Re: Hardware timestamp ?

[Guy Harris <guy () alum mit edu>]

On Feb 27, 2009, at 9:03 AM, Pierre KARAMPOURNIS wrote:

> I worked on old Linux Kernel versions so I will try the latest ones  
> to see
> hardware timestamping. So now I have to search for Network cards  
> which can
> timestamp the packets with nanosecond resolution (Endace DAG cards can
> apparently do that)

Yes, but they're not regular networking cards, so they won't use that  
kernel code path on Linux; they supply packets through their own API,  
and that API does provide nanosecond timestamps, which libpcap turns  
into microsecond timestamps.

If you want a network card that supplies its own timestamps *and*  
functions as a regular network adapter rather than a capture-only  
adapter, it would need to have a Linux driver that time-stamped the  
skbuff containing the packet.  I don't know whether any cards of that  
sort exist, or whether they have Linux drivers that do that (if they  
have open-source Linux drivers that don't, you could perhaps modify  
them to do so).

If, as you said, you're planning to capture traffic on a gigabit-or- 
faster network, you might *want* a capture-only NIC for that purpose,  
in which case the Endace cards would be sufficient.
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