The switch also refreshes the timer in
its port-mapping table for the sender. Figure 2-13 shows the frame being sent out the port
to the receiver.
I just received a frame for a host that
is not in my MAC table. Let me add
it to the table (0800:0222:1111 = port2).
DST MAC
0800:0222:2222
SRC MAC
0800:0222:1111
ARP
Reply
Layer 3 = 192.168.3.2
Layer 2 = 0800:0222:1111
Layer 3 = 192.168.3.1
Layer 2 = 0800:0222:2222
The destination MAC is in my MAC
table, so I??™ll send the frame out Port1.
Packet
Parking Lot
150 Chapter 2: Ethernet LANs
Figure 2-12 Sender Builds Frame
Figure 2-13 Switch Forwards Frame
Summary of Exploring the Packet Delivery Process
The key points that were discussed in the previous sections are as follows:
?– Operating systems use Layer 3 (IP) and Layer 2 (MAC) addresses to provide host-tohost
communications.
?– Layer 2 switches forward frames based on entries in the port-mapping MAC address
table.
DST MAC
0800:0222:2222
SRC MAC
0800:0222:1111
ARP
Reply
ARP
Reply
Layer 3 = 192.168.3.2
Layer 2 = 0800:0222:1111
Layer 3 = 192.168.3.1
Layer 2 = 0800:0222:2222
Packet
Parking Lot
ARP: I just got an ARP reply from 192.168.3.2.
Let me add its IP and MAC to my ARP table.
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