Re: TCP timestamp option

Andi Kleen (
22 May 1998 04:28:06 +0200

Meelis Roos <> writes:

> AK> To align the timestamp option to a 32bit boundary. Many CPUs get
> AK> a significant slowdown while accessing non aligned data.
> OK, but now there are nop,nop,timestamp or even
> nop,nop.timestamp,nop,nop,[|tcp] options by default.
> (BTW, what's [|tcp] ?)
> This seems to forbid sacks from being used. SackOK is used in SYN packets,
> this is not a problem. But I can see sack options only when timestamps
> are off. Do they take too much room or is there another reason?

[|tcp] means that tcpdump did not get all tcp options. Increase the
snaplen with -s and you'll see them all, including the SACKs.


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