Technical data

168 Agilent Connectivity Guide
7TCP/IP Network Basics
As packets are sent through the network, each host on the network looks
at the packet to see if the packet is addressed to the host’s hardware
address. If not, the host ignores the packet.
The Internet Layer
The Internet Layer of the TCP/IP model contains the protocols
responsible for addressing and routing of packets. The Internet Layer
includes several protocols, including:
• Internet Protocol (IP)
• Address Resolution Protocol (ARP)
• Internet Control Message Protocol (ICMP)
For TCP/IP communications to be successful, the packet examined by
the Network Interface Layer must include a hardware address. As the
packet moves up to the Internet Layer, it also must include an
IP
address
. The Internet Layer provides the protocols to determine the
hardware address for routing the packet to its destination.
Internet Protocol (IP) Internet Protocol (IP) is responsible for
determining the source and destination IP addresses of every packet sent
on the network. Typically,
IP addresses are assigned by a
System Administrator. An IP address is
assigned to each host on a network and each host must have a unique
IP address.
In contrast to a hardware address that refers to a physical network
interface card, an IP address is a
logical address that is assigned to the
host. The IP address can be changed, since it refers only to the host. A
typical IP address is 167.155.21.45. See IP Addressing for a description
of IP addresses.
Address Resolution Protocol (ARP) Address Resolution Protocol
(ARP) is a protocol used to
resolve (translate)
a
logical address to a physical (hardware) address. ARP is used when a
source host wants to communicate with a destination host, but has only
the IP address. After the hardware address is resolved, ARP maintains
that information for a short period of time.