1 TCOM 509 – Internet Protocols (TCP/IP) Lecture 02_b Instructor: Dr. Li-Chuan Chen Date: 09/08/2003 Based in part upon slides of Prof. J. Kurose (U Mass), Prof. B. Yener (Rensselaer Polytechnic Institute)

2 Outline  Chapter 4 – Classful Internet Address  Chapter 5  Chapter 6  Chapter 7

3 Flat vs. Hierarchical Addresses  Flat addresses no structure in them to facilitate scalable routing. e.g., Ethernet addresses  Hierarchical addresses Network part (netid) and host part (hostid). Helps identify direct or indirectly connected nodes. Efficient for routers to send packets. netidhostid

4 Internet Addresses  Classful Internet Address Class A Class B Class C Class D Class E  Goal: Allows any computer to communicate with any other computer in a global communication network.

5 IP Address Formats Class A netid hostid bits netidhostid bits Class B: netidhostid bits Class C: Multicast Group addresses bits Class D: Class E: Reserved for future uses bits

6 IP Addresses  IP Address 32-bit global internet address Network part (netid) and host part (hostid) Class D addresses are for multicasting (packet is delivered to a subset of hosts). Unicast: a packet is delivered to a single host. Reserved addresses –All 0 (binary ) is reserved –All 1s broadcast address (limited broadcast) can be used in start-up to get its IP address. –Loopback 127.x.x.x –hostid 0 refers to the network itself, not individual host. –hostid consist of all 1s is for directed broadcast to all hosts on the network.

7 IP Addresses – Class A  Class A – small networks with large number of hosts. Starts with binary 0, followed by 7-bit Network field, and then 24-bit Host field netid of 127 (binary ) is reserved for loopback Only 2 7 – 2 = 126 octets left, range 1.x.x.x to 126.x.x.x Covers 50% (2 31 ) of the entire IP address space 2 24 for each Class A network. Millions of Class A addresses are wasted netid hostid bits

8 IP Addresses - Class B  Class B – intermediate size networks. Starts with 10, followed by 14-bit Network field, and then 16-bit Host field Range 128.x.x.x to 191.x.x.x 2 14 = 16,384 class B addresses Covers 25% (2 30 ) of the entire IP address space 2 16 for each Class A network. Many of Class B addresses are wasted netidhostid bits

9 IP Addresses - Class C  Class C – large networks with small number of hosts. Starts with 110, followed by 21-bit Network field, and then 8-bit Host field Range 192.x.x.x to 223.x.x.x 2 21 = 2,097,152 networks, 2 8 = 256 hosts in each network Covers 12.5% (2 29 ) of the entire IP address space netidhostid bits

10 IP Addresses - Class D, E  Class D – Multicasting Starts with 1110, followed by 28-bit multicast group address multicast groups Covers 6.25% (2 28 ) of the entire IP address space Multicast Group addresses bits  Class E – Reserved Starts with 1111, followed by 28-bit multicast group address. Covers 6.25% (2 28 ) of the entire IP address space Reserved for future uses bits

11 Dotted Decimal Notation  IP address (32 bits) can be written as four decimal integers separated by decimal points.  IP address is divided into 4 parts, convert each part from binary to its equivalent decimal integer. Example  Binary:  Dotted Decimal:

12 IP Addressing  IP address: 32-bit identifier for host, router interface  Interface: connection between host, router and physical link router’s typically have multiple interfaces host may have multiple interfaces IP addresses associated with interface, not host, router  Hosts in the same network have same network ID =

13 IP Address ClassRange A B C D E Lowest Address Highest Address Some values are reserved.

14 Reserved Addresses  Loopback: test for inter-process communication on the local host.  Hostid “this” (0s), “all” (1s) All 0sHostNetworkAll 1s All 0s All 1s 127anything This host Host on this network Limited broadcast Directed broadcast Loopback

15 IP Addresses - Cons IP Address Cons:  IP address is associated with network connection, not to the host.  Difficult and time consuming to change network addresses. e.g., when class C network grows to > 255 (2 8 ) hosts.  If a host has multiple addresses (multi-homed host), knowing one address may not be sufficient to reach it when this particular path to that address is down.  Nearly all allocated Need next-generation IP protocol - IPv6

16 Subnet and Supernet Extensions  Classful addressing inefficient: Everyone wants class B addresses  Can we split class A, B addresses spaces and accommodate more networks ? Need another level of hierarchy. Defined by subnet mask, specifies the sets of bits belonging to the network address and host address respectively.  Supernetting or classless addressing allows prefix and suffix to occur at an arbitrary point. NetworkHost Boundary is flexible, will cover in details later

17 Network Byte Order  Use standard byte ordering (Big Endian) within protocol fields so all hosts interpret the IP addresses the same way.  Big Endian: integers are sent with the most significant byte first.  Little Endian: integers are sent with the least significant byte first.

18 Chapter 4 Summary IP address uses 32-bit binary number. Unique IP address per interface. Provision for broadcast, multicast, loopback addresses. Classful (A,B,C) address allocation not efficient. Hierarchical addresses are more efficient with smaller routing tables. Extended address scheme: subnet and supernet addressing improved address allocation efficiency (cover later).

19 Homework 1 ChaptersProblems 27 41, 7 Due Monday 09/15/2003