Inter Vlan Routing - from different vlans to a native vlan

[User-H]

Hallo !

I know this sounds a little bit confusing,so I have to explain the purpose of it.

Right now our network only contains unmanaged switches and managed switches (traffic only native vlan 1).

I want to build a new campus network with a coreswitch, distributionswitches and accessswitches, like it is used to do nowadays.

Because it is not possible to change everthing in a short time, I have to find a possibilty to communicate between the new campus network (vlan's) and the old network (traffic only native vlan 1).

Is it possible to do it via inter vlan routing on the coreswitch ?

If not, do you have any other suggestion ?

Thank you for your help !

Best regards !

[Seb Rupik]

Hi there,

Take a connection from the old core and connect it to the new core.

On the new core switchport use the following config

!
vlan 999
  name old_network
!
int vlan 999
  ip address <ip_from_your_old_subnet> <netmask>
!
int gi1/0/1
  switchport mode access
  switchport access vlan 999
!

This will recieve the untagged frames on gi1/0/1 and place them into VLAN999 allowing inter-VLAN communication on your new core.

If your old and new networks share the sae subnets then you will need to place VLAN999 SVI in a separate VRF to keep the routing tables separate.

Cheers,

Seb.

[User-H]

Hello Seb !

Thank's for that information !

But I still don't really get it !

A VRF seperates the traffic, right ?

Those networks have to communicate with each other.

I need a solution where I can bundle the traffic from multiple vlan's into one native vlan and vice versa.

Or do I misunderstand you ?

And yes, I have the same subnets on both sides !

I tried to route the traffic from the different vlan's into the native vlan 1 on the coreswitch and got an error:

#overlaps with other vlan

>> I understand, but I don't have got another solution !

Best regards !

[Jon Marshall]

If you are building a new network infrastructure then when are you trying to use the same subnet ? 

You need to create new vlans using different IP subnets than your existing one and then you can do a phased migration and route between the old and new infrastructure. 

Jon

[Seb Rupik]

OK, well since you have a IP subnet overlap a possible solution would be to NAT the entire old network behind an IP on your new ore switch, ie PAT. If you still need to access resources in your old network then you will then need to configure static NAT with the global-outside IP coming from the new network IP allocation and translating to the old_network IP.

cheers,

Seb.