[Winpcap-users] Pcap_list_datalinks return bad number of links.

[Steve Beaudoin]

Thank you for the precisions.

-----Original Message-----
From: winpcap-users-bounces at winpcap.org
[mailto:winpcap-users-bounces at winpcap.org] On Behalf Of Guy Harris
Sent: August 24, 2006 21:29
To: winpcap-users at winpcap.org
Subject: Re: [Winpcap-users] Pcap_list_datalinks return bad number of links.


On Aug 24, 2006, at 3:11 PM, Steve Beaudoin wrote:

> You are absolutely right.  The received array was the wrong item of  
> the two.  Following your suggestion, I changed my ref int[] for a  
> ref IntPtr and I now receive two items, the other one is DOCSIS  
> (Data Over Cable Service Interface Specifications,
http://en.wikipedia.org/wiki/DOCSIS 
>  for those interested) as I have a cable modem.
No, the other one is DOCSIS because

	1) you have an Ethernet (or something that claims to be an Ethernet)

and

	2) Cisco has a device, the Cisco Cable Modem Termination System:

	
http://www.cisco.com/en/US/tech/tk86/tk804/tsd_technology_support_protocol_h
ome.html

	   that can be configured to take raw DOCSIS frames and transmit
them  
on an Ethernet (using only the low-level Ethernet framing and *no*  
encapsulation, so the first byte of the Ethernet frame is the first  
byte of the DOCSIS frame, *NOT* the first byte of an Ethernet  
destination MAC address):

	
http://www.cisco.com/univercd/cc/td/doc/product/cable/cab_rout/cmtsfg/ufg_cm
on.htm#wp1031861

	   so that a network analyzer can capture and process them.

Wireshark is one analyzer that can process DOCSIS frames; if you're  
plugged into an "Ethernet" that's connected to a Cisco CMTS, and the  
CMTS is putting DOCSIS frames on the Ethernet, you'd capture with the  
link-layer type set to DOCSIS, which would cause the device to appear  
to have a link-layer type of DOCSIS and thus cause Wireshark to  
analyzer the frames as DOCSIS frames.

Unless your cable modem has a similar capability, or you have some  
device that can capture on the cable side of the cable modem, you  
won't be able to see DOCSIS frames.
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