packet transfer mechanism using routers and ip addresses
Post on 23-Dec-2014
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Topic : Basics of WAN &WAN Protocols
Sub-Topic : Packet Transfer Mechanism using Router and IP address
In the previous classes, you have learnt about
• IP Address
• Network prefix and host number
• Internet address
• Sub-netting and no sub-netting
• Default gateways
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Objectives
On completion of this period ,you would be able to know about
• Packet transfer mechanism using routers and IP addresses
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Computer Network
SynApp: equipped routers or hosts. Primary function is to create synopses of network traffic. May have limited query processing and storage component as well.
Forensic Server: Responsible for archiving synopses, query processing & routing, enforcing monitoring, security policies, for the domain.
ForNet Domain: A domain covered by single monitoring and privacy policies.
Fig .1
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Recap
• Let us remember the functions of a router and also IP address details in the following slides
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Routers
• A router is a hardware component used to interconnect networks
Router
LAN WAN
Fig .2
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• A router has a network interface card for each network that it is connected to
• Networks can use different technologies
• Router forwards packets between networks
• Router’s job is to transform packets from one network to meet the standards of the second network
Routers
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Routers with More Than Two Interfaces
Fig .3
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Internetwork
• An internetwork is composed of arbitrarily many networks interconnected by routers
Router
Fig .4
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WAN78.0.0.0
Token Ring227.240.129.0
78.0.0.17
227.240.129.17
227.240.129.2
131.108.99.5
Ethernet 131.108.0.0
Router
Fig .5
Internetwork
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Routers and IP Addressing
• What about routers - connected to two networks ?
• Router has multiple IP addresses - one for each interface as shown in the previous slide
• IP address depends on network address
• IP address specifies an interface, or network attachment point, not a computer
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TCP/IP Addresses
• Addressing in TCP/IP is specified by the Internet Protocol (IP)
• Each host is assigned a 32-bit number
• This 32-bit number is called the IP address or Internet address
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TCP/IP Addresses
• Each IP address is unique across entire Internet
• The format of IP addresses makes routing efficient
• Each IP address is divided into a prefix and a suffix
• Prefix identifies network to which computer is attached
• Suffix identifies computer within that network
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Packet Transfer Mechanism Using Routers And IP Address
• The network layer monitors the delivery of the packet
using physical networks
• In direct delivery source and destination of packet are
located on same physical network
• In an indirect delivery, packet moves from router to router
until it reaches its final destination
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Packet Transfer Mechanism Using Routers and IP Address
• When a packet is placed in its route to its destination it is
known as forwarding
• It requires a router or a host to have a routing table
• There are many forwarding techniques
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Forwarding Techniques
• Next hop method
• Network / host – specific method
• Default method
• The path from source to destination is a function of
routing protocols
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Examples of Routing Protocols
• Routing Information Protocol
• Open shortest path first
• Intermediate system to Intermediate system
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• Packets from one network protocol are wrapped in a
packet for another protocol
• It is called tunneling done by wrapper network protocol
• The routing protocols determine best path for the packet
to travel
• They maintain routing tables that contain information
about networks topology
Examples of Routing Protocols
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• In the internet world, IP is used to transport packets
through the internet
• It uses the information contained in the routing tables
with routers
• The routing tables may contain several possible routes
• The routing algorithm calculates the least-cost path from
source to destination
Examples of Routing Protocols
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• Routers also maintain routing tables that contain
destination address of a node or network
• It also has network interface associated with a particular
router address
• A special type of route is called static route (fixed) that
can be entered manually or through software in routing
table
• The static route cannot be changed dynamically
Examples of Routing Protocols
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• Two general routing algorithms are used for computing
metric information. i.e. hops, propagation delay,
bandwidth, time, channel utilization error rates etc
Examples of Routing Protocols
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Example of Routing Table
• Routing Table generated on a Unix system with IP address 187.96.25.2 [Local-Host Routing]
Destination Gateway Flags Interface
Local host Local host UH le O
215.103.16.227
187.96.25.13 UGHD le O
215.103.16.141
187.96.25.35 UGHD le 1
Default 187.96.25.1 UG
187.96.25.0 187.96.25.2 U leO
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where
• U = route is up & operational
• G = packet must pass through at least one router
• H = route to a specific host and not a network
• D = route was created dynamically
Example Routing Table Contd…
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• The table’s first entry illustrated local host-routing
• It indicates that any packets meant for local network
87.96.25.0
• It will be forwarded through gateway 187.96.25.2 (IP
address of the host). Local host acts as router
Example Routing Table Contd….
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• The second entry in the table indicates that the packets are
forwarded to another router
• The Packets whose destination address is 215.103.16.227 are
forwarded to the router (187.96.25.13) through interface leO
• This router will have the information to where this packet is to
be delivered
Example Routing Table Contd….
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• The third entry indicates the packets with destination
address 215.103.16.141 are to forwarded to gateway
• The gateway whose address 187.96.25.35 accessible
through le 1 interface
Example Routing Table Contd….
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• The Fourth entry entry of table is a default route
• When router receives a packet with unknown destination
address
• The router forwards packet to default router
Example Routing Table Contd….
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• If host system receives a packet with destination address
212.133.65.3
• It forwards to router with destination address 187.96.25.1
(since there is no entry in host’s routing table for
212.133.65.3
Example Routing Table Contd….
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• Routers exchange routing table information with
neighbor routers periodically depending upon routing
protocol used
• They do so in order to update the routing tables as one
router may be connected to more than one router
Example Routing Table Contd….
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Summary
In this class, you have learnt about
• Packet transfer mechanism using routers
• And IP addresses with routing options used
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Quiz
1) What is the length of the IP address
a) 16-bit
b) 32-bit
c) 8-bit
d) 64-bit
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Quiz
2) A routing table specifies about
a) various routes that can be used
b) identifies the address
c) it’s a table of IP addresses
d) none of the above`
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Frequently Asked Questions
1) Explain how packet transfer mechanism is done using
routers & IP addresses
2) What are the various forwarding techniques used ?
3) Discuss with an example importance of a routing table
along with its options
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