Internetworking: Concepts, Architecture, and Protocols Chapter 20 Internetworking: Concepts, Architecture, and Protocols © Bobby Hoggard, Department of Computer Science, East Carolina University These slides may not be used or duplicated without permission

Extending a Network A computer in a network can only communicate with other computers physically attached to the same network Bridges (and other extension techniques) are used to connect networks of the same type; they cannot connect different types of networks Ethernet Ethernet Token Ring

Extending a Network Each network protocol has its own packet format and addressing scheme To change from one to another, a translator is needed --- bridges do not do this Ethernet 802.11 Wi-Fi type payload src addr dest ctrl dur AP addr src dest seq payload 14 bytes 46 - 1500 bytes 24 bytes 0 - 2312 bytes

Internetworking Uses hardware and software to join together networks that are of different types Additional hardware is used to interconnect the physical networks Software on the attached computers provides universal service, and gives the illusion that the whole system is one large homogeneous network Internetworks that are owned by private organizations and designed for use by only their employees is an intranet The term Internet is used to refer to the global Internet

Routers Routers connect networks that are of different types, so they operate as one large network Hosts (devices connected to the routers) do not know whether they are connected to a single LAN segment or a large network connected by routers A router can connect two LANs, two WANs, or a LAN and a WAN Routers contain a processor, memory, and an I/O interface for each network to which it connects Network 1 interface processor Network 2 interface memory unit Network 3 interface

Routers Contain Protocol Software Routers must rewrite a packet received from one network, into the format required by the destination network, and thus must understand the protocols from both networks Ethernet 802.11 Wi-Fi A X type Hello dest X src A type Hello src A dest X ctrl dur AP 3 src A dest X seq Hello ctrl dur AP 3 src A dest X seq Hello

A Virtual Network Routers create the illusion of a single, seemless communication system Each computer is assigned an address, and any computer can send packets to any other Internet protocol software hides the details of physical network connections, physical addresses and routing information

A Virtual Network Routers create the illusion of a single, seemless communication system Each computer is assigned an address, and any computer can send packets to any other Internet protocol software hides the details of physical network connections, physical addresses and routing information Net 2 Net 1 Net 4 Net 3 Net 5

Chapter 21 Internet Addressing © Bobby Hoggard, Department of Computer Science, East Carolina University These slides may not be used or duplicated without permission

Universal Addressing To give the appearance of a universal network, all host computers must use a universal addressing scheme that's independent of the underlying hardware MAC addresses cannot be used since the Internet consists of multiple network technologies, and each network technology can define its own MAC address IPv4 uses 32-bit addresses and IPv6 uses 128-bit addresses Transition to IPv6 is necessary because, although IPv4 allows for millions of networks, the Internet is growing exponentially and all IPv4 addresses are running out

IP Address Hierarchy IP addresses are split into two parts: prefix or network address – identifies the physical network to which a host is attached (i.e. each network is assigned a unique number) suffix or host address – identifies a specific computer on the network network address host address Uniqueness is guaranteed because: network addresses are coordinated globally to ensure that no two networks have the same number host addresses are assigned by local network administrators, and they should ensure that no two computers in their network have the same suffix

IP Address Hierarchy Example: Consider three networks, numbered 1, 2, and 3. Notice how local admins have assigned some of the same suffixes, yet the overall addresses remain unique Network 2 Network 1 2 3 2 1 Network 3 1 5 2 2 1 1 1 3 3 5 3 2

Dotted Decimal Notation Although IPv4 addresses are 32-bit binary numbers, software uses dotted decimal notation to make it easier to read and understand Each byte of the 32-bit address is expressed as decimal value, and is separated by periods byte 1 byte 2 byte 3 byte 4 0000 0101 0000 1000 0000 0010 0000 0001 5 8 2 1 5 . 8 . 2 . 1

Dotted Decimal Notation The smallest value that can be expressed with one byte is 0000 0000 = 0 The largest value that can be expressed with one byte is 1111 1111 = 255 Thus, IP addresses range from 0.0.0.0 to 255.255.255.255 0000 0000 0000 0000 0000 0000 0000 0000 0 . 0 . 0 . 0 1111 1111 1111 1111 1111 1111 1111 1111 255 . 255 . 255 . 255

How Many Bits? How many bits are in the prefix (network), and how many are in the suffix (host)? A large number of bits in the prefix allows: A lot of networks Few devices in each network A large number of bits in the suffix allows: A lot of devices in each network Few networks network address host address network addr host address millions of values few hundred values few hundred values millions of values One single choice isn't sufficient – the Internet consists of a few large networks and many small networks

Original Classes of IPv4 Addresses Three classes were developed – which split the prefix/suffix after the 1st, 2nd, or 3rd byte Class A - splits after first byte Class B - splits after second byte Class C - splits after third byte Two more classes were developed for special purposes Class D - multicast: used to deliver a packet to all computers in a predefined multicast group; restricted to individual sites Class E - reserved for special purposes You can determine which class the address belongs to by analyzing the first 4 bits

Original Classes of IPv4 Addresses byte 2 Class A network host byte 1 byte 3 byte 4 Class B 1 network host Class C 1 network host Class D 1 multicast Class E 1 reserved (not assigned)