Hello, everyone. My name is Tyler McMinn with Aruba Networks. This is the Network Essentials series of videos. In this particular video, we're going to actually apply what we learned in the last video, covering layer 3 and layer 4. We're going to apply that concept to our lab that we've been building, actually trying to get a ping to work between PC-1 and PC-3. We'll follow each step along the way as to exactly what happens between the PCs and the switch, how the switch can actually switch traffic at layer 2, matching the frames as they come in on the individual ports to the PCs. Enjoy. In this example, we're going to go back to our lab that we've been working with. Taking a look at our 6300 switch, our connection with PC-1. What I've done, is I've added a connection with PC-3. We're not going to worry about PC-4 just quite yet, so let me hide that right now. PC-3 is going to be connected to port 3 of our 6300, just to make it easy to remember what plugged into what. Ultimately what I'd like to do is get a ping to go from PC-1. I'll draw this in green. PC-1 snake card through the switch and be able to reach PC-3. Then PC-3 to respond back with its replies for each one of those ping attempts from PC-1. If successful, we should ultimately learn the MAC address of PC-3 as we go through this process, as well as get our traffic to be reachable without any errors. Let's go through and take a look at what's involved, I'm going to get rid of that there. What I've done, is I've opened up my link, my console port, if you will, to PC or to the 6300 software. PC-1 is there as is PC-3. The first thing I want to do is validate that everything is working as I would expect. I can log in to my 6300, just logging in with Admin, skipping the password. We can add that later. I will show you how to save though as we go through this. For right now, if I show my MAC address table, what am I going to see? It should be empty given that PC-1 has done nothing in the last five minutes, so no MAC address entries have been found yet. What we'd like to see is that our traffic, and if you notice I did show int, instead of interfaces. You can type the whole thing out or just enough of it, that if I were to hit question mark, it knows exactly which command you're talking about. You can either press enter now or space and then whatever else you want to add to it. Or you can go back and hit tab and it will auto-complete it for you. Really nice how the command line tries to aid you during your configuration. The video is showing interface brief. Port 1 is up but we might have an issue here, given that port 3 is administratively down. Let's take a look at PC-1. If I do a show just in this case it's a little Linux machine. I'm just going to do a show IP all. That shows that I do have an IP address with a slash 24. That means the first 24 bits of this 32-bit IPv4 address is going to match my other devices, or I should say, needs to match my other devices in the same local area network. If not, I'm not going to be able to reach them. Let's do a show, IP all on PC-3. If we take a look here, I did go in and I did make sure that the first three octets or first 24 bits, match up with the first 24 bits on PC-1. They both begin with 10.251.12. whatever. The dot whatever is your host portion for last 8-bits. The first 24-bits are ones, and they indicate the network portion of your IP address. The last eight bits making a total of 32. The last eight bits are going to indicate the host portion and those need to be unique. If you think of this as the street you live on, you might live on a street with several other neighbors. That's fine, no big deal. You all live on the same name of the street, but you better make sure you each have a unique house number or apartment number or whatever. Otherwise, your mail might get misrouted and that could be bad. That's been set up okay. We currently have no gateway, which means we can only talk to each other. We can't get out to the Internet but that's something we'll deal with later on. We both have unique MAC addresses, and you can see that those are unique to each other. So there shouldn't be any issues at Layer 2 as well. So far so good. What I'd like to do is be able to ping my neighbor over here, send them some data using the Ping application here and what's going to be the result when I press Enter? Can you guess? It's going to fail. Now, why is it going to fail? It's going to give you a response back, 'Not Reachable', and that is because of this issue with a port being down. My Port 1 is up, which is good. My traffic should be actually arriving on that node, but I'm not able to actually get my traffic back. So it's being sent to the switch, and the switch is looking up the MAC address of this destination. In fact, it's not even going that far because my host, when I go to ping this, is looking up the MAC address of the destination in order to complete its frame and if it can't find the destination MAC address, it doesn't have a complete frame. It actually runs another protocol that's built into your computer's known as Address Resolution Protocol. I think you can see it here by running the 'Arp' command Address Resolution Protocol or ARP. It doesn't matter what operating system you have. They all use this tool in IPv4 as a way to discover what Layer 2 address belongs to this Layer 3 IP address. This Layer 3 address is tied to this MAC address. We know the Layer 3 address we're trying to go to because I literally told the computer what that address is and so it went to build the frame. It got as far as is all the Layer 4, 5 through 7, Layer 4, Layer 3. But then suddenly it stops because the Layer 2 can't be completed and it commits