Layering and the TCP/IP protocol Suite The TCP/IP Protocol only contains 5 Layers in its networking Model The Layers Are Physical -> 1 in OSI Network Interface -> 2 in OSI Internet -> 3 in OSI (loosely) Transport -> 4 in OSI Application -> 5, 6, 7 in the OSI Model

Internet Protocol Addresses (IP) The IP standard (IPV4) states that each host on a network will contain a unique 32 bit number. This number is known as the IP address of the host. Both the Sender’s IP address and the Receivers IP address are sent in each packet over the internet.

IP Address Hierarchy Each IP is divided into two parts Network Number (prefix) Host ID (suffix) Prefix or network numbers are granted globally The hierarchy guarantees two important properties. Each computer can have a Unique ID Each suffix can be granted locally without global coordination.

IP address Classes Network numbers can be further divided into different classes. Choosing large prefixes provided large number of network numbers but small number of host ID’s Choosing small prefixes provided a small number of network numbers but a large number of Host IDs

IP address Classes (Continued) Designers compromised with providing different classes of numbers for each network. Depending on the class, determines the size of the network number (ID) The first four bits of an address determine the class. This determines how the address is divided into prefixes and suffixes.

IP address Classes (Continued) IP Classes are A, B and C (primary classes) D (used for multicasting) E (used for future use) Classes use octet boundaries A (the network number is the first octet of the address and the host ID is the last three octets) B (the network number is the first two octets and the host ID is the last two) C (the network number is the first three octets and the host ID is the last octet of the address)

IP address Classes (Continued) Classes can be determined from the address itself and there for are considered to be self identifying Most computer hardware can examine bits faster than comparing integers. The first four bits are extracted and compared to determine the class or network the address belongs. Speeds up routing of IP addresses by sorting traffic according to their intended network.

IP address Classes (Continued) Although difficult for us to understand, computers can distinguish the class of a network by examining the first four bits of an address

Dotted Notation Dotted notation is used to display the IP address for people. Binary numbers are translated into four numbers separated by a decimal point. Each number is called an octet and each number can range from 0 to 255.

Classes and Dotted Notation Determining the Network Class by examining the first octet of an IP Address Class A network ID, the first octet will range between 0 and 127 Class B network ID, the first octet will range between 128 to 191 Class C network ID, the first octet will range between 192 through 223

Classes and Dotted Notation (Continued) As you can see, each network class can be divided according To the value of the first octet

The Division of IP Addresses Class A Max number of Network IDs 128 Max Number of Hosts IDs per network 16777216 Class B Max number of Network IDs 16384 Max number of Hosts IDs per network 65536 Class C Max number of Network IDs 2097152 Max number of Host IDs per network 256

Authority for IP Addresses Internet Assigned Number Authority governs the issuing of Network Addresses to ISPs. ISPs (Internet Service Providers) provide clients with available network ID’s. Network administrators of the clients will determine the assignment of Host IDs on each network.

Subnets Network numbers can be logically divided into sub networks. This divides the host numbers among different subnets and network traffic is routed on each sub net. This benefits the network by Dividing network traffic of IP addresses in a particular part of a network according to traffic patterns Unused Host IDs from a network can be reclaimed and redistributed to other clients.

Address Masks Are used to “mask” the traffic intended for a particular subnet. This is accomplished by applying the “AND” function to the Mask and the IP address. This will provide the means of abstracting the network ID, and the host ID from the IP address. EXAMPLE subnet mask 255.255.255.0 will pull out the network ID for a Class C network 255.255.0.0 will pull out the network ID for a Class B network. Routers can then just compare the network numbers in their tables and route them accordingly.

CIDR Notation Used by people to denote the prefix (network number) and the subnet mask. Uses the network number followed by the mask (denoting the number of bits). For example for the class B network 130.14.0.0/16 This shows the network number is 130.14 and the mask for this network is 255.255.0.0 (16 bits or 2 Bytes) Makes it easier for people to understand the networks and their corresponding masks Increasing the number of bits on a network can divide classes into many subnets providing additional addresses for more clients.

Special IP Addresses Network Addresses – Host 0 is reserved to denote the number of the network and is never assigned to a computer. Broadcast Addresses – A host address (ID) that contains all 1s is reserved for broadcasts only. Limited Broadcasts – Used only on the local network 255.255.255.255 is reserved when computers boot up on a network.

Special IP Addresses (Continued) This Computer – 0.0.0.0 when booting a computer may request IP and network information. In this case the address of 0.0.0.0 refers to the computer booting up. Local Loop back – 127.0.0.1 is used by programmers to test client/server applications. Both client and server software are run on one machine and communicate with each other without sending out a packet on the network.

Routers and the IP Addressing Principle Routers are assigned IP addresses as well Routers usually have host ID of 1 for each network it is attached. This is not the case all of the time. In all the router IPs are reserved by the system Administrator and are never given to other hosts on a network. The IP address of a router is often defined as the networks Gateway.

Multi-Homed Hosts A computer that connects to multiple networks is called a Multi-Homed computer. Often used to increase reliability Can also improve performance by avoiding routers when sending messages onto a network.