This is shown in Figure 2-6.
Figure 2-6 Checking the ARP Table
Host 192.168.3.1 sends out the ARP (broadcast) request to learn the MAC address of the
device using the IP address 192.168.3.2. However, in this example, the ARP broadcast
frame is received by the switch before it reaches the remote host, as illustrated in Figure 2-7.
UDP: I??™ll put in a UDP header.
APP
DATA
SRC IP
192.168.3.1
DST IP
192.168.3.2
APP
DATA
UDP
HR
APP
DATA
UDP
HDR
IP: I??™ll put in a IP header.
IP: Layer 2 send this to 192.168.3.2.
Layer 3 = 192.168.3.2
Layer 2 = 0800:0222:1111
Layer 3 = 192.168.3.1
Layer 2 = 0800:0222:2222
UDP: IP send this to 192.168.3.2.
Layer 2: ARP, do you have a mapping for 192.168.3.2?
ARP: Is 192.168.3.2 in my ARP table?
No, Layer 2 will have to put the packet in
the parking lot until I do an ARP.
SRC IP
192.168.3.1
DST IP
192.168.3.2
APP
DATA
UDP
HDR
Layer 3 = 192.168.3.2
Layer 2 = 0800:0222:1111
Layer 3 = 192.168.3.1
Layer 2 = 0800:0222:2222
Exploring the Packet Delivery Process 147
Figure 2-7 Sending the ARP Request
When the switch receives the frame, it needs to forward it out the proper port. However, in
this example, neither the source nor the destination MAC address is in the switch??™s MAC
address table.
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