The draft in question has nothing to do with MPLS; clarify that.

[tcpdump] / print-mpls.c

diff --git a/print-mpls.c b/print-mpls.c
index fe15a86edf3db951291d0547cdb336a76422407a..13ad0fddecd927765fe838ccb3c8840bcc49f6b0 100644 (file)
--- 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;
                }
        }