basic routing

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Basic Routing

18-Feb-13 Jaringan Komputer_D3 TT 1

OSI layers 1, 2 and 3

18-Feb-13 Jaringan Komputer_D3 TT

Receive signals from cable, convert to binary.

Check layer 2 address, decapsulate

Find destination network, check routing table for route, direct packet to correct outgoing interface

Encapsulate with frame for next link

Encode binary, place signals on cable

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Routing tables

A router uses the routing table to select the best path to a network

Directly connected networks are taken from the interface configuration

Static routes can be added by administrator

Routes can be learned dynamically from other routers by using a routing protocol


Static routes Dynamic routesEntered by administrator

Time consuming, different for each router

Must be updated if routes change

Little processing

No bandwidth used

Gives nothing away

Learned from other routers

Start the protocol then it runs by itself

Automatically updates when routes change

More processing

Uses bandwidth

Gives away information


Routing Table Principles

1. Every router makes its decision alone, based on the information it has in its own routing table.

2. The fact that one router has certain information in its routing table does not mean that other routers have the same information.

3. Routing information about a path from one network to another does not provide routing information about the reverse, or return, path.


Metrics

A routing protocol may learn of several possible routes to a destination.

It uses metrics to pick the best route.

RIP uses hop count as its only metric.

OSPF uses cost based on bandwidth.

EIGRP uses bandwidth and delay and can use load and reliability as well.


Metrics


RIP uses hop count. It picks this route as the best.

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Metrics


OSPF uses cost based on bandwidth. It picks this route as the best.

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Administrative distance

There may be more than one routing protocol running. There may also be static routes.

Static routes have administrative distance 1 or 0 by default.

RIP routes have administrative distance 120

OSPF routes have administrative distance 110

The route with the lowest administrative distance goes in the routing table


Router as a computer

CPU: control unit handles instructions, ALU for calculations

RAM: volatile working storage

ROM: permanent storage for POST and start-up instructions

Operating System: software that runs the computer

System bus, Power supply


Router differences

Long term storage is Flash and NVRAM, not hard disk

Range of different interfaces all on different networks

No input/output peripherals. Connect via a console PC and use PCs keyboard and screen


Router functions

Connect networks together

Find best routes

Switch packets from one network to another

Do this efficiently 24/7

Provide security by permitting or denying specified types of packet

Provide quality of service by prioritising packets


RAM

Dynamic random access memory: as in a PC

Temporary memory while the router is on

Loses content when the router loses power or is restarted

Holds running configuration

Holds routing tables

Holds ARP cache

Holds fast-switching cache etc.


NVRAM

Non-volatile RAM: keeps its contents when the router is off

Stores the startup configuration file

When you have configured a router, you must save your configuration to NVRAM if you want to keep it


Flash

Electronically erasable, programmable ROM (EEPROM)

Keeps its contents when the router is off

Holds the operating system image (IOS)

Allows the IOS to be updated

Can store multiple versions of IOS software if it has enough capacity

Can be upgraded by adding SIMMs


ROM

Permanent memory: cannot be upgraded without replacing the chip

Holds power-on self test (POST) instructions

Stores bootstrap program

Stores ROM monitor software (for emergency download of IOS, for password recovery)

May store basic IOS for emergency use (less common than it was)


Router storage

ROM

Permanent

Holds POST, boot instructions, basic IOS

Flash

Keeps contents

Holds IOS image


NVRAM Keeps contents Holds startup

configuration file

RAM Volatile Holds runnning config,

tables, queues etc

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Router startup


Normal start up

1. Run POST and bootup instructions from ROM

2. Load IOS file from flash

3. Load configuration from NVRAM

4. Fully operational


Show version

IOS version

Bootstrap version

Router model and CPU

Amount of RAM

Number and type of interfaces

Amount of NVRAM

Amount of Flash

Configuration register



Default condition

By default, interfaces have no IP addresses and are administratively shut down.

They need to be configured.

