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Now that we've configured ether channel on the core switches we need to configure layer three interfaces

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on the core switches and enable inter VLAN routing.

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Core 1 is gonna be configured with IP addresses 10.1.1.251 in VLAN 1 and core 2 with IP

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address 10.1.1.252 and then something similar will be configured on all of the other

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VLANS on both switches. So here's core 1 to enable inter VLAN routing

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We need to use the command IP routing now before I type that command.

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Notice the output of show IP route.

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It shows us that a default gateway is not set.

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That means that IP routing is not enabled on the switch, as soon as I enable IP routing the show IP route

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command shows us a very different output.

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We see something like this instead of what we saw previously.

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So one of the first things you need to do on a layer 3 switch is enable IP routing, IP routing is not

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enabled on most switches by default.

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So you need to enable that first and then what we can do is configure IP addresses on what are called

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the switched virtual interfaces or SVIs. So the command VLAN 1 or VLAN 10 would create a VLAN

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in the VLAN database but the command interface VLAN 1 creates a switched virtual interface or a

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layer 3 interface

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and notice the difference

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now when I use the command show IP route. We don't see that route in the routing table

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but notice what happens when I no shut the interface

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show IP route, shows us that route in the IP routing table.

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As soon as I create another switched virtual interface, let's say for VLAN 10 and give the switch

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an IP address in that VLAN, that network becomes available in the IP routing table.

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These switched  virtual interfaces or SVI's, all layer 3 interfaces for specific VLANs on the

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layer 3 switch.

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So this is the layer 3 interface for VLAN 10.

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This is the layer 3 interface for VLAN 1 and I would do something similar for VLAN 20 10.1

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.20.251

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interface V Line 30 IP address 10 1 3 2 5 1 Notice the difference of villain 1 was shut down by default

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but these SVIs come up by default. In the real world

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verify the state of your SVIs by using the command show IP interface brief, make sure that these

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interfaces are up on your switch. So show IP route now

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notice the interfaces are shown in the IP routing table and I should as an example be able to ping my

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local IP addresses. There's VLAN 1, VLAN 10, VLAN 20,30, and 100.

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So that looks good.

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We need to do something similar on this switch.

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So just to show you the point again.

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Show IP route shows nothing in the IP routing table at the moment this command and output shows us that

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IP routing is enabled.

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Notice we see this rather than this, to show IP route here shows us ICMP redirect caches empty.

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If you see that output it means that IP routing is disabled IP routing shows us gateway of last result

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and you see all of these codes that means IP routing is enabled on the switch.

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No routes are currently in the routing table by default VLAN 1 is shut down.

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We can see that by using the command show IP interface brief and in this case I'm gonna use do because

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I'm in config interface mode.

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Notice VLAN 1 is down, administratively down I need to no shut the interface to bring it up.

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So if we do the show IP interface brief command again.

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Notice the interface is now up as soon as I use the command IP address 10.1.1.251 on this

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case 252 and now use the command

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do show IP route.  We can see that route in the IP routing table.

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So let's create additional SVIs, VLAN 10 IP address 10.1.10.251

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or should I say 252. VLAN 20

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this will be 20 252, VLAN 30

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this will be 30 252 and then interface VLAN 100, IP address 10 1 100 252 with /24 mask

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always verify what you've done. So show IP interface brief make sure that you have done what you think

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you've done.

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I like the following saying "a Cisco device does it what you tell it to do not what you think it should

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do."

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It will only do what you tell it to do through the commands that you've typed through the CLI.

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Sometimes we think we've done something when we haven't.

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So make sure that you verify your configuration.

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As an example, can we ping ourselves on VLAN 1?

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Yes, we can.

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What about core 1?

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Yes, we can

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on VLAN 1.

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So let's test it this way.

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Can core 1 ping core 2 on VLAN 1? Yes, it can.

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What about  VLAN 10?

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Yes, it can.

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VLAN 20? Yes, it can.

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30? That's good.

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100?

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That's good.

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So we've configured IP addresses on the two core switches per our instructions and we've configured

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inter VLAN routing. The command IP routing enables inter VLAN routing on layer 3 switches and interface

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VLAN and a number such as 1 creates the SVI on the switch allowing us to configure IP addresses. The

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next step is to configure IP addresses on our access switches.