TCP/IP and the DoD Model
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Ethernet Header
Destination: FF:FF:FF:FF:FF:FF Ethernet Broadcast
Source: 00:A0:24:48:60:A5
Protocol Type: 0x0806 IP ARP
ARP - Address Resolution Protocol
Hardware: 1 Ethernet (10Mb)
Protocol: 0x0800 IP
Hardware Address Length: 6
Protocol Address Length: 4
Operation: 1 ARP Request
Sender Hardware Address: 00:A0:24:48:60:A5
Sender Internet Address: 172.16.10.3
Target Hardware Address: 00:00:00:00:00:00 (ignored)
Target Internet Address: 172.16.10.10
Extra bytes (Padding):
................ 0A 0A 0A 0A 0A 0A 0A 0A 0A 0A 0A 0A 0A
0A 0A 0A 0A 0A
Frame Check Sequence: 0x00000000
Reverse Address Resolution Protocol (RARP)
When an IP machine happens to be a diskless machine, it has no way of ini-
tially knowing its IP address, but it does know its MAC address. Reverse
Address Resolution Protocol (RARP) discovers the identity of the IP address
for diskless machines by sending out a packet that includes its MAC address
and a request for the IP address assigned to that MAC address. A desig-
nated machine, called a RARP server, responds with the answer, and the
identity crisis is over. RARP uses the information it does know about the
machine's MAC address to learn its IP address and complete the machine's
ID portrait.
RARP resolves Ethernet addresses to IP addresses.
Figure 3.9 shows a diskless workstation asking for its IP address with a
RARP broadcast.
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