Network Layer, and Logical Addresses Chapter 18 COMP 3270 Computer Networks Computing Science Thompson Rivers University

Host-to-host delivery of packets Network Layer ☺ Main responsibility? Host-to-host delivery of packets

Position of the network layer Sour port number Source address Source & destination port number Logical destination address TCP, UDP IGMP Source address Logical destination address IP ARP RIP, OSPF Physical destination address Interface Ethernet, Token ring, W-LAN, FDDI, …

Network layer duties A view of a global Routing and Network over many different physical networks Routing and forwarding Globally unique addressing scheme

1. INTERNETWORKING Topics discussed in this section: In this section, we discuss internetworking, connecting networks together to make an internetwork or an internet. ☺ What is an internetwork? Review of the IP packet forwarding mechanism. Topics discussed in this section: Need for Network Layer Internet as a Datagram Network Internet as a Connectionless Network

☺ How do A and D exchange data? Need for Network Layer Links between two hosts LAN ☺ How do A and D exchange data?

Host-to-host delivery Each data link handles its own network interface only; There is no interaction between them even though they are in the same switch system S1. Host-to-host delivery ☺ How to decide the next hop for the traffic from A to D, through f2 or f3? LAN Data link layer; Physical layer

S1 is connected to S3 through f3. It decides the next hop (the IP address of S3 and the interface f3) f1 f3 f1 f2 LAN

Internet as a Datagram Network The datagram approach to packet switching, and connectionless service. Telecommunications networks ATM, FR, X.25 The Internet

There is no specific route established from the source to the destination. They can arrive in a different order; Reordering does not occur in the network layer. ☺ Then in which layer?

☺ How many different types of address are used in the Internet 5 layers?

4. IPv4 ADDRESSES Topics discussed in this section: An IPv4 address is a 32-bit address that uniquely and universally defines the connection of a device (for example, a computer or a router) to the Internet. Topics discussed in this section: Address Space Notations Classful Addressing DHCP

Address Space An IPv4 address is 32 bits long. The address space of IPv4 is 232 or 4,294,967,296. The public IPv4 addresses are unique and universal.

Notations

Dotted-decimal notation & binary notation

Example: Change the following IPv4 addresses from binary notation to dotted-decimal notation. Solution:

Example: Change the following IPv4 addresses from dotted-decimal notation to binary notation. Solution:

Example: Find the error, if any, in the following IPv4 addresses.

Addressing An IP address consists of Netid (or also called address block id) + Hostid. A netid represent a logical IP network. Two addressing schemes. classful addressing classless addressing

Classful Addressing In classful addressing, the address space is divided into five classes: A, B, C, D, and E.

Finding the classes in binary and dotted-decimal notation An IP address consists of Netid + Hostid. A netid represent a logical IP network. ☺ How to get the netid to which an IP address belongs?

Example: Find the class of each address. b. 11000001 10000011 00011011 11111111 c. 14.23.120.8 d. 129.5.15.111

Number of blocks and block size in classful IPv4 addressing 3 bytes In classful addressing, classful address blocks are allocated to IP networks (logical networks), and a large part of the available addresses were wasted.

Default netmasks for classful addressing ☺ Given an address, how to find the address block to which the address belongs ??? ☺ IP address BIT_AND netmask = ??? E.g., 198.162.21.132 & 255.255.255.0 = 198.162.21.0 198.162.21.0 /24 represents the address block of addresses from 198.162.21.0 to 198.162.21.255.

Classless Addressing In classless addressing, the netids do not have to use 1B, 2B, or 3B. Any number of bits can be used for netids. ☺ How? /n and netmask Classless addressing is used in IP packet forwarding and routing.

DHCP (Dynamic Host Configuration Protocol) DHCP provides static and dynamic address allocation that can be manual or automatic. ☺ DHCP server must be in the same physical network? ☺ There could be two DHCP servers in the same physical network? ☺ What information is assigned by DHCP?

An IPv6 address is 128 bits long. IPv6 ADDRESSES IPv6 is a next generation IP. Despite all short-term solutions, address depletion is still a long-term problem for the IPv4 Internet. This and other problems in the IPv4 protocol itself have been the motivation for IPv6. An IPv6 address is 128 bits long.