In trying to troubleshoot an L2TP tunnel I had to grab a packet trace.
In the initial packet from the LAC, I'm seeing the L2TP header 
(value CC 02) setting a bit (6th bit) that RFC2661 says MUST be 
zero.
Ethereal shows the reserved bit values as '.' (not the true value).
Although these bits should be ignored when received , I wondered if 
Ethereal should better show these reserved bit values and not mask 
them out? (is there an option to not mask them?).
A packet trace is attached.
If replying, please do so directly as I am not subscribed to the list.
thanks,	
Garry Peirce   peirce@xxxxxxxxx   1-207-581-3539
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==                   Network Analyst                            
==     UNET Technology Services, Network Operations         
==              University of Maine System                        
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