# Packet acknowledgement question - TCP-IP

This is a discussion on Packet acknowledgement question - TCP-IP ; Hi, I am doing some tcpdump-ing and have one question: Host A sends Packet 1 to Host B with 1448 Bytes Data: SeqNr = a677 1af7 Host A sends Packet 2 to Host B with 1448 Bytes Data. SeqNr = ...

1. ## Packet acknowledgement question

Hi,
I am doing some tcpdump-ing and have one question:

Host A sends Packet 1 to Host B with 1448 Bytes Data: SeqNr = a677 1af7

Host A sends Packet 2 to Host B with 1448 Bytes Data. SeqNr = a677 209f
Host B sends ACK to Host A with ACKNr: a677 2647.

I suppose that the ACK Paket is for Paket 2 because a677 209f + 5a8
(Data) = a677 2647, am I right? And since I am not getting an ACK for
Paket 2 my question is: Does the ACK Paket acknowledge both Pakets, 1
and 2, or just the second one??

Thank you.

2. ## Re: Packet acknowledgement question

"inf009" wrote:

> Hi,
> I am doing some tcpdump-ing and have one question:
>
> Host A sends Packet 1 to Host B with 1448 Bytes Data: SeqNr = a677 1af7
>
> Host A sends Packet 2 to Host B with 1448 Bytes Data. SeqNr = a677 209f
> Host B sends ACK to Host A with ACKNr: a677 2647.
>
> I suppose that the ACK Paket is for Paket 2 because a677 209f + 5a8
> (Data) = a677 2647, am I right? And since I am not getting an ACK for
> Paket 2 my question is: Does the ACK Paket acknowledge both Pakets, 1

I assume you mean "not getting an ACK for Packet 1"

> and 2, or just the second one??

You don't acknowledge packets, you acknowledge sequences. ACK = X means
"I have received everything up to X-1, and expect X next." So it
acknowledges both segments. It's normal to send an ACK for every other