Router Introduction 1

7/27/2019 Router Introduction 1

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Router Introduction


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Router

There must be some scheme for reducing theamount of information, each computer has to holdlocally in order to communicate with every other

computer.

?


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Router

The scheme used to involve splitting an large networkinto many separate but connected networks


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Router

Using this method, the network computers need only keeptrack of the networks on the internetwork , rather thankeeping track of every network computer.


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Internetwork

An Internetwork is an accepted networking industryterm for a set of interconnected networks.

Network 1

Network 2

Network 3

Internetwork


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Internetwork

Each individual network will have its own network number thatmust be unique for that internetwork.

203.162.1.0

180.135.0.0

124.153.1.0

Internetwork


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203.162.1.0

180.135.0.0

124.153.1.0

Internetwork

Internetwork

Routers direct traffic through an internetwork, based oninformation learned from network protocols.


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Routers Function Routers are used to route packets from one network number toanother.There are two things to consider with router:

You cannot configure the same network number on more than oneinterface on a router.A router does not forward broadcasts by default.


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Network Communications

Lets take a look at the way Layer 3 network devicescommunication with each other.

A typical workstation (a PC running a popular TCP/IP stack, for example) will require some manual configuration before it canoperate on a TCP/IP network.


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Network CommunicationsThe routing decisions of a workstation configured in this manner are simple.If the workstation has to send a packet to another machine that ison the same network number, the packet is sent directly to the

destination machine.

192.168.1.3

E0: 192.168.1.1 E0: 172.16.1.1

S0: 200.100.100.1S0: 200.100.100.2

192.168.1.2 172.16.1.2

To 192.168.1.3


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E0: 192.168.1.1

192.168.1.2

E0: 172.16.1.1

172.16.1.2

S0: 200.100.100.2S0: 200.100.100.1

Network CommunicationsThey must know how to get to all other network numbers on theinternetwork and the best way to route the packets.

203.162.4.0 240.250.100.0

s1

s0 s1

s1

190.180.2.1 180.180.2.0

s2

s0 s1

s2

Which way ?


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E0: 192.168.1.1

192.168.1.2

E0: 172.16.1.1

172.16.1.2

S0: 200.100.100.2S0: 200.100.100.1

Network Communications And they need to keep track of an internetwork topology that isconstantly changing due to equipment or other failures.

203.162.4.0 240.250.100.0

s1

s0 s1

s1

190.180.2.1 180.180.2.0

s2

s0 s1

s2

180.180.2.0up or down?


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E0: 192.168.1.1

192.168.1.2

E0: 172.16.1.1

172.16.1.2

S0: 200.100.100.2S0: 200.100.100.1

Routing tableTo accomplish these responsibilities, a router maintains a routingtable , which lists all the known network numbers and how to getto them.

203.162.4.0 240.250.100.0

s1

s0s1

s1

190.180.2.1 180.180.2.0

s2

s0 s1

s2

Routing table-----------------------------

S - 172.16.1.0 via s0R - 240.250.100.0 s1

I - 180.180.2.0 s2

The bestway to

172.16.1.0 is

throughs0.


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E0: 192.168.1.1

192.168.1.2

E0: 172.16.1.1

172.16.1.2

S0: 200.100.100.2S0: 200.100.100.1

Routing tableRouters also use routing protocols that keep the routing tableaccurate for a changing internetwork.

203.162.4.0 240.250.100.0

s1

s0s1

s1

190.180.2.1 180.180.2.0

s2

s0 s1

s2

Routing table-----------------------------

S - 172.16.1.0 via s0R - 240.250.100.0 s1

I - 180.180.2.0 s2

Network180.180.2

.0 isdown,so


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Routers Components There area two kinds of routers components:

Internal componentsCPU (Central Processing Unit)ROM (Read Only Memory)

FLASHNVRAM (Nonvolatile RAM)RAM (Random Access Memory)

External component (interface)WANLANConsole/AUX (Auxiliary : h tr)


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Routers Components

RAMROM FLASH NVRAM

Console

AuxiliaryInterface

CPU


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Internal Components: CPU

The Central Processing Unit (CPU) executes instructions in theoperating system.system initializationrouting functionsnetwork interface control.Large routers may have multiple CPUs.

