Changing DHCP's subnet mask and static clients
Just wondering if anyone know why changing an active dhcp scope's subnet mask causes no harm to current active leases and also changing the subnet mask of a network to a different but large subnet doesn't impact any static users as well.
We recently changed a /24 subnet to a /23 and this didn't impact any active users (who still has an IP with the /24 subnet) and also there are still static clients with the /24 subnets. They are all pointing to the same default gateway. Why don't the static users who have the /24 need to change their subnet also to the /23 subnet?
We recently changed a /24 subnet to a /23 and this didn't impact any active users (who still has an IP with the /24 subnet) and also there are still static clients with the /24 subnets. They are all pointing to the same default gateway. Why don't the static users who have the /24 need to change their subnet also to the /23 subnet?
ASKER
so what do we need to this in case? Re-IP 172.16.0.10/24 to 172.16.0.10/23?
All hosts on the subnet should be using the same mask.
ASKER
Well, we changed it (the subnet mask of existing active DHCP scope from /24 to /23) while still having static hosts on /24 and some active hosts. We also cleared the DHCP leases after changing. It appears to still work and heard that the active hosts would just the default gateway to communicate to any hosts outside of it subnet. So just wondering how it worked but I guess the thought is that once clients have their IP addresses, that is all they need and if they were issued with a /24, they don't care what the subnet of the gateway anymore but just use gateway to communicate with hosts outside of its /24 subnet.
Correct. If 172.16.0.10/24 was trying to communicate with 172.16.1.10/23, it would send the frame to its default gateway (let’s say 172.16.0.1/23) because the destination host is on a different network.. The router would look at the packet and simply forward it back out the same interface it came in on but in a frame to 172.16.1.10.
Obviously, the correct thing to do is get the masks changed on the old hosts.
Obviously, the correct thing to do is get the masks changed on the old hosts.
ASKER
Hmm, we left (advised that it would be ok to leave it as it would be too time consuming to change everything and it was during a critical outage). So looks like leaving the static hosts would still be fine?
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Thank you Don. Weird how it would work with static hosts on a different subnet mask but I guess subnet masks do not matter if that host has a default gateway and it knows destination IPs.
So if 172.16.0.10/24 tries to access 172.16.0.50/23, no problem.
However, when 172.16.0.10/24 tried to access 172.16.1.60/23, then you'll see a problem.