Ethernet port vs VLAN interface

[tmahan1234]

On the 3448 router, what is the functional difference between an Ethernet port and a switch port that has been configured as a vlan interface?   Are there functions that I cannot do with a vlan interface that I can with an Ethernet port?

Thank you

[Anonymous · Accepted solution]

:

Thank you for asking this question in the support community.  There are differences between the two Ethernet ports (which are routed ports) and the eight switchports.  For example, you can configure a VLAN interface (The difference between VLANs and VLAN interfaces), and have multiple switchports assigned in that VLAN and they will all be in the same broadcast domain, which cannot be done with the Ethernet ports.  Another difference between the Ethernet ports and the switchports is that a VLAN interface (assigned to a switchport) will not transition to a "down" state if the switchport assigned in that VLAN goes down.  Therefore, regardless of the switchport states, the VLAN interface will always remain active/up, until manually shutdown.  Furthermore, the VLAN interface/switchport combination also participates in spanning-tree protocol (STP), which can potentially cause slower convergence, when compared to a routed Ethernet port.

This is a general overview, but let me know if you have any specific questions.  I will be happy to help in any way I can.

Levi

[Anonymous]

Can you make an ethernet interface a switchport?

[Anonymous]

No.  If this was 100% necessary for you for some reason, you could setup bridging.  Create a bridge group, assign one of the Ethernet interfaces to it as well as a VLAN interface.  Then place a switch port in the same bridge group VLAN and it should allow traffic to bridge between the interfaces.  I haven't played with this in a while but you may need to create a BVI interface and put an IP on it as well.  It doesn't really work the same as switching but depending on what you need to accomplish it comes close.

[Anonymous]

Couldn't I set up the ethernet interface for 802.1q & then create a sub interface with the vlan id that I need?

[Anonymous]

Yes, that works fine.  But that isn't the same as working as a switchport, which is what I thought your question was more about.  You can setup your ethernet port for trunking and have multiple subinterfaces with VLAN encapsulation enabled.  These will all be layer 3 interfaces however, requiring an IP address on the subinterface. 

[Anonymous]

:

I went ahead and flagged the "Correct Answer" on this post to make it more visible and help other members of the community find solutions more easily. If you don't feel like the answer I marked was correct, feel free to come back to this post and unmark it and select another in its place with the applicable buttons.  If you still need assistance, we would be more than happy to continue working with you on this - just let us know in a reply.

Thanks,

Levi