Problem with DHCP

[haji_akhundov]

Hello everyone,

I'm typing in the following:

router(config)#ip dhcp excluded-address 172.16.2.0 172.16.15.255

and getting this:

% Address range contains an already reserved address.

How can I fix this issue?

Regards,

Haji

[Nagendra Kumar Nainar]

Hi Haji,

Can you check your

dhcp

binding table to see if there is any address in this range is assigned?. You can check using

show ip dhcp binding

-Nagendra

[haji_akhundov]

Nagendra,

I do have some devices in that range, but they are all of type 'Manual'.

[blau grana]

try this:

router(config)#ip dhcp excluded-address 172.16.2.1 172.16.15.254

if this wont help, could do provide entire configuration of

dhcp

?

[haji_akhundov]

blau grana,

this does not help.

thanks

[Milan Rai]

Hey Haji,

I think you are doing wrong configuration........As we know.... there is always one broadcast & network address in each subnet.......

you are trying 2.0 which is network address and

15.255

which is broadcast address.....

And while trying to excluded the address will you try different configuration for different subnet..plz...

ip dhcp excluded-address 192.168.2.1

ip dhcp excluded-address 192.168.15.254

If you are doing with the subnet then go with

ip dhcp excluded-address 192.168.2.1 192.168.2.254

Dont forget to rate if this helps you

[haji_akhundov]

Dear Milan,

That is not an issue.

In fact, the network address and the broadcast addresses should never be assigned to hosts.

We had the following configuration before that worked fine:

      ip dhcp excluded-address 172.16.1.0 172.16.15.255

The problem was that the amount of computers has reached the available pool amount, so we had to increase the pool.

we did this:

no ip dhcp excluded-address 172.16.1.0 172.16.15.255

and now we have a huge pool and all computers on the network are able to get a proper DHCP configuration. (problem solved)

But we would still like to limit that range for now, by applying:

ip dhcp excluded-address 172.16.2.0 172.16.15.255

(this is where i get the error)

(So basically add another 255 ip addresses to the pool)

Thanks.

[Milan Rai]

Hey Haji

Then that must be totally with the network pool that you are creating......

May i know what is your network pool ???/

Is that been started from 1.0 network????

If you want to use the second option of

172.16.2.0

then did created the network pool with the 2.0 network...??

Or you are just using the same network pool????

[haji_akhundov]

ip dhcp pool a-pool

   network 172.16.0.0 255.255.240.0

   default-router 172.16.15.254

   dns-server 172.16.2.1 172.16.2.2

   lease 10

[cadet alain]

Hi,

But we would still like to limit that range for now, by applying:
ip dhcp excluded-address 172.16.2.0 172.16.15.255 (this is where i get the error)

(So basically add another 255 ip addresses to the pool)

by excluding addresses you won't add them to the pool but you will do the opposite.

i'm not aware of your subnet mask but  this is more than 255 addresses in this range.

Regards

Alain

Don't forget to rate helpful posts.

[haji_akhundov]

Dear alain,

Changing FROM:

ip dhcp excluded-address 172.16.1.0 172.16.15.255

TO:

ip dhcp excluded-address 172.16.2.0 172.16.15.255

will add 255 more hosts to the pool. Correct me if I'm wrong.

[cadet alain]

Hi,

yes you're correct I had misunderstood what you were explaining.

Regards

Alain

Don't forget to rate helpful posts.

[Jeff Van Houten]

If you want to limit what is advertised, why not just change the subnet mask to

255.255.254.0

Then you'll have 510 host addresses available in the pool and you won't have to worry about exclusions.

Sent from Cisco Technical Support iPad App

[blau grana · Accepted solution]

Try this one: instead excluded addresses, configure

dhcp

class where you allow range of IP addresses which you want.

ip dhcp pool a-pool

   network 172.16.0.0 255.255.240.0

   default-router 172.16.15.254

   dns-server 172.16.2.1 172.16.2.2

   lease 10

   class LIMIT-DHCP-SUBNET

      address range 172.16.0.0 172.16.1.255

!

ip dhcp class LIMIT-DHCP-SUBNET

   remark LIMIT-SUBNET

[haji_akhundov]

blau,

never knew about this

ip dhcp

class stuff. seems

like a cool shortcut. looking for documentation online right now...

thanks