On Thu, Jul 26, 2001 at 01:19:51PM +0200, Rabeeh Khoury wrote:
> Hi All,
>
> I have noticed (using tcpdump and simple TCP client-server application)
> that TCP frame are always sent with ACK flag even if the sender doesn't
> receive new frames (i.e. it send the same Acknowledgment Number).
>
> RFC 2581 (section 4.1) states that:
> "A TCP receiver MUST NOT generate more than one ACK for every
> incoming
> segment, other than to update the offered window as the receiving
> application consumes new data"
>
> According to the above statement it seems that LINUX TCP / IP violates this
> rule.
ACK in this context means a new packet that only contains the ACK.
If there are packets send for other reason it is ok to contain an ACK,
in fact RFC793 (that's the real TCP standard) even states that every
packet in Established should carry an ACK flag.
-Andi
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