if i keep the IP addresses privte on each SM is there a negative rather then assigning each SM a Static IP address.
example
would 10 SM’s with the same IP address of 169.254.1.1 interfere with eachother rather then having 169.254.1.1,169.254.1.2,169.254.1.3…??
A negative would appear in how much functioality you ant to have on the system. For example if you are monitoring devices and you are assigning DHCP to the subscribers you can only monitor subscribers by using IP.
In other words the 169.254.1.1 address on a SM is not routable. If you want to monitor uptime for example by using IP the default address will not work unless you put your monitor box on the same switched network as the SM’s, you would then also have to go in and change the SM’s from 169.254.1.1 >> 169.254.1.2 >> 169.254.1.3 etc etc. You monitor box ( machine running the monitor softare such as servers alive etc) would have to have a 169.254.1.* address. If between your SM’s and the monitor machine there is a router the monitor will not be successful because 169.254.1.* will not route.
If you monitor the DHCP addresses you hand out to Subsciber devices then your monitor will not be an accurate account of uptime on the network as customer will shut down their machines at all times during a day.
Therefore you must use a routable IP address on the SM to get an accurate account of uptime. You can do this by putting routable Internal IP addresses on devices such as 192.168.0.1 etc.
For example if you use 10.1.1.1 with 255.255.254.0 subnet addresses for subscribers or an Internet IP address assignment and then use a 192.168.0.* with 255.255.255.0on the SM’s you can monitor all devices and give subscribers no access to the range because the subnets assigned to them are different then the subnet assigned to the SM devices
Now whether or not the subnets I just worte work or not who knows, its late 
Second reason for putting routable IP addresses on the devices is for NAT. If you have to NAT an Internet IP to an internal IP then you have to get rid of the 169.254.1.1 address that is default on the SM.
Be careful about the terms PUBLIC and PRIVATE!
Motorola Canopy SMs use the terms PUBLIC and PRIVATE to describe the SM’s accessibility within your local IP network:
PRIVATE NET ACCESSIBILITY means the SM’s IP address
is only usable from its own Ethernet port.
PUBLIC NET ACCESSIBILITY means the SM’s IP address
can be used from its own Ethenet port and from anywhere
within the local IP network BEYOND the AP.
When you look at the AP and see the IP Configuration field labeled:
Lan2 Network Interface Configuration (RF Private Interface)
This “PRIVATE” has to do with the intimate relationship the AP has with its SMs. This is a psuedo-IP network that, while cool, it’ll confuse the heck out of you if you’re just learning about IP.
And to make matters worse, the rest of the networking industry uses the terms PUBLIC and PRIVATE to mean something entirely different. Wy-COM’s post is a discussion of this industry-wide distinction between PUBLIC and PRIVATE. It’s good information, but I wasn’t sure it answered your question.
Maybe I haven’t either.
Teknix
It is an industry standard I was discussing to use for Local access to your SM from your network.
A good resource to learn about IP in the industry standard world is
http://www.learntcpip.com/