Specifications

Installation and startup procedure
52
3.4 Basic settings
RS2-4R
Release 1.0 03/04
Lorenzo receives the letter and removes the outer envelope. From the
inner envelope he recognizes that the letter is meant for Juliet. He places
the inner envelope in a new outer envelope and searches his address list
(the ARP table) for Juliet's MAC address. He writes her MAC address on
the outer envelope as the destination address and his own MAC address
as the source address. He then places the entire data packet in the mail
box.
Juliet receives the letter and removes the outer envelope. She finds the
inner envelope with Romeo's IP address. Opening the inner envelope
and reading its contents corresponds to transferring the message to the
higher protocol layers of the ISO/OSI layer model.
Juliet would now like to send a reply to Romeo. She places her reply in
an envelope with Romeo's IP address as destination and her own IP
address as source. But where is she to send the answer? For she did not
receive Romeo's MAC address. It was lost when Lorenzo replaced the
outer envelope.
In the MIB, Juliet finds Lorenzo listed under the variable
hmNetGatewayIPAddr as a means of communicating with Romeo. She
therefore puts the envelope with the IP addresses in a further envelope
with Lorenzo's MAC destination address.
The letter then travels back to Romeo via Lorenzo, the same way the first
letter traveled from Romeo to Juliet.