Addressing (Cont. Introduction to Networks)

Transcription

1 Addressing (Cont. Introduction to Networks) - Introduction - Purpose of this course - Your work - Definitions - The machine identification - Segmentation of networks - One address for the price of two - empirical definition of the mask - Why control masks? - IP Address and Mask - IP addressing - Number of Engines - Separation through mask - Torque IP address and mask - Coding - The binary coding - Why a binary encoding for computers? - What is a byte? - binary Write the IP address - Masks - Summary - How do we represent a mask? - How the mask and the IP address are they related? - specific addresses (network broadcast) - Bits 1 and 0 they must be contiguous? - Which addresses for masks? - Ignoring writing - What is this notation with / as / 24? - How to choose a mask? - From the existing - Depending on the number of machines - How to determine the address range from the mask and an address? - The easy way to find possible addresses for your network - How to define any network range as the sum of several beaches? - Beaches reserved (RFC 1918) - How to cut a beach address multiple subnets? - How to Determine the masks for each subnet? - How to determine the address ranges of the subnet? - The result - What are the address classes A, B, C, D...? - History - Definition - Is there a shortage of IPv4 addresses? - The addressing system classes is it viable? - What Do CIDR addressing? - Tips and Tricks with masks - How to determine a machine belongs to my network? - machines on the same network they can have different masks? - Can I use a tool that calculates for me? - It's all good, but when will I use this mask me? - Mini lexicon - IP - Logical Network - subnet - The ET Logic - Appendices - Resources used - Conclusion

2 1 - Introduction Purpose of this course Main aim presented and discussed through out of this chapter is the computer networks addressing, masks and subnet IPs assignment. Worldwide networks, unintelligible terms are often used for the common man does not have a computer training push. The masks are a part, especially as their understanding and use is not always simple (initially ;-)) The purpose of this course is to present the most understandable way possible what are the masks to what they are, how to use them well and be familiar with. For this, we will also discuss some related topics that will help us better understand the usefulness of masks, as logical networks, some basic routing, etc.. - Your work The only task I ask you to do is to correct my mistakes (both in the consistency of advanced features for spelling) give me advice on what is wrong explained to make it more accessible, add elements relating to the masks and make the most full, fill any gaps to improve the course. 2 - Definitions - The machine identification The aim is to send mail to a friend, using his mailing address. So you are sure that you send the package will arrive to the right person. And for both computers is the same. When you connect your computer to a network (eg the Internet), it has an address that identifies a unique way so that other computers on the network can send information. This identification process and configuration step starts by assigning an IP address to each computer network segmentation Imagine a huge network like the Internet where each machine would have to know all the millions of other machines (including their addresses) and how to access them. This would require our poor computers have huge tables containing all of this information. This would also lead times very large responses to browse the table. To address this problem, we have segmented this huge network into different small networks. And it is in these small systems we give addresses to machines to send their information. Thus, it suffices to know the network address to send information to a machine for it, and it is within this network that the information will be redirected to the correct machine. Exactly like when you send a packet in the mail, you put the name of the city, the packet arrives at the station of the city, and it is she who distributes the package to the correct address One address for the price of two As you understand, we need two addresses to identify a machine, for the network and the machine itself. However, the address that has been selected for the machine defines only a single address. You may say that this is not enough. And if, just this address segment into two separate parts, one for the network, and one for the machine. This is where the mask comes into action; it is he who acts as a separator between the two addresses Definition of empirical mask The mask is a separator between the network part and the machine IP address Why control masks? The use and control of masks must be able to afford one hand, know that you are handling, and secondly to optimize the operation of your network. Indeed, the use of masks will allow you to segment the most correct way of addressing your network, and thus to separate the sensitive equipment from the network, reduce congestion, and predict the evolution of your network, etc.. Unfortunately, the separation of a network into several subnets has not only advantages. A major disadvantage is the complexity of the particular routing tables given the larger number of network router. 3 - IP Address and Mask

