1. Chapter 4-2 IP address

2. Chapter 4: Network Layer
4. 1 Introduction
4.2 Virtual circuit and datagram networks
4.3 What’s inside a router
4.4 IP: Internet Protocol
Datagram format
IPv4 addressing
ICMP
IPv6
4.5 Routing algorithms
Link state
Distance Vector
Hierarchical routing
4.6 Routing in the Internet
RIP
OSPF
BGP
4.7 Broadcast and multicast routing
IP address 2

3. The Internet Network layer
Host, router network layer functions:
Routing protocols
path selection
RIP, OSPF, BGP
Transport layer: TCP, UDP
IP protocol
addressing conventions
datagram format
packet handling conventions
Network
layer
forwarding
table
ICMP protocol
error reporting
router “signaling”
Link layer
physical layer
Computer network-Link Layer and LANs
IP address 3 3

4. Objectives Concept of IP Address Class of IP Address
Reserved and Private IP Address
Network Mask and Subnetting
VLSM and CIDR
IP address

5. IP Address
Each computer in a TCP/IP network must be given a unique identifier, or IP address. An IP address is a 32-bit sequence of 1s and 0s.
IP address

6. Representation of IP Address
To make the IP address easier to use, the address is usually written as four decimal numbers separated by periods
IP address

7. Structure of IP Address

8. IP地址的类别（Class of IP Address）

9. Class A
Address Range:1-126(127 Reserved)
IP address

10. Class B
Address Range:
IP address

11. Class C
Address Range:
IP address

12. Address Allocating Allocate A class IP：(国际网络信息中心NIC)
Allocate B class IP ：InterNIC、APNIC、ENIC
Allocate C class IP (国家或地区的NIC)
IP address

13. Reserved Address
Certain host addresses are reserved and cannot be assigned to
devices on a network.
An IP address that has binary 0s in all host bit positions is reserved
for the network address.
An IP address that has binary 1s in all host bit positions is reserved
for the broadcast address.
An IP address that has binary 0s in all bit positions is reserved for default
route ，
An IP address that has binary 1s in all bit positions is reserved for flood broadcast
IP address

14. Private IP Address
Private IP addresses are another solution to the problem of the impending exhaustion of public IP addresses.
Private IP addresses are not routed on the Internet backbone.
IP address

15. Exercise: IP Address Classes
Network
Host
IP address

16. IP Address Classes Exercise Answers
Network
Host A B C
Layer 2 of 2:
Purpose: This answers to the exercise are given in the figure.
Note: Students can also find the answers to this exercise in the “Answers” appendix. C B
Nonexistent
IP address

17. Network Mask Class A：255.0.0.0 classB：255.255.0.0
class C：
IP address

18. Function of Network Mask 
Network ID
IP address

19. Subnetting
To efficiently manage a limited supply of IP addresses, all classes can be subdivided into smaller subnetworks.
IP address

20. Reasons for Subnetting
Provides addressing flexibility Provides
Broadcast Containment
Low-level security on the LAN
IP address

21. Introduction to Subnetting
Host bits must are reassigned (or “borrowed”) as network bits.
3 bits borrowed allows 23-2 or 6 subnets
5 bits borrowed allows 25-2 or 30 subnets
IP address
12 bits borrowed allows or 4094 subnets

22. Introduction to Subnetting
不考虑子网
Net id
Host id
Net mask
Net id
Host id
考虑子网化
Net mask
Net id
Subnet id
Host id
Extended net id
IP address

23. Comparison between decimal and binary
IP address

24. E.g1 Two Bits Subnetting for Class C
Subnet range
~ ~62
~ ~127
~ ~191
~ ~255
IP address

25. Number of Usable Subnets and Hosts
(2 power of borrowed bits)–2
usable hosts=
(2 power of remaining host bits)–2
IP address

26. Summary of Class C Subnetting
IP address

27. Written Exercise: Subnet Masks
Address
Subnet Mask
Class
Subnet
IP address

28. Subnet Mask Exercise Answers
Address
Subnet Mask
Class
Subnet B A
Layer 2 of 2:
Purpose: This answers to the exercise are given in the figure.
Note: Students can also find the answers to this exercise in the “Answers” appendix. A
IP address

29. Broadcast Addresses Address Subnet Mask Class Subnet Broadcast
IP address

30. Broadcast Addresses Exercise Answers
Subnet Mask
Class
Subnet
Broadcast C A B
Layer 2 of 2:
Purpose: This answers to the exercise are given in the figure.
Note: Students can also find the answers to this exercise in the “Answers” appendix. B
IP address

31. Subnets IP address: What’s a subnet ? subnet part (high order bits)
host part (low order bits)
What’s a subnet ?
device interfaces with same subnet part of IP address
can physically reach each other without intervening router
subnet
network consisting of 3 subnets
IP address 31

