Wireshark-users: Re: [Wireshark-users] subprotocols
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From: Pascal Quantin <pascal.quantin@xxxxxxxxx>
Date: Tue, 11 Nov 2014 20:19:01 +0100
2014-11-11 20:13 GMT+01:00 Charles Smith <cts.private.yahoo@xxxxxxxxx>:
That did the job!  Thank you

  5052    2.651163    127.0.0.1    127.0.0.1    LTE RRC UL_DCCH/NAS-EPS    245    RRCConnectionSetupComplete  Attach request  PDN connectivity request  MAC=0x00000000 (19 bytes data)  [24-bytes]


(note that the first time I did it, I got this:

   Unhandled exception ("tvbuff.c:634: failed assertion "tvb && tvb->initialized"", group=1, code=4)
   Aborted (core dumped)

but it worked on restart

I'm curious - the RLC configuration also has a line like;

  Call RRC dissector for CCCH pdus

That's not checked, but it's doing it anyway.  Do I not understand that right, or is just an old check box?

It's supposed to be checked by default and is useful for CCCH based PDUs like RRC UL CCCH (RRC Connection/Reestablishment Request) DL CCCH (RRC Connection / Reestablishment Setup / Reject), PCH (Paging), BCCH BCH (MIB) and BCCH DL SCH (SIBs).


On Tue, Nov 11, 2014 at 7:01 PM, Pascal Quantin <pascal.quantin@xxxxxxxxx> wrote:
Hi Charles,

2014-11-11 14:53 GMT+01:00 Charles Smith <cts.private.yahoo@xxxxxxxxx>:
Hi Pascal,

You helped me a lot, thank you.  My dissector does almost everything I want.

Of course, there's just more thing ...  :)

I get RRC decoded magically on CCCH, but as soon as it switches to SRB1, it recognizes the AM mode but not the contents, e.g. the following is an RRCConnectionSetupComplete:

5052    2.651163    127.0.0.1    127.0.0.1    RLC-LTE    245    [UL] [AM] UEId=1 SRB:1  [DATA] (P) sn=0     [24-bytes]

and there's just raw contents.

Everything else has been done so wonderfully, I suspect that I'm just not doing something right here.

Any help is appreciated...

You want to go to Edit -> Preferences -> Protocols -> RLC-LTE and check the box "Call PDCP dissector for SRB PDUs"
Then go to Edit -> Preferences -> Protocols -> PDCP-LTE and check the box "Show unciphered Signalling-Plane data as RRC"

Note that ciphered PDCP PDUs can also be deciphered if you know in ciphering key, if no handover / reestablishment happens (no key derivation is supported) and if you use AES (SNOW3G and ZUC are not supported dur to patents issues).

Pascal.

 


On Wed, Oct 15, 2014 at 1:48 PM, Charles Smith <cts.private.yahoo@xxxxxxxxx> wrote:
Great, thanks alot!

On Wed, Oct 15, 2014 at 11:07 AM, Pascal Quantin <pascal.quantin@xxxxxxxxx> wrote:


2014-10-15 10:41 GMT+02:00 Charles Smith <cts.private.yahoo@xxxxxxxxx>:
Hello Pascal,

I don't find any .c files under (ubuntu) /usr/share/wireshark - is this only available to a dissector that's linked-in to the executable?  Or can I access it via lua, as well?  Or, do I only need to get the source tarball in order to study the example?  Would it be wiser to ditch my lua code and do it in c?

TIA
cts

Hi,

this is the first time you mention that you are doing a Lua plugin. But I guess internal dissectors can be called from Lua also (note: I have never written any Lua plugin myself but I know there is quite a lot of documentation on http://wiki.wireshark.org/Lua and it seems you can retrieve the MAC LTE dissector by using Dissector.name("mac-lte") and call it with dissector::call()).
Depending on the Wireshark version you are using, you might consider browsing to the right version by clicking on the summary link and selecting the right tag or head.

Pascal.


On Wed, Oct 15, 2014 at 9:13 AM, Charles Smith <cts.private.yahoo@xxxxxxxxx> wrote:
Thank you.

On Tue, Oct 14, 2014 at 10:34 PM, Pascal Quantin <pascal.quantin@xxxxxxxxx> wrote:
2014-10-14 22:15 GMT+02:00 Charles Smith <cts.private.yahoo@xxxxxxxxx>:
Is it built in, I just have to get the linkage right?  Or do I have to fetch it from somewhere?

Yes it's a built-in dissector. Please have a look at packet-catapult-dct2000.c for an example on how to call a sub dissector via call_dissector_only() function (it is easier than using the UDP framing protocol which is more suitable when calling Wireshark from an external program).


On Tue, Oct 14, 2014 at 7:22 PM, Pascal Quantin <pascal.quantin@xxxxxxxxx> wrote:


2014-10-14 17:33 GMT+02:00 Charles Smith <cts.private.yahoo@xxxxxxxxx>:
Hi.

I have created a dissector for our tunnel protocol.  I have the feeling that if I want to decode a payload protocol, say LTE MAC protocol, I'd use the proto() statement to hang that into my tree and some library code somewhere would do the rest of the decoding ... but I can't find these libraries (e.g. http://wiki.wireshark.org/MAC-LTE).  Can someone set me straight?

cts

Hi Charles,

LTE MAC dissector is a bit specific as it requires some meta data allowing it to know how to decaode the payload. You have 2 ways to configure it:
- either look at epan/dissectors/packet-catapult-dct2000.c and check how it is configuring those meta data (mac_lte_info structure attached to each frame)
- or use the UDP framing format as described in epan/dissectors/packet-mac-lte.h file. Some sample code demonstrating how to use it can be found here: http://wiki.wireshark.org/MAC-LTE

Regards,
Pascal.

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