Ip Routing i

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IP ROUTING


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INTRODUCTION

IP Routing is a term defining the set of protocols that

determine the path that data follows in order to travel

across multiple networks from its source to its

destination. Data is routed from its source to its destination through

a series of routers, and across multiple networks. The IP

Routing protocols enable routers to build up a

forwarding table that correlates final destinations withnext hop addresses


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INTRODUCTION

When an IP packet is to be forwarded, a router uses its

forwarding table to determine the next hop for the

packet's destination (based on the destination IP

address in the IP packet header), and forwards thepacket appropriately. The next router then repeats this

process using its own forwarding table, and so on until

the packet reaches its destination. At each stage, the IP

address in the packet header is sufficient informationto determine the next hop; no additional protocol

headers are required.


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DNS

DNS resolves hostnames to their corresponding IP addresses

DNS Server

DNS Server


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DNS

If the name cannot be resolved, a DNS query is sent outto other DNS servers

DNS query

DNS query


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ARP

ARP resolves IP addresses to their corresponding MAC addresses

Resolved addresses are stored in an ARP cache


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ARP

My address is not192.168.10.2

I should not respond

192.168.10.3

192.168.10.1

Resolved addresses are stored in an ARP cache


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PROXY ARP

The ARP query is a broadcast and will not reach host 172.12.0.2 because of the router


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PROXY ARP

The router responds with its own MAC address


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DHCP

DHCP is used to automatically assign IP addresses to hosts on a

network segment


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ROUTING

The term routing means sending packets to their appropriate destinations

Routers are only able to forward packets to networks known to them

To route, a router needs to do the following:

o Know the destination address

o Identify the sources it can learn from

o Discover possible routeso Select the best route

o Maintain and verify routing information


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ROUTING

A route is a defined pair of addresses: adestination and a gateway. The pair indicatesthat if you are trying to get to this destination,communicate through this gateway.

There are three types of destinations: individual hosts

subnets

default

The default route is used if none of the otherroutes apply.


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ROUTING

Routers store routes in a table called routing table

If the destination address is not known to the router (in

the routing table), the packet is deleted

Router>enable

Router#show ip route


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TYPES OF ROUTING

There are two types of routing that can be

configured on a network device:

Static routes are hard-coded on a network device.

They tell the device exactly where to send traffic

Dynamic routes, on the other hand, use a routing

protocol to determine the best path. If one route

becomes less preferred, the route being used maychange.


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ADMINISTRATIVE DISTANCE

When there are two or more routes to the samedestination, routers use administrative distance todecide which routing protocol (or static route) to

trust more.


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ADMINISTRATIVE DISTANCE

Route Administrative distance

Direct connection 0

Static route 1

EIGRP 90

IGRP 100

OSPF 110

RIP 120

External EIGRP 170

Unreachable 255

The lower the AD the more trustworthy the route

Because of how administrative

distance works, when you

enter static routes that are the

same as a dynamic route

(learned from another router),

your static route will be used

over the dynamic route. As youmay be overriding routes

manually, you must make sure

your routes are accurate.


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STATIC ROUTES

Static routes are unidirectional routes and should be pointed

in the right direction.


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STATIC ROUTES

Router> enable

Router# configure terminal

Router(config)# ip route 10.10.20.0 255.255.255.0 192.168.100.1

ip route [destination network] [destination mask] [exit int]

or

[next hop ip]

Static routes must be configured for all routes in the internetwork in the appropriate

direction


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STATIC ROUTES


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STATIC DEFAULT ROUTES

Default routes are used to flag a network as a

candidate default


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Ip Routing i