 Hi everyone welcome to the Linux and the programming basics class today we will continue to the next section which is the Linux networking I am calling it lecture one but recall this is lecture number five we just finished the Linux basics where we introduce the concept of Linux how Linux developed over time we also talked about the various parts of the Linux or external shell and the file system and then when we we went through several commands for running some basic commands like LSE kind of things and when we moved on to more esoteric commands and we also like had some fun exercises to see how these commands can work together so today again we will continue finish off that section there are a couple of things that are remaining so these are the things that we saw already like the files and commands rep fgrep locate unix or touch etc so today we will finish up this section there were few commands that are missing I will just talk about those comments and then we will start the Linux networking piece of the lecture so without wasting much time let's begin so some more commands so these are some of the key commands which are slightly advanced commands than what we saw before the first command is tar it's the short form for to archive so essentially tar is used to archive a directory structure so assume that you have a directory a under that there are some files B and C and then another directory B and then the D contains E and then maybe like G as an another directory structure this entire directory structure is there and then the archive you want to archive a flat file so the tar command actually combines all these it goes down the hierarchy collects all these files and puts them all together in a single file so that way it is easy to actually transfer this file and then once we extract to this archive then we can get back the old the file itself and usually this tar archives all the files in the ASCII format actually like I mean it is a exactly format independent so whatever the format is there underneath thing it puts them in that form so here is one example this is essentially like tar CVFP and then in tar multiple files and then we come puts together in one and here the destination is given first in the argument so lab one tar is the destination and then the lab one can be the entire directory or just can be a single file whichever one that you want to and then when you want to actually extract the file we just replace the C with X here the command you can actually go to man pages and man tar and then look at what these options are but it's it to be straightforward I think that we will stand for verbose I think like I will I would like you to actually explore this a little bit more so again the command is tar it stands for to archive and then you basically give the destination first and then you specify which files or which folders that you want to archive again here you can actually do multiple files and then I want to explore this I want you to explore this particular command the other command that we will use is the gzip this is actually for compressing a file so typically a file has it could be like some of these files can run into multiple gigabytes of information but sometimes these files will have a lot of empty holes or they could be encrypted and made it much tinier so gzip is a compressing utility which compresses the file and again I want you to do a man to find out what man entry is there for gzip so one thing is this minus 9 what is minus 9 stands for you can find it out when you do the man here we do the man I mean when you do the gzip minus 9 the lab one from this command the tar it generates another file called lab one dot tar the gv the end gv the subscript stands for the gzip file and gzip is definitely a binary file so you want to use the read it and there are utilities that you can use to open the gzip and read it nowadays like a lot of these utilities are becoming more commonplace to get back this I told you like tar minus xvf which is shown here you can also do the first thing is what you do is like you do a gzip minus cd to get the the untarred you can also do the there are other commands like done zip g unzip which is essentially unzips a file which is from the compressed file it brings back the larger file and there is nowadays like a short cut which is fvf z the z stands for unzip and then untar the file so this is another handy command that you can use it for doing your operations then there are a few other commands echo echo I am fine essentially like echo whatever you put in it just displays back so like I mean typical first command that you write in Linux will be echo and then you within the ports you say hello world and then it echoes back that hello world and then the other one is clear which is also an important command which is basically clears the screen so that whatever you type in it goes up and then basically the blank screen is left for you to begin your world then there are some special characters you we already saw this greater than sign and then followed by a file name essentially like when we do the any command and then pipe in greater than a file name the output of that command will go into that file again there are special ways to actually distinguish what is the standard out and what is the standard error you can look it up when you do the math pages for that and then you should be able to see lot of entries for that and then there is also like a less than that you can use which is essentially like contents of the file now goes into the command and then the pipe one that we already saw basically like that is so you can type the output of one command into another command using the pipe format there is also another nifty operator which is the back tick it is also called back tick here you can see that there is this date has a back tick in front of it and then also like it is a single code that is or actually it is called a back tick and so when we do this I want to see like what you get as an output this is back tick date you know that echo command actually echoes whatever is inside the code if you use a back tick what will be the output and then also like I mean there is a small programming puzzle for you seek 1 to 10 what will be the output on this one essentially like the back tick is used as command the command expander essentially what it does is actually executes whatever following the back tick as a command so since the date is a command it will execute the date and mostly produces what the value of the date is same thing for sequence 1 to 10 prints the sequence in the number 1 to 10 I think it is so it is fun to actually do the