Downstream L3 Routing

[Erik_R]

Let's say a virtual stack is currently setup with L3 routing enabled and several defined VLANs. One of those VLANs is 104.

Now, you connect a new flexible stack to the existing virtual stack. You are a glutten for punishment and need to enable L3 routing on the new flexible stack.

Do you have to create the same VLAN (say 2500 for this example) on each stack (with different interface IPs) as a transit link between the two stacks?

Existing virtual stack: VLAN 2500, 192.168.10.0/24, interface 192.168.10.1

New flexible stack: VLAN 2500, 192.168.10.0/24, interface 192.168.10.2, (what would the default gateway be for the first time L3 routing setup?

VLAN 104 was already setup on the existing virtual stack. Do you need to "recreate" it on the new stack if you will be using it on the new flexible stack or no?

[Brash]

I'm not sure I understand what you're trying to achieve.

Is there a reason you need to create L3 interfaces on the downstream stack as well as the upstream switch?

On Meraki switches, VLAN's are already present and tagged traffic can be passed by default. They do not need to be created on the switch as you would on a traditional Cisco switch via CLI.

If you already have a VLAN 104 interface on the upstream switch, you don't need to create one on the downstream stack. You would configure that upstream IP as the gateway for the VLAN.

If you have L3 interfaces for some VLANs (Eg, 1,3,5) on the downstream switch and L3 interfaces for other VLANs (2,4,6) on the upstream switch, then it makes sense to create a transit VLAN between the two switches.

MS Layer 3 Switching and Routing - Cisco Meraki

[Erik_R]

I have a stack of two MS425 switches that I may use for top of rack purposes. I wanted to create two separate VLANs for iSCSI traffic. They will not be routed out of this stack, but I would still need to define VLANs for them.

[Brash]

Right, ok that makes sense.

If the traffic is not being routed, an L3 VLAN interface shouldn't really be needed (unless you have some other requirement for it).
You also don't need to explicitly define the VLAN anywhere like you would in traditional switches.

https://community.meraki.com/t5/Switching/How-can-I-create-VLANs-on-MS-220-switch/m-p/11117/highlight/true#M818

You would really only need to ensure:
- iSCSI traffic is tagged (either on the Meraki switchport or elsewhwhere)

- The applicable Meraki switchports have the VLAN allowed on the trunk

You would probably also want to restrict the iSCSI VLANs from traversing to unnecessary switches.

[Erik_R]

So, I can tag a switchport with a VLAN number that is not defined as an L3 routing interface?

In other words, if I created a VLAN of 3010 on paper only, I can still tag a port on the switch with a VLAN number of 3010 without it actually existing (defined) anywhere?

[Brash · Accepted solution]

Yes correct.

I've done that here with two switchports.
They are set as access ports tagging VLAN 500.

As you can see, no L3 interface for that VLAN exists on the switch (or anywhere else in the network in this circumstance)