On Tue, Jul 23, 2002 at 03:19:54PM -0600, Gabe Anderson wrote:
> I have some questions regarding tcpdump timestamps.  When exactly does
> tcpdump stamp the arriving and leaving packets?

Tcpdump doesn't timestamp packets, it just gets a timestamp from
libpcap, and libpcap, in turn, just gets it from the OS.

The answer to the question would depend on the OS...

> Given a scenario, where I was 
> sending data out over an encrypted channel (say, ipsec), would timestamps 
> detected over device ipsec0 correspond to the packets arrival after being 
> decrypted, or do the stamps correlate to the eth0 timestamps.

...and, as you said "eth0", the OS is probably Linux.

If you sniff on "eth0", the time stamps on incoming packets come, I
think, from either the driver or low-level code in the Linux networking
stack; I don't remember where outgoing packets are time stamped.

I don't know when it'd happen on "ipsec0"; you might want to ask the
linux-net mailing list about that.
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