32. Subnets
/24
/24
/24
Recipe
To determine the subnets, detach each interface from its host or router, creating islands of isolated networks. Each isolated network is called a subnet.
Subnet mask: /24
IP address 32

33. Subnets
How many?
IP address 33

34. IP addressing: CIDR CIDR: Classless InterDomain Routing
subnet portion of address of arbitrary length
address format: a.b.c.d/x, where x is # bits in subnet portion of address
subnet
part
host
/23
IP address 34

35. Subnet Programming 30 hosts per subnet Class C address: 201.222.5.0
Other
subnets
30 hosts per subnet
Class C address:
IP address

36. Variable-Length Subnet MaskHQ
/16
IP address

37. Variable-Length Subnet Mask
/24 HQ HQ
/16
/24
IP address

38. Variable-Length Subnet Mask
/27 A
/24
/27 B HQ HQ
/16
/24
/27 C
Subnet /24 is divided into smaller subnets:
Subnet with one mask at first (/27)
IP address

39. Variable-Length Subnet Mask
/27
/30 A
/24
/27
/30 B HQ HQ
/16
/27
/24 C
/30
Subnet with one mask at first (/27)
Further subnet one of these subnets not used elsewhere (/30)
IP address

40. Calculating VLSMs
Subnetted Address: /20 In Binary
IP address

41. Calculating VLSMs
Subnetted Address: /20 In Binary
VLSM Address: /26 In Binary
IP address

42. Calculating VLSMs
Subnetted Address: /20 In Binary
VLSM Address: /26 In Binary
1st subnet: 1 1 1 1 . 1 . 1 . =
/26
Network
Subnet
VLSM subnet
Host
IP address

43. Calculating VLSMs
Subnetted Address: /20 In Binary
VLSM Address: /26 In Binary
1st subnet: 1 1 1 1 . 1 . 1 . =
/26
2nd subnet: 1 7 2 . 16 . 1 . 1 =
/26
3rd subnet: 1 7 2 . 16 . 1 . 1 =
/26
4th subnet: 1 7 2 . 16 . 1 . 1 1 =
/26
5th subnet: 1 7 2 . 16 . 1 1 . =
/26
Network
Subnet
VLSM Subnet
Host
IP address

44. Exercise:Design Network Using VLSM
Derived from the /20 Subnet
(62 Hosts)
(62 Hosts)
(62 Hosts)
(62 Hosts)
IP address

45. Exercise Answer Derived from the 172.16.32.0/20 Subnet 172.16.32.0/26
/30
/26
/30
/30
/26
/30
/26
Derived from the
/26 Subnet
30-Bit Mask
(2 Hosts)
26-Bit Mask
(62 Hosts)
IP address

46. Again
IP address

47. Net-id and host-id A class host-id 8 bit B class 16 bit C class 1
A class
B class
C class 1
D class
Multicast address
E class
reserved
IP address 47

48. range Class network No.s from to hostnumber
IP address 48

49. Five classes IP address
1/2
1/4
1/8
1/16
1/32 6
IP address
IP地址与网络层 49

50. Some special IP address50

51. Available? Which class?
IP address 51

52. 参考：Internet的IP地址和AS号码管理结构
ARIN
RIPE NCC
APNIC
(Possible future RIRs)
ICANN ASO (The Address Supporting Organization)
NIR
LIP
ISP EU
CNNIC
End Users
Internet Service Providers
Local Internet Registries
National Internet Registries
CERnetNIC
USTCNIC
IP address 52

53. More about IP addressing
DHCP
CIDR/VLSM
NAT
IP address

54. IP addresses: how to get one?
Q: How does a host get IP address?
hard-coded by system admin in a file
Windows: control-panel->network->configuration->tcp/ip->properties
UNIX: /etc/rc.config
DHCP: Dynamic Host Configuration Protocol: dynamically get address from as server
“plug-and-play”
IP address 54

55. DHCP: Dynamic Host Configuration Protocol
Goal: allow host to dynamically obtain its IP address from network server when it joins network
Can renew its lease on address in use
Allows reuse of addresses (only hold address while connected an “on”)
Support for mobile users who want to join network (more shortly)
DHCP overview:
host broadcasts “DHCP discover” msg
DHCP server responds with “DHCP offer” msg
host requests IP address: “DHCP request” msg
DHCP server sends address: “DHCP ack” msg
IP address
Network Layer 55

