Chapter 2

Planning a TCP/IP Network Infrastructure

2-55

Key Points

■

Every computer on a TCP/IP network must have a unique IP address. Computers

visible to the Internet must have registered addresses. Computers accessing the

Internet through NAT routers or proxy servers can use unregistered addresses.

■

Routers are network layer devices that connect networks into an internetwork

while keeping their collision domains and broadcast domains separate.

■

Switches are data-link layer devices that connect networks into one large network.

Although switching all but eliminates collisions from an Ethernet installation, the

network still consists of one large broadcast domain.

■

To subnet a network, you borrow some bits from the host identifier and use them

to create a subnet identifier. You can then split a network address into separate

subnets, each of which is a separate entity on a TCP/IP network.

■

Most TCP/IP communications problems are the result of incorrect configuration

settings on the TCP/IP client. The problems can result from typographical errors

during a manual client configuration or from incorrect configuration of a DHCP

server or relay agent.

Key Terms

Network address translation (NAT) A router function that enables client comput-

ers on a private network with unregistered IP addresses to access Internet

resources without exposing themselves to possible intrusion from the Internet.

Proxy server An application layer software component that relays transmissions

between unregistered client computers on a private network and the Internet.

Proxy servers can also regulate client access to specific Internet resources and

cache Internet information for rapid access by other clients.

Collision domain A group of computers connected so that any two systems trans-

mitting packets at the same time will cause a collision. Computers connected to a

shared Ethernet hub, for example, are said to be in the same collision domain.

Connecting two LANs with a router creates an internetwork with two separate col-

lision domains.

Broadcast domain A group of computers connected so that a broadcast message

transmitted by any system will reach all other connected computers. Computers

connected by hubs or switches form a single broadcast domain. Connecting two

LANs with a router creates an internetwork with two separate broadcast domains.