# DHCP - IP address is not available????



## Ricks76 (Aug 26, 2011)

:4-dontkno

Hi All

Not sure if anyone has experienced this one before but here goes...

OS: Windows Server 2008 R2 SP1 

Roles: DHCP , DNS, AD Services, File Services

Problem:

I'm trying to reserve IP addresses for a couple PC's , i created an exclusion IP range (.40 - .80) and now i want to reserve the IP addresses within this range to a couple PC's.

This is what i get when i try to reserve an IP:

" The specified IP address is not available"

Then when i click OK and click on ADD again i get the following:

" The specified IP address or hardware address is being used by another client"

I check my list of IP leases and there is a blank reservation with the MAC address i specified and it does not assign the IP address successfully.

If i click on RECONCILE , the IP appears in the list, i reconcile the DB but that makes no difference.

Now theres a hotfix which was released for R2 i.e KB981776 but this was for R2, the same hotfix was built into SP1 which is what my server has installed, but the problem persists!


FYI - The IP addresses i want to reserve is definitely not part of the scope for distribution and it is definitely not being used or assigned to another client. I triple checked that.

I have IPV6 enabled in the DHCP service.


Any ideas??

I would reeeaaallllly appreciate it if someone could shed some light on this.


----------



## espcdr (Aug 26, 2011)

you have excluded the IP range .40 to .80 from the dhcp table so in theory DHCP can't reserve these ip address for clients as the IPs simply don't exist so the DHCP server thinks

-Rich


----------



## Troy_Jollimore (Dec 31, 2007)

^^ x2 what he said. You would use an exclusion range if you wanted to set up some static IPs within that range of addresses. When you reserve an IP address to a MAC address, you automatically get an 'exclusion' for that particular address.


----------



## Wand3r3r (Sep 17, 2010)

In other words lets say you have printers and managed switches that you assigned ips between .10 and .50. You would EXCLUDE those ips from the dhcp scope so they would not be assigned by dhcp to prevent a ip conflict.

ip reservations are when you apply mac to ip reservation in the ACTIVE dhcp scope.


----------



## Ricks76 (Aug 26, 2011)

Thanks for the replies guys, but i dont think that is the case.

You are able to create reservations whether or not the IP's are included in an exclusion range. Ref: Using client reservations: Dynamic Host Configuration Protocol (DHCP) 

If 2008 works differently then it's a possiblility but i doubt that would change.
I was able to reserve .40 - .47 successfully before experiencing the problem.


----------



## Troy_Jollimore (Dec 31, 2007)

That's quite possible, too. Have you tried removing your exclusion range and seeing if it works? If it doesn't, well THAT'LL be a bit of a pickle to solve...


----------



## Wand3r3r (Sep 17, 2010)

Ricks76 you misread the link.

It is talking about MULTIPLY DHCP servers serving out the SAME IP SUBNET. That is what that 80/20 referance was about.

This does NOT apply to your situation at all.

Remove the exclusion list. Simple as that.


----------



## Ricks76 (Aug 26, 2011)

Wand3r3r said:


> Ricks76 you misread the link.
> 
> It is talking about MULTIPLY DHCP servers serving out the SAME IP SUBNET. That is what that 80/20 referance was about.
> 
> ...


" You can create reservations using any IP address in the scope's address range, even if the IP address is also within an exclusion range. Because of this design, when the 80/20 rule is implemented and all addresses in the scope are excluded (80% at one server, 20% at the other), reservations still function correctly"

That sounds pretty straight forward Wand3r3r, the article is not focussing specifically on a multiple DHCP server scenario, it is merely saying that a split scope works well because of this ability to create reservations for clients regardless of whether the IP range is contained within a scope or exclusion and if a reservation is configured it should be configured on all DHCP servers .



Anyways, i removed the exclusion i created , and i'm still experiencing the same issues. 

Again, the IP i'm trying to reserve is not being used, i ran PINGs and scanned the firewall, and its definitely not in use by any clients.

Is anyone currently administering a 2008 R2 SP1 DHCP server ? Are you able to reproduce this by any chance?


----------



## IT-Barry (Sep 6, 2010)

> when the 80/20 rule is implemented and all addresses in the scope are excluded (80% at one server, 20% at the other)


This is for multiple dhcp servers in one domain, you just have one dhcp server.

