Jeff,
the easiest way is to use a compliant M2?A implementation. Isn't
this a possibility to change the code to provide the SCTP stack
with the correct PPI?
On the other hand it is not OK to register the m2pa dissector
under the M2UA port number. There is no reason to do it: The
number is not mentioned in the ID, nor at IANA.
So the registration should be removed. It only brings up
problems once IANA has assigned a number.
For the port based ULP selection the SCTP dissector uses the
provided infrastrukture: It calls:
gboolean
dissector_try_port(dissector_table_t sub_dissectors, guint32 port,
tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
from epan/packet.c
It simply uses a hash table. So this stuff would have to be modified
to support a list of dissectors and return the first one which is
not activated. That would be the way to provide the feature. Gerald
is the author of that file, so you may ask him if this could be changed.
But the problem is due to a bug in the M2PA dissector, because it
registers
for it port which is not assigned to that protocol. So I'm not sure
what Gerald thinks.
Best regards
Michael
On Thursday, June 20, 2002, at 09:20 PM, Jeff Morriss wrote:
Michael,
SCTP tries first to find the ULP by looking at the Payload
Protocol Identifier. Only if that does not work the port is
used.
M2UA uses PPI = 2 and M2PA uses PPI = 5.
This means if you use the correct PPI in your M2UA, M2PA
implementation ethereal will find always the correct ULP.
Yo do not need to disable a protocol. By using this you
can also transport M2UA and M2PA over the same assoc and
ethereal will dissect it correctly.
Oops, I forgot to mention that these captures are from an older M2PA
implementation which didn't set the PPI... (In fact I also have to use
version 1.1 of "packet-m2pa.c".) SCTP has code to look at the ports if
the PPI doesn't find a sub-dissector, but then we run into the problem
that M2UA and M2PA have the same port...
Regards,
-Jeff
-- Jeff Morriss
Senior Support Engineer
Ulticom, Inc.
Helpdesk: +1-856-787-2765
Fax: +1-856-222-9947
Michael.Tuexen@xxxxxxxxxxxxxxxxx
