DHCP Clients Renewing Lease At Every Startup : TCP/IP, DHCP

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01.30.2008 at 10:28AM PST, ID: 23123742

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6.8

DHCP Clients Renewing Lease At Every Startup

Zones: Dynamic Host Configuration Protocol (DHCP, Windows 2003 Server, SBS Small Business Server

Tags: TCP/IP, DHCP

Hi there,

We run an SBS server which looks after a network of about 60 XP clients. We also have secondary DC and DNS server. The SBS server is acting as the only DHCP server on the network.

The problem I have is that the XP clients are looking for a new DHCP lease every time they boot. If the SBS server is down, they get an APIPA address. This can happen in day 1 of the lease. I know that clients will look to renew the lease at 50% of the duration, but this is happening every time. My understanding is that a client should be able to retain a newly obtained lease if the DHCP server is down. Is this correct?

I'm pretty new to all this, so I may missing something. At the moment, even having a secondary DC and DNS server has no real benefit because if the SBS server goes down, the clients lose network connectivity.

Please could someone advise why this is happening?

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Question Stats

Zone: Networking

Question Asked By: gcz

Solution Provided By: DrDave242

Participating Experts: 1

Solution Grade: A

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01.30.2008 at 11:11AM PST, ID: 20780052

Rank: Master

DrDave242:

I think there's a bigger question here: Why is your SBS server going down often enough for this to be an issue? Bypassing that for the moment, by default, XP doesn't release it's DHCP address upon shutdown, so the clients should be requesting to renew their existing addresses when they boot back up, rather than requesting a new lease. They can be configured to release their leases upon shutdown, though. To see if this is in place, open the DHCP console on your server. Expand your server, expand your scope, and click Scope Options. In the list of options in the right pane, look for an item called "002 Microsoft Release DHCP Lease on Shutdown Option." If it exists, that's what causing the clients to release their addresses on shutdown. You can delete the item from the options list to discontinue that behavior. If you don't see that item in the list of scope options, click Server Options and see if it's in there.

01.31.2008 at 02:57AM PST, ID: 20785472

gcz:

The server isn't going down all the time - I am looking at contingency - should the SBS server go down, could users login and access resources (alebit without Exchange/Sharepoint). I noticed this behaviour while working on the server recently and noticed it wasn't right.

The above option is not included in the scope or server options. I have even added in the option with a '0' value to disable, but clients are still releasing the lease. Looking at the address leases today, all clients have a new lease starting from today.

Is there anywhere this configuration setting could be taking place?

02.01.2008 at 02:16PM PST, ID: 20801269

Rank: Master

DrDave242:

This is very odd behavior. XP should not be releasing its address on shutdown without being specifically configured to do so. There was a registry key that could be set in previous versions of Windows (up to WinME, I believe) to enable this behavior, but it is not included in 2000 or XP. You're not running a shutdown script that could be doing this, are you?

02.02.2008 at 02:53PM PST, ID: 20806332

gcz:

No, only login scripts are running for users.

I did read that clients attempting to renew a lease, in the event of no DHCP server not responding, try to ping the default gateway defined in the given options. If the ping is successful, then the client should keep it's config and continue, providing the lease hasn't expired - it assumes it's still on the same physical network. I have checked the settings and the default gateway is available.

This sort of leads me to think that it must be that the clients are releasing the lease on shutdown, rather than failing to renew on startup.

Could there be any GPO settings that define this sort of behaviour? The DC is an SBS server - do you think this may have something to do with it? (pre-defined GPOs?) I haven't looked after the network for long so I wasn't around when the SBS server was installed.

02.04.2008 at 12:29PM PST, ID: 20817682

Rank: Master

DrDave242:

Yeah, I read that same thing about the clients pinging the default gateway. That's what prompted me to ask about a shutdown script. You could run a sniffer on the server and then shut down a client to see if it's sending a release packet. That'll at least tell you whether it's actively releasing the address on shutdown. It's got to be, though; there's no other reason why it would issue a new request on startup.

