1. Unit 2: IP addressing (Contd.). Delivery and routing of packets
Special IP addresses
Private networks: , ,
Subnetting and subnet masks
Supernetting and CIDR (Classless Interdomain Routing)
Delivery and routing of packets
Routing table organizations
Dynamic v.s. static routing

2. Network addresses: Network ID + All 0’s hostid is commonly referred to as a network address

3. Direct broadcast address

4. Limited broadcast address

5. Provide initial configuration information
“this” host on “this” network address
Provide initial configuration information

6. Specific host on this network

7. Loopback address

8. Figure subnetting

10. Subnet mask

11. Logical AND

12. Special addresses in subnetting
These can never be assigned to a host
Restrictions can be relaxed so that these numbers may be assigned to subnets

13. Example: An organization with a class B address needs at least 12 subnetworks.

14. Range of addresses in the example

15. Subnetworks in the example

16. = 0
X.Y.Z.0
= 64
X.Y.Z.64
= 128
X.Y.Z. 128
= 192
X.Y.Z. 192
=224
X.Y.Z. 224
And the last two subnets must have 11 as the leading 2 bits in the 4th byte. The 3rd bit can varies between 0 and 1. Therefore the last two subnets have addresses of the following format in the 4th byte: 110xxxxx and 111xxxxx
So the last byte can be 00xxxxxx, 01xxxxxx, 10xxxxxx, 11xxxxxx. 3 of these can be chosen to label the first 3 subnets. Let say we pick the first 3
= so the first mask uses the first 2 bits of the 4th byte as the subnet ID
= so the second mask uses the first 3 bits of the 4th byte as the subnet ID

17. Supernetwork

18. Supernet mask

19. Two ways of defining a supernet
Example of supernetting. Which address belong to supernet X.Y.32.0?

20. Classless Interdomain Routing (CIDR)

21. Same network/subnet/ supernet address
Direct and Indirect delivery
Same network/subnet/ supernet address

22. Next-hop routing

23. Network-specific routing

24. Host-specific routing

25. Default routing

26. Routing tables: static v.s. dynamic
Routing module and routing table
Fields in routing table
Routing tables: static v.s. dynamic

27. For each entry in the routing table
Routing Module
Receive: an IP packet
For each entry in the routing table
Apply the mask to packet destination address
If (the result matches the value in the destination field)
If (the G flag is absent)
Use packet destination address as next hop address
Send packet to fragmentation module with next hop address
Return
If no match is found, send an ICMP error message

28. An example network.

29. Routing Table for R1 in the example
Mask
Destination
Next Hop F.
R.C. U. I. - U m0 m2     m1      
 UGH  0
 m0 UG