Tag: Internet

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What is the Linux Host File?

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Hey guys, in this video we’re going to talk about hosts briefly, so in terms of our local host actually. So, there’s two parts to this video, the first we’re going to cover is the hosts file and we briefly touched on that in a previous video I think when we were, when we were deploying I think our Meteor application with Apache 2. We went into our hosts file to create some routes for the, for the application. So, basically the host file is in “/etc/hosts” so we can go ahead and open that up just type “sudo nano /etc/hosts” and hit enter. Put in your password and this is our hosts file. So, we actually did we were in here for app.localhost, subdomain in python, so the virtual hosts, and Python deployment, and Meteor deployment we were in here, and I didn’t really explain to what extent you can use this file. So, as I explained in the networking introduction video, a DNS server basically hold records of what domains point to what IP addresses. Think of this file as an internal DNS lookup functionality. So, when I go to apt.localhost the first place my computer checks for a route is the hosts file. If it doesn’t find an entry for a domain in the hosts file, then it goes out to the router, and then your ISP, and then a DNS server, and it checks there if there’s any records for it. So, by adding entries here we can actually override default behavior of known domains that we want to change. So, what I’m going to do is open up Firefox here for a moment, and I’m going to go to a website that will allow us to get the IP address of google.com, because we’re going to be using that. Just gonna go to network-tools.com and I’m gonna type in here google.com, and we can see that this IP address is the one we’re looking for. So, I’m going to copy this here and I’m gonna jump back into this file. Now, this file can take three columns and we’ve only discussed two so far, so let’s go ahead and cover all the columns here in great detail. So, the first one is the IP address that we want a route to. The second column is gonna be the domain or the host’s name that we want to route to that. So, let’s just type in go.com and then the third column is an alias, so we can just type “go”. And, so when we save this file what we’re gonna is when we go to go, it’s going to go to google.com and their their servers have actually, their not ok so they’re doing a lot of internal routing there. Let’s try YouTube. So, what we’re gonna do again, we’re gonna get actually let’s try something that we know is going to work. So, I’m just gonna type in my own server name here, and grab that IP address, jump back into our hosts file, and I’m gonna paste that there. Now I’m gonna save this again and go to go.com. It’s saying it’s not found, weird this just worked.

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How to use Netstat to Track Detailed Network Statistics

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Hey guys, welcome back. So, last video we looked at a way to really track packets and the packets that are actually being sent to and from this machine individually as packets, and now we’re going to talk about a man called “netstat” which is an abbreviated term for network statistics. So, basically the command that we’re going to be using throughout this video is netstat, and based on the flags that we pass it it’s going to return different statistics. So, if I put “netstat -nr” the “n” option makes netstat print addresses as dots, you know dotted IP addresses rather than symbolic host network name, so this is gonna make sense if you want to see the actual IP addresses rather than the domains that are connected to the machine. And, so this is what I’ve got right now. Basically, gives us the information that were looking for regarding the IP routing table, and so the “r” flag in that command that I just put basically states that we’re looking for the kernel IP routing table, and that basically shows what certain things are routed to. So, let’s actually display network interface statistics themselves, and we’re gonna do that with the “-I” command. So, we’re gonna take “netstat -I” and this shows us the usage of each of our devices, and so we can see the local host here which was configured has sent this many packets right here, and it’s received this many packets. As compared to our wireless interface which so far has received that many, and actually this is bytes not packets, and this many. So, you can kind of see how this would be useful. We can actually display connections to our machine as well, and so I think my system update is still going, it is, so this is going to be good. What we’re gonna do is run the “netstat” with the flags -ta, and this is going look for active sockets and it’s going to print out the status of them, and basically you know the foreign address in the local address. So, this obviously is our local machine here. These are the foreign addresses that it’s connecting to, and so what I’m going to do is I’m going to run “netstat -tan” and it’s gonna show IP addresses instead of the host names. And so you can see how that’s gonna be useful because we can actually combine elements of the different flags that we’re passing to the netstat command, and it’s basically you know going to change the way that each of these outputs works. And, so that is how you would use netstat to view active connections and active route of IP addresses internally through through the command line here, and you know if you’re not sure if you think your computer may be connecting to a malicious host or something, what you can do is you can take these IP addresses and you can actually look them up through through a website like network-tools. I think it’s network-tools.com it could be .org I’m not sure, but you can find information about each one of these hosts if you’re not sure where it came from. And, just by looking at these you might be able to you know the actual host names themselves you may know what they are. I think these are all my updates that are happening through the software update, or so that’s I don’t recognize any of these. So, that’s how to use netstat. I hope you guys enjoyed this video and found informative. I hope you guys can basically understand what netstat does. It’s a very simple command but it’s a very useful in a lot of circumstances. So, thank you guys for watching this video, I’ll see you guys soon.