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Configure interface

R1(config)#interface fastethernet 0/0

R1(config-if)#ip address 172.16.3.1 255.255.255.0

R1(config-if)#no shutdown

*Mar 1 01:16:08.212: %LINK-3-UPDOWN: Interface FastEthernet0/0, changed state to up

*Mar 1 01:16:09.214: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/0, changed state to up

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Check interfaces

R1#show interfaces fastethernet 0/0

FastEthernet0/0 is up, line protocol is up

Hardware is AmdFE, address is 000c.3010.9260

Internet address is 172.16.3.1/24 etc.

Note MAC address of Ethernet interface

Interface takes part in ARP with its network and keeps an ARP table

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Check interfaces

R1#show run

interface FastEthernet0/0

ip address 172.16.3.1 255.255.255.0

(Does not say no shutdown)

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Interface not up?

If the interface does not come up check the cable, check link lights, check the configuration at the other end.

If the protocol does not come up for Ethernet check that you have the right cable (straight-through or crossover) for serial check that the clock rate is on the right end of the cable, check that the same Layer 2 protocol is used.

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Directly connected

Configure IP address on interface

It appears in routing table

Note subnetting information

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Serial interface

R2(config)#interface serial 0/0

R2(config-if)#ip address 172.16.2.2 255.255.255.0

R2(config-if)#no shutdown

This is DTE end

DCE end needs an additional command

R3(config-if)#clock rate 64000

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Usual show commands

Check that interface and protocol are up

show interfaces show ip interface brief show running-config

Check that network is in routing table

show ip route

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Show controllers

R1#show controllers serial 0/0

Interface Serial0/0

Hardware is PowerQUICC MPC860

DCE V.35, no clock etc.

Shows if a cable is connected

Shows the type of cable

Shows if clock rate set

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debug ip routing

R2#debug ip routing

If you give this command before configuring the interfaces then you see a report of the networks being added to the routing table.

R2#no debug ip routing or R2#no debug all

Switch off debugging as soon as possible after use it takes up resources.

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Cisco Discovery Protocol

Works at layer 2

Directly connected devices only

Cisco devices only

Devices send CDP advertisements to neighbours at regular intervals

Use it to find out about networking devices

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Show cdp neighbors

Does not show IP address

You need show cdp neighbors detail for that.

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Going further

CDP only shows immediate neighbours, but it does tell you their IP addresses.

Telnet to the neighbour and then use CDP to find out about its neighbours and so on.

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Disable CDP

Disable CDP for the entire device:

Router(config)#no cdp run

Stop CDP advertisements on one interface:

Router(config-if)#no cdp enable

Do this for security.

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Static routes

Use for stub networks: only one entry.

Stub networknetworks

Static route

Default route

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Configure a static route

R1(config)#ip route 172.16.1.0 255.255.255.0 172.16.2.2

Give the next hop address

R1(config)#ip route 172.16.1.0 255.255.255.0 Serial 0/0

Or give the exit interface

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Show ip route

Routing table now includes:

S 172.16.1.0 /24 [1/0] via 172.16.2.2

OrS 172.16.1.0 /24 is directly connected, serial 0/0

Administrative distance 1

Metric 0

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Return route

If you use static routing, you need to configure static routes in both directions.

A route in one direction does not ensure that there is a route in the other direction.

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Find a route to 172.16.1.0/24

Recursive lookup

There it is, via 172.16.2.2

How do you get to 172.16.2.2?There it is via serial 0/0.

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Static route giving interface

R1(config)#ip route 192.168.2.0 255.255.255.0 serial 0/0

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Interface down

If the interface used by a static route goes down, then the static route is removed from the routing table.

The static route remains in the configuration.

If the interface comes up again then the static route goes back in the routing table.

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Delete a static route

R1(config)#no ip route 192.168.2.0 255.255.255.0 serial 0/0

Give the same command again with no in front.

Most commands can be reversed like this.

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Next hop or exit interface?

For a point to point serial link, configure the static route with the exit interface.

Only one look-up, less processing.

For an Ethernet link, configure the static route with the next hop address (or with both).

This identifies the device that should receive the packet next. The MAC address can be found and used in the frame header.

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Summarizing static routes

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Default route

All packets from the stub network need to go on the same route to the right hand router.

Configure a static default route.

Stub networknetworks

Static route

Default route

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Configure a default route

Router(config)#ip route 0.0.0.0 0.0.0.0 serial 0/0Using exit interface.

