Cisco - CCNA Certification 200-301 - Introduction to Subnetting .13

[Music] so in thinking about what to do for these next couple of videos around subnet in because it's such a crucial topic but yeah it's also a topic that I think warrants understanding the history now I also think that's true with land switching and Ethernet but not everything can be pushed into the CCNA because otherwise it'd be massive and of course I'm gonna miss you something doesn't always give you value in your day to day and it certainly won't be part of the network in any networking exam moving forward you know you're not gonna get tested on bridging your hubs like you are the switches because we don't use them anymore and to an extent the same is true regarding address addressing well ipv4 addressing around classless and classful you know you only gotta really get test on classless however what I'm gonna do in this video is the match is going to keep the video I done for the icnd1 exactly the same so that means the first part of this video it gives you an example of a network using classful addressing it then introduces you into a subnet mask of water the mask is and how it's used to identify the network and host portions of addresses and then we look at the same network that was originally introduced at the beginning but this time approaching it with that classless mindset now for me this is important because I think if you can understand a subnet mask and the reason it was invented it makes more sense of why subnetting is even needed in the first place and it also makes sense when you get into like your ccmp level topics understanding summarizing and super netting so I'm gonna keep it in the video so the battery ran out on the camera so I'm gonna keep it in the video and I think it will add value if you're not interested I put the timestamp in the video click it and it'll take you straight to subnet mask in and straight into classless but I think it's important because you don't be the engineer that doesn't understand what clase means I think that's you know especially from engineering I've been in the field for a long time it's really trivial thing and I think it's it's good to know but anyway let's get going so before we dive into subnet mask and classless inter-domain routing I just want to just hammer down the point of the problem with classful so we've got a network here let's say our wine provider gave us a public IP of one nine five zero one zero we know looking at the first octet this is actually classy and because it's a classy we also know that the first three octets they're gonna be for the network portion and the last pot set it's gonna be for the house portion so what we've done then was on the back of this was assign these IPS to our network so this particular route here let's say got one nine five zero one one this one down here got one nine five zero one two and then we had dot three all the way up to let's say dot 100 all being used for our pcs over here so we had a lot of IP s be news but remember in a Class C there were 254 usable and we're only using 100 of them so we still had a hundred and fifty four left over let's say for example for ever reason we needed to strip this network up because the broadcast domain was having too much chatter or let's say we had to have a never part of our network put aside for public access as they maybe we want to put our servers there or something like we obtained another company so for whatever reason we needed to essentially have a different network okay so now I modify the network you can see that I've added this new section now because it connects after the back of a Rooter here it's considered a different network so it needs a different IP range and it's in a different broadcast domain now for those who don't know what a broadcast domain is we'll come into that a bit later when we get to our Ethernet section but essentially because it's different part the network it needs a different IP range now even though we have 154 I piece left down here we can't utilize them and the reason being the 1 9 5 0 1 0 these three are pets were taken known as can use them not even us on a different network because when a packet would become in destined for let's say 1 9 5 0 1 3 over here if it was configured in two locations this route here wouldn't know where to pass it so because of that we need a unique IP range for here so what we need to do at this point is actually go to our ISP our service provider and ask for another Class C range and sure enough if we pay him enough money they give us another IP range let's say that give us one nine seven five four zero and then we can use this IP range to assign inside this network but what we've noticed here is we've wasted a hundred and fifty four IPS here and we're going to waste a lot more eyepiece in this network so to get around this problem of having these IPS wasted we came up with this concept of taking away these classes taken away Class A B and C and having a different method to identify where the network and host portions begins and ends and because we have this new method what were able to do is something similar to this you can see that we have the 195 0 1 0 network that our isp originally gave us but what we can do is have anything from 0 to let's say a hundred and twenty seven to be in this original large network and then we can have anything from 128 so picking up where this one left off up to let's say 36 for this network and what