address as the source MAC address and Blue’s IP address as the source IP address. Green
receives the ping reply and determines that the frame is meant for Red because of the Layer
3 address (IP).
10. Green transmits a broadcast ARP request on Network 1.0.0.0 asking for Red’s MAC
address.
NOTE: This step will not occur if Green’s ARP table still contains an entry for Red resulting
from Steps 1 and 2.
Green looks in its ARP cache for a MAC address for Red. If one is not found, Green broadcasts
an ARP request frame on network 1.0.0.0 asking for Red’s MAC address.
11. Red transmits a unicast ARP reply to Green providing its MAC address (A).
NOTE: This step will not occur if Step 10 does not take place.
Red sees the ARP request frame and responds with a unicast ARP reply frame to Green.
Also, Red enters Green’s MAC address and IP address into its ARP cache. Green receives
the ARP reply from Red and enters Red’s MAC address (A) and IP address (1.1.1.1) into its
ARP cache.
12. Green forwards Blue’s ping reply to Red using the destination MAC address of Red (A).
Green transmits Blue’s ping reply frame onto Red’s network using Red’s MAC address (A)
and Red’s IP address (1.1.1.1) as the destination MAC and destination IP address. The source
MAC address is Green’s MAC address (C) and the source IP address is Blue’s IP address
(2.2.2.1). The user sees the ping REPLY message printed on the screen. This completes the
entire conversation.
Example Scenarios of Network Addressing and Communication 93
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