This document discusses packet forwarding and delivery in computer networks. It describes two types of forwarding - destination address-based forwarding for connectionless protocols like IP, and label-based forwarding for connection-oriented protocols using IP. Common forwarding techniques include next-hop, network-specific, host-specific, and default methods. The document also covers forwarding with classful and classless addressing, including examples, as well as techniques like address aggregation and longest mask matching to reduce routing table sizes.

1. Network Layer Part II
Computer Networks
Tutun Juhana
Telecommunication Engineering
School of Electrical Engineering & Informatics
Institut Teknologi Bandung
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2. DELIVERY AND FORWARDING
OF IP PACKETS

3. Direct Delivery
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4. Indirect Delivery
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5. Forwarding
• Forwarding means to place the packet in its
route to its destination
– to deliver the packet to the next hop (which can be
the final destination or the intermediate connecting
device)
• Two kinds of forwarding
1. The destination address –based forwarding (when
IP is used as a connectionless protocol)
2. Label-based forwarding (when the IP is used as a
connection-oriented protocol)
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6. FORWARDING BASED ON
DESTINATION ADDRESS
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7. Forwarding Techniques
1. Next-Hop Method
2. Network-Specific Method
3. Host-Specific Method
4. Default Method
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To make the size of the routing table manageable

8. Next-Hop Method
• The routing table holds only the address of
the next hop instead of information about
the complete route
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9. Network-Specific Method
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10. Host-Specific Method
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11. Default Method
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12. FORWARDING WITH
CLASSFUL ADDRESSING
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13. Forwarding without Subnetting
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15. • Example 6.2
Router R1 in Figure 6.8 receives a packet with destination address
192.16.7.14. Show how the packet is forwarded
Solution
The destination address in binary is 11000000 00010000 00000111
00001110. A copy of the address is shifted 28 bits to the right. The
result is 00000000 00000000 00000000 00001100 or
12. The destination network is class C. The network address is
extracted by masking off the leftmost 24 bits of the destination
address; the result is 192.16.7.0. The table for Class C is searched.
The network address is found in the first row. The next-hop address
111.15.17.32. and the interface m0 are passed to ARP
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17. Forwarding with Subnetting
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19. Forwarding with Classless Addressing
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23. Address Aggregation
• In classful addressing, there is only one
entry in the routing table for each site
outside the organization
• In classless addressing, it is likely that the
number of routing table entries will
increase  The increased size of the table
results in an increase in the amount of
time needed to search the table  to
alleviate the problem, the idea of address
aggregation was designed 23

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25. Longest Mask Matching
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The routing table is sorted
from the longest mask to the
shortest mask
Packet arrives with
dest. add.140.24.7.200
By longest mask
matching
correctly routed
to Organization 4

26. STRUCTURE OF A ROUTER
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27. Components
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performs the functions of the network layer

28. Switching Fabrics
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