Richard Burts Thu, 04/10/2008 - 08:21


I do not believe that the 3750 supports subinterfaces. Subinterfaces like that are frequently associated with trunk interfaces. But the 3750 configures trunking on physical interfaces not subinterfaces. What are you wanting to do with subinterfaces on the 3750? If we knew what you are trying to accomplish then perhaps we could suggest alternatives that would work.



dywersantos Thu, 04/10/2008 - 08:29

I have an old 4908 switch. Each physical interface has 3 sub-interfaces like:

interface GigabitEthernet2.10

description data 10

encapsulation dot1Q 10

no ip directed-broadcast

bridge-group 10


interface GigabitEthernet2.11

description voice 11

encapsulation dot1Q 11

no ip directed-broadcast

bridge-group 11


interface GigabitEthernet2.99

description management

encapsulation dot1Q 99

no ip directed-broadcast

bridge-group 99


And there is a BVI to route the information.

I'm trying to do the same with 3750 switch.

Richard Burts Thu, 04/10/2008 - 08:35


I do not believe that you can do literally the same thing on the 3750. I believe that you can achieve the same result but the way to do it is different. On the 3750 configure an interface as a trunk, configure VLANs 10, 11, and 99, and make sure that these VLANs are included on the trunk.



ciscograyaw Thu, 04/10/2008 - 13:33

The equivalent configuration for 3750s would be something like:

vlan 10

description Data 10

vlan 11

description Voice 11

vlan 99

description Management

interface Vlan 10

description Data 10

interface Vlan 11

description Voice 11

interface Vlan 99

description Management

interface GigabitEthernet2/0/1

switchport trunk encapsulation dot1q

switchport trunk allowed vlan 10,11,99

switchport mode trunk

dywersantos Fri, 04/11/2008 - 08:44

Thanks for your help.

Another question.

How do I configure diffent interfaces in the same bridge-group ? and How do can be controlled the traffic among the Vlans when and SVIs interfaces ?

Edison Ortiz Fri, 04/11/2008 - 08:53

First, you create a Layer2 Vlan:

switch(config)#vlan 2 name test

Second, you assign ports to this Vlan:

switch(config)#interface fx/x

switch(config-if)#switchport mode access

switch(config-if)#switchport access vlan 2

Optional, you enable routing for that Vlan

switch(config)#interface Vlan 2

switch(config)#ip add x.x.x.x y.y.y.y

I highly recommend reading this document:




dywersantos Mon, 04/14/2008 - 10:27

Thanks for help.

I'm asking all those question because I would like to have the Inside, DMZ and Campus Network in the same switch stack.

How can I isolate the DMZ from the others subnets?



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