DEMO: Configure Legacy Routing

What legacy inter-VLAN routing looks like

We're going to talk about inter-VLAN routing, and specifically legacy routing.

This is our network so far. We have our demo laptop, which is set up on VLAN 10, and we have our demo Pi, which is set up on VLAN 10, and we've already pinged between these devices, so we know we have VLAN connectivity throughout this network. What we can't ping right now is anything on VLAN 20, so we're just going to set up pinging between VLAN 10 and VLAN 20. That's all we're going to do for this demo.

The way we're going to do it is we are going to set up two cables going between the switch and the router. The first cable on the router is going to be connected into fa 0 0, and the second one is going to be connected into 0 1. On the switch I will have fa 1 0 1 on this side and fa 1 0 2 on this side. Then what we'll do is assign an access port to fa 1 0 1 to be in VLAN 10, and fa 1 0 2 to be in VLAN 20, and they'll be access ports as well, so they will not be trunk lines.

Then we just configure the router like normal. I will assign an IP address to fa 0 0 that's in the management VLAN, VLAN 10, and fa 0 1 is going to have an IP address of VLAN 20. Then the router is going to only get packets that are within fa 1 0 1 on fa 0 0, so it knows that it will then be able to route that to fa 0 1, which will only be getting packets and will only be communicating to those devices that are on VLAN 20. And then we will have connectivity.

So what we'll do is set up a ping, so we'll ping each one of these devices, and start programming them with these configurations, and we'll see how it goes.

The setup on screen

Before we get too far along, let me explain a little bit what I have set up on my screen right now. Right here you can see the network map, and so I'm going to be communicating from this demo laptop, pinging both the demo Pi here on VLAN 10 and the demo Pi on VLAN 20. Those are the two devices that I'm going to communicate to. In fact, I've got down here, I've got pinging demo Pi 1, which I've got communication because it's on the same VLAN, and then I'm trying to ping demo Pi 2 and it's on a different VLAN, so the request is timing out.

Up here I have my notes. I've filled in and added to my notes. Now I've added router 1 onto here so that it can show up on VLAN 10, VLAN 20, VLAN 30. In fact, actually at this point in time we can remove this 10.1.0 0.1, because we won't be using that anymore, and just specify the different VLANs. So I've got my notes all updated.

Then here I've already logged into, or virtually have, or I've SSH'd into switch one, two and three, although switch one is going to be the only one that we're configuring in here. And I have a console port into our router, because I don't have the router configured at this point for any kind of setup. So I've got that consoled into there, and I'm using the serial connection onto that.

Configuring the switch ports

Let's get into our configuration. Now, I said that I've got this plugged into switch fa 1 0 1, that is the first port, so let's just do a show IP interface brief, one of my favorite commands. There we can see that zero one zero one and one zero two are administratively down right now.

So let's take a look at the configuration of those. I'm going to do a 1 and hit enter, and we can see that yes, in fact it is down right now. Description null access port, switchport VLAN access 5, so it's part of 5. So let's go ahead and bring that up first, as part of this, and configure fa 1 0 1 first.

I'll get into global configuration mode, I'm getting into interface fa 1 0 1, and we're going to say description, and legacy, or how about we just say VLAN 10 routing, or VLAN 10 to router. Then we will do a switchport. It's already switchport mode access, so it's already in the access mode, so let's just change the VLAN to VLAN 10. And we're going to do a no shut on it, and that will bring that live.

Then we're going to do pretty much the same thing on interface fa 1 0 2. The one thing that I don't like about going straight into fe1102 is I'm always paranoid about, am I in that interface or not, because it just doesn't actually specify the interface. But I am, it didn't give any kind of error message. We're going to call this VLAN 20 to router, and we'll do switchport access VLAN 20, we'll specify VLAN 20, and a no shut on there. And that's it, that's all the configuration I have for switch one.

As you can see right now, I'm still not pinging my demo Pi 2, which is understandable because I haven't configured the router yet.

Configuring the router

What I'm going to do is jump into the router here. I need to log into it, so I'll pull up my usernames and passwords that I've created for these. Let's take a look at the programming that we have for these right now, so show IP interface brief. We can see zero zero is administratively down, 0 1 is up. That makes sense.

In fact, I could even check that on here. Do show run interface brief, and, let's do IP interface brief, how about that. And I can see that yes, one zero one, which is plugged into zero one on the other side, is down, and that is because it's administratively down on the router, and the other one is up. So that makes sense.

Now let's get into those interfaces, so I'm going to do a show run interface fa. Okay, there it is. We'll program it now, so let's get into it. IP address, and we'll program the address to be something that is in, this is supposed to be a VLAN 10, so we'll do the VLAN 10 network right there. I've just got it configured so dot one is the router, and that's pretty standard, so we'll do that one. Then we've got to give it a default gateway, or excuse me, a subnet mask, so we'll enter in the subnet mask in there. That is now configured. We'll do a no shut on it, and it brings it live.

At this point in time we should be able to ping this, so let's go ahead and bring up another command prompt and ping 10.1.10.1 to see if we've got connectivity.

That interface doesn't come up right away. It is plugged into a switch, and the switch does some communication to make sure it's not going to get into a routing loop, so it can take a while for that interface to connect in and set up. I'll continue to ping this until this comes up, but with the configuration that we've done so far, if I've done everything correctly then we should be able to ping it.

All that waiting made me wonder if I did it right, but yes, it is in fact pinging now. It just took a while for STP to do its thing. So we are pinging that, we've got connectivity there. But as you can see, I still don't have connectivity to that demo Pi 2, so let's configure that IP address now.

I'm going to exit out of here, interface fa 0 1, and I'm going to set it 10.1.20 because it's the 20 network, and 255.255.255.0, and we'll hit enter, and the no shut on there.

Confirming VLAN-to-VLAN connectivity

Now we have connectivity. I am pinging a resource, demo Pi 2, on a different VLAN. I have connectivity from VLAN to VLAN.

So let me show you what's happening here. I'm on this demo laptop, that frame is being sent all the way to the router on fa 0 0. That router is then looking in its routing table and puts it on another cable, another interface, fa 0 1, sends it back to the switch, and then the switch sends it to demo Pi 2.