3 3.1 - IP addressing We talked addresses for machines, it is now time to set these addresses. We're talking about IP address (Internet protocol ) because it is the protocol used to identify the machines and route information on the Internet. These addresses are coded on 4 bytes (see Chapter 4 of the binary coding) and are usually written in decimal numbering separating the bytes per time point. It goes something like this: Number of machines If you look a little closer, we can calculate the number of machines that can be identified using this address. Thus, 4 bytes are used, either 32-bit or even 2 ^ 32 addresses (2 exponent 32 addresses) Or 2 ^ 32 = 4,294,967,296, we can define a little more than 4 billion addresses! Separation with mask However, we saw the need to separate this address into two parts in order to identify both the network and address. But how is this separation? In fact, the mask as the IP address consists of 4 bytes or 32 bits. Each of these bits can take the value 1 or 0. Well we just have to say that 1 bits represent the network part of the address, and 0 bits machine part. Thus, an association will be made between an IP address and mask to find out what that IP address is the network portion and which is the host portion of the address Torque IP address and mask The mask used to separate two parts of an IP address, it is inseparable from it. One address will mean nothing because we do not know which is the network portion and which is the machine part. Similarly, a single mask will not because value will not address on which to apply. The IP address and the mask are bonded to each other, even if one would choose one independently of the other. 4 - Coding Binary encoding We use every day a decimal numeral system. So with 10 symbols ( ) that allows us to enumerate all kinds of numbers by placing them in a certain order. This place is paramount as it represents the transition to tens, hundreds, thousands, etc.. Thus, any number can be decomposed into powers of 10, eg 324 = = 3 * 10 ^ * 10 ^ * 10 ^ 0 However, there are other modes according to base in which we place ourselves. When the base 2 is used, it is located in binary notation where only two symbols are used (01) can, in the same way, decompose any power of 2 in number Why a binary encoding for computers? For computers, it is the choice of the binary coding was done. Yet it would have been easier to use the base 10 with which we are familiar. However, information related to computers run on electric son. On the son, it is difficult to distinguish more than two states for the signal; we can for example choose a state to 0 volts, and another for 5 volts. So we end up with two possible values. That is why we chose a binary encoding with two possible values, 0 and What is a byte? A byte is a sequence of eight bits. So it is encoded with eight bits number. For this, the value is rearranged in decimal number which may vary between 0 and 255. So, in an IP address is obtained, we cannot find other than numbers between 0 and 255. Address A as cannot be a valid IP address because the last byte is not between 0 and binary Write the IP address

4 We have seen that the IP address was composed of 4 bytes written in decimal notation, separated by dots, for example: This address may as well be written in binary: We shall see later why it is useful to return to this notation to understand the functioning of masks. 5 - Masks Summary We have already seen several important aspects of masks he will always try to keep in mind: - Coded 4 bytes, or 32 bits - They help make the separation between the network and host portion of the IP address - The network portion is represented by one bit and the machine part by bits 0, - The mask is nothing without the IP address to which it is associated How do we represent a mask? As the mask is 32 bits, here is a possible example of mask: Network Machine What is written in decimal Now, several questions may arise. So far I understand, but how can I associate this mask to an IP address, and what is the result? Why the 1 bits are separated from those at 0? How the mask and the IP address are they related? Consider a machine that has IP address We must associate a mask to determine which part of the address represents the network. Associate her mask previous. We note that the first three bits are 1 byte, so they represent the network part of the address or , the 147 to identify the machine within the network. In this example, we see that a byte has been reserved for the Machine address, which gives us 2 ^ 8 = 256 addresses available for machines on the network. Addresses available for the machines will be: (reserved for the network, see 5.4) (reserved for broadcast, see 5.4) We observe that this is the mask that determines the number of machines on a network. Thus, we will see later that choose mask on the number of machines that you want to install specific addresses (network, broadcast) There are specific addresses within a network. The first address range and the last have a special role. The first address is the address range of the network. This is very important because it is through it that we can identify networks and routing information from one network to another. The last address of the range represents what is called the broadcast address. This is the address that allows you to broadcast to all machines on the network. So when you want to send information to all machines, it uses this address. In our example, the network address will be , and the broadcast address It is therefore noted that there remains more than 254 addresses to identify machines. Thus, whenever a mask based on the number of machines that you want to send is chosen, it will take into account these two addresses displayed Bits 1 and 0 they must be contiguous?

