Now that we've configured ether channel on the core switches we need to configure layer three interfaces
on the core switches and enable inter VLAN routing.
Core 1 is gonna be configured with IP addresses 10.1.1.251 in VLAN 1 and core 2 with IP
address 10.1.1.252 and then something similar will be configured on all of the other
VLANS on both switches. So here's core 1 to enable inter VLAN routing
We need to use the command IP routing now before I type that command.
Notice the output of show IP route.
It shows us that a default gateway is not set.
That means that IP routing is not enabled on the switch, as soon as I enable IP routing the show IP route
command shows us a very different output.
We see something like this instead of what we saw previously.
So one of the first things you need to do on a layer 3 switch is enable IP routing, IP routing is not
enabled on most switches by default.
So you need to enable that first and then what we can do is configure IP addresses on what are called
the switched virtual interfaces or SVIs. So the command VLAN 1 or VLAN 10 would create a VLAN
in the VLAN database but the command interface VLAN 1 creates a switched virtual interface or a
layer 3 interface
and notice the difference
now when I use the command show IP route. We don't see that route in the routing table
but notice what happens when I no shut the interface
show IP route, shows us that route in the IP routing table.
As soon as I create another switched virtual interface, let's say for VLAN 10 and give the switch
an IP address in that VLAN, that network becomes available in the IP routing table.
These switched virtual interfaces or SVI's, all layer 3 interfaces for specific VLANs on the
layer 3 switch.
So this is the layer 3 interface for VLAN 10.
This is the layer 3 interface for VLAN 1 and I would do something similar for VLAN 20 10.1
.20.251
interface V Line 30 IP address 10 1 3 2 5 1 Notice the difference of villain 1 was shut down by default
but these SVIs come up by default. In the real world
verify the state of your SVIs by using the command show IP interface brief, make sure that these
interfaces are up on your switch. So show IP route now
notice the interfaces are shown in the IP routing table and I should as an example be able to ping my
local IP addresses. There's VLAN 1, VLAN 10, VLAN 20,30, and 100.
So that looks good.
We need to do something similar on this switch.
So just to show you the point again.
Show IP route shows nothing in the IP routing table at the moment this command and output shows us that
IP routing is enabled.
Notice we see this rather than this, to show IP route here shows us ICMP redirect caches empty.
If you see that output it means that IP routing is disabled IP routing shows us gateway of last result
and you see all of these codes that means IP routing is enabled on the switch.
No routes are currently in the routing table by default VLAN 1 is shut down.
We can see that by using the command show IP interface brief and in this case I'm gonna use do because
I'm in config interface mode.
Notice VLAN 1 is down, administratively down I need to no shut the interface to bring it up.
So if we do the show IP interface brief command again.
Notice the interface is now up as soon as I use the command IP address 10.1.1.251 on this
case 252 and now use the command
do show IP route. We can see that route in the IP routing table.
So let's create additional SVIs, VLAN 10 IP address 10.1.10.251
or should I say 252. VLAN 20
this will be 20 252, VLAN 30
this will be 30 252 and then interface VLAN 100, IP address 10 1 100 252 with /24 mask
always verify what you've done. So show IP interface brief make sure that you have done what you think
you've done.
I like the following saying "a Cisco device does it what you tell it to do not what you think it should
do."
It will only do what you tell it to do through the commands that you've typed through the CLI.
Sometimes we think we've done something when we haven't.
So make sure that you verify your configuration.
As an example, can we ping ourselves on VLAN 1?
Yes, we can.
What about core 1?
Yes, we can
on VLAN 1.
So let's test it this way.
Can core 1 ping core 2 on VLAN 1? Yes, it can.
What about VLAN 10?
Yes, it can.
VLAN 20? Yes, it can.
30? That's good.
100?
That's good.
So we've configured IP addresses on the two core switches per our instructions and we've configured
inter VLAN routing. The command IP routing enables inter VLAN routing on layer 3 switches and interface
VLAN and a number such as 1 creates the SVI on the switch allowing us to configure IP addresses. The
next step is to configure IP addresses on our access switches.