Normal ARP Behavior
Figure 6-1 ARP Request in a Broadcast Frame a
0000.C5C0.0000
0000.C5C0.0000
0000.CAFE.0000
Host C IP: 10.0.0.3 MAC 0000.0666.0000
Host C IP: 10.0.0.3 MAC 0000.0666.0000
All hosts on the same Ethernet LAN or VLAN receive the ARP request and process it. Only host B reacts on the ARP request because its IP address, 10.0.0.2, matches the IP address inside the ARP request.
As Figure 6-2 shows, host B sends a solicited ARP reply to host A. This frame contains the binding between host B's MAC address and its IP address.
Figure 6-2 ARP Reply
0000.CAFE.0000
0000.CAFE.0000
Host C IP: 10.0.0.3 MAC 0000.0666.0000
Upon receipt of the ARP reply addressed to it, host A updates its ARP table, as shown in Table 6-1, with the <IP, MAC> address mapping for host B.
Back to ARP Basics 107
The <IP, MAC> Notation
In mathematics, it is common to write a pair of items, say FOO and BAR, between angle brackets like <FOO, BAR>. Therefore and for sake of clarity, the compact notation <IP, MAC> is used in this book to denote the pair of one IP address and one MAC address.
|
IP Address |
MAC Address |
|
10.0.0.1 |
0000.CAFE.0000 |
|
10.0.0.2 |
0000.C5C0.0000 |
As soon as an entry exists in the ARP table, host A can send IP packets to host B.
Continue reading here: Gratuitous ARP
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