Routers determine the best path for data packets to travel between networks. They maintain routing tables that contain the destination address, cost of the path, and next hop to forward each packet. Routing protocols allow routers to share information and dynamically update their tables to route around failures and choose the lowest cost path. This allows packets to be properly forwarded from any source to destination on the internet through a system of destination-based connectionless forwarding.

1. Internet Protocol
Routing
Prepared by:
Mahmoud Hikmet Haval Sliman Zhakaw Hashm
Supervisor :
Omer Sheerko

2. Overview
• What's Router?
• What does a router do?
• What's Routing & How do packets get from A to B in the
Internet?
• Routing Table.
• Connectionless Forwarding
• ISP Routing Tasks
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3. What's Router?
• A router consists of a computer networking device that
determines the next network point to which a data packet has
to be forwarded on its way to its destination
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4. What does a router do?
• find path
• forward packet
• find alternate path
• forward packet
• repeat until powered off
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5. What's Routing Protocol?
• Routing Protocol decide on routes to be taken data and transmit
• How do packets get from A to B in the Internet?
A B
Internet
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6. Routing Protocols
• Distribute the knowledge of the current topology
state of the network to all routers
• This knowledge is used by each router to
generate a forwarding table, which contains the
local switching decision for each known
destination address
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7. Routing Protocols
• correct operation of the routing state of a
network is essential for the management
of a quality network service
• accuracy of the routing information
• dynamic adjustment of the routing
information
• matching aggregate traffic flow to network
capacity
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8. The routing table
One routing table is needed for each router
The routing table consists of at least three information
fields:-
the Network ID : i.e. the destination network id
Cost: i.e. the cost or metric of the path through which
the packet is to be sent
Next Hop: The next hop, or gateway, is the address of
the next station to which the packet is to be sent on the
way to its final destination
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9. The routing table
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10. Connectionless Forwarding
• Each router (switch) makes a LOCAL decision to forward the
packet towards B
A B
R1 R4
R2
R3
R6
R7
R5
R8
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11. Connectionless Forwarding
• This is termed destination-based connectionless forwarding
• How does each router know the correct local forwarding
decision for any possible destination address?
• Through knowledge of the topology state of the network
• This knowledge is maintained by a routing protocol
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12. Exterior routing
ISP Routing Tasks
Interior routing
Customer routing
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13. Interior Routing
•discovers the topology of a network
through the operation of a distributed
routing protocol
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14. Cont…
• describe the current network topology.
• Routing protocols function through either
• distributed computing model (distance
vector)
• parallel computing model (link state)
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15. Routing Protocols
• Distance Vector Routing Protocols
• RIP is the main laible to choice the best way to
transmit data from A to B
• Each node sends its routing table (dest,
distance) to all neighbors every 30 seconds
• Lowest distances are updated with the
neighbor as next hop
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16. Routing Protocols
• Link State Routing Protocols
• Each router re-computes the routing
table in parallel using the common link
state database
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17. A
20
10
4
10
40
5
6
10
15
10
5
B
5
5
45
R1 R4
R2
R3
R6
R7
R5
R8
Path Selection
Minimum time to transmit data from A to B is 39 units 17

18. A
20
10
4
10
40
5
6
15
10
5
B
5
5
45
R1 R4
R2
R3
R6
R7
R5
R8
Dynamic Path Adjustment
If R5 – R7 breaks, minimum cost path from A to B is
Now 51 units
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19. Thank you
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