5 In the example of mask we chose, we saw that the bits 0 and 1 were combined. This is not an obligation, but it greatly simplifies network operations. Maintaining contiguity bit addresses of the machines in the network follow. It would not be the case if we had chosen a mask with non-contiguous bits. Example, if the following screen is selected: Here we have as before 8 bits that represent the machine part, against, they are no longer in the same place. This translates into decimal by the given mask We thus see that the addresses whose last bit is a 1 will not be in the same network as those whose last bit is 0. This means that the addresses whose last byte is odd will not be in the same network that even addresses. In this example, it is still easy to differentiate odd and even addresses, but when more complex mixtures is made between the significant bits, it quickly became inextricable. So we always maintain the contiguity of significant bits! Which addresses for masks? Since the contiguous bits is maintained, we will always meet the same numbers for byte mask. These are the following: Either decimal: 255, 254, 252, 248, 240, 224, 192, 128, and 0. Thus, we can immediately tell if a mask seems valid first glance. A mask will be correct when a mask will not be (at least not want to respect the contiguous bits) You can see all of the possible masks in the following RFC: Rfc Ignoring writing byte Writing the IP address in 4 bytes separated by a dot is easy to use. But when we look at the problem a little more closely, you realize it is not very suitable... It has two main drawbacks: - Writing a decimal as we think in binary - separation of bytes by dots Thus, when masks where network / machine separation is done on a byte (all bits bytes are either 1 or 0) uses this is simple. Take for example the / network. All machines starting with belong to this network. Taking the / network and I ask you if the machine belongs to the network?it becomes more complicated... To understand, we must then go binary. Given that the first three octets of the mask have all their bits set to 1, it is the fourth that will make the differentiation. He wrote 248 is in binary. So the first 5 bits of this byte represent the network portion. For our network, the last byte is 32 or for our machine, it is 47 or We see that the first 5 bits of these two bytes are not identical (00100! = 00101) and therefore these two addresses do not belong to the same network. This may sound very complicated, but we will see the following simple methods to quickly determine the membership of a network What is this notation with / as / 24? Another notation is often used to represent the masks. It is often found because it is faster to write. In it, there is directly the number of significant bits in decimal, whereas in contiguity is maintained. Thus, for our example 0, we can also write /24, because 24 bits are significant for the network portion of the address. Similarly, the following entries are equivalent: / = / 8 = / /29 Since the mask determines the number of machines that may be on a network, it is often this information one hand to choose the mask. Since we work in binary, the possible number of machines within a network will be a power of 2. For a given number of machines, it must therefore choose the power of 2 in order to address the above machines. In addition, it will provide a number of additional addresses to

