2
TCP
SYN
Exploring the Packet Delivery Process 95
Figure 1-77 IP Packet Is Received
In response to the SYN, TCP passes a SYN ACK down the stack to be encapsulated.
Figure 1-78 shows this operation.
Figure 1-78 Receiver Acknowledges Frame
The sender receives the ACK along with a SYN from the receiver that it must respond to.
This is shown in Figure 1-79.
TCP: I need to send a SYN ACK
to the TCP SYN that I received.
SRC IP
192.168.3.1
SRC MAC
0800:0222:2222
DST MAC
0800:0222:1111
DST IP
192.168.3.2
TCP
SYN
SRC IP
192.168.3.1
DST IP
192.168.3.2
TCP
SYN
TCP
SYN
Layer 3 = 192.168.3.1
Layer 2 = 0800:0222:2222
Layer 3 = 192.168.3.2
Layer 2 = 0800:0222:1111
SRC IP
192.168.3.2
SRC MAC
0800:0222:1111
DST MAC
0800:0222:2222
DST IP
192.168.3.1
SYN
ACK
TCP: Send this.
SRC IP
192.168.3.2
SRC MAC
0800:0222:1111
DST MAC
0800:0222:2222
DST IP
192.168.3.1
SYN
ACK
SRC IP
192.168.3.2
DST IP
192.168.3.1
SYN
ACK
SYN
ACK
Layer 3 = 192.168.3.1
Layer 2 = 0800:0222:2222
Layer 3 = 192.168.3.2
Layer 2 = 0800:0222:1111
96 Chapter 1: Building a Simple Network
Figure 1-79 Sender Receives ACK
The sender sends the ACK to the receiver that it must respond to. This is shown in
Figure 1-80.
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