we can do here is create small network so we can essentially what we call this network down into smaller networks to accommodate and in turn we would waste less addresses so as time moved on it was clear we needed a better way to break up the classroom ranges into much smaller blocks so a subnet mask was introduced to help identify the dividing line between the network and house bits so no longer would it just be a 130 is a Class A therefore the first 8 bits is a network the engineers could now further subdivide that block into smaller blocks this technique was called sub name so previously we said if you were given a 192 we know this was going to be a Class C so previously we would say 192 168 0 0 would say this was the network portion and this was the house portion well what engineers can actually do was take bits because remember there's 8 bits here inside this host portion and move a bit into the network portion allowing the engineer to have more networks but that for the sacrifice of less house and essentially this is the key or the idea around subnet will also done was it got rid of this classful boundary so for example let's say we were giving this particular Class C range it doesn't mean that we've always got 254 IPS in that range in fact what we can do is break it up so we can have two ranges of 128 IPS each or we can have 4 IP ranges with 64 ip's each using this subnet in technique allowed us to make better use of the IPS that were given to us by our supplier okay so the other thing to pick up is there is a default subnet mask for the classful ranges because remember at the time when seven a mask or a release there were still networks out there utilizing classful addressing so to make things a little bit simpler they gave a default subnet mask to each class so they gave Class A 255 0 and 0 0 class B 255 255 0 0 and Class C 255 255 255 0 now the 255 as far as the default classical ranges are concerned would equal the network portion and the zeros equalled the house portion so just like before of a Class A only the first octet was the network and the remaining three are texts where the host and for Class C the three octet to the beginning we used for the network and only the last octet was used for host I've also put here a slash a slash 16/20 for this is referred to as the slash notation also sometimes called The Cider notation and sometimes called the network prefix and when we get into understanding subnet masks in a bit more detail these will come quite clear to you but essentially it's a different method to represent the subnet mask so I'm representing a subnet mask a subnet mask purpose is to inform the host network and device whether that's firewall router or PC how to calculate its network address now a few things to know about subnet mask on how its kind of represented and some importance around the binary and decimal elements first of all observe that mass is 32 bits long just like an IP address i've subnet mask can either be awful on remember anything can binary same with an IP address can either be off or on if it's on as in it's a 1 it represents the network portion and if it's a 0 it represents the host portion now if we take for example our decimal format of a Class A which we know was 255 0 0 0 and we know that the 255 element is the network portion and the three zeros are the host portion so why is 255 the network portion and the zeros are the host portion and that doesn't come clear until we look at in binary you'll notice in binary having all the ones turned on in the first octet equals 255 in decimal and you can see the 3 house octet at all set to 0 and the reason that hosts is because like we said in the second bullet point here we said one represents the network piece so the first eight bits are for the network and we said zero represents the host so that means the remaining three are tents for the host the last point is a southern mask gives us ability to determine the line between the house and network which may sit inside an octet so what we mean by this is initially lean on two point three and four where we said this decimal format and we converted it into binary if we need to change what bits are the network and what pitch other hosts that will have to be done in binary and the reason for that is because if I give you something like 255.255.255.0 the decimal number so when we compare it to binary what we can do is decide what bits we want off and on so an example of that is I've put together this chart and we can see that in this particular set we have all the bits turned on therefore equals 255 in this octet we decided to only turn on the first bit and that left us seven bits turned off and in binary the first one's 128 so one bit on 128 here we've got the first three bits turned on and the remaining bits turned off and that equals to 2 for the reason being is because the first bit here is 128 the next bit is 64 the next bit is 32 and if you add up all three numbers equals 2 to 4 so in order to actually is subnet we need to understand it at a binary level because that binary is where we can turn the bits into hosts or network bits by turning it on or off for example if we look at a Class C in binary we know it's 255 255 255 0 it will look something like this 1 1 1 1 1 1 1 one so it's eight ones and then one two three four five six seven eight one two three four five six seven eight dot zero zero zero zero zero zero zero zero so it's eight zeros which of the house portions