program this way so now let us look at just what the activities are for for this week so again I want you to use map to find the details on the commands that we mentioned we saw earlier and then I want you to actually explore some more in the Linux command structure these following commands so I have given this as an example for you you can use this and then see what all things that you can get this will also become your lab once you start doing this okay so now we start our today's lecture which is essentially the lecture on Linux networking so in today's lecture we will be covering the main ideas what is really networking what does networking mean you saw that Linux is a multitasking multi user multi CPU system so the multi CPU and multi user key aspects of what networking is then we will talk about the OSI model which is one of the key concepts that was developed for networking in fact there are graduate courses on OSI model so we won't go into like go to details as to like what all the things you'll at least look at the basics as to what exactly it stands for and why is it important in our context and then we will move to the various other things in the Linux networking area so today we will be mostly like dealing with this OSI model and why is it important for us so how does it make the machines interrupt that is the key things that is in today so let's look at what is networking so the classical definition for networking is how computer or components in our now the terminology will move to just we call that moves how they talk to each other that's the key aspects of so that's what networking is all about so the so far we saw how a single window single user how he interacts with the Linux system which is good in the sense that you can still one program but you cannot interact with other machines other users using Linux so far so today we will break that barrier and actually start talking about how we can communicate with other users how other users can also view your system how they can communicate your your session or you can also see how we can ask remote machines perform a job for us which is again crucial for LSF or the load balancer type of application in fact that the entire computer industry is built on this networking basis basics as you know the today like I mean most of the browsing that you do like when you do the various interaction with the various websites they are all using the networking principles and we saw you'll see how we can do that using this so before we talk about networking a network itself which is a passive entity where several computers are there and they are all interacting that network has few characteristics the few characteristics are number one is the size which is essentially you can define it as the number of nodes in that network so for example if there are five computers connected or in your university you have a you have many computers connected to a central server or many community computers connected to each other the number of computers becomes the size of the network the second characteristic of a network is the topology here essentially we talk about what is the configuration okay we know that there are five computers that are interacting with each other how are they connected now they connected one is disconnected to one or one is connected to all of them those kind of what kind of configuration that's the main aspects that we will talk about the third item in a network is physical which is how are they connected are they connected using copper wires are they connected using fiber channel here we will go a little bit deeper not just consider the physical medium but also like what is the speed are they connected on a table with so many many megahertz or how they are connected so we will talk about that and then finally the protocol protocol is how do they talk to each other so then one wants to talk what does it do or if somebody is talking and how do you interrupt that person so again these are the rules of conversation very similar to how humans interact with each other so we will see some of these concepts in the next slide so the characteristics the size is determined by the the number of nodes as I mentioned earlier and there are many systems that are prevalent today the LAN or the wide area network LAN or local area network are two examples but there are many many such networks are already available in use today so that's where the size comes into picture what is the topology topology as I mentioned is one computer is connected to all of them or to the next door neighbor how do they can how do they connect that is the one or are they connected in a hierarchy so based on that you can have like a star connection or ring connection or point to point connection things like that and then hierarchically connected those are all like point to be used to follow physical as I mentioned the it's the medium by which the computers are connected to each other and today we have several such medium one is the ethernet the other one is the gigabit ethernet fiber channel these are all like characterized as various speeds so that you have a you can establish the connectivity in fact I should add here that even Wi-Fi also can be considered as a physical connection which is what is the characteristic of connecting wirelessly even though there is no the medium is actually the air that enables you to come out and finally the protocol there are many many types of protocol the earliest one is the round robin then the round robin is essentially every computer is connected in a circle big circle and each one gets specified time for communicating so essentially I communicate for my 100 millisecond and then pass the command to the next one or the next one is implicitly it will take over so every say like 10 computers are connected in this network every computer gets just 100 milliseconds so by one second you cover all the computers so every second the computers get to connect get to talk you can see like how inefficient this system can be because if somebody doesn't want to talk still he will hold up for 100 millisecond before he pass it on I mean before the control goes from person then there were token ring that was developed which is mostly there is a token that it gets passed if you want to talk so if I want to talk I request the token from whoever has the token if I get the token then I can talk and then when I have when I finish talking I still hold on to the token until the another person asks for it and then in that case I can just pass the token to one person again you can see that how inefficient this kind of system could be so there are the in real terms