1. Topic : Basics of WAN &WAN Protocols
Sub-Topic : Packet Transfer Mechanism using
Router and IP address
1

2. 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

3. 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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4. Computer Network
ForNet Domain: A domain covered by single
monitoring and privacy policies.
Forensic Server: Responsible for archiving synopses,
query processing & routing, enforcing monitoring,
security policies, for the domain.
SynApp: equipped routers or hosts. Primary
function is to create synopses of network
traffic. May have limited query processing and
storage component as well.
Fig .1
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5. Recap
• Let us remember the functions of a router and also IP
address details in the following slides
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6. Routers
• A router is a hardware component used to
interconnect networks
Router
LAN WAN
Fig .2
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7. Routers
• 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
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8. R
Fig .3
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9. Internetwork
• An internetwork is composed of arbitrarily many
networks interconnected by routers
Router
Fig .4
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10. Internetwork
Ethernet 131.108.0.0 227.240.129.2
Token Ring
227.240.129.0
227.240.129.17
131.108.99.5
Router
78.0.0.17
WAN
78.0.0.0
Fig .5
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11. 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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12. 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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13. 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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14. 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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15. 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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16. 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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17. Examples of
Routing Protocols
• Routing Information Protocol
• Open shortest path first
• Intermediate system to Intermediate system
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18. Examples of
Routing Protocols
• 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
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19. Examples of
Routing Protocols
• 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
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20. Examples of
Routing Protocols
• 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
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21. Examples of
Routing Protocols
• Two general routing algorithms are used for computing
metric information. i.e. hops, propagation delay,
bandwidth, time, channel utilization error rates etc
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22. 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
215.103.16.22 187.96.25.13 UGHD le O
7
215.103.16.14 187.96.25.35 UGHD le 1
1
Default 187.96.25.1 UG
187.96.25.0 187.96.25.2 U leO
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23. Example Routing Table Contd…
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
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24. Example Routing Table Contd….
• 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
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25. Example Routing Table Contd….
• 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
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26. Example Routing Table Contd….
• 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
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27. Example Routing Table Contd….
• 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
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28. Example Routing Table Contd….
• 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
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29. Example Routing Table Contd….
• 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
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30. Summary
In this class, you have learnt about
• Packet transfer mechanism using routers
• And IP addresses with routing options used
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31. 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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32. 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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33. 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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