I don't think there are Group Policy settings that will cause this behavior, and I'm 99% certain that the built-in SBS GPOs will not do so.

02.05.2008 at 01:02AM PST, ID: 20821581

gcz:

That sounds like a good idea. I'm out of the office for the next few days, but I'll try look at this ASAP.

Thanks, I'll let you know the results.

02.12.2008 at 01:54AM PST, ID: 20873541

gcz:

Thanks for your patience.

I have run protocol analyser on our DHCP server and I'm a little bit more confused now.

The client I tested did not send a release request on shut down, although when I fired it back up, it went through the complete DORA process, and initially sending it's broadcasts without an IP address (I checked that the MAC address was the same). It is then allocated it's previously leased IP config back as part of a new lease.

Furthermore, I seem to read conflicting info as to whether this is normal behaviour. I have read that a DHCP server must be present when a client starts up every time, and gets an APIPA if not, and the only way to remedy this is to have two DHCP servers to provide fault tolerance. I have also read that a client will not need to do this until 50% of it's lease is up, and even then, in the event of no reponse from a server, it will checks its default gateway is still valid and happily carry on with the same config (this is also on the MS website).

I would appreciate it if someone could confirm what the normal process really is, then I can determine if the system is working properly or not!

Thanks....

02.13.2008 at 09:29AM PST, ID: 20886141

Rank: Master

DrDave242:

I've just done some testing with an SBS 2003 R2 server and XP SP2 client, and it's behaving exactly as yours does. I first checked the lease on the client, and it was only two days old (lease expiration is set to the default of eight days on this server), so it was nowhere near 50% expired. I then rebooted the client, and it renewed its lease with the same address. I stopped the DHCP Server service on the SBS server and rebooted the client again, and it got an APIPA address, even though its previous lease was brand new. This is not what I was expecting according to the documentation I've read, but it does seem to be the default behavior, as I have not made any changes that would affect DHCP on the client in any way. I will do more research and see what I can come up with.

02.13.2008 at 10:07AM PST, ID: 20886535

Rank: Master

DrDave242:

Hold on, I stand corrected! The server and client I'm testing with are in a virtual environment with no connection to the Internet, and it just occurred to me that I had configured the DHCP server to give out a gateway address which does not correspond to a device on that virtual network. This could obviously affect the behavior of the DHCP client on a reboot, so I changed the gateway address in DHCP to the server's own address, since it and the client are the only two machines on that virtual network. I then renewed the lease on the client, made sure that it got the new gateway address (and that this address responded to a ping from the client), and stopped the DHCP Server service on the SBS server. When I rebooted the client, it maintained its previous lease, presumably because it was able to contact the gateway. So apprently the client DOES attempt to contact the gateway on a reboot, and if successful, maintains its current lease, just like the documentation says.

Now, two questions: Does your gateway respond to a ping from the client? In your packet trace, do you see any sign of the client trying to contact the gateway before sending a DHCP Discover packet?

Accepted Solution

02.14.2008 at 02:40AM PST, ID: 20892254

gcz:

Thanks for the info. Our gateway is a Draytek Vigor 2800 router, and does respond from pings to it's internal LAN interface (when manually pinging it). I tried disabling any firewall settings which may have affected this (DoS defence etc.), but still no joy. When the client starts up, it gets an APIPA address in the absence of a DHCP server.

What I did do, though, was change the default gateway in the scope options to my PC, ensured those settings had been applied to the client, disabled DHCP and restarted the client. This time, it kept it's IP config.

So it seems it's a problem with the router not responding to pings from clients during startup. I completely disabled any DoS defence but this didn't make a difference, so I'm still a little stumped.

Although I haven't fully got to the bottom of this, I think you've earned your points as you've answered the DHCP side of things! I'll investigate this further as it's obviously an issue with our Draytek Router.

Many thanks for your help.
(you'll probably see another post from me in a day or two if I can't figure it out!).

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