Changing subnet mask to get more hosts

[mspaw]

I run a private 192.168.177.0/24 inside. I need more hosts on the same subnet than the current 254. Can I simpy change the subnet mask to 255.255.254.0 on all thedevices without losing any connectivity? What if any other issue will I need to consider? Thanks in advance for your advice.

[lgijssel]

This will effectively alter your network address to:

192.168.176.0/23. Problems are introduced when the broadcast address for the supernet is different from the one that is in use for existing subnet. This would have been the case if you were using net 176 instead. Your broadcast address will remain 192.168.177.255. This is good, all hosts in subnet 177 should remain reachable.

It is for this reason that I think you can make the move without much disturbance. I would pick a pair of non-critical devices and test the change on those before altering all nodes.

It is adviseable to make the change for the whole network as rapid as possible. Good luck!

Regards,

Leo

[pkhatri · Accepted solution]

Hi,

Firstly, you'll have to understand that the 255.255.254.0 mask is not valid for the 192.168.177.0 network. The network used has to be 192.168.176.0/255.255.254.0 (which includes 192.168.177.x). But that is fine... you can grow your addresses down into the 192.168.176.x range.

You can change the mask to 255.255.254.0 in the following way:

- change the mask on your router interface to 255.255.254.0

- start changing the masks on your PC one by one. You can even assign them 192.168.176.x addresses in the process. You will have full connectivity between all your PCs as you do this.

Hope that helps - pls rate the post if it does.

Paresh

[Richard Burts]

I have a couple of additional points.

- it matters the order in which you change the mask. Be sure to change the mask on the router interface before you change the mask on any of the end stations.

- if you are running a dynamic routing protocol be sure that it will accept, process, and advertise the /23 mask.

- when you change the mask on the router it will introduce some mismatch about what is included in the local subnet. One way to minimize the impact of this is to be sure that proxy arp is enabled on the router interface. (changing the mask would have more impact if you were making the subnet smaller. it will have less impact when you are making the subnet larger.)

HTH

Rick