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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.
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