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DHCP Reservation Names change unexpectedly in a Windows 2003 Scope

Question

Monday, October 25, 2010 7:33 PM

I create a reservation within a scope, and give it the name our corporate naming convention mandates it to have, such as CityStT05.  This designates this reservation as being for the fifth IP telephone located at our location designated CitySt.  The IP phone boots up and receives the IP address just fine.  All options it should get are received just fine.  The phone works perfectly.

However, when I look back at this reservation in my DHCP admin interface ( I use the DHCP snap-in for MMC ), I notice that the value of the string located in the "Reservation Name" field has now changed.  I entered "CityStT05", but now it shows the Reservation Name to be "AV009E4C15", which does not comply with corporate naming policy.  

When I run WireShark to sniff the DHCP traffic, I discover that the IP phone itself has the host name of AV009E4C15 hard coded into it.  I can't change it.  This hard coded host name is being included in the DHCP Discover packet, and my DHCP server is changing my "Reservation Name" to a value that the device itself is supplying, and not one that I want to use.

Sometimes this can be helpful, say if a PC gets renamed the I want the DHCP reservation to change and match it. 

But this behavior is not wanted for this particular device ( or printers either ).  How can I disable the DHCP server from changing the Reservation Name for specific devices, while allowing it to change the Reservation Name for others ?

thanks

Kirt

All replies (7)

Thursday, October 28, 2010 2:33 PM ✅Answered

Microsoft Support has responded ( case# 110102567553445 ) that it is normal behavior for the 2003 DHCP server to overwrite the original Reservation Name with the hostname that is included from the DHCP client in the DHCP Discovery and DHCP Request packets.

However they did admit that this behavior has not been documented adequately to date, but they are moving forward with updating the documentation. It may include a KB article, and this blog may also help.

A very helpful suggestion was to use the option 12 to have the DHCP server tell the client what its name SHOULD be, and if the client can update its own config, the hostname and reservation name should be in sync thereafter.

However, in my case, the Avaya 5610 IP telephone doesn't support administrative changes to its hard coded configuration. This is a minor problem since the phones work excellently in all other regards.

A product enhancement request could be to display the description field in the MMC snap-in interface for DHCP, and allow sorting by it. Currently, the only listing is by IP address concatenated with the reservation name ...

Reservations

[10.65.34.47] NYCDC1.domain.com

[10.65.34.103] NYCDHCP1.domain.com

It requires a Premier Support Agreement to make a product enhancement request to Microsoft. I don't have one of these.

If anyone reading this who does like this enhancement proposal, perhaps they could request it.

Hope this clears up a couple of questions anyway.

Kirt

Monday, October 25, 2010 10:18 PM

Hi Kirt,

From my research, DHCP picks up the name from the machine. The reservation name is the host's hostname.  When the lease expires it checks back in to renew and at this time DHCP will change the reservation name to the device's hostname.

Stop DHCP Reservation Name from being Overwritten- OpenG.info
http://www.openg.info/entry/stop-dhcp-reservation-overwritten

DHCP Reservation Name : The Reservation Name I assign doesn't stick.
http://www.experts-exchange.com/OS/Microsoft_Operating_Systems/Server/2003_Server/Q_23168038.html

You could populate the Description field with your SLA name. Otherwise, the only way I see to stop it is to change it on the phone. I'm somewhat surprised to hear the names are hardcoded on the phones. Have you contacted the vendor asking if there are any options to changing the hostnames?

Ace

Ace Fekay
MVP, MCT, MCITP EA, MCTS Windows 2008 & Exchange 2007, MCSE & MCSA 2003/2000, MCSA Messaging 2003
Microsoft Certified Trainer
Microsoft MVP - Directory Services

This posting is provided AS-IS with no warranties or guarantees and confers no rights.

Monday, October 25, 2010 10:44 PM

Ace

Thanks for your answer.  I had seen those other threads.

The answer was "...change the device...", but there are some devices you just cannot change parameters on.  I've got some.

I used a Microsoft DHCP server for several years on NT4.0 back around 1999 that did not do this. The reservation names stayed exactly as I put them in.

If Microsoft has added this feature, then they should be able to control it.  I couldn't find any reference to this type of behavior in any of the DHCP RFC's.  I think this is completely a Microsoft implementation issue.

The new version of DHCP Server does a whole lot of other cool stuff that I want to use. 

Besides, as a point of honor, I just can't have my equipment telling me what it wants ... I must tell it what I want   ;-)

Kirt

Tuesday, October 26, 2010 7:51 AM

Hi Kirt,

What I thought you might consider to add DHCP option 12 for reservation object to assign a host name for it .

Thanks.

Tiger Li

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Tuesday, October 26, 2010 2:42 PM

Tiger

I had already tried pushing the hostname out with option 12, but the Avaya IP phone didn't really accept it.

I then reset the reservation name back to what I wanted, and rebooted the phone, but it still provided the hardcoded name, which the DHCP server then corrupted my reservation name again.

This option basically changes nothing in the phone. That was the main clue I got that all the values are hard coded and cannot be changed.

I've got Microsoft support working on this.  I'll post the solution they come up with.

thanks

Kirt

Tuesday, October 26, 2010 2:53 PM

Kirt,

I'm curious what PSS comes up with.

Ace

Ace Fekay
MVP, MCT, MCITP EA, MCTS Windows 2008 & Exchange 2007, MCSE & MCSA 2003/2000, MCSA Messaging 2003
Microsoft Certified Trainer
Microsoft MVP - Directory Services

This posting is provided AS-IS with no warranties or guarantees and confers no rights.

Thursday, October 28, 2010 3:15 PM

Kirt,

Thanks for the update. It's possible that a Microsoft rep reading this thread may be able to do that for you.

At least you got an answer. :-)

Cheers!

Ace

Ace Fekay
MVP, MCT, MCITP EA, MCTS Windows 2008 & Exchange 2007, MCSE & MCSA 2003/2000, MCSA Messaging 2003
Microsoft Certified Trainer
Microsoft MVP - Directory Services

This posting is provided AS-IS with no warranties or guarantees and confers no rights.