6 accommodate new machines. example, let's say we have the / network and you want to do in a network of 60 machines thereof. We want 60 machines; we must add two addresses for the network and broadcast, which makes a total of 62 addresses. The power of 2 greater than 62 is 64, but that would leave us two places to change, which is a fair bit. We therefore prefer a network of 128 addresses. To identify 128 addresses, we need 7 bits (128 = 2 ^ 7) So in our mask, 7 bits are 0 to identify the machine part, and the remaining 25 bits are 1 Which gives: and decimal How to choose the right mask? From the existing Most of the time, the choice of addressing is based on expressed needs, and limitations that we have the right to do. A certain range you is allocated by your ISP. You can then cut this range different network, but especially not exceed it. So if you have a range of 128 addresses and you want to send 500 machines, you will have a few small problems Depending on the number of machines Since the mask determines the number of machines that may be on a network, it is often this information that you choose from the mask. Since the possible number of working machines are in binary, in a network will be a power of 2. For a given number of machines, it will be necessary to choose the next higher power of 2 in order to send the machines. In addition, it will provide a number of additional addresses to accommodate new machines. Example, let's say we have the / network and you want to do in a network of 60 machines thereof. We want 60 machines; we must add two addresses for the network and broadcast, which makes a total of 62 addresses. The power of 2 greater than 62 is 64, but that would leave us two places to change, which is a fair bit. We therefore prefer a network of 128 addresses. To identify 128 addresses, we need 7 bits (128 = 2 ^ 7) So in our mask, 7 bits are 0 to identify the machine part, and the remaining 25 bits are 1 Which gives: and decimal How to determine the address range from the mask and an address? We saw earlier that the mask should be associated with an IP address to have a value. The choice of the range of addresses to which it applies is equally important! We chose a mask that will allow us to identify 128 machines. But we have a range of 256 addresses. Where should we put our 128 addresses in this range? Can they be placed anywhere? The answer is of course not. We have only two options to choose our beach, addresses and addresses Choose a range of 32 to 160 would be a mistake, and the network does not work.. Following explanation: differentiation of the network will be the first bit of the last byte (because our first three octets are set to ) If this bit is set to 0, this corresponds to the addresses from 0 to 127. If 1 this corresponds to the addresses 128 to 255. Thus, if an address range of 32 to 160 is selected, the addresses of have the first bit of their last byte to 0, then the addresses have the same bit to 1, then they will be considered in two different networks! Thus, whatever the number of machines to be placed in a range, you cannot choose the address anyhow. PS: In our case, the two choices are the same, but we will see later that this is not always the case for smaller beaches...

7 6.4 - The easy way to find possible addresses for your network It is not always clear whether an address corresponds to that of a network according to the mask that was selected. With the following method, you should be able to get away. It must first of all you have determined the mask according to the number of machines you need. Then, according to the significant byte (which is not 0 or 255) make-cet_octet = 256 X. The network address must be a multiple of X. this is a small example to be a little clearer. We want eg 50 machines, so we chose a mask This is the last byte is significant, so it is = 64. This requires that the last byte of the network address is a multiple of 64 Taking / the beach, you can choose the following network addresses How to crop any network range as the sum of several beaches? We have seen that network range could not be chosen haphazardly. As the masks and the IP addresses is based on a binary coding, the numbers used in the resulting addresses may only be multiples of powers of 2 in accordance with the mask. Thus, a range can not have a mask that defines more than two digits in the first byte, because 70 is a multiple of 2, but not 4. It is not clear? An example should help you comprendre.disons that we want to describe the address range from to question is what associated with any network address mask allows us to define this range. the first byte ranges from 69 to 79. therefore takes 11 values. 11 is not a power of 2, we know already that we can not define this range with a single network, but we will have to split it into a sum of several networks. The goal, however, is to optimize the amount of networks to have the least possible. One could simply use networks with masks, but it must surely be able to own more and more of these networks together into one. The first power of 2 is less than Now we know if we can place a network, the first 8 byte values described in this range. Multiple only 8 of this beach is 72. Was then describe a network whose first byte vary from 72 to 79, which is well understood in our original range / the network is well suited to describe our beach, but it remains to describe the addresses to the same reasoning is performed. (Here the first byte takes 3 values, the power of 2 less than 3 is 2, and the multiple of 2 of this beach is 70) It is therefore the network / It remains for us to describe the range to which can be defined by / And now! We cut our original range that went from to 79,255,255,255 three subnets: / / and / reserved Beaches (Rfc 1918) Some address ranges have been reserved for local use. Thus, to configure a LAN when not in range of public addresses available, you must use the private address ranges. If you want to have multiple networks, it is up to you to do the cutting in these beaches as you wish. following these address ranges: / more than 16 million addresses / nearly 65,000 addresses / more than a million addresses after If you do not find your happiness, is that you have a pretty damn big network, or you take it wrong Rfc1918.