RAMROM FLASH NVRAMConsoleAuxiliary Interface

CPU


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Internal Components: ROM

Contains power-on diagnostics, a bootstrap program, andoperating system software.The main tasks for ROM are hardware diagnostics during router bootup and loading the Cisco IOS software from flash to RAM.ROMs are not erasable.They can only be upgraded by replacing the ROM chips in thesockets.

RAMROM FLASH NVRAMConsoleAuxiliary Interface

CPU


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Internal Components: RAM

Random Access Memory (RAM) is split by the IOS into Main andShared memory.Main memory is used to store router configuration and IOS datastructures such as running-config , routing tables, switching cache,

and ARP tables ...Shared memory buffers packets waiting to be processed (This typeof memory is only used by 2500, 2600, 4000 routers. The 7000 routers have aswitch processor that controls the flow of packets through the router).The contents of RAM are lost when power is removed.RAM can be upgraded.

Main SharedROM FLASH NVRAM

Console

AuxiliaryInterface

CPU


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Internal Components: Flash

Flash memory holds the full current version of IOS running on therouter.Flash memory is erasable memory that can be overwritten withnewer versions of the IOS.The IOS may be in uncompressed or compressed form.In most routers (2600, 3600, 4000,) an executable copy of theIOS is transferred to RAM during the boot process.In other routers such as 2500, the IOS may be run directly from

flash.

RAMROM FLASH NVRAM

ConsoleAuxiliary Interface

CPU


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Internal Components: NVRAM

Nonvolatile random-access memory (NVRAM) is used to storethe startup configuration.(NVRAM) does not lose its contents when the router is turn off.

RAMROM FLASH NVRAMConsoleAuxiliary

Interface

CPU


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External Components: Interface

The interfaces are the router connections to the outside.The three types of interfaces are:

Local Area Network (LANs).Wide Area Network (WANs).Management Ports (Console/AUX).


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External Components: Interface(LAN)

LAN interfaces allow the router to connect to the Local AreaNetwork media.This is usually some form of Ethernet.However, it could be some other LAN technology such as TokenRing or Asynchronous Transfer Mode (ATM).


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External Components: Interface(WAN)

Wide Area Network connections provide connections through aservice provider to a distant site or to the Internet.

ISP - Internet


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With some types of WAN interfaces, an external device such asa CSU/DSU is required to connect the router to the localconnection of the service provider (serial)


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With some types of WAN interfaces, an external device such asa CSU is required to connect the router to the local connection of the service provider (serial)With other types of WAN connections, the router may be directly

connected to the service provider (ISDN)- Intergrated Services Digital Network


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External Components: Interface(Management ports)

The function of management ports is different from the other connections.The LAN and WAN connections provide network connectionsthrough which frame packets are passed.

The management port provides a text-based connection for theconfiguration and troubleshooting of the router.The common management interfaces are the console andauxilliary ports.


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External Components: Interface(Management ports)

These are EIA-232 asynchronous serial ports. ( EIA: Electronic Industries Association Hip hi cng nghip in t )They are connected to a communication port on a computer. Thecomputer must run a terminal emulation program to provide a

text-based session with the router. Through this session thenetwork administrator can manage the device.


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Router Connections: Console (2)

To connect to the console port, a rollover cable and a RJ-45 toDB-9 adapter are used to connect a PC.


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Router Connections: Console (3)

The PC or terminal must support terminal emulation. Terminalemulation software such as HyperTerminal is usually used.


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Router Connections: LAN

In most LAN environments, the router is connected to the LANusing an Ethernet or Fast Ethernet interface.


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In most LAN environments, the router is connected to the LANusing an Ethernet or Fast Ethernet interface.


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The router is a host that communicates with the LAN via a hub or aswitch.

A straight-through cable is used to make this connection.

Straight-through cable


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In some cases the Ethernet connection of the router is connecteddirectly to the computer or to another router.For this type of connection, a crossover cable is required.

Crossover cable Crossover cable


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Router Connections: WAN (1)

Among these WAN connection types are leased line, circuit-switched, and packet-switched.


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Router Connections: WAN (2)

For each type of WAN service, the customer premises equipment(CPE), often a router, is the data terminal equipment (DTE).This is connected to the service provider using a data circuit-terminating equipment (DCE) device, commonly a modem or

channel service unit/data service unit (CSU/DSU).This device is used to convert the data from the DTE into a formacceptable to the WAN service provider.


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Cisco Popular Router

Cisco 1700 module series router 1721

Cisco 2500 built-in series router 2501 2514

Cisco 2600 module series router 2621

Router Introduction 1

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