From the course: LPIC-1 Exam 102 (Version 5.0) Cert Prep

About private and public "dotted quad" IP addresses - Linux Tutorial

From the course: LPIC-1 Exam 102 (Version 5.0) Cert Prep

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About private and public "dotted quad" IP addresses

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- [Instructor] Each computer or device on a TCP/IP network will have an IP address. This could be an IP version four address or an IP version six address. We won't go into details about the differences in this video, but just know that every device has an address of either type, or both. IP version four has a 32 bit address space, meaning there are roughly four billion IP version four addresses. However, there are 18 million addresses reserved for private space, and 270 million addresses reserved for multicast networks. Each IP version four address comprises of four dotted quad octets. They're called octets because they're made up of eight bits each. Four octets of eight bits makes 32 bits total. These octets are delimited by dots. Since an octet is an eight bit number, its values range from zero to 255 in decimal notation. There are several ranges of private IP addresses. These are 192.168.0.0 to 192.168.255.255, which comprises 65,000 IP addresses. 172.16.0.0 to 172.31.255.255 which comprises of about one million IP addresses 10.0.0.0 to 10.255.255.255, which comprises about 16 million addresses. These are private address ranges and are not routable across the internet. This means they're free for anyone to use as long as these addresses are translated to public addresses before the data enters the public Internet. We usually do this with NAT or network address translation. There are some other address blocks that we can't use for public networking. The address range of 169.254.0.0 to 169.254.255.255 is only used for link local addressing, meaning they're used when an IP address can't be assigned automatically. Every host also has non-routable addresses called loopback addresses. Those addresses are from 127.0.0.0 - 127.255.255.255 These addresses are only used inside of our computer and are never routed over a network. Any packets received on the loopback address must be dropped because our host should never receive one outside its own network interface. Addresses ending in zero or 255 are also special. The dot zero addresses define the network or sub network and addresses ending in .255 are for the broadcast address. The broadcast address is one address that lets data be sent to every host on the network. Generally, we are given a public IP address from our internet service provider, which is assigned to our router. Behind the router we use one of these private address ranges for our local hosts. When a local host wants to communicate with the outside public world, their address is translated to the public address. Return traffic is then translated back to the private address. This lets us get by with fewer public addresses, as most computers and internet cafes, private homes, and business offices are using private addresses behind NATs.

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