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I have a default VLAN whose subnet mask is a /28. I now intend to use the default VLAN for imaging, so clients need to be able to receive DHCP leases from this VLAN. In order to have enough addresses to provide leases to multiple clients, I should enlarge my subnet mask to maybe a /24 or /23.

Before I do so I'd like to confirm that changing the subnet mask of the network as defined on the router won't cause connectivity problems for connected hosts.

If it will cause connectivity problems, what is the correct way to go about this? Change the subnet mask on the hosts first, then change the subnet mask on the networking equipment?

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It depends on where your imaging server is located. Is it located in the local network (same VLAN as clients) or behind the router?

I suppose it's located in the same network/VLAN as the clients, so by setting its mask to /24, the only thing that will change is that it will no longer be able to reach anything outside of the initial /28 because it would have to go through the router which it cannot. If that is no problem then issue DHCP leases with /24 if possible. If that is possible depends on whether the network used by the clients when the OS is running is the same network and addresses are also given via DHCP (or maybe another DHCP server, or assigned statically).

To get a better answer, you have to provide more details (like a network map, list of VLANs and address ranges, etc.).

  • I don't think you 2nd sentence is quite right. If you have a device on 192.168.0.2/24 and a router on 192.168.0.1/28 it would still work wouldn't it? Both device and router IPs are within the /28 even if their own subnets don't match – Drifter104 Apr 6 '16 at 16:31
  • If 192.168.0.2/24 would try to talk to say 192.168.0.100/something then it wouldn't even try to go through its router at 192.168.0.1 no matter what the netmask of the router. – Marki Apr 6 '16 at 16:48
  • So for the purposes of resizing the subnet, I'm fine to first change the netmask on the router and then change the netmask of each host on that network since they'll still be accessible after the change? – Adam Apr 6 '16 at 16:58
  • I didn't say you should go touch the router. Since we don't have any network map I certainly will not advise you to go touch the router. I was talking about the hosts. If you want more details please provide more info as stated before. – Marki Apr 6 '16 at 17:00

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