Go to address leases found under the scope in dhcp, if you have multiple scopes check under each under address leases and make sure the ip isnt leased if it is delete the lease, retry the reservation.

If the ping to the ip doesnt work and its not in the address lease, then any pc that doesnt allow pings could be using the ip via static, confirm none are.

If you are 100% sure no one is using the ip, make the machine static to the ip, if this works then there should be no reason why the dhcp shouldnt allow you to reserve the ip, when not using it.


----------



## Ricks76 (Aug 26, 2011)

IT-Barry said:


> This is for multiple dhcp servers in one domain, you just have one dhcp server.
> 
> Go to address leases found under the scope in dhcp, if you have multiple scopes check under each under address leases and make sure the ip isnt leased if it is delete the lease, retry the reservation.
> 
> ...


For admin reasons, making the the IP static is not feasible for me, i would rather get this fixed.

I am 200% sure the IP is not leased from any scope. i ran multiple scans , scripted an auto PING to check availibility of all IP addresses which confirmed that the IP is not in use. All our clients have ICMP enabled.


----------



## IT-Barry (Sep 6, 2010)

What is the error it gives you now providing you have removed the dhcp exclusion.

When you try to manually add the pc into a reservation.

Take note of the mac address.

Shut the pc down
Create new reservation > ip address when you type the mac address dont include the - - - - after every 2 digits, make it a full number 00320320f324 blah blah etc.

Really cant see it not working.


----------



## Wand3r3r (Sep 17, 2010)

Looks like we may again have a case of conflicting docs from microsoft.

I read the link above to be split scope [which did not apply to the situation] as well as though on one server the ip is excluded, on the other server its reserved which is why it works. 

Not that you can assign reservations to excluded ips.

Which is confirmed here:
Configuring a DHCP Scope

"By setting an exclusion range for these addresses, you specify that DHCP clients are never offered these addresses when they request an IP address from the server. Excluded IP addresses can be active on your network, but only by manually configuring these addresses at hosts that do not use DHCP to obtain an address."

Yet this link says you can with excluded
Limitations Creating DHCP Reservations

"1. You may create a reservation in any scope range.
This can include Excluded ranges


Being old school you have never been able to use dhcp for excluded ip ranges. That was the whole idea behind an exclusion. Don't dish out these ips.

I always designed my dhcp scopes/ip plan not to have exclusions. I only made the scope of dhcp ips I wanted which were usually in the center of the range. I would keep the bottom range for servers/network devices and the higher end range for printers/print devices.

So I then go to a Microsoft press Windows Server 2008 inside out book. Lookup dhcp reservations [pages 712-716]. Using exclusions pg 712-3. Using reservations pg 713-716.

Not a single mention of using an excluded range of ip for reservations.

Sorry but old school and book beat Microsoft docs any day. Not the first time I have found errors in them or conflicts between two or more of them.


----------



## Ricks76 (Aug 26, 2011)

Wand3r3r said:


> Looks like we may again have a case of conflicting docs from microsoft.
> 
> I read the link above to be split scope [which did not apply to the situation] as well as though on one server the ip is excluded, on the other server its reserved which is why it works.
> 
> ...


Thanks for the info Wand3r3r.

I will be deleting the existing scope today and re-configuring from scratch, if that does not solve my problem i will have to contact Microsoft.

Will post the outcome.

Thanks again..


----------



## Ricks76 (Aug 26, 2011)

IT-Barry said:


> What is the error it gives you now providing you have removed the dhcp exclusion.
> 
> When you try to manually add the pc into a reservation.
> 
> ...


Nothing has changed since i removed the exclusion range , i never include the seperators when creating reservations.

I've created thousands of reservations before and never had this problem until Server 2008 R2.

I will be removing the superscope , if that does not solve the problem i will be re-configuring the scope from scratch. Its gonna be painful but this problem is doing more damage the longer it persists. Hopefully the re-configure is successful.


----------



## Troy_Jollimore (Dec 31, 2007)

I'm sure Barry meant to try a static IP temporarily just to make sure it CAN be used, and the client doesn't show a conflict. Re-reading your original post, you say the MAC address associated with that client shows up as a blank with that error. Does this stay the same with any address you try to assign to it? Can you assign a 'problem' IP address to a different client? What about installing another NIC into the 'problem' client and seeing if it will take the DHCP address?


----------

