DHCP problems

[att-sgcops]

I have a AP 1100 role as a DHCP server, the IP address of the router is 10.1.1.1/24. If I define the IP range 10.1.1.0 - 10.1.1.254 to as the DHCP pool, the user can get the IP address.

but If I change the pool to 20.1.1.0 - 20.1.1.254. user cannot get the 20.1.1.x IP address.

Can some one tell me where is the problem and how to fix it?

[rajinikanth]

Hi,

Are you also changing the ip address of the router to

20.x.1.1 /24

HTH

Thanks

Raj

[att-sgcops]

i didn't. is it necessary?

[gpulos · Accepted solution]

yes, in your case, this would be necessary...

if you change the pool that the hosts are to grab an IP Address from, then you need to assure those hosts actually reside on the subnet that is defined in the dhcp pool.

(what is happening in your case is that you have a subnet 10.1.1.0/24 defined. hosts attempt to get a dhcp address based on what subnets they are attached too. when the host requests a dhcp address, the dhcp server will notice the broadcast request came from the subnet 10.1.1.0/24. the dhcp server does not have a pool for that subnet, only a pool for 20.1.1.0/24. the dhcp server does not hand out any addresses because it does not have the proper pool to pull them from)

for example, you have your AP configured for subnet 10.1.1.0/24; its ip address is 10.1.1.1 255.255.255.0.

unless you have another subnet (vlan) defined and interVLAN routing, you cannot have a dhcp pool defined for your hosts that hands out addresses for one subnet when the AP is on a different subnet.

(you have an AP that defines a subnet of 10.1.1.0/24 and you have hosts that connect to that AP but you're telling them they must use ip addresses from another subnet, ie: 20.1.1.0/24. this will not work)

if you wish to change your pool to 20.1.1.X/24 then you'll also need to change your APs interface to belong to the same subnet instead of subnet 10.1.1.0/24.