actually like I mean the 100 base t 10 base t things like that are more appropriate for the protocol and then finally the hyper transport this is another protocol where it is all point-to-point connections so let us move on so the next one so now that we understand what the network is now how do we make them connect so one one of the significant achievement in the 80s is the development of this open systems interconnection model to enable how computers can talk to each other until this time like I mean all the communication used to be very ad hoc every company had its own rules and every computer used to communicate in its own ways but this open systems interconnection model pretty much standardized how the computers need to connect and this helped develop the whole internet itself which is now as you know we cannot live without so the open systems interconnection model divided the whole communication framework into seven layers so the first layer here is the lowest layer which is physical then there is a layer called data link layer then there is another layer called the network layer and then the transport layer so these four layers are the lower layers lower layer these are the ones by which the data actually gets transmitted okay so now the next three layers the session layer presentation layer and the application layer are at the top of the pyramid they are more concerned with the semantics of the message which is okay I am sending a message so the lower four layers are just concerned about how can I get it to another person but the top layer is the one that gives the intelligence to that message so that it is routed in the proper way so again so if you think about like an human the the brains are all in the top the application presentation the session layer and then these are all the other sense organs which make them make us walk around so if you if you just left it to these layers this four layers we will be just walking on in because we know how to walk but in order to reach a destination we need these three layers so let us look at how these layers are positioned again as I mentioned the OSI is a big topic there are graduate courses on just this just one one aspect of it just explaining all these layers and how they communicate how to build those layers so we won't go into that gory details we only will limit ourselves to why this is important and how can we use them use it in our networking phase and then we will just move on at the point let's look at we look at look from now the top down it is we look at the brains and then we are going to more details the lower physical layers so the lay layers seven and six and five there is a reason why we combine these three things that I will explain a little later but the application layer provides some different services to the application so this is where the top most the the all the gory details are shown I mean or the gory details are hidden but the actual semantics is shown so it uses the underlying layers to do the work and here the application layer can be just your mail program the HTTP which is a website or the telnet and we will study in more details regarding the next two which is the FTP or the file transfer protocol and then the DNS so this next layer is the presentation layer this converts the data from application into a common format and vice versa vice versa here is when it gets the common format data from the down below it converts that into the application so that applications can be corrected the session layer essentially is the layer that organizes synchronizing the exchange of data between the application processes again we combine this because one of the key protocol that we will learn which is the IP the internet protocol combines these three these three layers into this one okay so now let us look at the next layer which is the transport layer this is where the messages are actually getting transported and it provides end-to-end transportation of the segments so example here is the TCP which we will browse through now in the next section again this actually this layer encapsulates the TCP segments like what we are we want things to be done into layer packets and it also adds reliability by detecting and transmitting the last packet so here so whenever a packet gets lost this is the layer that returns which that until it gets a message saying that that packet was by whoever was the receiver and then it uses these acknowledgment and sequence of number and sequence numbers to keep track of successful out of order and lost packets there are timers that are also included in this layer that help differentiate between the log and the delay so if the timer is waiting indefinitely you know that actually like there is a loss and there are fixed number of time fixed amount of time of it how much it will wait before it can declare that something is a lost packet so we have seen like I mean from this one it's more like the real program or a command or something that you want service out of and now we talk about packets in this slide where we now take that thing take the program from this slide break that into small pieces and then we try to send it to whoever wants to service that particular program or service request so now when we go into the next layers they are much more granular so we will go into that so before that I would just wanted to say a couple of words so I gave you the example in layer 4 that it is tct as the example which is it stands for transient in terms of protocol this is a connection oriented protocol there is also another one that is prevalent which is the user datagram protocol which is more like connection less protocol and but this is little bit unreliable so I just wanted to wanted you to know these terminologies because in future you will be using these terminologies or somebody may ask you about these so now let us go to the the next layer which is the layer 3 layer 3 is essentially it is the network layer this is the layer that route the information within the network so this mainly deals with all the address spaces addresses so essentially IP is a network layer implementation and it defines the addresses in such a way that the route selection can be determined so we will look at what is an IP address and how to do how to actually assign an IP address or how the IP addresses are assigned today and then again the it uses a single address space for the entire internet into network it adds an additional layer of processing so it is different from the the MAC address that we know so here essentially like I mean for unreliable networks essentially like I mean if the packet gets lost the network