Cisco 6500 Trunking

[NewComer]

Hello,

I was recently asked to trunk a VLAN across two trunk interfaces that use sub-interfaces. My question is, how can I trunk VLANs only without having to add an IP and the VLAN to trunk across the sub-interfaces. See example below.

Current setup has about 100 sub-interfaces configured on multiple interfaces.

Example  1:

interface TenGigabitEthernet1/3.150
encapsulation dot1Q 150
ip address x.x.x.x 255.255.255.252

interface TenGigabitEthernet1/4.250
encapsulation dot1Q 250
ip address x.x.x.x 255.255.255.252

I want to allow a VLAN tag across the two sub-interfaces, is this possible? I don't have a lab to test this and wanted to see if anyone had this issue before. The two trunks connect two separate buildings.

Will this work? 

interface TenGigabitEthernet1/3.400 <--- different sub-interface IDs
encapsulation dot1Q 400 <--- vlan 400 tagged
!

interface TenGigabitEthernet1/4.401 <-- different sub-interface IDs
encapsulation dot1Q 400 <-- vlan 400 tagged

Will I have to create the VLAN in the 6500 as well? 

Thanks

[Reza Sharifi]

Hi,

I am not sure how would your config work as there is no corresponding subnet associated with vlans 400 and 401.

Since this is a 6500, can't you just trunk the vlans on a layer-2 link?

HTH

[NewComer]

Hey Reza,

Thanks for the quick reply. The problem is that I can't convert the main interfaces to L2, or at least I don't know how this can be done. All ports in this 6500 are being used by sub-interfaces. Here is the configs for the parent interface.

interface TenGigabitEthernet1/3
no ip address

!

interface TenGigabitEthernet1/4
no ip address

I don't believe I can create a subinterface in example "interface TenGigabitEthernet1/4.250" and just tag a VLAN across. This is what I'm trying to figure out. 

[Reza Sharifi]

Hi,

I don't believe I can create a subinterface in example "interface TenGigabitEthernet1/4.250" and just tag a VLAN across. This is what I'm trying to figure out. 

That is correct because a sub-interface is a layer-3 interface. So, can't you just use an unused interface on the 6500 and add vlans 400 and 401 (for example) to it?  Maybe you can explain further what you are trying to do with these new vlans and what the design is like, so I can help better. Where are the layer-3 interfaces for vlans 400 and 401 located?

HTH

[NewComer]

I need to tag a VLAN across two buildings which the uplinks to each building is a L3 trunk. 

Building1 vlan 400 --> Te1/3 --> Te1/4 --> Building2 (no other uplinks available to reach the buildings) 

I'm guessing I will need to convert the L3 uplinks to L2 and just use interface-VLANs for DIA's. This will give me the capability to run VLANs across and configure DIA's at the same time. 

I was hoping there was an easier way to achieve tagging VLANs across two L3 interfaces.  

[Reza Sharifi]

I'm guessing I will need to convert the L3 uplinks to L2 and just use interface-VLANs for DIA's. This will give me the capability to run VLANs across and configure DIA's at the same time. 

That is correct. If you need to span vlan(s) between these building, then the connection needs to be converted to layer-2. But if you can put each site devices in a different vlan, you can keep the connection as layer-3. 

Building1 vlan 400 --> Te1/3 --> Te1/4 --> Building2 vlan 401

I guess the question to ask the customer is why do they need to have devices in the same vlan (400) across 2 buildings.

HTH