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30 Οκτ 2013 (πριν από 5 χρόνια και 7 μήνες)

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By:Jordan Johnson

Bridges and Routers

Bridging and Routing are both ways of performing data
control, but work through different methods. Bridging
takes place at OSI Model layer 2 (Data
Link Layer) while
Routing takes place at the OSI Model Layer 3 (Network
Layer). This difference means that a bridge directs
frames according to hardware assigned MAC addresses
while a router makes its decisions according to arbitrarily
assigned IP addresses . As a result of this, bridges are
not concerned with and are unable to distinguish
networks while routers can.

What is a Router?

Routers are specialized computers that send your messages and
those of every other internet user speeding to their destination along
thousands of pathways. Routers also connect two or more logical
subnets which do not necessarily map one
one to the physical
interfaces of the router.

The router works at the “layer 3 (the network link layer), which
means that it must be able to understand the data packets so that it
can route them to their destination.



Router History

The very first device that had fundamentally the same functionality as a
router does today, was the Interface Message Processor (IMP)

The first true IP router was developed by Virginia Strazisar at BBN.

The earliest Xerox routers came into operation sometime after early

By the end of 1976 three types of routers were in service in the
experimental prototype Internet.

Types of Routers

Static Router

In static routers, the system
administrator is giving the shortest path by
giving some commands.

Static routing have some limitations.

Types of Routers

Dynamic Router

In the dynamic routing
the router can define the shortest path by
itself between the nodes.

Dynamic routing is the clever type of
routing and normally used in lot of places
in the world while routing.

Types of Routers

Core Routers

A core router is a router
designed to operate in the Internet
backbone, or core.

Components of the Router

Input ports


The signals are received at this
port. It acts as physical and data link function for

Output ports

It works exactly opposite to the
input port. All the outgoing packets are queued
into a single frame, and then these frames are
transformed to signals by physical layer function,
to send these signals on the line.

Components of the Router

Routing Processor

it performs the
functions of network layer.

Switching fabrics

moves the packets
from the input queue to output queue.

How it works

As a packet reaches a router, the router reads the
packets header.

It then uses the configuration table and the configuration
table is a collection of information including,
Priorities for
connections to be used
Rules for handling both routine
and special cases of traffic and, Information on which
connections lead to particular groups of addresses
, This
is what determines what the best route is for the

And then forwards the packet on the best route.

How it works

If too many packets reach a router at
once, some are stored in a queue.

If the queue is full, some packets might be
dropped, requiring the TCP (Transmission
Control Protocol) to request that

packets be resent.

How it Works

Major Manufactures of Routers


Bridging is an older technology that
connects multiple network segments at
the data link layer (layer 2) of the OSI

Bridges inspect incoming traffic and
decide whether to forward or discard


Types of Bridges

Transparent bridging

This method uses a forwarding
database to send frames across network segments. The
forwarding database is initially empty and entries in the
database are built as the bridge receives frames. If an
address entry is not found in the forwarding database,
the frame is rebroadcast to all ports of the bridge,
forwarding the frame to all segments except the source

Types of Bridges

Source route bridging

With source
route bridging two frame types are used in
order to find the route to the destination
network segment.

Types of Bridges

route translational bridging

Method of bridging where source
stations can communicate with
transparent bridge stations with the help of
an intermediate bridge that translates
between the two bridge protocols.

How it Works

Each packet of data on an intranet has more information in it than just
the IP information. It also includes addressing information required for
other underlying network architecture, such as for an Ethernet network.
Bridges look at this outer network addressing information and deliver the
packet to the proper address on a LAN.

Bridges consult a
table that has the addresses of all the network
nodes in it. If a bridge finds that a packet belongs on its own LAN, it
keeps the packet inside the LAN. If it finds that the workstation is on
another LAN, it forwards the packet. The bridge constantly updates the 1
earning table as it monitors and routes traffic.

Bridges can connect LANs in a variety of different ways. They can
connect LANs using serial connections over traditional phone lines and
modems, over ISDN lines, and over direct cable connections. CSU/DSU
units are used to connect bridges to telephone lines for remote

How it Works

Major Manufactures


A brouter is a hybrid device that merges bridging
and routing technology. Basically, a brouter is a
bridge that can bridge multiple protocols and
provide routing for some of those protocols. In
this sense, a brouter is a device that forwards
packets between networks at the network layer
and the data link layer in the OSI (Open Systems
Interconnection) protocol stack.