c
+++ b/print-mpls.c
@@ -109,62 +109,73 @@ mpls_print(const u_char *bp, u_int length)
 	default:
 		/*
 		 * Generally there's no indication of protocol in MPLS label
-		 * encoding, however draft-hsmit-isis-aal5mux-00.txt describes
-		 * a technique that looks at the first payload byte if the BOS (bottom of stack)
-		 * bit is set and tries to determine the network layer protocol
-		 * 0x45-0x4f is IPv4
-		 * 0x60-0x6f is IPv6
-		 * 0x81-0x83 is OSI (CLNP,ES-IS,IS-IS)
-		 * this technique is sometimes known as NULL encapsulation
-		 * and decoding is particularly useful for control-plane traffic [BGP]
-		 * which cisco by default sends MPLS encapsulated
+		 * encoding.
+		 *
+		 * However, draft-hsmit-isis-aal5mux-00.txt describes a
+		 * technique for encapsulating IS-IS and IP traffic on the
+		 * same ATM virtual circuit; you look at the first payload
+		 * byte to determine the network layer protocol, based on
+		 * the fact that
+		 *
+		 *	1) the first byte of an IP header is 0x45-0x4f
+		 *	   for IPv4 and 0x60-0x6f for IPv6;
+		 *
+		 *	2) the first byte of an OSI CLNP packet is 0x81,
+		 *	   the first byte of an OSI ES-IS packet is 0x82,
+		 *	   and the first byte of an OSI IS-IS packet is
+		 *	   0x83;
+		 *
+		 * so the network layer protocol can be inferred from the
+		 * first byte of the packet, if the protocol is one of the
+		 * ones listed above.
+		 *
+		 * Cisco sends control-plane traffic MPLS-encapsulated in
+		 * this fashion.
 		 */
-		if (MPLS_STACK(label_entry)) { /* only do this if the stack bit is set */
-			switch(*p) {
-
-			case 0x45:
-			case 0x46:
-			case 0x47:
-			case 0x48:
-			case 0x49:
-			case 0x4a:
-			case 0x4b:
-			case 0x4c:
-			case 0x4d:
-			case 0x4e:
-			case 0x4f:
-				pt = PT_IPV4;
-				break;
+		switch(*p) {
+
+		case 0x45:
+		case 0x46:
+		case 0x47:
+		case 0x48:
+		case 0x49:
+		case 0x4a:
+		case 0x4b:
+		case 0x4c:
+		case 0x4d:
+		case 0x4e:
+		case 0x4f:
+			pt = PT_IPV4;
+			break;
 				
-			case 0x60:
-			case 0x61:
-			case 0x62:
-			case 0x63:
-			case 0x64:
-			case 0x65:
-			case 0x66:
-			case 0x67:
-			case 0x68:
-			case 0x69:
-			case 0x6a:
-			case 0x6b:
-			case 0x6c:
-			case 0x6d:
-			case 0x6e:
-			case 0x6f:
-				pt = PT_IPV6;
-				break;
-
-			case 0x81:
-			case 0x82:
-			case 0x83:
-				pt = PT_OSI;
-				break;
-
-			default:
-				/* ok bail out - we did not figure out what it is*/
-				break;
-			}
+		case 0x60:
+		case 0x61:
+		case 0x62:
+		case 0x63:
+		case 0x64:
+		case 0x65:
+		case 0x66:
+		case 0x67:
+		case 0x68:
+		case 0x69:
+		case 0x6a:
+		case 0x6b:
+		case 0x6c:
+		case 0x6d:
+		case 0x6e:
+		case 0x6f:
+			pt = PT_IPV6;
+			break;
+
+		case 0x81:
+		case 0x82:
+		case 0x83:
+			pt = PT_OSI;
+			break;
+
+		default:
+			/* ok bail out - we did not figure out what it is*/
+			break;
 		}
 	}
 
@@ -188,7 +199,7 @@ mpls_print(const u_char *bp, u_int length)
 
 	case PT_IPV6:
 #ifdef INET6
-		ip6_print(p, length - (p - bp));
+		ip6_print(gndo, p, length - (p - bp));
 #else
 		printf("IPv6, length: %u", length);
 #endif