1. Chap 10 Routing and Addressing Andres, Wen-Yuan Liao Department of Computer Science and Engineering De Lin Institute of Technology andres@dlit.edu.tw http://www.cse.dlit.edu.tw/~andres

3. Importance of a Network Layer Identifiers Segmentation and autonomous systems Communication between separate networks Layer 3 network devices

4. Identifiers Move data through a set of networks (internetwork) Network layer: hierarchical addressing Unique addresses across network boundaries A method for finding a path MAC addresses: flat addressing

5. Segmentation and autonomous systems Multiple networks are necessary The growth in size of each network The growth in the number of networks Network segments (or just segments)

6. Communication between separate networks Internet is a collection of network segments Internet service providers (ISPs) offering services that tie together multiple network segment

7. Layer 3 network devices Routers are internetworking devices which operate at OSI Layer 3 Tie together, or interconnect, network segments or entire networks

8. Layer 3 network devices Routers make logical decisions regarding the best path on an internetwork and then direct packets Routing is sometimes referred to as Layer 3 switching

10. Path Determination Path determination Network layer addressing Layer 3 and computer mobility Comparing flat and hierarchical addressing

11. Path determination Routing the packet The process that the router uses to choose the next hop in the path for the packet to travel to its destination Make their decisions based on the traffic density and the speed of the link

13. Network layer addressing Network address The router uses the network address to identify the destination network of a packet within an internetwork. Host address

15. Layer 3 and computer mobility A MAC address can be compared to your name The network address to your mailing address

16. Comparing flat and hierarchical addressing A flat addressing scheme Assigns a device the next available address The postal system ZIP codes are a good example of hierarchical addressing

17. IP Addresses within the IP Header Network layer datagrams Network layer fields IP header source and destination fields IP address as a 32-bit binary number IP address component fields

23. The network number of an IP address identifies the network to which a device is attached The host portion of an IP address identifies the specific device on that network

25. IP Address Classes IP address classes IP addresses as decimal numbers

27. The first (leftmost) bit is always 0 First octet of its IP address: 0-126 A Class A IP address can have assigned up to 2 24 - 2 or 16,777,214, possible IP addresses Class A

28. Class B The first 2 bits: 10 First octet of its IP address:128 to 191 A Class B IP address can have assigned up to 2 16 - 2, or 65,534, possible IP addresses

29. Class C The first 3 bits: 110 First octet of its IP address:192 to 223 A Class C IP address can have assigned up to 2 8 - 2, or 254, possible IP addresses

31. Reserved Address Space Purposes for network IDs and broadcast addresses Network ID Network ID analogy Broadcast address analogy Hosts for classes of IP addresses

32. Purposes for network IDs and broadcast addresses An IP address that ends with binary 0s in all host bits is reserved for the network address The wire address Class A network: 113.0.0.0 Contain the host 113.1.2.3

34. Network & Host ID A network ID Enable a router to put a packet onto the appropriate network segment The host ID Help the router address the Layer 2 frame to the specific host on that network

37. Basics of Subnetting Classical IP Addressing Subnetwork Purpose for subnetting Subnet mask Boolean operations: AND, OR, and NOT Performing the AND function

38. Classical IP Addressing Network administrators sometimes need to divide networks into smaller networks Subnetworks Provide addressing flexibility Be simply referred to as subnet

39. Subnetwork Subnet addresses include The Class A, Class B, or Class C network portion A subnet field A host field To create a subnet address Borrows bits from the original host portion

44. Subnetwork The minimum number of bits that can be borrowed is 2 The maximum number of bits that can be borrowed can be any number that leaves at least 2 bits remaining, for the host number

46. Purpose for subnetting A primary reason for using subnets is to reduce the size of a broadcast domain

47. Subnet mask The subnet mask determines which part of an IP address is the network field and which part is the host field

49. Subnet Routers determine the destination network/subnet address Perform a logical AND using the destination host's IP address and the subnet mask The result will be the network/subnet address

51. Creating a Subnet Range of bits needed to create subnets Determining subnet mask size Computing subnet mask and IP address Computing hosts per subnetwork Boolean AND operation IP configuration on a network diagram Host/subnet schemes Private addresses

54. The subnet field always follows immediately after the network number

55. Example Class C address 197.15.22.131 Subnet mask of 255.255.255.224 224:11100000 Been extended by 3 bits: 27 bits The 131: the third usable host address in the subnet 197.15.22.128

56. Example The routers in the Internet (that don't know the subnet mask) will only worry about routing to the Class C network 197.15.22.0 The routers inside that network, knowing the subnet mask, will be looking at 27 bits to make a routing decision

58. Example Class B network:subnet mask of 255.255.240.0 The number 240 decimal is 11110000 4 bits for the subnet field.

59. Example Number - 0000 ~ 1111 (15) Sixteen subnets Cannot use subnet 0 (network address), and subnet 15 (1111) (broadcast address) Fourteen usable subnets (1-14)

60. Computing hosts per subnetwork Borrow 2 bits from the default 8 bit host field The total number of possible hosts: 64 (2 6 ) The number of usable host numbers would be reduced to 62

62. IP configuration on a network diagram When you configure routers, you must connect each interface to a different network segment Then each of these segments will become a separate subnet

65. Private addresses There are certain addresses in each class of IP address that are not assigned Private addresses might be used by hosts that use network address translation (NAT), or a proxy server, to connect to a public network

67. Summary Network addressing and best path selection Flat and hierarchical. Three classes of IP addresses Subnetworks or subnets Subnet masks