I currently have a 10.10.0.0/16 network that I would like to re segment to 10.10.0.0/17. Currently I have about 20 work group level cisco 2900 series switches all on Vlan1 with management IP's. I'm currently looking to add VOIP on a separate VLAN with QoS. Am I right to assume that I will need to remask all network and networked devices? And that may be a little more work and require a large work window? What are the best options or practices?

Before I answer, let me ask what you either know or feel you need to change this for. Also what is your current useage? Any core switches? I prefer the java web based application. The java based tools are frowned upon by cisco and may slow the switches but provide very good graphical displays of your current state. You can print all that to a text file too. Then you'd have to estimate what the voip would consume. I read it wrong and answer it wrong too. So get off my case you peanut.

Might want to consider instead of remasking use a completely different subnet for the voip. You can implement with no impact on your existing ip configuration. Imagine the power if you knew how to internet search

Don't use the SDM that came with your switch. The main reason is the lack of functionality. /16 should be more than enough for any network. Why do you want to change it to /17 for? doing so will require you to change all the subnet mask on all the DHCP server. If you do not have enough documentation on your network, don't do it, else you might screw things up.

Thanks for confirming my thoughts guys, as wanderer suggested I've decided to go with a different subnet. My thoughts on it is that it will require to much to remask the current segment.