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I also think it'd be super effective

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and useful at this point to take a look

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at some of the details here at the NSX manager,

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which is acting as the centralized control plane

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for the entire operation of NSX.

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So the NSX manager is acting

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as the centralized control plane,

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it's also acting as the management plane.

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So you and I log in, we connect to the NSX manager,

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we specify what we want to have happen,

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and then the NSX manager communicates

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with the transport nodes to make it happen and vice versa.

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The transport nodes are also communicating information

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back to the NSX manager as well.
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back to the NSX manager as well.

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And you might think, well, what does the NSX manager

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need to know about an ESXi host that set up

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as a host transport node?

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Well, if we launched a VM on ESXi-A, for example,

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we connect it to a segment, there's all kinds of activity

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that this VM is gonna be doing.

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Things like ARPing, looking for other layer two addresses,

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maybe this VM, we'll call it VMA,

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is looking for the layer two address

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of this VM, VMC and stuff that ARP request comes in.

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Initially, that ARP request is gonna have to be sent

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over the tunnel to ESXi-B,
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over the tunnel to ESXi-B,

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and then this VM can go ahead and respond to it.

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But how does ESXi know that it should send that traffic

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over the tunnel for flooding of that initial ARP request?

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The answer is the NSX manager has information

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about exactly which ESXi hosts are participating

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and also which VMs are connected to which segments,

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and the cool thing is if we have lots of clients,

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we probably don't want all that traffic

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to have to go across the tunnel.

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So if we have ARP tables that are being built

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and the control plane knows about it,

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it can actually share that information with other ESXi hosts
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it can actually share that information with other ESXi hosts

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so that in the future, for example,

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another VM right here that's also connected,

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if it's doing an ARP request

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and ESXi-A already knows about the information

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on that same segment about what that address is,

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the actual ESXi host can respond back

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and that traffic won't have to go across the network.

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So the NSX manager has the responsibility

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of a centralized control plane for NSX.

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It's also the management plane and then the data plane,

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the actual forwarding of traffic

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is being done by our transport nodes.

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In this example, we have two ESXi host transport nodes
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In this example, we have two ESXi host transport nodes

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and those are responsible for the data plane.

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For example, moving the traffic between VMA,

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who's trying to communicate with VMC.

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Another element that's committed back and forth

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are MAC address tables.

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So that way, if we have like six computers over here

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on ESXi-A all connected to segment 10,

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I'll put that here in yellow,

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and let's also imagine we have two or three VMs

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also connected to this segment that are being hosted here

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on ESXi-B, so I'll draw that connectivity in as well.

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In a switch environment, the switch would be responsible,

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or the combination of switches if there's trunking involved,
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or the combination of switches if there's trunking involved,

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or connectivity between the VLANs here on these switches,

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they would maintain MAC address tables

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of which ports are associated with which MAC addresses.

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So in NSX, if we have six over here

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and three over here all connected

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to the same overlay segment,

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all that information about the MAC addresses

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and how they're reachable is maintained by the NSX manager,

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and the NSX manager can also make sure

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that each of the ESXi hosts connected to that segment,

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that they also have that information,

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and that's an example of the local control plane

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on our ESXi host transport nodes,
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on our ESXi host transport nodes,

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so they have that information.

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So the benefit is if we're doing forwarding here

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between VMs on segment 10, ESXi-A has all the information

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it needs to know to make that forwarding decision locally,

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and if it needs to forward traffic over to ESXi-B,

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it can go ahead and forward that

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through the tunnel over to ESXi-B.

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So let me clean that up just a little bit.

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So I think it'd be super valuable to take a peek

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at the information about this segment.

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Currently we have no VMs that are connected

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to any of the segments, and let's take a peek

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at this initial state at the information
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at this initial state at the information

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about that segment that ESXi-A has

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and compare that to the centralized control plane down here,

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the NSX manager, to compare and contrast

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what they both know about this segment.

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And to do that, I'm gonna go ahead

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and open up a terminal emulator

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and let's log in with SSH over to ESXi,

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which is our host transport node,

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and we'll have a separate screen opened up

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over to our NSX manager.

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All right, so here's our connection over to the NSX manager

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and let's go over to ESXi-A,

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and it says the remote system refused the connection
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and it says the remote system refused the connection

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and that's because SSH isn't enabled.

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Let's fix that real quick.

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So here in the vSphere client,

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let's go to the host and clusters view.

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Let's go to ESXi-A.