8 7 - How to cut a range of addresses to multiple subnets? Determination of masks for each network It is often necessary to cut a range of addresses to multiple subnets. For this, it is often better to consider cutting the networks as a whole rather than to each separately and realize at the end that they are inconsistent... So we have from the number of machines in each networks. Consider the previous example network / It is desired to previously as a sub-network of machines 60, but also a network of machines and a final machines. In the same way that we have seen above, for 44 machines, it will reserve 64 places, a mask. For 20 machines will require 32 address book, a mask Determination of network ranges We will have to place three ranges of 128, 64 and 32 addresses in a range of 256 addresses, it should not be a problem. It begins with the largest range of 128 addresses. If we start with the smallest and the one placed anywhere, it could be problematic. Suppose we place the range of 32 addresses from 0 to 31, and the 64 addresses from 128 to 192, it will not stay us more room for the range of 128 addresses! So we have two choices for this range of 128 addresses, or addresses from 0 to 127, from 128 to 255 priori. A, there are two choices and not decisive. Is selected from 0 to 127. Thus, our subnet will be characterized by / For the second range of 64 addresses, we have two ranges of addresses, from 128 to 191, and Again the choice is not critical. One chooses to Thus, our subnet will be characterized by / (here, the first address our beach (the network address) that is 128 and the last octet of the mask 192 tells us that this subnet contains 64 addresses) Finally, the last track of 32 addresses, we still have two possibilities or was chosen from 192 to 223. Thus, our subnet will be characterized by / The result So we cut our original network / three we have even a range of 32 unused addresses from 224 to What are the address classes A, B, C, D...? History As we saw in section 2, the subnet mask to segment all Internet addresses in different networks. But this segmentation has not made any comment! was cut the range of addresses available in five distinct parts.classes A, B, C, D and E, also known as global addresses Definition Class A: First bit of the address 0, and subnet mask network. This gives the address range to or addresses Class A network Class B: First two bits of the address to 10 (1 and 0), and subnet mask in This gives the address range to be addresses per network Class B Class C: The first three bits of the address to 110, and subnet mask network. This gives the range to address is 255 addresses per network Class C Class D: first four bits of the address to 1110, and subnet mask network.this gives the address range to is 255 addresses per network Class D Class E: First Four bits of the address to 1111, and subnet mask network. This gives the address beach Classes A, B and C are reserved for internet users (companies, administrations, service providers, etc.) Class D is reserved for multicast stream and class E is not used today (at least I do not have knowledge...) Thus, a company seeking 80,000 addresses was assigned a class A network, and spoiled by same time (16,777, =)

9 Address! Then unnecessary to show you how many addresses were lost in this way Will it has a shortage of IPv4 addresses? The answer is no. There is today no shortage of IP addresses. However, it is certain that, given the rapid development of Internet, we will soon reach a critical situation. This is also why a new IP version was created and will soon be deployed The addressing system classes is it viable? The answer is no, and has been studied for a long time and transformed. We have seen that based on this classification scheme, we risk wasting a large number of addresses. Classes global addresses are quickly turned obsolete and we had to create a new model, addressing CIDR What is the CIDR address? Since addressing by classes proved incompatible with the evolution of the Internet, it was necessary to imagine a new model that simplifies both routing and addressing allows finer. For this, we created addressing (CIDR Classless Inter- Domain Routing). This address does not consider global classes and allows the use of subnets in all address classes. Thus, a company wishing to 80,000 addresses will be assigned a more complete class A, but a subnet this class A. For example, we will provide either 16 million addresses, but 130,000 (the power of two greater than 80, 000) Thus the remaining 16 million addresses can be used for other entities. Addressing CIDR therefore no longer holds all account masks associated with global address classes. This avoids arbitrary and inflexible in cutting classes. We can easily find a class B network with a Class C mask, for example / Tricks with masks How do I determine a machine belongs to my network? It's very simple. For this, we will have to determine whether the address of the machine belongs to the range of addresses defined by my address and mask. For that, I am a logical AND between my address and network mask, so obviously my network address (for an explanation of the logical AND, look at paragraph 10.4) I do this with the address of the other machine and network mask, and I get a network address. If the two network addresses are the same, it means that the machine belongs to the same network. Say for example my machine has to / address and I want to know if the machines A and B for Address (A) and (B) are on the same network? I AND = same with the other two addresses For A AND = and B AND = Thus we see that the numbers obtained are the same for my machine and B. We therefore deduce that B is on the same network, and A is on a different network.

