We recently moved a customer from a datacenter at one of their locations to a large datacenter in the Dallas/Ft. Worth area. One of the devices we moved was a Meraki MX84 being used as a VPN concentrator. A VPN concentrator works by extending the network the VPN concentrator is on to the access points. Basically, wireless clients at all locations get an IP address on the same layer two network. This is important for a few reasons. First, the VPN concentrator needs to be in it's own VLAN/DMZ. Second, something on the layer two network the VPN concentrator is connect to needs to be handing out DHCP addresses. In our case, we used a Fortigate UTM to run the DHCP server for that subnet. Third, traffic needs to be allowed outbound to the Internet from all clients on the VPN concentrator layer two network so clients can connect to the Internet. The traffic is tunneled from the access points to the VPN concentrator, so the traffic does not intermix with the normal network traffic.

One of the issues we had was that the access points would not create the tunnel back to the VPN concentrator. After talking to Meraki support, we found that the issue was that the access points and the VPN concentrator would not connect to each other if their public IP address was the same. This does not work because Meraki uses the same technology to build the VPN from the MX to the access points as they use to build a VPN mesh between MX devices. Our devices were both using the default overloaded outbound NAT rule, so they were coming from the same public IP address. The solution is to make the MX come from a different public IP address, which can be accomplished via an inbound and outbound NAT statement. After we made this change, the access points connected to the VPN tunnel and wireless began to work.

One other thing to note is that the access points will not broadcast SSIDs if the VPN to the concentrator is not up when configured to tunnel traffic through a VPN concentrator. This can be helpful when troubleshooting wireless when there are not clients at the location of the access points.