1. Introduction to Internetworking

2. 2 The IP Addressing Scheme (IPv4) 146.186.15.17 (psu.edu) Dotted Decimal Notation: A notation more convenient for humans – Dividing 32 bits into four 8-bit sections (4 bytes) – Value range of a byte: 0 (all 0) -- 255 (all 1)

3. 3 The IP Addressing Scheme (IPv4) IP address is divided into two parts – A prefix: network identifier Coordinated globally. – Internet Corporation for Assigned Names and Numbers (ICANN) – A suffix: host identifier Assigned locally (within each network). 146.186.15.17

4. 4 Original Classes of IP Addresses The original classful IP addressing divided the IP address space into three primary classes – Determined by the first four bits. – Each class has a different size prefix and suffix

5. 5 Division of the Address Space The address space has unequal sizes – Class A contains half of all addresses Major ISPs, large organizations, government, MIT, etc. – Each network in Class C only has 256 available addresses. Small organizations http://www.iana.org/assignments/ipv4-address- space/ http://www.iana.org/assignments/ipv4-address- space/

6. Exercise Which class does each of these addresses belong to? 1st byte Class 0-127 A 128-191 B 192-223 C 224-239 D 240-255 E

7. 7 Subnet and Classless Addressing As the Internet grew, the original classful addressing scheme became a limitation – Everyone wants a class A or class B address – Address are often wasted

8. 8 Subnet and Classless Addressing Allow the division between prefix and suffix to occur on an arbitrary bit boundary – initially used within large organizations – Classless addressing extended the approach to all Internet

9. 9 Specifying Network Boundary: Address Masks A 32-bit value that specifies the exact boundary between the network prefix and the host suffix – All 1s for network prefix and all 0s for host suffix. – Examples: 11111111 11111111 00000000 00000000 (255.255.0.0) 11111111 11111111 11111111 00000000 (255.255.255.0) 11111111 11111111 10000000 00000000 (255.255.128.0)

10. 10 Address Masks When forwarding an IP packet, hosts and routers need to determine if an IP address (D) belongs to a specific network with prefix (N) and mask (M): N == (D & M) NetworkMaskNext Hop 128.10.0.0255.255.0.0Router 2 ……

11. 11 Address Masks Example: – Destination IP address: 128.10.2.3 NetworkMaskNext Hop 128.10.0.0255.255.0.0Router 2 …… 10000000 00001010 00000010 00000011 128.10.2.3 = 11111111 11111111 00000000 00000000 255.255.0.0 = & = 10000000 00001010 00000000 00000000 128.10.0.0 = N == (D & M)

12. 12 Exercise: Masks with Arbitrary Boundary Given the address mask: 11111111 11111111 10000000 00000000 = 255.255.128.0 Which are the network prefix (in dotted decimal notation) of the following destination addresses? a)10000000 00001010 00000010 00000011 = 128.10.2.3 b)10000000 00001010 10000010 00000011 = 128.10.130.3

13. 13 CIDR Notation Classless Inter-Domain Routing (CIDR) – An easy way to specify a mask ddd.ddd.ddd.ddd/m – ddd.ddd.ddd.ddd: IP address. – m: the number of one bits in the mask 128.211.0.16/28 – A mask of 28 bits

14. 14 CIDR Prefix and Host Addresses Once an ISP assigns a customer a CIDR prefix, the customer can assign host addresses for its network users. – 128.211.0.16/28

15. 15 Special (Reserved) IP Addresses (1) Network address: host address 0 – A network address should never appear as the destination address in a packet

16. 16 Special (Reserved) IP Addresses (2) Directed broadcast address: – Adding a suffix that consists of all 1 bits to the network prefix

17. CIDR Exercise 1 Is the CIDR prefix 1.2.3.4/29 valid? Why or why not?

18. CIDR Exercise 2 Suppose you are an ISP that owns the 192.10.6.0/24 (C class) IPv4 address block. Show the CIDR allocation you would use to allocate address blocks to three customers who need addresses for 100, 60, and 60 computers respectively.