Layer 3 InterVLAN switching

[Stein Rune Risa]

I am reading this tutorial:

http://www.cisco.com/c/en/us/support/docs/lan-switching/inter-vlan-routing/41860-howto-L3-intervlanrouting.html

First the vlan database is updated with the 3 vlans:

Switch#vlan database
Switch(vlan)#vlan 2
VLAN 2 added:
    Name: VLAN0002
Switch(vlan)#vlan 3
VLAN 3 added:
    Name: VLAN0003
Switch(vlan)#vlan 10
VLAN 10 added:
    Name: VLAN0010
Switch(vlan)#exit

But when interfaces are defined, those exact vlan names are not used - e.g.:

Switch#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Switch(config)#interface Vlan2
Switch(config-if)#ip address 10.1.2.1 255.255.255.0
Switch(config-if)#no shutdown

In one case "vlan 2" is used, while the interfaces has name "Vlan2".

Is the interface names in any way related to the vlan names? If yes - how can they be spelled differently?

[devils_advocate]

Unfortunately Cisco is not know for consistent naming conventions.

The first image you have posted is the creation of the Layer 2 VLAN itself. This will allow you to add switchports to those VLANs.

The second image is the creation of an SVI for the corresponding Layer 2 Vlan.

So, although the names do not match 'exactly' as such, they are related to each other. First you need to create a Layer 2 Vlan, then you can create a corresponding SVI for that Vlan.

Thanks

[Stein Rune Risa]

Thanks for your reply. Some follow-up question:

When creating the SVI, is the name "checked" towards the vlan database, or is the name given to the interface use choosen?

E.g. could I say: 

#interface MyCoolVlanWithNumber2

or is there actually a check saying that interface name also must exist in the vlan database and Cisco internally knows that "Vlan2"="vlan 2"?

I find it very strange that a "strict relation" can exist - but the names does not need to be exact...

[devils_advocate · Accepted solution]

When creating an SVI, the switch does not check to see if the VLAN exists within the database, however the SVI will remain in an Up/Down state until the corresponding Vlan is created in the database.

The only anomaly as far as I can see is that you cannot create a Layer 2 Vlan unless you put a space between 'vlan' and the 'ID'.

Switch_1(config)#vlan 90
Switch_1(config-vlan)#exit
Switch_1(config)#vlan130
                                  ^
% Invalid input detected at '^' marker.

However when creating the SVI, the switch doesn't seem to care whether there is a space or not:

Switch_1(config)#interface vlan 90
Switch_1(config-if)#exit
Switch_1(config)#i
*Mar  1 18:31:31.419: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan90, changed state to up
Switch_1(config)#interface vlan130
 

It is just Cisco being inconsistent with their naming to be honest.

You can have a Layer 2 Vlan in the database without an SVI.
You can also have an SVI without a Layer 2 VLAN in the database BUT the SVI remains in an Up/Down state until you create one in the database.
When creating L2 Vlan's or SVI's, the word 'VLAN' is not case sensitive/.

[Stein Rune Risa]

Thank you for a very good answer to this question!