this ARP attempt which fails. If I look at my switch now, I should see that I was able to get that ARP broadcast received on my switch. I'll just hit the up arrow here a couple of times till I get my MAC address table show Command. And you'll see that the MAC address of my PC1 did indeed get resolved. So we did do it with the MAC address because we saw that frame come in but the switch doesn't know. It flooded out all of its available ports. Unfortunately, all of its ports other than Port 1 are shut down. Here's how we fix this problem. We need to bring up Port 3, show interface, brief and I can see that Port 3 is administratively down. I'm going to go ahead and go into global configuration mode that we saw in one of our previous videos. This allows me to make edits and I'm going to edit or configure interface 1/1/3 and you remember that the command to bring up a port that's been administratively shut down; the command is shut it down, was shut down. The command to bring it up, I can just Arrow or normally, I could jump to the beginning of the line with a Control A. But in this case I think it triggered a shortcut. If I do Interface 1/1/3 and I do a no shut down, then it should bring the interface backup. How do I validate that that actually happened? Well, I could just test my pinging and see if everything works, but that may be a little shoot in the moon. Instead I'm going to do it properly. I'm going do my show interface brief again or I could show interface for that specific interface if I wanted to and get all sorts of information. I'm just going to show Interface brief for now. In case you're curious, I'll show the 1/1/3 as well. You need a little more distance on this so you can see everything on the screen. But with a show interface, for a specific interface, you get all the information. It is now up, administratively set up, and we can see that the different aspects of the traffic that's going across, we see some traffic being transmitted, but we have yet to see anything being received oddly enough. Let's go in and if we do a show interphase brief, we can validate, indeed port one and port three are both up and operational. That means that my PC now should be able to do a ping when it will ARP, which will cause it to do an ARP request because the ping will see that it doesn't have the MAC address for PC3, so it will send an ARP request, which is a broadcast. If you remember, broadcasts will flood out all available interfaces that are currently enabled. Unfortunately, none of these are enabled, except maybe the management, but that's a totally different story. None of these other default ports are enabled yet. Only port three is running. With that being the case, you should only see the flooding occurring on that one interface, and you figure out why it's doing that. But see it flood on that interface, hit PC3. PC3 is going to send an ARP reply, telling PC1 about its MAC address. When PC3 sends that response back, that's going to update our MAC address table and the switch will now learn the MAC address of PC3. Let's check that out and see if that's actually the case. I'll do a little clear here. If I do a show MAC address table currently, the MAC address table is not only not learned PC3, but if forgot about PC1 because I've been chatting too much. Let's do the ping and see what happens. What I should expect to happen is the ARP to take place, the learning to take place, all layer two ports are going to be learned on the switch, and we're going to get a reply. See how long this takes. About three milliseconds, about a three thousandths of a second essentially. If I do a show MAC address table, I'm going to see I now have both entries. I learned when the ARP request came in, I learned the MAC address of PC1 as that arrived inbound, and then I heard the response coming back from PC3 here as that ARP got flooded out. The ARP reply responded back, and that populated my port three information right there with my MAC address. The switch was then able to forward that directly out to PC1. Even if these ports were open, you wouldn't see the reply go to them because that's a one-way or unicast type of frame. It arrived on PC1, PC1 then was able to build its forwarding table, get its layer two MAC address, and actually be able to send its traffic to our designated recipient. I can tell because if I go to PC1 and I do that ARP, again, I'll see, look at that. I learn this MAC address and it's about to expire in 60 seconds if I don't send any other traffic. Again in the real world, you're sending traffic all the time. You're checking email, and updates, and all sorts of stuff, so your switches never lose these MAC address tables. But both PC1 and PC3 have learned about each other through the use of ARP. That means I can ping PC1 from PC3 as well, and that's going to refresh all these cached tables and everything else. In this video, we covered layer three, IP addressing, and discovering paths to our remote destinations. We covered layer four, where we talked about segmentation, our source destination ports batch into an application, and saw a hands-on demonstration end-to-end of going from PC1 to PC3 using ICMP, internet controlled messaging protocol to ping that destination, which inadvertently triggered an address resolution protocol in order to handle our layer three addresses to our layer two port mapping on our PCs, and ultimately build our MAC address table at layer two on our switch. In the next video, we're going to be looking at how to save the work on CX switch, all the work that we just did, and how to erase it, as well as some basic troubleshooting commands. Thank you for your time, I'll see you in the next video.