MX Router On A Stick

[Twitch]

I'm wondering if it is possible to have an MX operate as a router on a stick?

We currently have one MX100 at our primary site connected to a switch stack of three MS250-48P switches. The current setup that I inherited has several VLANs configured as access VLANs, each connected to their own port on the MX. Obviously, this solution has a finite limit that directly correlates to the number of physical ports on on the MX, and it therefore not a solution for us going forward due to upcoming changes in our network. Therefore, I need to transition one physical port on the MX to be a true trunk carrying traffic for multiple VLANs.

In the Old Days of the IOS, I recall that this could be accomplished through the use of subinterfaces and a routing protocol such as OSPF to provide inter-VLAN routing with a single trunk connection between a switch and the router. 

- How does this setup translate to the world of the MX?

- Does it behave the same way, with the creation of a VLAN acting as the subinterface in this case?

- Will the VLAN still be in an "up/up" state, even if it is not assigned to a physical interface?

- Will any specific routing need to be configured, or will OSPF handle inter-VLAN routing automatically?

I have an outage window this coming Friday at midnight to make the changes, so I am trying to make sure I have my head wrapped around how Meraki handles this beforehand.

The backstory for the change involves implementing new VPLS circuits to our remote sites. We have decided to collapse the gateways from the remote sites back to our MX, and remove the remote site MXs entirely, hence the need for additional VLANs at our primary sites to accommodate the additional gateways, which comes back to needing a trunk instead of physical ports on the MX.

Anyway...

If someone has implemented this setup and made it work, please let me know.

Thanks.

Twitch

[BrandonS]

Short answer, yes.  Each VLAN you create will need an interface IP.  When you change one of the MX ports to trunk you will choose the native VLAN and the tagged VLANs you want enabled on it.  There is no routing protocol needed and all VLAN's will route to each other by default.  You may restrict that with firewall rules if you don't want them all to communicate freely.  Any client that uses the MX VLAN IP address will be able to route to clients on other VLAN's doing the same.

[BrandonS]

I should add this presumes your switches are configured with matching VLANs and I am honestly not sure what you are describing with VPLS circuits.  My answer is purely about basic inter-VLAN creation and routing.

[Twitch]

Thanks @BrandonS. I appreciate the info. That confirms what I suspected as far as how the MX would handle the trunk and the VLANs.

No worries on the VPLS stuff. Up until a few months ago I had never even heard of it. The learning curve has been rather interesting, but thanks to several fine folks out here on the forums I think I have a good understanding of how to get it to work correctly. I hope...  😬

Twitch