HP Rx2620-2 - Integrity - 0 MB RAM Manual page 94

is. First, Red checks its own ARP cache for an entry that matches 1.1.1.3. If Red does not
have an entry cached, then it must broadcast an ARP request frame on network 1.0.0.0 asking
Green to respond and provide its MAC address.
2. Green transmits a unicast ARP reply to Red providing its MAC address (C).
Green sees the ARP request and responds with a unicast ARP reply to Red. Also, Green
enters Red's MAC address and IP address into its ARP cache. Red receives Green's ARP
reply and enters Green's MAC address (C) and IP address (1.1.1.3) into its ARP cache.
3. Red transmits a ping request to Blue (2.2.2.1) using the destination MAC address (C) of
Green's 1.1.1.3 interface, because Green is Red's gateway to Blue.
Red can now create a ping request frame using Green's MAC address and Blue's IP address.
Red sends the ping request. Green receives the ping request and determines that the frame
is meant for Blue because of the Layer 3 address (IP).
4. Green transmits a broadcast ARP request on Network 2.0.0.0 asking for Blue's MAC
address.
Green looks in its ARP cache for a MAC address for Blue. If one is not found, Green
broadcasts an ARP request frame on Blue's Layer 2 network asking for Blue's MAC address.
5. Blue transmits a unicast ARP reply to Green providing its MAC address (B).
Blue sees the ARP request frame and responds with a unicast ARP reply frame to Green.
Also, Blue enters Green's MAC address and IP address into its ARP cache. Green receives
the ARP reply from Blue and enters Blue's MAC address (B) and IP address (2.2.2.1) into its
ARP cache.
6. Green forwards Red's ping request to Blue using Blue's destination MAC address (B).
Green now transmits Red's original ping request frame onto Blue's network using Blue's
MAC address and Blue's IP address as the destination MAC and destination IP address.
The source MAC address is Green's MAC address (D) and the source IP address is Red's IP
address (1.1.1.1). Blue receives the frame and notices that a station with an IP address of
1.1.1.1 is asking for it to respond to a ping. Before Blue can respond with a ping reply, it
must determine whether or not 1.1.1.1 is on the same layer 2 network. Blue runs an algorithm
(details of this algorithm are beyond the scope of this document) using its own IP address
(2.2.2.1), its own subnet mask (not shown) and the IP address of Red (1.1.1.1). Blue then
determines that Red is on a different network. Because of this, Blue must use its gateway
(Green) to get the ping reply back to Red.
7. Blue transmits a broadcast ARP request on Network 2.0.0.0 asking for Green's MAC
address.
NOTE:
from Steps 4 and 5.
Blue checks its ARP cache for the MAC address that corresponds to the IP address of 2.2.2.3
(Blue's gateway). If an entry is not found, Blue must broadcast an ARP request asking for
Green's MAC address.
8. Green transmits a broadcast ARP reply to Blue providing its MAC address (D).
NOTE:
Green sees the ARP request and responds with a unicast ARP reply directly to Blue. Also,
Green enters Blue's MAC address and IP address into its ARP cache. Blue receives the ARP
reply and puts Green's MAC address (D) and IP address (2.2.2.3) in its ARP cache. Blue now
has all the information it needs to send a ping reply to Red.
9. Blue transmits a unicast ping reply to Red (1.1.1.1) using the MAC address of Green's
2.2.2.3 interface (D).
Blue transmits a unicast ping reply to Red through Green by using Green's MAC address
as the destination MAC address, Red's IP address as the destination IP address, Blue's MAC
94 – Overview of Network Addressing and Communication
This step may not occur if Blue's ARP table still contains an entry for Green resulting
This step will not occur if Step 7 does not take place.