Introduction to Computers Network Addressing

Review of Binary 0 = 00000000 1 = 00000001 2 = 00000010 3 = 00000011 4 = 00000100 5 = 00000101 6 = 00000110 7 = 00000111 8 = 00001000 16 = 00010000 32 = 00100000 64 = 01000000 128= 10000000 255= 111111111 Binary is base 2, meaning the only symbols we’ll ever see are 1 and 0 To translate from binary to decimal (our base 10 number system) we can use a chart and the powers of 2 and addition To translate from decimal to binary we can use the same chart and subtraction The other numbering systems we need to be aware of are octal (base 8) and hexidecimal (base 16). Octal uses 1-8. While hexidecimal uses 1-0, and A-F To translate from binary to octal or hex, we have to separate our number into chunks and translate each peice To translate from octal or hex to binary, the easiest way is to memorize the binary numbers from 0-16 This skill is very useful to have for technicians, especially those working with networks, since IP address are expressed in binary and MAC addresses in hexadecimal

MAC Address Facts Media Access Control (MAC) addresses are burned into the read-only memory of every single network interface. This makes it extremely hard to change the device's MAC address MAC addresses are globally unique. No other network interface in the world has the same MAC address MAC addresses can be used to identify the manufacturer of the network interface card. Each manufacturer is assigned a six digit sequence by the Institute of Electrical and Electronic Engineers, or IEEE, and all of their devices start with this number. If a manufacturer runs out, they apply for a new one

MAC Address and Packet Structure MAC addresses can be displayed as either a 48 bit binary number, or a 12 character hexadecimal number. They are equivalent You will most often see a MAC address in the following format - 5C-F3-70-7D-E0-FC Again, remember that the first 6 numbers (5C-F3-70) will be dictated by the manufacturer, and the last 6 (7D-E0-FC) will be unique to the device When sending information through a network, we’ll take our message and create a network packet. A network packet consists of the message with both the sender and receiver MAC address as a header By inspecting the to and from address in the packet, hosts on the network can communicate with each other

Logical Addresses Unlike MAC addresses, logical addresses are assigned by software, not hardware. This makes them much more malleable Logical addresses are used by a lot of different network protocols, but the most common logical addresses are those assigned by the IP protocol One thing to note is that these addresses do not replace MAC address, each host will still have a MAC address. The IP address will be used for certain tasks, and the MAC address for others To use IP addresses, hosts will take their network packet and encapsulate it into an IP packet. Just like the network packet, we’ll include a header with the sender and receiver IP address

ARP For hosts to use IP addresses, we need to associate them with a MAC address To accomplish this, we have the address resolution protocol (ARP) If we want to send a message to a known IP address without a MAC address assigned to it, we’ll send out an ARP broadcast Broadcast messages are delivered to every host on a network. This message will say to each host “I am looking for the MAC address for this IP address. Is it you?” Every host with a different IP address will ignore the message, but the host with that IP address will respond with it’s MAC address. Since the packet for this message has the sender’s information, both hosts will now know each other’s IP and MAC addresses

IP Address Facts It’s important to note that there are actually two different formats of IP address being used currently; IPv4 and IPv6 While the world will likely be forced to switch to IPv6 eventually, IPv4 is used more often right now, so that is what we’ll focus on An IPv4 address is a series of four numbers between 0 and 255 separated by dots. 192.168.1.23 for example Just like MAC addresses, IPv4 addresses can be split in two parts; a network address and a host address. Unfortunately, unlike MAC addresses, it is not always down the middle Also, like MAC addresses, IPv4 addresses are comprised of binary bits

IP Address Structure An IP address is comprised of four different 8 bit binary numbers This is where the range of 0 - 255 comes from, since 00000000 is 0, and 11111111 is 255 We call each number an octet since it is an 8 bit binary number An IP address can be split into two parts- network address and host address The network address identifies which network this host is in. If we used home addresses as an analogy, this would be the street address. Every host in the same network will have the same network address The host address identifies the host inside the network. In our home analogy, this can be thought of as a house number. Every host on the network will need a unique host address, but there can be hosts on other networks with the same host address

Subnet Mask To split the IP address up, we’ll need a subnet mask The subnet mask is composed similar to an IP address - four octets of binary numbers. This is because it is used to decode an IP address To use a subnet mask, we would line it up with an IP address. Then, every bit that was 1 would be part of the network address, and every part that was 0 would be part of the host address Because of this structure, we know that the subnet mask will be a number of 1’s followed by a number of 0’s. Once the subnet mask switches, it will not switch back

Default Subnet Masks When configuring an IP address on a host, we must supply the subnet mask in addition to the IP address, since the host will not be sure where the network address ends and the host begins That being said, IP addresses do have a default subnet mask, which is identified by the address class IP addresses are divided into five different classes with each class having a different default IP subnet mask. If you see an IP address without a mask, and if the default mask is being used, you can determine the subnet mask by identifying the address class and using the default mask value We can determine the IP address class by its first octet

Address Classes There are five IP address classes. They are defined by their first octet Class A: 1-126. Default subnet is 255.0.0.0. There exists 126 possible Class A address. Each has up to 16,777,214 hosts per network Class B: 128-191. Default subnet is 255.255.0.0. There exists 16,384 possible Class B address. Each has up to 65,534 hosts per network Class C: 192-223. Default subnet is 255.255.255.0 There exists 2,097,152 possible Class C address. Each has up to 254 hosts per network Class D: 224-239. Multiclass Class E: 240-255. Experimental/R&D addresses 127 in the first octet points to the local host. 127.0.0.1 is the local computer system

IP Address Restrictions We can’t use a subnet’s address for a host For example, say I have an address of 195.64.21.200, and use the default subnet mask of 255.255.255.0. The subnet’s address is 195.64.21.0. We could not assign a local device that IP address. Similarly, a host address of all “1”s, or 0.0.0.255 in this case, is the broadcast address, designed to send a message to all hosts on this network A host address on this network has to be between 0.0.0.1 and 0.0.0.254 in this case