Check for the IP SAP value in the LLC header, and note some of the

problems with that particular heuristic.

diff --git a/print-atm.c b/print-atm.c
index 74f19a858b16278ef2de577e66433a351d811a48..a87d1042f5c776d66180d3e8538cec728d42c6ae 100644 (file)
--- a/print-atm.c
+++ b/print-atm.c
@@ -20,7 +20,7 @@
  */
 #ifndef lint
 static const char rcsid[] =
-    "@(#) $Header: /tcpdump/master/tcpdump/print-atm.c,v 1.28 2002-12-09 05:12:25 guy Exp $ (LBL)";
+    "@(#) $Header: /tcpdump/master/tcpdump/print-atm.c,v 1.29 2002-12-10 08:03:36 guy Exp $ (LBL)";
 #endif
 
 #ifdef HAVE_CONFIG_H
@@ -39,6 +39,7 @@ static const char rcsid[] =
 #include "ethertype.h"
 #include "atm.h"
 #include "atmuni31.h"
+#include "llc.h"
 
 #include "ether.h"
 
@@ -80,6 +81,12 @@ atm_llc_print(const u_char *p, int length, int caplen)
        }
 }
 
+/*
+ * Given a SAP value, generate the LLC header value for a UI packet
+ * with that SAP as the source and destination SAP.
+ */
+#define LLC_UI_HDR(sap)        ((sap)<<16 | (sap<<8) | 0x03)
+
 /*
  * This is the top level routine of the printer.  'p' points
  * to the LLC/SNAP header of the packet, 'h->ts' is the timestamp,
@@ -112,12 +119,28 @@ atm_if_print(u_char *user _U_, const struct pcap_pkthdr *h, const u_char *p)
         * Extract the presumed LLC header into a variable, for quick
         * testing.
         * Then check for a header that's neither a header for a SNAP
-        * packet nor an RFC 2684 routed NLPID-formatted PDU.
+        * packet nor an RFC 2684 routed NLPID-formatted PDU nor
+        * an 802.2-but-no-SNAP IP packet.
         */
        llchdr = EXTRACT_24BITS(p);
-       if (llchdr != 0xaaaa03 && llchdr != 0xfefe03) {
+       if (llchdr != LLC_UI_HDR(LLCSAP_SNAP) &&
+           llchdr != LLC_UI_HDR(LLCSAP_ISONS) &&
+           llchdr != LLC_UI_HDR(LLCSAP_IP)) {
                /*
                 * XXX - assume 802.6 MAC header from Fore driver.
+                *
+                * Unfortunately, the above list doesn't check for
+                * all known SAPs, doesn't check for headers where
+                * the source and destination SAP aren't the same,
+                * and doesn't check for non-UI frames.  It also
+                * runs the risk of an 802.6 MAC header that happens
+                * to begin with one of those values being
+                * incorrectly treated as an 802.2 header.
+                *
+                * So is that Fore driver still around?  And, if so,
+                * is it still putting 802.6 MAC headers on ATM
+                * packets?  If so, could it be changed to use a
+                * new DLT_IEEE802_6 value if we added it?
                 */
                if (eflag)
                        printf("%08x%08x %08x%08x ",