layer doesn't care for higher layers and since the higher layers actually can recent packet so this layer is not really that the intelligence is already lost when you come here and then basically like it powers packets hop by hop so again as we know that if you want if you have like many computers connected and from one computer it can actually hop through multiple computers then reach the final destination you will see like how this is done in more more chart in a little bit while but I just wanted to give you the introduction on this and also it makes the routing decision as to how can a packet be sent closer to its destination so all the time it is looking at the address and comparing with where it is and where is the destination and see what will be the next the the half point that it needs to route and then if it routes to that point whether that will make it closer to the destination or it's going to be far away from this based on that it transmits that okay and so essentially like I mean you have these since I talked about all these things like I mean so there are powering tables and the routing table and that kind of it knows that please it's nearest neighbors as to who they are what is their address things like that so based on that it can actually like send these packets so out again the routers can talk to each other to exchange information about the network topology so if another router which is having this table routing table it can actually share the table with this computer so that it to know what is the surrounding network of that particular now let's look at the data link layer here the intelligence is completely lost so we started with the packet information or actually the actual message then we split into packets then the the previous layer the network layer was only concerned with that is it now when we go into data link layer even like we are losing that intelligence also here the data link layer is only responsible to provide reliable transmit of data across the physical network it bundles bits into frames and moves frames between the holes on the same wing and the key characteristics of the frame is it has a definite start and end and the size so the receiving computer can determine from the looking at the header of the frame it can determine when the message will end and it also has a definite source and the destination link layer addresses so this is the Ethernet MAC addresses for the computers essentially so again once the network layer decides okay this is where I am going to go so then it knows that exactly okay I am receiving it from this computer things like that so it is clear addressing is already specified so and then the link layers detect corrected frames and some of them also can recent so some of the upper level tasks can be done at the lower level also this is the things are evolving so you will see more of that and finally the physical layer which is essentially the actual connection itself and here it moves the bits using voltages so we don't even talk about the bits and the bytes these are all like just the the real communication channels so one of the examples is the modern day example is service or the serializer be serializer essentially like I mean there we don't worry about okay what is the address that it is going is it going in the right direction things like that here we just move one bit from one point to the other and that uses just the voltage so here we look at the eye-opening various other characteristics whether the RF interference is there or not things like that that is all worried at this level so again there is no concept of bytes or frames the bits are defined by just voltage level very similar to so this is there the VLSI designers really contribute in the sense of our knowledge about how things transmit through copper or any other or fiber so again so now we understood the various layers now let's put together and see like I mean how we can make use of this that I mentioned the distinction between the TCP IP and OSI protocol is the top three layers are combined for the TCP IP which is essentially like what we will be dealing with in the Linux networking side the OSI is more like a generalized policy specified specification so the TCP IP is pretty much the implementation for Linux I think of it that way again just a recap is the application layer provides the main application support the applications can be like mail the web or HTTP etc. Transport layer this is basically the TCP end-to-end reliability that is the main reason or main use of this layer the network is essentially like it is basically like the IP forwarding essentially it looks at a particular packet in its address and it forwards to the neighbor using a best-effort algorithm so you can think of it as what is the routing table and what is the forward table tells it and then based on that it will do the forwarding and then once that it decides like that put it in then the data link layer takes over and that helps in framing the message and then the delivery of the message itself to the destination and it uses the physical layer essentially the wires to send it and again here there will be like other protocols that will take over as to whether how to clock the system whether to send the clock along with the data or separately or is it a serial data or plus type of communication there are several things like study and nowadays it's all like the studies is basically it's a serial data that goes on so those are the things that that that are done in the physical layer so here is how it is important for our Linux application so the application layer is there the kernel resides in and kernel also uses some of the concepts basically then these are all the various protocols and that is actually sent to the network interface which is then is a physical interface to the subsequent computers and if you look at it this kind of this model helps isolate some of the the various areas for example if we are using a Wi-Fi or or a fiber channel or any of the wire wire line communication those are all like isolated from the top because only the network interface is going to change so this helps us to actually reuse all the programs that we are writing all the protocols all the intelligence that we are building upfront to still reuse and gain benefits even when the lower level lower layers changes to some other thing again same thing like I mean if you consider any layer that those layers can be changed independently of the other layers and that is one of the key benefits of this model so let's look at the the layer interaction because this is one of the things that we want to just browse