Routed interfaces are the Layer 3 counterparts to switch ports, requiring manual IP address assignment and activation before they can pass traffic. This content covers how to view interface status, assign an IP address, and bring a router interface online using Cisco IOS commands.
Routed Interface Configuration
A routed interface is generally associated with routers, like a switch port is generally associated with switches. So let's go ahead and jump into a router here and take a look at some of the settings, and then how to configure a routed interface.
The first thing that I'm going to do is do a show ip interface brief. This allows us to see all of the different ports that are on this device, and we can see that there are two fast ethernet ports and a serial port. The first thing that we'll see is that these say that they're administratively down. The routed interface generally comes with it already shut down, and you have to bring it live. Then we can see that there are no IP addresses that are associated with this. So let's jump in here and let's start figuring out how to configure these.
The other thing I want to do is a show run and take a look at the configuration that exists on these interfaces already. So it has a no ip address, it's in shutdown, and it actually calls out duplex auto and speed auto. Whereas with the switch port, we didn't actually see it call out duplex auto and speed auto — that was the default, but it didn't actually say it on the interface.
Now let's do some configuration of this. First of all, we can do a range of interfaces with this as well, but let's just get into the fa0/0. I'm going to get into global configuration mode, and then I want to get into interface, so I'll type that in. Now I'm into fast ethernet 0/0, and let's configure it.
One thing that I can configure it with is an IP address, so let's type ip address, and then it needs to know the IP address. We're going to assign a 10.1.0.1 to this address, and this is pretty typical of a router that is the default gateway for the network, which is what this router will be in the future. So this is 10.1.0.1, the first usable address in the network.
Then we have a mask that we need to add to it, so for this network it's going to be a 255.255.255.0. And there we have it. We can hit enter and now that IP address is assigned to it.
It's still not live at this point in time. It has that shutdown command put on the interface, so we have to do a no shut to take that off, and now that port will go live. Let's just see: if we do a show ip interface brief and hit enter, we see now that it is up. Usually you'd see like a notification that would pop up here, but I have notifications turned off on this machine right now, so we don't see that it comes up. But now this device is up — this port is up, rather — and the IP address is set on it.
Just like a switch port, we can do things like set the duplex on it, so I could set the duplex on it, I could set the speed on it, and I can set some of the other settings on it just like the switch port, like we looked at with the switch port.
If I wanted for some reason to bring it back down and turn it off, all I'd have to do is the shutdown command on it and it would go back off. I do want it to be live, so I'm going to do a no shut on it, and now it's back up and running.
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