and 24 bits turned on which is the network portion well in binary what we can do is we can decide to turn on more bits in this host portion and therefore create a different subnet mask and creating a different subnet mask allows us to have a different value of host bits as compared with the new network bits and this is the first step of subnetting okay so let's start with an example as you can see I'm inferring - yeah let's say we were giving this particular subnet mask we can see that the first three are tetes or 255 255 255 set is our house portion in binary we know that 255 all the bits turned on so that means that there are in total 24 bits turned on and that left us eight bits turned off because a subnet mask is 32 bits long now what you decided that we don't need this many host bits in fact what we'd rather do is split those host bits up and give them to the network portion so the way we do that as you can see here we don't need that many host bits so we moved the husband into the network bits and now we have two additional Network bits if we were to convert this into decimal weird again have 255 255 255 but in the last heart site wherever 192 the reason wherever hundred 92 which is if we took these eight bits and we put them into decimal and all just do that we need to bring up the decimal to binary format table that we discussed in the last video we can see that we have the first two on and the rest turned off and if we add up the two values that we've got turned on so it's 128 plus 64 equals 192 hence why in decimal this is 192 however because now we finished and we've given them to narrow bits we leave the rest of the bits turned off and these are now our new host bits so we've got less house that we've got more networks now also keep in mind that before we had 24 bits turned on now we have 26 bits turned on so this is why the Sider notation or / notation or network prefix was as I was 24 and now it's a 26 so using our example the bottom here you can see that we have the network portion we have the new bits that we've turned on which we're going to refer to as the subnet ID and then we also have all these zeros which we know is the host portion so keeping that in mind let's have a look at these formulas so to figure out the number of subnets we need to do 2 to n where n is the ones in the subnet ID so in this case we need to go to we need it 2 times so that's 4 right so it's 2 4 so we have 4 new networks ok by turning on these 2 bits we have 4 new networks now how many hosts are in each Network we figure out that by doing the next formula which is again 2 to the power of n minus 2 and the reason we minus 2 is because we have the network and the broadcast address so again all the host ID so here we have 1 2 3 4 5 6 so that's 2 4 8 16 32 64 1 2 3 4 5 6 so that means that we have four networks and in each network there's 64 available hosts but we also need to - - so that means there's 62 available host and the reason for that is because in each Network there's a network address and a broadcast address and we'll get into that in a moment and explain in a bit of detail what they actually mean okay so now we've seen a very brief example of the technique around subnet and I appreciate it only being one example so we want to get into more examples as the video series continues I want to go back to the big picture and tackle what we've learnt today against this existing network so let's say our ISP gave us a 2 dot 190 . 0 now the first things first is we're talking here class less and not class full if we were taught in class 4 we would look at the first octet and say this is a Class A and because it's a Class A the first author is the network portion and the following three octet is the host portion however that's not the case we're dealing with classless and because we're dealing with classless it's not the network and identification bits that determined the network and host portion of the IP address but it's actually the subnet mask now the subnet mask that we've been given from our supplier is a slash 24 which is the subnet mask but presented in what we call a cider notation sometimes called a network prefix and essentially this means how many bits of the available 32 bits are turned on and remember those on bit represents our network so first things first let's figure out the subnet mask or this last 24 that we were given for my supplier and in order to do that we need to turn on 24 out of the 32 available bits so going from left to right let's turn them on 1 2 3 4 5 6 7 8 . 1 2 3 4 5 6 7 8 . 1 2 3 4 5 6 7 8 . so that's 8 16 24 and then the remaining bits because now we've got this all turned off and because it's 32 in toe take away 24 leaves 8 so 1 2 3 4 5 6 7 8 so there's our host portions so this is actually our host and all of these here in actually our network so by default that any subtend how big is the network that we've been given from our supplier and again we use that formula which is 2 2 n minus 2 on the amount of bits that are turned off so they're eight bits turned off which means it's 2 4 8 16 32 64 128 256 so that's 1 2 3 4 5 6 7 8 8 bits turned off 2 ^ how deep it's turned off is 256 but remember need 2 minus 2 because of that network and broadcast which I'll come back to in a moment which gives us 254 use usable IP addresses however even though that's great we've got 250 for user by piece what it doesn't do is it doesn't hit what we need here because what we actually do need is 2 