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communicate with the Internet, all devices on the LAN will be assigned private IP
addresses. Although they are free to communicate with the outside world, they are not
reachable from the Internet, making the LAN a private network to the outside world.
Protocol
A protocol is a set of rules for interaction agreed upon between multiple parties so
that when they interface with each other based on such a protocol, the interpretation
of their behavior is well defined and can be made objectively, without confusion or
misunderstanding.
A communication protocol is a set of rules defined for data communication that
potentially define the format and the meaning of messages exchanged between
communicating devices. The idea is to define a standard that every product conforms
to, so that devices from different vendors can communicate with each other without
confusion or misunderstanding. Such a standard definition is important today since
users have learned their lessons over the years not to be locked in to any company's
proprietary way of communicating with each other.
For example, the Point-to-Point Protocol (PPP) is the most popular protocol that is
used when a user connects through an ISP to the Internet using a modem or an ISDN
line. It defines a sequence of message exchanges between the user's device and the
ISP's device for the purpose of authenticating the user (asking for the user account
name and password) and assigning an IP address to the user. Other commonly used
protocols are Ethernet, ATM, TCP/IP, ISDN call set-up/take-down, etc.
Remote Access Server
A remote access server (RAS) allows a remote PC user to dial in through it to the
local LAN environment to share resources on the LAN.
RIP, RIP II, OSPF, Routing Protocol
RIP stands for Routing Information Protocol. It is a routing protocol used by routers
to exchange routing table information with each other. RIP II is a newer version.
OSPF stands for Open Shorted Path First, and is a newer routing protocol. Because of
its ability to exchange routing table information faster in a large network
environment, it is commonly used in a large network (such as the Internet network),
while RIP/RIP II are more popular in corporate or private networks.
Router
An intelligent, internetworking device that will forward or filter packets between
different networks based on data link layer (MAC) address information.
A router is an intelligent, internetwork device that forwards packets between different
networks based on network layer address information. An IP router uses IP addresses,
while an IPX router uses IPX addresses.
When a packet is received, the destination network address contained in the packet is
looked up in the routing table to determine which next-hop router to forward the
packet to. (The next-hop router is in theory one hop closer to the destination.)
Routing Table
A router relies on a routing table to determine where to forward a received packet.
