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Chapter 9 LAN
NBG-460N User’s Guide
155
Address Resolution Protocol (ARP) is a protocol for mapping an Internet Protocol
address (IP address) to a physical machine address, also known as a Media Access
Control or MAC address, on the local area network. IP routing table is defined on
IP Ethernet devices (the NBG-460N) to decide which hop to use,
to help forward
data along to its specified destination.
The following lists out the steps taken, when a computer tries to access the
Internet for the first time through the NBG-460N.
1 When a computer (which is in a different subnet) first attempts to access the
Internet, it sends packets to its default gateway (which is not the NBG-460N) by
looking at the MAC address in its ARP table.
2 When the computer cannot locate the default gateway, an ARP request is
broadcast on the LAN.
3 The NBG-460N receives the ARP request and replies to the computer with its own
MAC address.
4 The computer updates the MAC address for the default gateway to the ARP table.
Once the ARP table is updated, the computer is able to access the Internet
through the NBG-460N.
5 When the NBG-460N receives packets from the computer, it creates an entry in
the IP routing table so it can properly forward packets intended for the computer.
After all the routing information is updated, the computer can access the NBG-
460N and the Internet as if it is in the same subnet as the NBG-460N.