The document discusses packet transfer mechanisms using routers and IP addresses. It explains that routers forward packets between interconnected networks using routing tables that contain the destination address and interface to route packets. Packets are forwarded either directly, if the source and destination are on the same network, or indirectly by moving from router to router. Forwarding techniques include next hop, network/host specific, default methods. Examples of routing protocols and an example routing table are also provided.

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
3

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
4

5. Recap
• Let us remember the functions of a router and also IP
address details in the following slides
5

6. Routers
• A router is a hardware component used to
interconnect networks
Router
LAN WAN
Fig .2
6

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
8

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
11

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
12

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
30

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
33