User`s guide

147
TCP/IP Network Basics
TCP/IP Protocols
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.
Internet Control
Message Protocol
(ICMP)
Internet Control Message Protocol (ICMP) is primarily used to send error
messages, perform diagnostics, and control data flow. You can also use
ICMP with the Packet InterNet Groper (
Ping) utility. To ping another host
from a Command Prompt, type
ping <ip_address>.