networks and not one network because if you remember previously we've got a network here also referred to as a broadcast domain and we have a network here also referred to as a broadcast domain and we can have one network to satisfy or one IP range to satisfy these two networks what we need to do is subnet this down so we have some IPS here and some IPS in here so the way we're going to do that is first of all we need to understand what's our requirement now we've got two options we can either subnet based on house requirements which is what we've done earlier or we can son that base on subnet requirements which is what we're going to do here so no concern about how many hosts inside the range but why I'm concerned about is how many networks that gives us and to make that little more interesting we're actually gonna say that we have the total of let's say nine networks so we have two here we also have three four five six seven eight nine so let's pretend that we have actually nine Network so that's nine broadcast domain here's one here's one and then here's the rest of them down here all right off the screen so we're going to just pretend we have nine to give it a bit more of a more of a challenge with the sub lane so first of all we need to figure out how many bits we need to sacrifice of our health portion to create nine networks now if we trying to subnet based on hosts requirements we go from right to left and if we're submitting based on network requirements we go from left to right in this case because we're doing Network we're gonna use the left to right so doing our powers of two from left to right we've got 2 4 8 16 32 64 128 256 now in order to have nine we know that we're gonna at least have to look at turning on 16 so we're gonna turn on 16 and all the ones below that because 8 was to do 32 is way too much 16 is the lowest we can have turned on that allows 9 so because of that our new subnet mask is four ones and the rest is zeros if we had to calculate the other way around let's say we had a requirement well similar to what we had previously in the video where we add host requirements instead of subnet requirements then we would do it the other way around so for example let's say we had a requirement of 33 host then going from this time right to left we're gonna go to 4 8 16 32 64 128 256 well what we would need to do is have these bits turned off and 32 is too small and we'll turn on the bits once we've hit our requirement so you can subnet from left to right for networks and from right to left for hosts in this case we're going to be doing it based on the subnet requirement as previously explained so we're going to go from right to left we've done that and we've come up with 16 being the smallest that we can have and therefore we have to turn on all the bits that are left of 16 leaving all the bits right of 16 as our new host because of that our new subnet mask would be like this 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 and then the 4 turned on and then before turned off now to figure out how many networks we have we know that because 2 ^ how many bits are turned on is 16 so 2 4 8 16 and to figure out how many hosts per network it's also quite easy because we need to do 2 2 n minus 2 where n is the amount of bits that are turned off so again 2 4 8 16 minus 2 means there are 14 usable addresses per the 16 networks that we've created and 16 network is more than enough for this Nine Network requirement ok so just make it a bit of space it's going to be crazy here so let's think about the silent notation and the decimal format of this new subnet that we've created now think about the last octet we turned on four bits and we have two 4 bits turned off now previously it was just as 24 because 24 bits were turned on well here we have a 16 24 25 26 27 28 so say / 28 now to work out the decimal what we're gonna do is write out our decimal conversion and place these binary bits under the correct values so from left to right we've got 1 2 3 4 and then 4 zeros 1 2 3 4 all the bits that are turned on if we add them all up so that's 128 plus 64 plus 32 plus 16 is 240 so a decimal so damask in decimal format will be 255 dot 255 dot 255 240 ok so what we actually achieved of all of this hard work now initially we had 82 190 0/24 which gave us 256 IPS in the host portion two of which couldn't be used because one is the network and one is the broadcast now what we've done is we took those 256 IPs and we broke them down into 16 networks with every network having 14 useable hosts and the way that would write out now is here you can see I've popped 82 190 0 and that will go dot 1.2.3.4 to 5 all the way up to dot 15 then the next network will start 82 190 16 all the way up to 32 and the next narrow will start but like I said we lose two IP addresses you lose one for the network and one for the broadcast now the first one of each range so here is the dot zero here is the sixteen and here is the 32 these are network addresses and these can be used by any host you can see the first useable one is actually going to be dot one the second usable is dot 2 so those can be assigned to the host now the last one which is 15 and the last one in this one which is 31 is what we call the broadcast address now this 32 here I've stopped but ultimately this pattern will continue all the way up to 250 for being the last usable so in the end you have 80 to 190 . 