Information Technology Reference
In-Depth Information
Vocabulary Exercise: Completion
Complete the paragraphs that follow by filling in the appropriate words and phrases.
Routers Are Computers
A router is a computer, just like any other computer including a PC. Routers have many of the same
hardware
and
software
components that are found in other computers including
CPU
■
RAM
■
ROM
■
Operating system
■
Each
network
that a router connects to typically requires a separate interface. These interfaces are
used to connect a combination of both
local-area networks (LAN)
and
wide-area networks (WAN)
.
LANs
are commonly
Ethernet
networks that contain devices such as PCs, printers, and servers.
WANs
are used to connect networks over a large
geographical
area and are commonly used to connect a
LAN to the
Internet service provider's (ISP)
network.
The router's primary responsibility is to forward packets destined for local and remote networks by
Determining the
best path
to send packets
■
Forwarding
packets toward their destination
■
The router uses its
routing table
to determine the best path to forward the packet. When a match is
found, the router
encapsulates
the IP packet into the data-link frame of the outgoing or exit interface,
and the packet is then forwarded towards its destination.
It is likely that a router will receive a packet
encapsulated
in one type of data-link frame, such as an
Ethernet frame, and when forwarding the packet,
encapsulate
it in a different type of data-link frame.
Static
routes and
dynamic routing
protocols are used by routers to learn about remote networks and
build their routing tables.
Router CPU and Memory
Like a PC, the
CPU
in a router executes operating system instructions, such as system initialization,
routing functions, and network interface control.
Similar to other computers,
RAM
stores the instructions and data needed to be executed by the CPU.
It is volatile memory that loses its content when the router is powered down or restarted. For this reason,
the router also contains permanent storage areas such as
ROM
,
flash
, and
NVRAM
.
ROM
is a form of permanent storage. On Cisco devices, it stores
The
bootstrap
instructions
■
Basic
diagnostic
software
■
Scaled-down version of
IOS
■
In most models of Cisco routers, the IOS is permanently stored in
flash
memory and copied into
RAM
during the bootup process.
NVRAM is
nonvolatile random-access memory
that does not lose its information when power is
turned off. NVRAM is used by the Cisco IOS as permanent storage for the
startup configuration
file.
