[Click] specify DLT in FromDevice?

[Eddie Kohler]

Excellent, excellent, excellent.  The patch is applied.  I added to it 
documentation for the header file; in general any patch should include the 
appropriate documentation.  Thanks!

E


Ian Rose wrote:
> If you are interested, I have attached a candidate patch to add an ENCAP 
> configuration parameter to the userlevel FromDevice element.
> 
> - Ian
> 
> 
> Ian Rose wrote:
>> When using libpcap, some drivers support multiple datalink-types.  I 
>> believe this is why tcpdump exposes a -y flag (to set the datalink 
>> type) and a -L flag (to list the available datalink types for a 
>> device).  I think perhaps if you do not specify one (via 
>> pcap_set_datalink) then it will default to the first that appears in 
>> the -L list.
>>
>> For example, we are using the 'ath' FreeBSD 802.11 driver:
>>
>>> ianrose at somehost 9$ sudo tcpdump -L -i ath1
>>> Data link types (use option -y to set):
>>>   EN10MB (Ethernet)
>>>   IEEE802_11 (802.11)
>>>   IEEE802_11_RADIO (802.11 plus BSD radio information header)
>>
>> If I run tcpdump without -y, or if I use an unmodified FromDevice 
>> element, I receive ethernet packets from the device which is not what 
>> I want.  I just add a '-y IEEE802_11_RADIO' to make tcpdump work, but 
>> FromDevice cannot be made to do this with hacking it.
>>
>> - Ian
>>
>>
>> Eddie Kohler wrote:
>>> Hi Ian --
>>>
>>> I believe that user-level FromDevice detects the datalink type from 
>>> pcap, so there wouldn't be a point to the argument.  Did you find 
>>> this did not work?
>>>
>>> Eddie
>>>
>>>
>>> Ian Rose wrote:
>>>> I perhaps should also clarify that I am talking specifically about 
>>>> the userlevel FromDevice element ("FromDevice.u" on the wiki).
>>>>
>>>>
>>>> Ian Rose wrote:
>>>>> Hello all -
>>>>>
>>>>> I am new to this list - apologies if this question has previously 
>>>>> be answered.  I am looking at the FromDevice element, but I see no 
>>>>> way to specify a datalinktype (i.e. the equivalent of the '-y' flag 
>>>>> in tcpdump).  Is there any reason that an argument for this was 
>>>>> left out?  It seems pretty easy for me to add, but I wanted to 
>>>>> check first to make sure I wasn't overlooking or misunderstanding 
>>>>> something.
>>>>>
>>>>> thanks,
>>>>> Ian
>>>>>
>>>>> p.s. I am running on FreeBSD, so I am using the libpcap-based code 
>>>>> in FromDevice, as opposed to the Linux-based code.
>>>>>
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