You need the MAC number of each of the devices. Each router is different, but there is usually a way of entering those mac numbers to reserve a static I/P address for both of the units. Most routers indicate the MAC numbers of each DHCP subscriber. But, again, that depends on the router you are using.
But I don't see why anyone needs static address assignments, since SSDR and Maestro have their own radio discovery methods.
I suspect we are all viewing your question wrongly.
You seem to indicate that when you do a direct connection using a CAT 5 or CAT 6 UTP between the Maestro and the 6500, the Maestro finds the 6500 OK during the discovery process but does not actually connect the Maestro to the 6500
It is supposed to connect directly like that OK and work (mine does).. so clearly something is wrong with your Maestro and/or Cable and/or 6500
In which case, perhaps it would be best to open a HelpDesk ticket rather than all of us speculating incorrectly what might be the issue.
A Windows-based computer that is configured to use DHCP can automatically assign itself an Internet Protocol (IP) address if a DHCP server is not available. For example, this could occur on a network without a DHCP server, or on a network if a DHCP server is temporarily down for maintenance.
The Internet Assigned Numbers Authority (IANA) has reserved 169.254.0.0-169.254.255.255 for Automatic Private IP Addressing. As a result, APIPA provides an address that is guaranteed not to conflict with routable addresses.
The radio conforms to this standard as does the Maestro is a LAN cable is connected.
All that aside, the Maestro was designed to require a DHCP server. In 99.99% of the world, this is what we do today. It is much easier to accept that as the current design with the work around to have a DHCP Server auto assign an IP address based on MAC address.
You may not like that, however, today, the product is working as designed and is not busted by any means. My guess is that Flex has gone down this path to eliminate support calls as support calls cost money and will also drive up the cost of your radio.
You have to look at the bigger picture. We are a plug and play world. Spin up a DHCP server and your world is good.
On the subject of DHCP servers - A year back (isn't 20-20 hindsight great) a firmware change on multiple Netgear switches turned on a "DHCP Filter" feature. This feature stopped DHCP traffic from reaching the server and auto assign came alive on the Flex.
As most of my network is static addresses, only the Flex stopped working. (Tim/Dudley take note)