Cisco Support Community
Community Member

VLAN vs. interface VLAN

Hi All,

I`d have a question regarding VLANs. I`m still struggeling to clearly understand to correlation betwen layer 2 VLAN and layer 3 VLAN. I guess I know the difference, however having problem when seeing them both in operation at the same time. For example: let`s say I`m having a trunk, including VLAN 10 between SW1 and SW2, however SW2 is further connected to R1 and SW2 is layer 3 switch where "interface VLAN 10" is created and there`s layer 3 line between SW1 and R1.

Do I need to have interface vlan 10 configured on SW2 for the R1 to reach SW1? Is there any reason for configuring interface VLAN on SW2?

Hope it`s a bit clear:)




Community Member

It sounds like what you're

It sounds like what you're asking is about the concept of switched virtual interfaces - "interface vlan 10", for instance, is a switched virtual interface. This is different than a VLAN in that a VLAN is a logical network segment, a broadcast domain, whereas an SVI is a logical interface.

If SW2 is a layer 3 switch, you don't HAVE to have the SVI configured there. You could operate both SW1 and SW2 entirely as layer 2 devices, configure an interface on R1 to handle the inter-VLAN traffic, and configure the links from SW1-SW2 and SW2-R1 as trunks.

But that wastes the l3 capability of the switch. The idea is that you don't need to involve a router. When you have a vlan (layer 2), it has no way to communicate with other vlans (layer 2). That's where an SVI on a layer 3 switch, or an interface on a router (router-on-a-stick) using dot1q encapsulation comes in. It gives your devices in that VLAN something to point to as a gateway, something for routable traffic to address. So, think of a VLAN as a self contained network, and an SVI as the door that allows it to talk to everything else.

Also, in practice, assigning each discrete switch an IP address for management traffic makes things much easier - how else can you telnet/SSH into it? Beats having to use the console all the time!


Community Member

Thank you for your answer.

Thank you for your answer. Unfortunately, that`s not what i meant, which is not your fault but my bad explanation. I guess I understand the function, configuration of vlan (lay.2) and interf.vlan (lay.3). So concrete example would be better.For example the topology from CCNP Tshoot - ASW1 - layer 2, DSW1 - layer 3. what i dont fully understand is what role does the interface VLAN 10 play in this topology. Meaning:

1) Do I need interface VLAN 10  for this topology to be functional as it is now?

2) as to the HSRP configuration. it is configured under interface VLAN10, what would change if i configured HSRP under phycical interface?

3)as packet goes (e.g. from ASW1 to R4 through DSW1), if it gets to the DSW1 does make it through only because of interface VLAN10 configured on DSW1? what if the interface VLAN 10 on DSW1 weren`t there and only VLAN10 layer 2 were there instead?

Hope these questions are more correct.

Thank you,


CreatePlease to create content