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IP Routing: an
Introduction
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Quiz
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Routing
IP routing is the process of movingpackets from one network to another
network using routersA routing protocolis a tool used by routers
to dynamically find all the networks in theinternetwork, as well as to ensure that allrouters have the same routing table. Ex:RIP, OSPF
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Once all routers know about all networks,a routed protocolcan be used to send
user data (packets) through theestablished internetwork. Routed protocolsare assigned to an interface anddetermine the method of packet delivery.
Examples of routed protocols are InternetProtocol (IP) and IPv6.
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Routing Basic
Routers dont really care about hoststhey onlycare about networks and the best path to eachnetwork
The logical network address of the destinationhost is used to get packets to a network througha routed network
Hardware address of the host is used to deliverthe packet from a router to the correctdestination host.
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What should router knows ?
Destination address
Neighbor routers from which it can learn
about remote networks Possible routes to all remote networks
The best route to each remote network
How to maintain and verify routinginformation
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Learn about remote networks
From neighbor routers or from an
administrator.
The router then builds a routing table
If a network is directly connected, then the
router already knows how to get to it.
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Static and Dynamic Routing
Static routing, someone hand-type all network locationsinto the routing table
In dynamic routing, a protocol on one router
communicates with the same protocol running onneighbor routers.
The routers then update each other about all thenetworks they know about and place this information intothe routing table.
If a change occurs in the network, the dynamic routingprotocols automatically inform all routers about the event
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IP Routing Process
PC want to ping the laptop
IP determines whether the destinationaddress is local or remote
a remote request, the packet needs to besent to the default gateway
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For this packet to be sent to the default
gateway, the hardware address of the
routers interface Ethernet 0 (configuredwith the IP address of 172.16.20.10) must
be known.
Why ?
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LAN driver is used to provide media access type
A frame is generated
No remote host MAC address !!
When the frame is completed, its handed downto the Physical layer (ex: twisted pair)
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The router received the packet
Every device within the collision domainreceives these bits and builds the frame
Check the FCS Check the HW address
If its a match, then the Ether-Type field ischecked to find the protocol used at the
Network layer The packet is pulled from the frame, the
packet is then handed to IP.
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Router routes the packet
IP receives the packet and checks the IP
destination address
It is not router IP, check routing table
The routing table must have an entry for
the network 192.168.10.0
Otherwise discarded, network
unreachable message
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The router packet-switches the Ethernet 1
Packet is in the Ethernet 1 buffer, IP needs to
know the hardware address of the destinationhost
First checks the ARP cache or ARP request
Packet is framed send in physical layer
Remote host accept the frame
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At the destination
The destination host receives the frame,
and immediately runs a CRC.
If the result matches whats in the FCSfield, the hardware-destination address is
then checked.
If the host finds a match, the Ether-Typefield is then checked, give to IP
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At the Network layer, IP receives the packet and
checks the IP destination address.
Because theres finally a match made, theProtocol field is checked to find out whom the
payload should be given to.
The payload is handed to ICMP
ICMP send an echo reply
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Static and Dynamic Routing
When a router receives a packet for a
network that isnt listed in the routing table
It doesnt send a broadcast looking for theremote networkthe router just discards
the packet
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Dynamic Routing
IGP is interior and EGP is exterior routing of anautonomous system (AS).
An autonomous system is a collection of networks orsubnets that are in the same administrative domain
IGP operates and routes within an AS and an EGPworks outside or between more than one AS.
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Packet tracer static routing