Router(config)#ip route 0.0.0.0 0.0.0.0 172.16.2.2Using next hop address

0.0.0.0 network address and subnet mask is called quad zero. It matches anything.

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Routing table

S* 0.0.0.0/0 is directly connected, Serial0/0

The default route is shown with a *

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Troubleshooting tools

ping

traceroute

show ip route

show ip interface brief

show cdp neighbors

show running-config

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Basic Configuration (revision)

Name

Passwords

Interfaces

Routing

Banner (Message of the day)

Save configuration

Check configuration


Global configuration

Router>enable

Router#configure terminal (config t)

Router(config)#

Start in user exec mode

Go to privileged exec mode (no configuration so no password)

Go to global configuration mode


Hostname

Give the router a name to show at its prompt

Do this in global configuration mode

Router(config)# hostname Abingdon

Abingdon(config)#


Enable secret

Protect privileged exec mode with an encrypted password.

Abingdon(config)# enable secret class

You could set an enable password but this is not encrypted

There is no need to set both, but if you do then the enable secret will be used


Passwords for login

Set login password on console port for security

Abingdon(config)# line con 0

Abingdon(config-line) password cisco

Abingdon(config-line) login

Abingdon(config-line) exit

You can also put a password on the AUX port in a similar way


Passwords for Telnet login

Set login password on virtual lines to allow you to Telnet to the router

Abingdon(config)# line vty 0 4

Abingdon(config-line) password cisco

Abingdon(config-line) login

Abingdon(config-line) exit


Interface configuration

Abingdon(config)# interface serial 0/0

Abingdon(config-if)# ip address 192.168.3.1 255.255.255.0

Abingdon(config-if)# no shutdown

Abingdon(config-if)# exit

This is for a DTE serial interface

Ethernet interfaces are configured the same way


Interface DCE configuration

A DCE serial interface needs an extra line:

Abingdon(config)# interface serial 0/0

Abingdon(config-if)# ip address 192.168.3.1 255.255.255.0

Abingdon(config-if)# clock rate 64000

Abingdon(config-if)# no shutdown

Abingdon(config-if)# exit


Interface description

You can give an interface a description

This does not affect the operation of the router but it is useful documentation

Do it in interface configuration mode for the required interface

Abingdon(config-if) description Serial line to Witney 01993 876543


Message of the day

You can configure a message to be shown before the user logs on

Cisco recommend that you show a warning to unauthorised users (NOT welcome)

Abingdon(config)# banner motd # authorised users only #

# is a delimiter. Any character can be used.


Routing

The router knows its directly attached networks because you have put IP addresses on its interfaces

It can put these networks in its routing table

It needs to find routes to networks that are not directly attached

You can give it static routes

You can enable a routing protocol


Routing protocol: RIP

You choose the routing protocol

Then you tell the router which directly attached networks it should advertise

Abingdon(config) router rip

Abingdon(config-router) network 192.168.1.0

Abingdon(config-router) network 192.168.3.0 Abingdon(config-router) exit


Save configuration

Your configuration is held in RAM as the running configuration

If you want to keep this configuration then you must save it to NVRAM into the startup configuration file

Abingdon# copy running-config startup-config


Shortened commands

The Cisco IOS accepts shortened forms of commands

You need to type enough to distinguish the command from other commands

copy run start can be used instead of copy running-config startup-config

int s 0/0 can be used instead of interface serial 0/0


Show commands

Show running-config

Show startup-config

Show ip route

Show ip interfaces

Show ip interface brief


Show ip route


List of codes

List of routes

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Routing table


C 192.168.1.0/24 is directly connected, FastEthernet0/0C 192.168.2.0/24 is directly connected, Serial0/0S 192.168.3.0/24 [1/0] via 192.168.2.2R 192.168.4.0/24 [120/1] via 192.168.2.2, 00:00:20, Serial0/0

Directly connectedNetwork and mask

Exit port

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Routing table



Static routeNetwork and mask

Administrative distance and metric Address of next

hop router

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Routing table



Dynamic route, RIPNetwork and mask

Administrative distance and metric Address of next

hop routerTime since last update

Exit port

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Thank YouRef: S Ward Abingdon and Witney College


basic routing

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