LOSING SUBNET MASK

[djeddieed]

We run a DHCP simple network environment.
The problem I'm having lately is:

I lose the IP Address and subnet mask.

Normalexample)
IP Address 10.21.1.50
Subnet mask 255.255.255.0
Gateway 10.21.1.1

When it loses the IP address this is how it looks:

IP Address 10.21.1.50
Subnet mask 255.0.0.0
Gateway 10.21.1.1

The way I fix it: Release and Renew..

Why does this happen?

 

[jimbo4u]

The correct subnet is 255.0.0.0, for the class A address you used as an IP address and Default Gateway.

 

[djeddieed]

Really? This started to happening recently. How would I fix that across the board? (4000+ PCs) Would I have go into the DHCP config and change it from 255.255.255.0 to 255.0.0.0?

Thank you

 

[jimbopalmer]

while he used an IP that looks like a class A address, if I read his post right, he is treating it as a class C address (Explain more about the 4000 PCs, what does the gateway for one out side of 10.21.1.x look like?) If he is making multiple class C subnets in a Class A address space, then some device is occasionally assinging a Class A subnet mask by mistake, fooled by his choices.

(speculaation way in advance of the Facts) if his head office is using a class A subnet and given him one part of it he may use it as a class C but when the head office's DHCP server beats his local DHCP server, it may give a device the 'wrong' mask. If so not forwarding DHCP broadcasts in his router may be the solution I tried to remain child-like, all I acheived was childish.

 

[johnny99]

As Jimbo wrote something is wrong (or some info is missing)

A netmask of 255.255.255.0 will only allow for 254 hosts in the IP segment, so if you have more then 4000 hosts you must have a different netmask or different IP segments connected using routers.

Does this problem happen to one host at the time or to a lot of hosts?

What DHCP software are you using?

By the way all talks about stuff like A, B, C, D and E addresses are normaly total useless now a days. Now you use CIDR and this only talks about the netmask (and the network size) or numbers of bits set in the mask (eg. a /20 has a netmask of 255.255.224.0 and /16 a 255.255.0.0 mask)