254 and then what we can do with this is take one of these networks that we create it and here we can say 80 to 100 90.1 is here dot 2 is there this pc can have dot 3 this guy can have got 4 this guy can now dot 5 this guy can have got 6 and then what we can do is get the next network which starts with 16 remember 16 not been the first remember 16 not being a usable address get 17 and give 17 to this guy 18 to this guy 19 up here and what we've done is we've actually split what originally we had a slash 24 into multiple slash 28 and actually we have 16 slash 28 that we've created so just quickly we're going to finish up on what is a network address and a broadcast address so I said every time that we perform subnet in essentially every network will require a network address and every network or quite a broadcast address so a network address essentially is what bridges used to route towards so for example let's say that we had a 2-1 5000 slash 24 here this would be our network address with dot one being the freshers ball dot 2.3 and so forth all the way up to 255 but 255 would be our broadcast so the last usable beat 254 now the network address is what Ruta stood actually route towards so what I mean by that is it essentially represents the network that you were on hence network address so if we had a Rooter over here and narita had a routing table it wouldn't actually have 80 to 150 0 1 0 to 0-3 for every single host in fact all it would have is just this one entry because reuters route towards the network using the network address and then once communication is happening inside the network it then routes towards the host portion of that address as for the broadcast address which is the last address in the range in this case would be 255 essentially that means that if you were to communicate with 80 to 150 0 255 it will go out to all hosts inside the network so for example let's say I'm on this PC and I'm dot 3 and I decide to send a ping to 80 to 150 0 255 then essentially what happened is that ping will go to every single house that lives inside that network and that is what we call a broadcast message any other IP that I tried a pink let's say I ping 2 or dot 100 providing they've been assigned to a host on the network then that wouldn't be a broadcast communication that would be a unicast communication which is a one-to-one ok so that's all we've got time for in this lesson and if you carry on to the end well done it was obviously a longer than normal lesson I appreciate that subnetting is not an easy thing to understand and repetition is key when it comes to it we're gonna have the next couple of videos talking more about something in the different types of subnetting that we can do which is fixed them from variable lengths and then we're going to go into lots of q and a's around soar given you some questions some time transform and then we'll go through the answers together so what do we do this video we discuss what is the subnet mask we said that back in the classical days we used the networking bits to identify the network and health portion but that wasn't going to sustain us moving forward so we came up with a new method which utilizes this subnet mask to identify where the host and network portion starts and stops we talked about why we needed to move away from Class 4 or we gave that example the beginning where we had a particular network that was utilizing about 100 or so IPS but there is still quite a few IPS left but because we had a different network we had to go to a provider and ask for another IP range there is no possibility of actually splitting up that I really know Class C so when we went into what is the subnet mask how it represents in splayed so we said that there are Seidel notations and the decimal format both mean the same thing but they're presented in two different ways we said that if the bit is on it represents the network and if a bit is off it represents the host and we said in order to do subnet we had to translate it into its binary values and then turn the bits that we needed on or turn the bits that we needed it off we then went through an example of something only really one example to begin with but I like I said we'll get into more examples as time goes on we looked at the formulas that are used in subnet in which was 2 to the power of n to work out the amount of networks and then 2 to the power of n minus 2 to work out the number of hosts required and then we finished with the big picture essentially we got that production network that we had at the beginning where he ran into problems with the classful networks and then we essentially broken up into multiple slashed and assigned those nine networks that we had as a requirement each their own slash 28 that lived inside the slash 24 that was originally supplied to us from our ISP I hope this video has been informative and like to thank your viewing and it has been please do like and subscribe

Channel: Ryan Beney

Views: 3,223

Keywords: classless interdomain routing (cidr), ipv4 addressing and subnetting, classless and classful addressing, subnetting tutorial for beginners, ip subnetting made easy, ip address and subnet mask, ip address and subnetting, subnetting questions and answers, understanding cidr notation, classless interdomain routing, cidr notation explained, classless subnetting tutorial, subnetting examples, subnetting questions, ccna 200-301 subnetting, full CCNA course, Full CCNA 200-301

Id: QGYJETdpKyo

Length: 36min 8sec (2168 seconds)

Published: Tue May 12 2020