Resubnetting DHCP

[dezt]

Right, just a question about how to go about this and when would be the best time of day to do it.

 

From what i've found out about our network, the DHCP is setup wrong, the ip range is 192.168.0.x and the subnet mask is 255.255.0.0, what I want to do is change the subnet mask to 255.255.254.0 to allow us to have, according to the microsoft documentation, 510 ip addresses available to us.

 

The microsoft documentation tells me to delet the scope I have at the moment and create a new one with the subnet mask of 255.255.254.0 to allow 510 ip addresses.

 

My main question is after the new scope is created will I be able to get to my switches via their web interface to reconfigure the ip address on them, or will I have to reset them to factory defaults and re set them up?

 

Would it be best to do this after school when nobody is using the computers, or should I make sure that all the computers are switched on so they will get a new IP address?

[Geoff]

You could create static routes on your default gateway to route between the old and new ranges, so you maintain connectivity during the transition.

[srochford]

Change the lease time from the default 8 days to (say) 1 hour and wait at least 4 days before you do it otherwise you'll have chaos as machines will get new addresses which are the same as old ones. Alternatively, if you can't wait, create the new scope but exclude the old addresses; after 8 days you can remove the exclusions.

 

If your subnets overlap (eg you were 192.168.0.1 -> 192.168.0.254 and you're now 192.168.0.1 -> 192.168.1.254) then there's no problem in getting to the switches.

 

A good trick when you are changing ranges and you want to get to "old" fixed addresses is to put 2 IP addresses on a card - eg you were using 192.168.0.x and now you're using 10.0.0.x. Give a PC fixed addresses of 192.168.0.10 and 10.0.0.10 (say) on the same card - it can now talk to all your new stuff but can also get to the old equipment. Once you're finished, just get rid of the "wrong" address or set it to DHCP.

[dezt]

@srochford Thanks for that, I should be able to sort that all out that way. Fingers crossed it will all go smoothly.