Hello,
When I realized that my name (and my colleague's, Maria-Luiza) had
been removed from the AUTHORS file, I was so scared that I found some
motivation, courage and time to code the little patch I promised :)
As outlined earlier, our previous patch to decode the ICMP extensions
for MPLS couldn't handle the collisions between the IETF draft and RFC
1812.
This new patch allows the user to indicate how to decode ICMP payloads
that contain an original packet with more than 128 bytes.
It adds an "ICMP" panel in the "Edit > Preferences > Protocols" panel,
and a checkbox labelled "Favor ICMP extensions for MPLS", not checked
by default.
If the option is checked, only the first 128 bytes of the original
packet are decoded as an IP packet. The end of the payload is decoded
as MPLS extensions.
Note that, in the case when the original packet has less than 128
bytes, the dissector's behavior is not changed : MPLS extensions are
decoded as before.
Best regards,
Brice Augustin
Maria-Luiza Crivat
--- packet-ip.c.ORIGINAL 2005-07-23 01:19:17.000000000 +0200
+++ packet-ip.c 2005-07-23 01:19:17.000000000 +0200
@@ -71,6 +71,10 @@
/* Place IP summary in proto tree */
static gboolean ip_summary_in_tree = TRUE;
+/* Decode the end of the ICMP payload as ICMP MPLS extensions
+if the packet in the payload has more than 128 bytes */
+static gboolean favor_icmp_mpls_ext = FALSE;
+
static int proto_ip = -1;
static int hf_ip_version = -1;
static int hf_ip_hdr_len = -1;
@@ -1844,17 +1848,29 @@
/* Decode the IP header and first 64 bits of data from the
original datagram. */
next_tvb = tvb_new_subset(tvb, 8, -1, -1);
+
+ /* There is a collision between RFC 1812 and draft-ietf-mpls-icmp-02.
+ We don't know how to decode the 128th and following bytes of the ICMP payload.
+ According to draft-ietf-mpls-icmp-02, these bytes should be decoded as MPLS extensions
+ whereas RFC 1812 tells us to decode them as a portion of the original packet.
+ Let the user decide.
+
+ Here the user decided to favor MPLS extensions.
+ Force the IP dissector to decode only the first 128 bytes. */
+ if ((tvb_reported_length(tvb) > 8 + 128) &&
+ favor_icmp_mpls_ext && (tvb_get_ntohs(tvb, 8 + 2) > 128))
+ set_actual_length(next_tvb, 128);
+
call_dissector(ip_handle, next_tvb, pinfo, icmp_tree);
/* Restore the "we're inside an error packet" flag. */
pinfo->in_error_pkt = save_in_error_pkt;
- /* MPLS extensions */
- /* XXX - this doesn't handle ICMP packets with more than
- 128 bytes of the original datagram, which RFC 1812 doesn't
- disallow. Make whether to handle MPLS extensions a
- preference setting? */
- if (tvb_reported_length(tvb) > 8 + 128)
+ /* Decode MPLS extensions if the payload has at least 128 bytes, and
+ - the original packet in the ICMP payload has less than 128 bytes, or
+ - the user favors the MPLS extensions analysis */
+ if ((tvb_reported_length(tvb) > 8 + 128)
+ && (tvb_get_ntohs(tvb, 8 + 2) <= 128 || favor_icmp_mpls_ext))
dissect_mpls_extensions(tvb, 8 + 128, icmp_tree);
break;
@@ -2293,11 +2309,20 @@
&ett_icmp_mpls_object,
&ett_icmp_mpls_stack_object
};
-
+
+ module_t *icmp_module;
+
proto_icmp = proto_register_protocol("Internet Control Message Protocol",
"ICMP", "icmp");
proto_register_field_array(proto_icmp, hf, array_length(hf));
proto_register_subtree_array(ett, array_length(ett));
+
+ icmp_module = prefs_register_protocol(proto_icmp, NULL);
+
+ prefs_register_bool_preference(icmp_module, "favor_icmp_mpls",
+ "Favor ICMP extensions for MPLS",
+ "Whether the 128th and following bytes of the ICMP payload should be decoded as MPLS extensions or as a portion of the original packet",
+ &favor_icmp_mpls_ext);
}
void
