Ip Routing i
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Transcript of 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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