through it and then we can move on again when we start doing the communication the topmost layer essentially are essentially like I mean those are valid end to end what that means is when we start a communication we start at this layers and then the receiver wherever this application gets executed they also see all the way up to these top layers the transport protocol could be end to end and the network protocol is throughout the internet work itself and then basically like I mean the link and the physical layer may be different on the top so you can on one hobby you can use Wi-Fi the other hobby can be wire line things like that so this can be so now let's see how this is done so here is an OSI interaction which is essentially like the top layer so means the application starts the host essentially like I mean stop the process the various translations happen throughout the as the message goes down these four layers and then finally the physical layer transmits to the next one and in the next one the the message is put together all day up to the network layer there it is seen that okay this is not my destination something else is the destination so again this particular router transmits that message to the next one and in the next router again like I mean it tries to identify whether it needs to provide the service it's not so the message stops at the network layer and then it gets routed back and then it goes through the physical layer and finally we do the host where now it goes back all the way and then provides that service so we can see that actually like this top four layers are end to end and the message the network layer is throughout the internet working whereas this physical layer could be different for different messages and different destinations so similarly on a TCP essentially like we don't have the session in the presentation layer but working wise it's very much similar to the earlier model where it goes through the physical layer goes up and then the IP layer essentially disciples and say that okay hey this is not the destination so go to the next hop so the next hop point of the next router takes over and this could be like meaning actually as stated in the bottom diagram there could be one like couple of routers or many routers are if the host is directly connected to the other whole then you can directly go up also so it all depends on how your network configuration is you already saw that the characteristics of the network so that's what determines how these communications can happen so now we will be going into the IP overview I just wanted to give some basic overview of the IP addresses so here there are three different things basically like a network address or subnet address and the host address and then basically these are the numbers that normally encounter say like 140.12.112.28. something and then how that connects to the other ones and then this is the gateway which is essentially what is the router and that translates into or sends it to another one here this host is a 30.xx so you can see that okay the router is kind of an article between sitting between these two and enabling the community so how this is done so in the IP header essentially like I mean we have so this is what the consisting of a this is what is in the message you have various fields of identification again I don't require you to understand all of these in this course the main things that I want you to know are basically the length of them the message first is also encoded and then what is the source IP address and the destination IP address here we also talk about the time to live essentially like I mean this field make sure that after that particular time it is declared as a lost packet basically can be retransmitted so this time is used for to set the timer to enable the timer so that it can see like then it should retransmit and then there are some identification bits and then there is a header checks and so you can see that one two three four five six these six 32-bit words are essentially just to set up the communication and then after that the data will begin so and you can also see like from checks and essentially for the reliable transmission so when the destination encounters this and then basically the checks and then the bit streams don't match then you can discard that and then it will wait for the packet another packet to be delivered so then definitely it's how to communicate and it's achieved through these protocols and you can also see that actually like the overhead is this two three four five six times 32 bits over overhead of this protocol because for every packet that you send you need to send these bits and so on and this actually explains how the communication really happened so the data the transport layer attaches the header and it converts the data into a transport layer data and then when it goes to the network layer network layer adds more header it takes the whole thing the network layer data and then if you look at it actually it is it has this the transport layer header and then the data and then the data link layer now as it puts its own header and it also puts a trailer blocks and suddenly you can see that actually like the data is only like so much and all these are overheads for the communication so the I introduced several terminologies in this lecture the packets essentially are like it is a encapsulated or it is a capsule a message capsule so let us go back to this picture so the message capsule contains the data and then it contains a little bit more so you can think of this as a medicine say for example where the main ingredient main active ingredient is the data and then you put a coating or sugar coating maybe or using the header and then you have you are actually putting multiple coatings because it is going to go to multiple systems and finally like a top cover to cover the medicine and which is the actual the capsule itself and that is how you can picture this and then that that is how it goes from various form phases so in this lecture we use like I mean different name form so at the ethernet of the link layer we call it as a frame at the IP layer we can call it as a data gram and at the TCP layer we call it as a so you can look at this so here is the link layer the link layer is essentially now we call it as a frame and then we go into the the network layer the IP here and now this is a data gram which is very similar to a telegram or something like that and then at the transport layer it is still called as a segment so they are all referred to the data with various pieces added to it and we will briefly look at how these things are added and