Adding sub interface to existing interface


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Adding sub interface to existing interface

We are currently using our 3260 firewall to handle BGP to our MPLS router.
the connection is trunked through our core switch, Native 200, allowed 200 & 255 (mgt & bgp respectively)

Router 1:

G0/1 (mgt)


E4 Untagged 


We are adding a second MPLS router for redundancy, 
Router 2: 
G0/0/1 (mgt)


Question 1: can a sub interface be added to an interface which already has an IP?  or would i need to change the current IP to be a sub as well?
Question 2: since both IP's are transiting the same vlan, can i leave the sub interface untagged? they're destined for the same AS which resides on the firewall, and the mpls router is untagged


Tags (2)
Cyber Elite

I think the answer is YES to both questions.


You can have a sub interface with an IP interface.

You can configure the sub interface is not be tagged.



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L4 Transporter

@ClydeHarvey The Layer3 subintefaces need to be tagged. You can have IP address on the main interface, which will apply to untagged traffic and you can add multiple tagged subinterface to it, but you cannot have untagged L3 subinterface. 


This article may help:


Cyber Elite

@ClydeHarvey   As someone who has configured this as a work around for my IT team who was doing the tagging (and I did not need to do it), I am comfortable in my first response.


If you go to your first (main) interface, and modify the interface, go to the Advanced Tab and select "untagged subinterface"


This will allow you to keep your untagged main and sub-interfaces.


Has worked for me

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