Published on March 12, 2014
Network Layer Part II Computer Networks Tutun Juhana Telecommunication Engineering School of Electrical Engineering & Informatics Institut Teknologi Bandung 5
DELIVERY AND FORWARDING OF IP PACKETS
Direct Delivery 3
Indirect Delivery 4
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) 5
FORWARDING BASED ON DESTINATION ADDRESS 6
Forwarding Techniques 1. Next-Hop Method 2. Network-Specific Method 3. Host-Specific Method 4. Default Method 7 To make the size of the routing table manageable
Next-Hop Method • The routing table holds only the address of the next hop instead of information about the complete route 8
Network-Specific Method 9
Host-Specific Method 10
Default Method 11
FORWARDING WITH CLASSFUL ADDRESSING 12
Forwarding without Subnetting 13
• Example 6.2 Router R1 in Figure 6.8 receives a packet with destination address 220.127.116.11. 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 18.104.22.168. The table for Class C is searched. The network address is found in the first row. The next-hop address 22.214.171.124. and the interface m0 are passed to ARP 15
Forwarding with Subnetting 17
Forwarding with Classless Addressing 19
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
Longest Mask Matching 25 The routing table is sorted from the longest mask to the shortest mask Packet arrives with dest. add.126.96.36.199 By longest mask matching correctly routed to Organization 4
STRUCTURE OF A ROUTER 26
Components 27 performs the functions of the network layer
Switching Fabrics 28
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