if you've done anything with networking then you've probably run into an IP version 4 address in this video let's look at the different configuration options for IP version 4 the IP address is the unique identifier that every device on the network must have if it wants to communicate using that IP protocol an IP address is a series of four numbers separated by a period this would be something like 192.168 .11 165 to be able to properly communicate on the network every device needs to have its own unique IP address the IP address is combined with another value referred to as the subnet mask the subnet mask is also a four octet value for example 255.255.255.0 the subnet mask is used in conjunction with the IP address to determine what IP subnet this particular device is on this isn't something that us transmitted across the network it's instead used by your local device to make the determination of what devices are local on this IP subnet and what IP addresses may be outside of this local IP subnet this becomes especially important when you need to send traffic outside of your local subnet and you do that through the use of a default gateway the default gateway is the IP address of a device that's on your local subnet that allows you to communicate outside of this subnet for example if we have an IP address of 192.168.1.1 165 and a subnet mask of 255.255.255.0 a common default gateway could be 192.168.1.1 this is an IP address that is configured and assigned to the router on your local subnet by your network administrator and it must be an IP address that is on your local network there are also other IP addresses you should be familiar with one of these is a loop back address this is a way to define your local device without having to know a specific IP address every device on the network has a loopback address and it's a number that is between 127.0.0.1 through 12725 255.255 so if you wanted to Ping your local device you could ping 127.0.0.1 and hopefully your local device would be able to respond to you this is often used to conf confirm that your local IP stack is working properly and it would then be able to communicate to other devices we also have a range of IP addresses that we've set aside as reserved addresses this is a range of IP addresses that should never be assigned to other devices they're used for future use or for testing in the future this range of reserved addresses is 240. z.0 do1 through 254-255 255.255 anything that is a Class E address is also a reserved address we'll talk about classes of addresses in just a moment and another address type you might run into is one that is not real it's a virtual IP address or a VIP virtual IP addresses are not associated with a physical ethernet adapter instead VIPs are addresses that you would assign to the internals of a device so that you could always reference that device using that virtual IP address for example you might assign a VIP to a virtual machine or the VIP may be part of an internal address that you're associating with a particular router the IP protocol and IP version 4 operate at OSI layer 3 so anytime you're working with an IP address you're working at that Network layer of the OSI model let's break apart an IP version 4 address and really see what it's made of let's take the address 19216 81131 we refer to these four values as octets that's because they consist of eight individual bits and you can see the representation of that same IP address broken out into those four groups of eight bits sometimes you'll see these eight bits broken out and described as one bite or sometimes one octet so if you were to count up all of these bits there are 32 total bits in an IP version for address and that is the same as four bytes or four octets since each one of these individual groups inside of IP version 4 consist of eight bits the maximum value that you would ever have in decimal for any of these groups would be a maximum of 255 in the early days of networking we had to manually configure the IP address subnet mask and default gateway all in a manual way we had to visit that device change a configuration file and then that device would be able to communicate on the network if anything changed with our network configuration or we needed to change the IP address of that device we had to revisit the device and manually make those changes today of course we can plug in any of our devices and it automatically receives an IP address the way that we are able to receive this automated IP addressing is through a protocol known as DHCP or dynamic host configuration protocol when we plug into a wired ethernet Network or a WI wireless network and we're automatically able to communicate out to the Internet it's because we've received all of our IP configuration settings via DHCP but if you've ever connected to a network that does not have a DHCP server you may notice that you're still assigned an automatic address but this address is not quite as capable as a DHCP address instead it's what we call a link local address because it can only communicate to other devices that are on your local subject net and we cannot route that traffic outside of your local subnet for example if you're assigned a link local address you can't communicate to the internet because that's outside of your local Subnet in IP version 4 this link local address is assigned through a process known as automatic private IP addressing or apipa this range of IP addresses automatically assigned through apipa is 169.254 do1 through 169.254 2 55254 there are also Reserve sections of that range the first and last 256 addresses are reserved and they're not assigned to inst stations so if you receive an apipa address on your device it's between 169.254 1.0 through 169.254 254-255 just as DHCP Works automatically to assign your address apipa also has an automated process to assign this address it uses ARP to confirm that no one else on your local network has that link local address and if nothing responds to that address resolution protocol query then it will assign a random number between that functional block one of the challenges with ipv4 is that there are far more devices in the world than there are IP version 4 addresses and in recent years we've used up all of the available blocks of IP version 4 addresses there are no other IP version 4 addresses that can be assigned in these blocks so we need to find other ways to be able to communicate via IP version 4 one way that we've been able to extend the functionality of IP version 4 is to create an assignment of IP address ranges that can only be used on the inside of a network we refer to these as a private IP address range and anything that is a private IP address cannot be routed on the public internet fortunately these are very large ranges and we're able to use those ranges on the inside of our corporate networks if you were to look at the IP address that's assigned to your device right now it's likely that it's a private IP address so if your device is currently using a private IP address and you're watching this video on the internet how are you able to communicate on the internet with an address that is not able to be routed across the internet we're able to do that through a functionality called Network address translation this allows us to convert a private IP address into a public IP address and use that public IP address to communicate on the public network we'll learn more about Network address translation as we go through this training course if you want to learn more about private IP addresses you may want to reference a request for comment or RFC rfc1 1918 is the standard that defines these ranges of private IP addresses and how they can be used on our networks if we were to look into the details of rfc1918 you would see three different ranges have been set aside for private IP addressing these three ranges are 10.0.0.0 through 10255 255.255 and if you were to count up all of the possible addresses in that range it would be over 16 million addresses we often refer to this as a single class a block of addresses and we often write it as 10.0.0.0 sl8 if you were to write out the subnet mask of that sl8 address it's 5 5.0.0 this means the host size of this particular IP address range is 24 bits in length another range is 172.16.0.0 through 17231 255.255 this gives us a total of just over 1 million addresses that we can assign in 16 contiguous Class B address ranges if we were to write this out in cider block notation it would be 172.16.0.0 sl12 the decimal subnet mask for a /12 network is 25524 z.0 which means our host ID size is 20 bits in length and the last range is 192.168.0.0 through 192.168.255.255 this allows us to assign over 65,000 addresses as part of 256 contiguous Class C address ranges The Cider block notation for this would be 192.168 0.016 and that /16 subnet mask is the same as 255.255.0.0 half of this address is assigned for hosts so your host ID size is 16 bits in length as we step through the next series of videos you'll learn more about cider block notation the different classes of IP addresses and other details that you see associated with these private address ranges