then sometimes we just use packet for all these things so in the documentation and things like that you will see all these different terminology we may just use packet for so now we go into the more details which is here so we start with the lowest level which is the ethernet of the transport the link layer so in link layer we have a preamble we code in the destination with using a six bytes and then source is also six bytes the length of the data is given as two bytes and then what kind of what is the type of that message which is another two bytes and then we transmit the data the data can vary in size from 46 to 1500 bytes and then there is a NP which is like a CRC which is also like which is more like an encryption that constituted four bytes so the destination and source are the 48 bit MAC addresses and then the type is essentially given as these numbers so basically like 0800 means the data portion of the ethernet frame contains the IP data gram and then the 806 is for the ARP type of data so this is that the ethernet now when we go into the next higher level maybe so the IP in IP essentially like I mean now the bits are organized in this fashion again you see that actually like I mean this is the things may be small but the data is broken into multiple pieces there here once those the data gets added then it gets compiled into this form there we have a version some IHL the type of service the total length and then basically some identification there are some flags we saw this one the time to live protocol header checks and the source address destination address and then some options and padding and then finally that is that the six 32 bit or four byte thing so so far this is like 24 bytes of dimension but get scale it is same so here the addresses are now different here there are more like the MAC addresses then so here they are like the IP addresses more so again the MAC addresses just provide a point-to-point or one hop whereas now the IP addresses will provide us to go from one computer to another computer far far away then when we go to the next higher layer the TCP layer it is even so the way it is here now we are defining what is called ports there is a source port and the destination port and the sequence number and then an acknowledgement number then it has several flags and then finally like I mean this is checksum and then finally the data is also sent as with this in this segment so here the source and the destination are no longer the IP addresses now they are the ports so once you know the IP addresses this IP addresses are already implied by the IP header and we know which port to open on those IPs so we will we will go into more details when we talk about the directory services which will be coming in the next next sections and then the data offset is 5 which means like there are 20 updates after that the data so again there are predefined rules as to how to get the data get to the data and things like that so on the Ethernet layer again basically they are the 48 bit unique device addresses provided for each of them I encourage you to find the mac addresses for your machines you can try to find like what kind of command is needed to get to the mac addresses and basically it uses this ARP or the address resolution protocol in order to communicate this information so in the Linux world essentially like I mean so we saw all these things essentially the networking the inter-process communication they kind of they are called it uses a special kind of pipe support several address families and support several socket types so the socket is what we will see so here is the basically like the various families that it supports but you can also see that actually the amateur radio protocol is also there with the in the Linux itself but we will limit ourselves to mostly like the unit for the main pockets so and then the sockets are essentially whether it is a stream it is a datagram and then basically can be a reliable delivered messages or a sequence packet we will just touch upon these things we won't be going to be so I just wanted to give you an idea about so we saw from the TCP IP and the Ethernet layers below so they communicate through these sockets to the Linux so when we learned about this essentially like I mean though these are the next higher layers which are on top of the TCP layer itself and which provides the network so essentially like I mean the TCP and they open what are called the sockets which are essentially mentioned here and then these sockets are the ones that communicates to the network applications from the user side so here also like when you can see that the kernel is all the things that are below and then if they transform to the network applications on top so a simple client server mechanism is what we will talk about so in a server actually there is a socket that's created we bind an address to the socket and then the server just listen for the client client also creates a socket and then it connects that socket into to the server and once that connection is received and if the server is okay with the connection then it sends an accept signal back to the client and then the client starts sending whatever the message that it wants to send so this is a simple client server protocol an example of this is the HTTP so again when we make do a Google search essentially like to search something actually the that client is making all these kind of connections to the server and then getting the data out of it and all the things so like now we saw this much essentially like there it creates a socket and starts communicating that starting to communicate here represents all the things that we saw in this diagram which is below this portion and also all the things that we learn in all these this diagram so I hope like I mean now we have a good understanding as to what happens when we send a request and how that gets into the machine and how it gets communicated so this all goes back to that OSI layer definition of the PCTIP protocol that we talked about so there is a lot of things that goes in the background we do not we do not really understand or we do not really want to understand of the point again it is important from the real estate designers perspective because all these things ultimately end up in the designer's hand and real estate designers want to improve these designs and make sure that the communications are always reliable and proper so with that we conclude today's lecture and we will pick up some more of this IP addressing in the next session and then we will continue our other higher the advanced Linux networking topics in the next session thanks