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Practical Networking Commands pt.1

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Hey guys, welcome back. In this video we are going to get to some practical networking things, and this is all in terminal. And so the first thing we’re going to do is bring up terminal, and first I want to talk about the ping command and what this means and what it does. So, you can ping an IP address or a domain name to see if you can get a successful response from it. This is a great way let’s say you’re using a web, this is just an example, if you’re using a web browser and you’re trying to troubleshoot if the web browsers isn’t working or if your entire internet connection is not working, you might drop down here to command line and run a ping command on a known host that you know is always going to be up, for instance google.com. And so that’s exactly what we’re gonna do, so I’m just gonna type in the command ping and then the address of what I want to ping. And I’m getting a response and it tells us what length of time each response is taking to return to us, so yeah. It also shows other stuff like the exact IP address, the server that it’s reaching, and that good stuff. And this is gonna just go until you close it, so just CTRL+C to exit, and then it gives you a breakdown of what happens. You could let this run for a while to see if you’re getting any packet loss through your network card, and so that’s what pinging does. So I’m going to clear this up here and we’re going to talk about the command ifconfig. So, on Windows in command line you have a command called ipconfig and it spits out a whole bunch information about your network configuration. In Linux it’s ifconfig and it does the same here. I’m gonna run that command again. Alright, so this is going to link our addresses here or our network interfaces, and also any IP addresses that it has and whatnot. So, the first one is gonna be an ethernet which I don’t have plugged in right now, and so it’s gonna be basically not working. This is the name of that interface. This is our local loopback, so this is like a virtual interface that runs that it has our local host address here and it basically controls that, and then down here we have our wireless ethernet which we can see this is working as I have received bytes. So, “RX” basically means what you’ve received, “TX” basically means what you’ve transferred out. So, that’s how to read that. There’s an IP 6 address right here and my IP address, this is gonna be my NAT address and it gives ID’s and stuff of the network interface device. And so that’s basically how to use ifconfig, sometimes this might be useful to see if you know you’re getting a valid IP address from the router, to see you know if it’s actually working at all which you can see here mine is. I’m gonna clear this and what we’re going to go over now is a command called TCPDUMP. It’s a really powerful command line packet sniffer, so it can analyze the packets that are you know going in and out of your computer or your network. So, first thing we need to do is install it if we don’t already have it installed. So, “sudo apt-get install tcpdump” it’s probably already installed but just in case make sure, and it is it’s the newest version. So, this is a big command-line tool and I was gonna do more stuff in the video but I think we’re going to cut it off after this command. So, what we’re gonna do is basically just run the command “tcpdump” We don’t have permission to capture on that device so we’re going to run “sudo tcpdump” And this capturing all packets that are coming in and out of my computer. This is just gonna run until you cancel, so I’m just gonna cancel here. Now, as you can see that was a pretty big output and so what we can do is we can only capture a certain amount, so what we’re gonna do is that. How we do that is basically using the command “sudo tcpdump -c 10” and that’s good. Alright I have to run sudo. So, this is going to capture 10 packets.

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What is a Local Area Network (LAN)?

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So, in the last video we described how the internet works, what the internet is, is technically an interconnected collection of networks. So, all these little networks all over the world can now be connected to other networks in the world, and so we have the internet which is just that. So, to understand the network here we’re bringing it down from you know the top level stuff, down to a more localized thing. And so a local network is the type of network that you have set up in your house, where you connect to the router, the router then you know can interact with the internet for you, and then return the information to you computer. Now, I wanted to talk for a moment about IP addresses and the current issues that face them, while still using ipv4. So, let’s open up a document here. So, an IP address looks like this. This is an IP address of a server somewhere, probably, if you put this in your browser…actually let’s try. That was just a random one that I just wrote up, let’s see what happens. This is probably the address of somebody, somebody you know, somebody is connected to an internet service provider and they get one IP address for all their computers, and the reason why that happens is because these IP addresses can go from 1.1.1.1 all the way to 255. So, as you can imagine the range is pretty big but it’s not quite big enough for the human population, and so we’ve been running out of IP addresses for the last fifteen or twenty years. And, multiple solutions have been brought into the equation to try and solve this problem. One of them was called a NAT. What this is is a network address. Basically, you have one router you have one IP address. So, the IP address you have let’s say is this one up here at the top, this is your IP address that the internet service provider has given you. Without the use of a router you can plug one device into the modem and your computer will use this IP address in requests, so basically when you send a request to google.com to load a page or to load a search what happens is your IP address gets sent to Google as well so that Google can return this data to your device. But, what happens when you only have one IP address and seven computers, that’s when the NAT comes into play. So, this IP address now is the IP address of your modem or router, and it assigns NAT addresses to all the devices on your network. So, let’s say you just have two devices on the network. The first one, actually the IP address of your actual router is likely this. I’ve seen one instance where a network did not use this IP address as its routers IP address. The IP addresses that your router will assign to computers in your home all begin with 192. So, basically it would be something like that, right, that would be the IP address, actually hold up I got this wrong. This is the IP address of your router, this is the IP address of your first computer. So, it always begins with 192.168 Your second computer might be this, and your 3rd computer might be this. So, now you have three IP addresses, three devices on your network and your router here is keeping track of them. So, from this device I type google.com into the address bar, what happens is this IP address along with the request gets sent to my router, the router then sends the request off to the ISP and then over to the internet and stuff, with the IP address of the router which internally is this and externally this is our ISP IP address they gave us. So, what happens this gets sent to google.com, google.com sends the page back to this IP address connected to the router here, the router then takes that request and connects it with the device that requested it, and then it sends it back to that device. And so that’s how a router interfaces between a local network and the internet. So, in the olden days before the NAT address and routers really took off each one of these computers would have had a different IP address, so it would have looked something like this. So, that would have been 3 actual IP addresses when we found a way that you actually only need one IP address for our network, and so that’s what a router does and so these IP addresses are local and you’re gonna see these in terminal. Now, one other special IP address is 127.0.0.1 On every computer this means this computer. It’s basically a self identifying IP address. If I were to type this into my browser I would see my localhost, where if you put this in your browser you would see your localhost. The NAT IP address basically works the same way. So, if I were to go to 192.168.0.3 it would try to find a computer only on my network that has this address and then connect to it. So, that’s how a router works, in the next video we’re getting into the ifconfig. On Windows you have an ipconfig command, on Linux here you’ve got ifconfig and we’re gonna cover that in the next video, and a a few other commands as well. So, thank you guys so much for watching, and I’ll see you guys soon.

