https://bugs.wireshark.org/bugzilla/show_bug.cgi?id=6188
Summary: Enhancement in bgp dissector
Product: Wireshark
Version: 1.6.1
Platform: x86-64
OS/Version: Windows 7
Status: NEW
Severity: Enhancement
Priority: Low
Component: Wireshark
AssignedTo: bugzilla-admin@xxxxxxxxxxxxx
ReportedBy: maximivanov@xxxxxxx
Build Information:
Version 1.6.1 (SVN Rev 38096 from /trunk-1.6)
Copyright 1998-2011 Gerald Combs <gerald@xxxxxxxxxxxxx> and contributors.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
Compiled (64-bit) with GTK+ 2.22.1, with GLib 2.26.1, with WinPcap (version
unknown), with libz 1.2.5, without POSIX capabilities, without libpcre, without
SMI, with c-ares 1.7.1, with Lua 5.1, without Python, with GnuTLS 2.10.3, with
Gcrypt 1.4.6, without Kerberos, with GeoIP, with PortAudio V19-devel (built Jul
18 2011), with AirPcap.
Running on 64-bit Windows 7, build 7600, with WinPcap version 4.1.2 (packet.dll
version 4.1.0.2001), based on libpcap version 1.0 branch 1_0_rel0b (20091008),
GnuTLS 2.10.3, Gcrypt 1.4.6, without AirPcap.
Built using Microsoft Visual C++ 9.0 build 21022
--
Good day.
In some BGP captures the AS_PATH attribute was decode wrong, if the asn length
determines automatically (for example see
http://packetlife.net/captures/4-byte_AS_numbers_Full_Support.cap, packets #6).
Here is code for determine the asn length:
/* estimate the length of the AS number */
if (bgpa.bgpa_type == BGPTYPE_NEW_AS_PATH)
asn_len = 4;
else {
if (bgp_asn_len == 0) {
k = q;
while (k < end) {
k++;
length = tvb_get_guint8(tvb, k++);
k += length * 2;
}
asn_len = (k == end) ? 2 : 4;
}
else {
asn_len = bgp_asn_len;
}
}
This algorythm is based on one check - is the tail of the attribute is equal to
the tail of the last asn in the last segment.
I suggest to add 2 parameters: presence of asn==0 and presence of unknown
segment type. if at least one of parameters is "active", the length of asn is
4.
Here is codes example
/* estimate the length of the AS number */
if (bgpa.bgpa_type == BGPTYPE_NEW_AS_PATH)
asn_len = 4;
else
{
if (bgp_asn_len == 0)
{
unsigned unknown_segment_type = 0;
unsigned asn_is_null = 0;
asn_len = 2;
k = q;
while (k < end)
{
type = tvb_get_guint8(tvb, k++);
if (type != AS_SET &&
type != AS_SEQUENCE &&
type != AS_CONFED_SEQUENCE &&
type != AS_CONFED_SEQUENCE)
unknown_segment_type = 1;
length = tvb_get_guint8(tvb, k++);
for (unsigned d = 0; d < length; d++)
{
if(tvb_get_ntohs(tvb, k) == 0)
asn_is_null = 1;
k += 2;
}
}
if(k != end ||
unknown_segment_type ||
asn_is_null)
asn_len = 4;
}
else
asn_len = bgp_asn_len;
}
I hope my suggestion will be helpful.
P.S. Sorry for my english )
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