Technical basics
ELSA MicroLink Cable
60
not find an entry in the table for a particular IP address (in our example '137.226.4.20'), it
sends an ARP request packet to all hosts in the LAN (with the LAN broadcast address as
a target address).
This ARP request packet is simply a question to all hosts listening to the IP address
'137.226.4.20'. Host 'Miller' receives the packet, feels addressed and answers with an
ARP response packet that it sends directly to host 'Smith' (the MAC address '00-10-5A-
31-20-DF' of host 'Smith' is extracted from the sender field in the ARP request packet).
Host 'Smith' recognizes this as an answer to its request, extracts the MAC address '00-
10-5A-31-20-EB' from the ARP response packet and enters it into its ARP table.
Then it can finally turn to its original task: sending the IP packet to host 'Miller'. It now
finds the entry “IP address 137.226.4.20 corresponding to MAC address '00-10-5A-31-20-
Host 'Smith'
ARP request to
'137.226.4.20'
Host 'Miller'
Host 'Smith'
ARP response
'137.226.4.20' =
'00-10-5A-31-20-EB'
Host 'Miller'