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How does the internet work?

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In this video we’re not going to be doing anything, we’re not gonna be learning about networking specifically on Linux. We need to understand a few general concepts before we get to that. So, this video is going to be a sort of introduction to networking on Linux. An introduction to networking in general. So, right now you are on a computerized device watching this video which is on the Internet. And the way that’s happening is basically you’re connected to a router, or a modem router all-in-one device, and the router is connected to your internet service provider, and your internet service provider has devices that are connected to the bigger world of the internet. So, you send a request, if you open up a browser and type in google.com and then hit enter, your web browser sends that as a request. It’s basically saying okay this is the web page that this computer wants to look at right now. It sends that through your router, which sends it to your internet service provider, and your internet service provider has all these fancy computers that properly route certain requests to DNS servers, any requests actually. What a DNS server does is it says okay, you gave me this string of text, a domain name or URL, and I have a record here that shows this domain or string of texts is supposed to serve up the content at this IP address. And so how the internet works is it doesn’t understand Google.com or Facebook.com. The internet uses network addresses, right, and so think of it like each web server, each server out there has and address just like every house on your street has an address. So, if you were gonna send somebody down the street to Joe’s place, you would say okay well go to this address, then you would give them the address of Joe’s place and they would be able to find it. The same thing is happening on a DNS server. You give the DNS server a domain name that you want to look at, and then th the DNS server takes that and says okay well I know this domain name is supposed to route to this IP address. So, you request, you need to go over to the server to get that content, and so your request then gets translated to an IP address and other information, and it gets to the web server that it’s supposed to be at. And then the web server running Apache or anything really nginx, I’m sure there’s tons out there that I don’t know about, but the web server receives requests, it receives all of the information related to it. So, cookies you know session variable stuff like that as well as the exact item you want to look at it. So, if you go to website.com/something /something else, everything after the .com/ is called a URI and that indicates what piece of content on the server you want. So, think of the first part domain.com as what server you need to be communicating with, and then afterward you know /about.php or something that’s gonna tell the server once it gets the request what page it needs to send you. And then it does it’s you know rendering process and it sends you that page in the exact same route that your request took to get there. So, it’s like when you send your friend down the street to Joe’s place to pick up a box of pizza. So, your friend walks down the street he turns left you know maybe turns right, he gets to Joe’s place, he walks in says hey I need to get a pizza, Joe gives him the pizza, then he walks same way back to your house, and before you know it a web page has loaded within your computer box. That’s how that happens. I hope you guys understood that. In the next video we’re actually gonna cover a few more concepts before we dive into you know really understanding to the point that we can use applications to do certain things. So, I hope you guys found that informative. If you didn’t, if there’s any point in this video that you felt lost or confused, or even that I was just rambling, or even if you just want to tell me you know a few more web server applications aside from Apache, there is a comment section to the side of this video. You just leave a comment I will reply and get you whatever information you need, and hopefully this will make sense to you.

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Introduction to Networking on Linux

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So, we’re all done with the user accounts and groups and stuff and we’re gonna move on to networking. Networking is a big topic in and of itself, and so there’s no humanly way possible I’d be able to teach you everything there is to know about networking, and I don’t plan to. What I plan to do is give you guys the most essential and necessary information about networking and then take that as you want and you know further development, but this should be a starting point for you. It should help you understand what’s actually happening on a network, and even what network is. So, for people new to I guess computers, technology, and maybe not new but maybe you’ve used the internet before and you just haven’t thought about you know what’s actually happening, and that’s how I was for a long time actually. I had worked with an internet service provider and before I worked there I just though you know the internet was magic. That you know I opened up a web browser and type in a series of letters you know separated by a few dots that somehow, magically, I didn’t really care how it happened at that point it went out and found a page. You know magically brought it to my computer, and so if that’s the kind of understanding you guys have at this point this is going to be some really great information for you guys to take and really absorb.