Wan 1 interface with two separate ip address subnets assigned.

[MarkKruger]

I have a customer who has an MX250 with two wan interfaces configured. The wan 1 uplink is configured with two ranges of IP addresses. as follows:

Primary Comcast IP Range
Static IP Wan 1	216.45.223.218
Subnet Mask	255.255.255.252 /30
Default Gateway	216.45.223.217
Uasble IP Range	216.45.223.217 - 218
Additional Comcast IP Range
Static IP Wan 1	24.104.6.212
Subnet Mask	255.255.255.240 /28
Default Gateway	24.104.6.209
Uasble IP Range	24.104.6.209 - 24.104.6.222

How do I configure the second range of IP addresses to use on the WAN 1 Interface? 

Note the WAN 2 interface is being used for another carrier.  

[KarstenI]

You can use these addresses in your NAT config. There is no need to assign them to the interface.

[MarkKruger]

Okay and then I have to set the flow preferences is that correct?

do i need rules in the firewall for inbound and outbound traffic?

[PhilipDAth]

If you have two Internet circuits, then yes, a flow preference might be a safe option to choose.

You don't need firewall rules.  When you create the NAT it will automatically allow the traffic in.

https://documentation.meraki.com/MX/NAT_and_Port_Forwarding/Port_Forwarding_and_NAT_Rules_on_the_MX 

[KarstenI]

The flow preferences are used to select WAN1 and WAN2 for outbound traffic, They are not used to somehow select the IP range. That is purely the NAT config. But If you have a NAT config for WAN1, then you typically want to make sure that outbound traffic is also going to WAN1.

[MarkKruger]

On the one for one NAT on interface 1.  it is a completely different subnet than the Wan interface. 

How is the one for one NAT 24.104.6.216 going to know what its default gateway is? Unless Comcast is programming a sub interface on the port form their device. you would still need to tell the 24.104.6.212/29 subnet what its default address is.  

[PhilipDAth]

It will use the default route for that WAN interface.