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We'll click on configure,

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and we'll go down to services.

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Click on services, and then make sure that we're allowing,

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at least for now, SSH access.

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So I'll click on start and it is now running.

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Fantastic.

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Let's go back to our terminal emulator.

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So here in our terminal emulator,

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I'll go ahead and press enter.

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So for the logins, I logged into the NSX manager as admin,
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So for the logins, I logged into the NSX manager as admin,

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and over here at the ESXi host, I've logged in as root,

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and I'm also in this terminal emulator called secure CRT.

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I'm gonna open up a little window at the bottom,

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so if I need to do similar commands on both

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at the same time, I can.

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So to do that, I'm gonna click here on view

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and the menu for secure CRT,

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and I'm gonna ask it to show me the command window,

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which is right here at the bottom.

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So down here in the command window,

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if I right click and then hover

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where it says send commands to, I'm gonna say all sessions.

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So now if I effectively is pressing enter

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on both console windows simultaneously.
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on both console windows simultaneously.

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So over here on the left, on the ESX host side,

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lemme go ahead and move into NSXCLI

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by typing in NSXCLI,

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which gives us effectively the command line interface

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for the NSX stuff.

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Now press enter a few times,

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and there is context sensitive help

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on both of these interfaces.

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So if we did, for example, a get space

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and then press question mark,

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it's gonna show us a list of the next possible options,

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and one of those options is logical switches.

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So over here on this side, if we did a get space

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and a question mark, you'll notice over here,
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and a question mark, you'll notice over here,

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even though the commands are not all identical,

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we also here have the option if we scroll up

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of the option of getting a list of the logical switches.

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So at the command line at the very bottom,

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I'm gonna do a get logical switches and press enter.

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So this is interesting, on the ESXi host,

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this is prior to connecting any VMs to that segment,

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the ESXi host A, it's saying, you know what?

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As far as logical switches within NSX, I got nothing.

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Now, why is that?

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If we scroll to the right, nothing's there.

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So why is that?

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It's because this ESXi host,
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It's because this ESXi host,

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even though it could have VMs that are connected

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to that logical segment, it doesn't and as a result,

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its control plane doesn't have to worry about

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knowing about or working with that logical segment.

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So think of a segment

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like a logical layer two broadcast domain,

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here it's being referred to as a logical switch.

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But over here at the manager on the right hand side,

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it does know about one logical switch,

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and that's this VNI, this virtual network identifier,

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of 68608 with a very, very long UUID,
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of 68608 with a very, very long UUID,

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and if we scroll to the right a little bit more,

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it's also showing us the name of that segment.

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And again, host A doesn't really need to know about that yet

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or have anything regarding the control plane for it yet

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because it has nothing connected to it.

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So over here on the right,

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let's go ahead and do a get logical switch,

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and I'm gonna scroll up and grab that VNI.

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So we can either put in the VNI number

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or we could put this really, really long UUID,

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either way is great.

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So I'm gonna go ahead and just copy and paste the VNI,

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the virtual network identifier space
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the virtual network identifier space

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and then I'll do a question mark,

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and now we could ask for information

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regarding the ARP table associated with that virtual network

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or the MAC table associated

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with that virtual network segment

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or the transport node table, which if we had ESXi-A

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and ESXi-B, that both had VMs connected to that segment,

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they should show up.

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So let's do a few examples of this

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prior to bringing on any VMs.

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So let's go ahead and do an ARP table.

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Press enter and currently the command worked,

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but there's nothing there.

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There's nothing in the ARP table

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for that logical layer two segment because we have no VMs.
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for that logical layer two segment because we have no VMs.

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So we hit the up arrow key and we swapped out ARP table

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with mac table, same thing.

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Nothing's gonna be there because we have no VMs

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connected to that layer two segment.

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And if we use the command get logical-switch

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and the same VNI number again,

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and let's use this option here, transport node table.

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So I'll copy paste that, press enter,

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and that's also coming back empty.

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And the reason that there's no host transport nodes

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associated with that segment is because neither

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of our ESXi hosts, A or B,
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of our ESXi hosts, A or B,

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which are both host transport nodes,

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neither of them have any need for that information.

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Neither of them have VMs that are connected

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to that logical segment called Segment 10.

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So if you're ready for something cool, here it is.

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In the next video, we'll go ahead

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and bring up a couple of VMs,

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one on ESXi-A, one on ESXi-B, we'll power 'em up.

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So I'll see you in the next video in just a moment.