On May 7, 2009, at 1:10 AM, 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:
>>
>>> Personally I think different filters for different interfaces  
>>> doesn't
>>> make a lot of sense.  I really can't imagine a situation when you'd
>>> need to capture different kinds of packets on different interfaces  
>>> but
>>> write to a single file.
>> For SCTP I might want to capture on two different interfaces
>> traffic belonging to the same transport connection. I might want
>> to filter on different destination addresses:
>> dumpcap -n -i en0 -f sctp && host a.b.c.d -i en1 -f sctp && host  
>> e.f.g.h
>
> I'm not sctp knowledgeable, but is there a reason you couldn't just
> write a single filter for both interfaces as:
>
> sctp && (host a.b.c.d || host e.f.g.h)
You could do that... But this does not work for the -y option
when capturing on different physical interfaces...
>
>
>>> At least, I think it's fair to say that single filter w/ multiple
>>> interfaces is a more common case then multiple filters & multiple
>>> interfaces.  Ideally the more common case shouldn't require you to
>>> specify the same filter twice.
>> But I need a way to distinguish whether this filter applies for
>> all interfaces or only for one...
>
> Fair enough, but it is my opinion that the vast majority of users
> don't need this functionality.
>
>> So we could do
>> dumpcap -f sctp -n -i en0 -i en1
>> (filter before interface) to mean setting for all interfaces
>> and
>> dumpcap -n -i en0 -f sctp -i en1
>> (filter after interface) that sctp is used only for en0 and en1
>> has no capture filter.
>>
>> What do you think about this?
>
> 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).
>
> -- 
> 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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