DC DR Advertising Same Subnet

[rahmad]

Hi guys,

I want to ask regarding same subnet advertising in AutoVPN.

Here is the background, MX250 deployed in both DC & DR acting as Hub with NAT Mode. Both MX will be advertising subnet in AWS (172.16.1.0/24) so Branch will have failover route to AWS in case DC is down.

Recently, i've read that same subnet advertising only work in Passthrough Mode, so based on my case do i need to change the deployment model to Passthrough ? or is there some way to make it work even in NAT Mode ?

Topology is attached. This is still my rough plan, so no MX is deployed yet.

Any recommendation is appreciated, thank you 🙂

[PhilipDAth]

I assume the two sites have a layer 2 link between them since you are using the same subnet at both sites?  If so, just make the second MX a warm spare.

https://documentation.meraki.com/MX/Deployment_Guides/MX_Warm_Spare_-_High_Availability_Pair 

Otherwise this config makes no sense.  How could the system possibly now which site to route the DC subnet to.

[rahmad]

Hi Philip,

Whoops, i forgot to draw that, yes both DC DR is connected by L2 Metro E connection.

And about Warm Spare, i also forgot to put that MX in DC will be HA Pair already.

Attached the diagram revision.

About the same subnet advertised, it's actually subnet in AWS cloud not in DC DR sites. To make it short, the goal is to keep branch connected to AWS server even when DC site is blown up 😄

[PhilipDAth]

From what I can see - it will remain connected.  If one DC goes down that only leaves the remaining MX up and the remaining router connecting to AWS up.

[rahmad]

Hi Philip,

Thank you for your answer. Since both MX will have static route pointed for AWS via Core, is this allowed in AutoVPN ?
Because i've read in doc below it says "All subnets advertised from an appliance in Routed mode must be unique within the AutoVPN topology."
Source : https://documentation.meraki.com/MX/Networks_and_Routing/MX_Routing_Behavior

Or maybe can we advertise a slight different subnet ? for example, in DC we will make a static route to 172.16.1.0/24 and in DR site we will make a static route to 172.16.1.0/23 ?

[PhilipDAth]

If they are operating in warm spare mode, then they will look like a single site to the reset of the AutoVPN network.  It the primary site goes down the warm spare will take over as active.  The remaining AutoVPN sites wont see a change routing wise.