10 9.2 - machines on the same network can they have different masks? A priori, the answer is no. However, there may be cases in which such a configuration can be useful. To understand this, we must understand what happens at the level of communication between machines, including the operation of TCP / IP model. It is not part of the object of the course, we will only fly the subject. Actually, these are not the same mechanisms that manage communication between two machines on the same network, and two machines on two networks distinct. Communication takes place in both directions, ie for all communication, machine A must see machine B _AND_ machine B to see the machine A. Take the example of three machines A, B and C the address range /24. A must communicate with B and C, but B should not be able to communicate with C. For this, you can play on masks and machines network address ranges to which they belong. Through masks, we can cut this range two, thus obtaining, either a range of addresses... but three! The first: / to to be the 2nd: / either to The 3rd: / to either In fact, the first track includes the other two, and a machine for the first track can see all Other machines of the other beaches, but a machine of the second track will not see all the machines in the first track (only half addresses...) It is not clear? then look at an example: We provide the following addresses to machines A, B and C. A: / Beach 1 B: / Beach 2 C: / Beach 1 From what we have seen previously, the beach is 2 encompassed in the range 1, so A and C will assume that B is the machine on their network. A having an address in the same range as B (track 2), B will be as A in its network. By cons, B will not consider that C is in network address because C does not belong to the range 2. Thus, C can send a packet to B (C sees B as well as a network) but B could not answer him. This configuration corresponds to what we wanted to do. However, such a configuration is not recommended and should only be used if no other solutions. Apart from exotic as that described case should never have two machines belonging to the same network with different masks! Can I use a tool that calculates for me? No! Finally though; for what we have seen, you should be able to calculate any correct mask as fast as a machine. And it is always better to master that one uses. By dint of using automata, notions that are handled, we lose the other hand; software will not correct your mistakes! Most software for calculating mask is one hard and evil that can be miscalculated. Take the example of 6.3, or you want a range starting at , and a hundred machines. A bad software will be released on / network, and presto, it will not work It's all good, but when will I use this mask me?

11 Indeed, when you go on the Internet, using a mask without knowing it. On Windows, you are connected to a local network or directly via a modem, you can view the properties of your network interfaces by going to a DOS window and entering the command "ipconfig / all" You can also change these properties going into the properties of your network adapter and TCP / IP properties, and there you should see your IP address and the associated mask, and default gateway. You can change this information, but your system may no longer work (and the longer it will reboot in 98..) so be careful! mask thus defines the machines (or more precisely, interfaces) belonging to the same network. To interact with these machines, you use one of the mechanisms layer 2 of the OSI model, while for dialogue with other network machines, you will need to use mechanisms that enable Layer 3 routing including making... It is therefore important not to err in the choice of mask. But that it is not an integral part of the topic ;-) 10 - Mini lexicon IP Address The IP address is coded on 4 bytes number to identify uniquely a machine on the network Logical Network Logical network is called a set of IP addresses belonging to the same address range. This range is defined by the particular network address and the associated mask subnet A sub-network is defined as a subset of a range of network addresses. It is through the mask that we can define a subnet within a network, and so cut a network into several subnets The logical AND The logic AND function is often used in the masks. It is based on the binary principle: 0 AND 0 = 0 1 AND 0 = 00 AND 1 = 0 1 AND 1 = 1 can be deduced in mask AND decomposed into: AND = is Here we see that the first three octets of the mask have all their bits to 1, so the first three octets of the result will not be changed from the original address, and is easily obtained For the last byte, we must look in more detail Annexes Resources used I have not used many documents both online and on paper. Answers and knowledge made from mostly information that I gleaned while browsing on the net, especially on newsgroups and fr.comp.reseaux.ip fr.comp.reseaux.ethernet. I am still inspired some documents: The RFCs 943 (replaced in 1992 by RFC ),,,,. site And the excellent faq on firewalls Stéphane Catteau I was inspired to formatting. Available at: not hesitate to consult, we learn many things.

12 12 - Conclusion The notion of masks as affordable as possible and treat the subject in the best way. We realize that this course is as enough as per the information provided and not always easy to digest.