Hi Aaron,

being able to capture from multiple packets is a feature
requested by multiple people. Therefore, and because
I also need it, I'm (trying to) implement it.

Generating different .pcap files and combing them
with mergecap during postprocessing is how I do this
currently , but I would like to improve this.

Please note that when using Wireshark you use a GUI
which generate the command line to invoke dumpcap.

But tshark, wireshark and dumpcap share a lot of
the code processing the command line arguments,
so the possibilities might eventually also
show up in tshark and wireshark...

Best regards
Michael

On May 7, 2009, at 3:47 PM, Aaron Turner wrote:

> On Thu, May 7, 2009 at 12:26 PM, Michael Tüxen
> <[email protected]> wrote:
>> On May 7, 2009, at 2:34 PM, Nathan Jennings wrote:
>>
>>> On 5/7/2009 9:10 AM, Sébastien Tandel wrote:
>>>> On Thu, May 7, 2009 at 03:05, Stephen Donnelly <[email protected]>
>>>> wrote:
>>>>
>>>>> Aaron Turner wrote:
>>>>>> On Wed, May 6, 2009 at 8:59 PM, Michael Tüxen
>>>>>> <[email protected]> wrote:
>>>>>>> On May 6, 2009, at 3:40 PM, Aaron Turner wrote:
>>>>>> I think this is confusing to many people and is more likely to  
>>>>>> have
>>>>>> unintended consequences.   Most users don't consider CLI option
>>>>>> ordering to have special meaning.  Personally, I prefer Stephen's
>>>>>> suggestion of directly linking the filter to the interface ala -i
>>>>>> en0:"sctp && host a.b.c.d" if you want to get fancy.
>>>>>>
>>>>>> It also means the old style cli args could easliy be grand-
>>>>>> fathered in
>>>>>> (any interface without a specific filter uses the global filter).
>>>>
>>>> Completely agree to define something which is explicitly linked to
>>>> which
>>>> interface the filter belongs. Ordering parameters is not intuitive.
>>>>
>>>>
>>>> I you do decide to go this way, ':' might not be the best delimiter
>>>>> character to use. It is already used in libpcap interface names  
>>>>> and
>>>>> could cause parsing headaches.
>>>>>
>>>>> I think some OSes use ':' in vlan interface names? Also ':' is
>>>>> used in
>>>>> dag interface names to indicate sub streams, e.g. "dag0:2".
>>>>>
>>>>
>>>> ':' is indeed confusing. It is used by Linux to define virtual
>>>> interfaces
>>>> like eth0:1
>>>>
>>>
>>> I had also thought of suggesting ":", but see the overloading  
>>> problem
>>> now as Stephen D. pointed out... which reminded me of maybe another
>>> potential clash:
>>>
>>> From a "preferences" file:
>>>
>>> <... snip ...>
>>> # Interface descriptions.
>>> # Ex: eth0(eth0 descr),eth1(eth1 descr),...
>>> capture.devices_descr: \Device\NPF_{"Windows-string"}(Intel NIC)
>>> </snip>
>>>
>>> ... although I can't think of a clash with this off-hand right now.
>>>
>>> Maybe this is better?:
>>>
>>> dumpcap -n -i dag0:2,"sctp && host 1.2.3.4" -i en0
>>>
>>> In the parser, you should probably check for and allow use of single
>>> quotes too (e.g. shell scripts), like:
>>>
>>> dumpcap -n -i dag0:2,'sctp && host 1.2.3.4' -i en0
>> But we also have -y and -s... So taking this path requires something
>> like
>> -i interface_name,capture_filer,link_type,snap_length
>> How does this look like?
>
> ugh.  I think you've reached the point IMHO where you should just use
> two different instances of tcpdump to capture the packets.  It
> wouldn't be difficult to write a tool which would interleave the
> packets from multiple pcap files into a single using the timestamp for
> ordering... that way you can capture on as many interfaces with
> different options, even from different systems as you want without
> resorting to CSV hell.
>
> My .02.
>
> -- 
> Aaron Turner
> http://synfin.net/
> http://tcpreplay.synfin.net/ - Pcap editing and replay tools for  
> Unix & Windows
> Those who would give up essential Liberty, to purchase a little  
> temporary
> Safety, deserve neither Liberty nor Safety.
>    -- Benjamin Franklin
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