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C921-4P Subinterface support?


I wanted to ask if the router C921-4P has subinterface support? I dont see any mention of it in the manual. I love the price point. But wanted to find out if the subinterface support works on it. 


My objective will be to pass multiple vlans from the router (C921-4P) to a switch (to be determined) using 1 cable. 



Vlan 10,20,30 = Port 3



Vlan 10,20,30 = Port 9



If this router does not support this feature? What low-cost routers support this feature? 

1 Accepted Solution

Accepted Solutions
4 Replies 4


 This device does not support vlans. If you intention is to create a router on a stick topology, you can create all vlans on swtch side, then you plug one cable from the switch to router. Then, you configure the switch port as trunk. 

On the router side, you are going to do like this:

 conf t

int g0/3.20

encapsulation dot1q

ip add


int g0/3.30

encapsulation dot1q

ip add


int g0/3.40

encapsulation dot1q

ip add


This way all vlans will be communicating each other and with the rest of your network.

Perfect, this is exactly what I was looking for. Do you know what new low-cost routers support this feature? 

You mean, besides C921-4P? Pratically any router support it. 

@Flavio Miranda wrote:


 This device does not support vlans.[...]

This is the first concrete information on the subject that I have been able to find. I have been beating my head against the wall for a few days trying to create working VLANs on a C931-4P (probably the same as C921-4P w.r.t. configuration) and to trunk them to a switch, with no success. Most of the time the VLANs are created stuck into inactive state and don't turn active regardless of what I do. After completely deleting the VLANS from any interface that uses them, then deleting the VLANs in the VLAN database, I was able to create active VLANs, but they still don't work (their helper-address does not work with DHCP, and the VLANs on the router cannot be trunked to a separate switch). Only the default vlan1 does work.

You explanation seems to indicate that I have been wasting my time, and should create VLANs only on a separate switch. I may have been waylaid by instructions in other threads that say roughly "Don't create VLANs on the switch, do it on the router", but apparently this advice does not apply to C900.

If the C900 do not support VLANs, wouldn't it be a good idea to prevent VLAN creation in their IOS firmware?

However, on the C931 the command syntax
interface g0/3.20
is not accepted (and neither is interface g0.20). And there is no mention of subinterfaces in the C900 IOS v15.9 guide. So I am still stuck on how to configure working VLANs and DHCP on a switch connected to a C931.

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