--- Begin Message ---
On 05/05/2020 21:44, Gert Doering wrote:
> Hi,
>
> On Tue, May 05, 2020 at 08:47:04PM +0200, Francois-Xavier Le Bail wrote:
>>> So, given that the first 16 bits are "4 bit always 0, and 12 bits
>>> reserved-must-be-set-to-0", using these as heuristics for "if two 0-bytes
>>> are following the MPLS headers, it's a control word, so we skip 4 bytes
>>> and the rest is a regular Ethernet packet" should work.
>>
>> We should print "PW Ethernet Control Word" and the "Sequence Number", 2 last
>> 2 octets of the 4.
>> Like:
>> PW Ethernet Control Word, Sequence Number xxx
>
> I think we should only print this if "-v" is given. Most of the time,
> both control word and sequence number are of little interest.
>
> I really like tcpdump's very compact "only the most relevant info" output
> format (by default).
Proposed patch attached.
With new '-T mplsethnocw' option to force 'Ethernet without Control Word'
decode.
(from Francesco Fondelli comment)
--
Francois-Xavier
diff --git a/netdissect.h b/netdissect.h
index 65a0d987..cd76d654 100644
--- a/netdissect.h
+++ b/netdissect.h
@@ -294,6 +294,7 @@ extern void nd_pop_all_packet_info(netdissect_options *);
#define PT_PTP 18 /* PTP */
#define PT_SOMEIP 19 /* Autosar SOME/IP Protocol */
#define PT_DOMAIN 20 /* Domain Name System (DNS) */
+#define PT_MPLSETHNOCW 21 /* MPLS PW Ethernet without Control Word */
#ifndef min
#define min(a,b) ((a)>(b)?(b):(a))
diff --git a/print-mpls.c b/print-mpls.c
index 62b79957..0c0ab974 100644
--- a/print-mpls.c
+++ b/print-mpls.c
@@ -50,7 +50,8 @@ enum mpls_packet_type {
PT_UNKNOWN,
PT_IPV4,
PT_IPV6,
- PT_OSI
+ PT_OSI,
+ PT_ETHER
};
/*
@@ -133,52 +134,68 @@ mpls_print(netdissect_options *ndo, const u_char *bp,
u_int length)
/* nothing to print */
return;
}
- switch(GET_U_1(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;
+ if (ndo->ndo_packettype == PT_MPLSETHNOCW)
+ pt = PT_ETHER;
+ else
+ switch(GET_U_1(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;
+
+ case 0x00: /* RFC 4448 PW Ethernet Control Word */
+ if (ndo->ndo_vflag) {
+ ND_PRINT("\n\tPW Ethernet Control
Word");
+ p += 2;
+ ND_PRINT(", Sequence Number %u",
GET_BE_U_2(p));
+ p += 2;
+ } else
+ ND_PRINT(" PWETHCW");
+ p += 4;
+ length -= 4;
+ pt = PT_ETHER;
+ break;
+
+ default:
+ /* ok bail out - we did not figure out what it
is*/
+ break;
+ }
}
- }
/*
* Print the payload.
@@ -203,6 +220,10 @@ mpls_print(netdissect_options *ndo, const u_char *bp,
u_int length)
isoclns_print(ndo, p, length);
break;
+ case PT_ETHER:
+ ether_print(ndo, p, length, ND_BYTES_AVAILABLE_AFTER(bp), NULL,
NULL);
+ break;
+
default:
break;
}
diff --git a/tcpdump.c b/tcpdump.c
index 376d9a20..abefb50c 100644
--- a/tcpdump.c
+++ b/tcpdump.c
@@ -1798,6 +1798,8 @@ main(int argc, char **argv)
ndo->ndo_packettype = PT_SOMEIP;
else if (ascii_strcasecmp(optarg, "domain") == 0)
ndo->ndo_packettype = PT_DOMAIN;
+ else if (ascii_strcasecmp(optarg, "mplsethnocw") == 0)
+ ndo->ndo_packettype = PT_MPLSETHNOCW;
else
error("unknown packet type `%s'", optarg);
break;
--- End Message ---
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