56. DHCP client-server scenario
server B
arriving DHCP
client needs
address in this
network E
IP address 56

57. DHCP client-server scenario
DHCP server:
arriving
client
DHCP discover
src : , 68
dest.: ,67
yiaddr:
transaction ID: 654
DHCP offer
src: , 67
dest: , 68
yiaddrr:
transaction ID: 654
Lifetime: 3600 secs
DHCP request
src: , 68
dest:: , 67
yiaddrr:
transaction ID: 655
Lifetime: 3600 secs
time
DHCP ACK
src: , 67
dest: , 68
yiaddrr:
transaction ID: 655
Lifetime: 3600 secs
IP address 57

58. IP addresses: how to get one?
Q: How does network get subnet part of IP addr?
A: gets allocated portion of its provider ISP’s address space
ISP's block /20
Organization /23
Organization /23
Organization /23
… … ….
Organization /23
IP address 58

59. Hierarchical addressing: route aggregation
Hierarchical addressing allows efficient advertisement of routing
information:
Organization 0
/23
Organization 1
/23
“Send me anything
with addresses
beginning
/20”
Organization 2
/23 .
Fly-By-Night-ISP .
Internet
Organization 7
/23
“Send me anything
with addresses
beginning
/16”
ISPs-R-Us
IP address 59

60. Hierarchical addressing: more specific routes
ISPs-R-Us has a more specific route to Organization 1
Organization 0
/23
“Send me anything
with addresses
beginning
/20”
Organization 2
/23 .
Fly-By-Night-ISP .
Internet
Organization 7
/23
“Send me anything
with addresses
beginning /16
or /23”
ISPs-R-Us
Organization 1
/23
IP address 60

61. NAT: Network Address Translation
rest of
Internet
local network
(e.g., home network)
10.0.0/24
All datagrams leaving local
network have same single source NAT IP address: ,
different source port numbers
Datagrams with source or
destination in this network
have /24 address for
source, destination (as usual)
IP address 61

62. NAT: Network Address Translation
Motivation: local network uses just one IP address as far as outside world is concerned:
range of addresses not needed from ISP: just one IP address for all devices
can change addresses of devices in local network without notifying outside world
can change ISP without changing addresses of devices in local network
devices inside local net not explicitly addressable, visible by outside world (a security plus).
IP address 62

63. NAT: Network Address Translation
Implementation: NAT router must: outgoing datagrams: replace (source IP address, port #) of every outgoing datagram to (NAT IP address, new port #)
. . . remote clients/servers will respond using (NAT IP address, new port #) as destination addr.
remember (in NAT translation table) every (source IP address, port #) to (NAT IP address, new port #) translation pair
incoming datagrams: replace (NAT IP address, new port #) in dest fields of every incoming datagram with corresponding (source IP address, port #) stored in NAT table
IP address 63

64. NAT: Network Address Translation
NAT translation table
WAN side addr LAN side addr
1: host
sends datagram to
, 80
2: NAT router
changes datagram
source addr from
, 3345 to
, 5001,
updates table
, , 3345
…… ……
S: , 3345
D: , 80 1
S: , 80
D: , 3345 4
S: , 5001
D: , 80 2
S: , 80
D: , 5001 3
4: NAT router
changes datagram
dest addr from
, 5001 to , 3345
3: Reply arrives
dest. address:
, 5001
IP address 64

65. NAT: Network Address Translation
16-bit port-number field:
60,000 simultaneous connections with a single LAN-side address!
NAT is controversial:
routers should only process up to layer 3
violates end-to-end argument
NAT possibility must be taken into account by app designers, eg, P2P applications
address shortage should instead be solved by IPv6
IP address 65

66. NAT traversal problem
client wants to connect to server with address
server address local to LAN (client can’t use it as destination addr)
only one externally visible NATted address:
solution 1: statically configure NAT to forward incoming connection requests at given port to server
e.g., ( , port 2500) always forwarded to port 25000
Client ?
NAT
router
IP address 66

67. NAT traversal problem
solution 2: Universal Plug and Play (UPnP) Internet Gateway Device (IGD) Protocol. Allows NATted host to:
learn public IP address ( )
add/remove port mappings (with lease times)
i.e., automate static NAT port map configuration
IGD
NAT
router
IP address 67

68. NAT traversal problem solution 3: relaying (used in Skype)
NATed client establishes connection to relay
External client connects to relay
relay bridges packets between to connections
2. connection to
relay initiated
by client
NAT
router
1. connection to
relay initiated
by NATted host
3. relaying
established
Client
IP address 68

69. next 4. 1 Introduction 4.2 Virtual circuit and datagram networks
4.3 What’s inside a router
4.4 IP: Internet Protocol
Datagram format
IPv4 addressing
ICMP
IPv6
4.5 Routing algorithms
Link state
Distance Vector
Hierarchical routing
4.6 Routing in the Internet
RIP
OSPF
BGP
4.7 Broadcast and multicast routing
IP address 69