DHCP Server, BAD_ADDRESS

[abillybob]

Hey Guys,

 

So the network is a right mess since I've got back and it seems that the temporary technician they had in place in the meantime while I was gone has changed a lot of things and done more damage then good. But oh well these things happen.

 

One of my main concerns is the fact that random machines/iPads around the school aren't being able to pick up an IP Address instead they're assigning themselves local IP address like 169.*.*.*

I checked the DHCP server yesterday which had an error mark next to IPV4 (no tick) it seems that a lot of the IP's are coming up as BAD-ADDRESS saying that the particular address is already being used by another machine, although I don't think this is the case unless the other chap has setup static addresses around the school though he'd have no reason to have to do this and even then surely DHCP should just assign that machine a different address because it's already being used.

I have deleted all the entries and restarted the entire server and now I have a little green tick and everything seems ok although certain addresses are still... BAD!!

Any ideas how I could sort this out!?!

 

Thankyou

[abillybob]

Here's a picture of what's going on!!

[win]

The fact that they are in numerical order suggests that you are right, he has probably set up statics somewhere and not excluded the range.

 

If you know what the bad IPs are, i recommend excluding them from distribution which is what he should have done prior to adding the statics.

[Ergo_Computing_IS_Support]

I would start my investigating those 'BAD ADDRESSES' to see if they are actually being used i.e. try pinging them.

 

If they respond, you could then begin trying to isolate them by looking at ARP tables on the server and the network switches. With a bit of digging you should be able to track a given IP to a MAC address, and then a MAC address to a switch port.

 

If you find these devices you can then check their IP settings. If they are indeed static you could revert them to DHCP, if they are already DHCP perhaps try an ipconfig /release and then ipconfig /renew to obtain a new IP/lease from the DHCP server.

 

I would also investigate if there is a 'rogue' dhcp server on your network. You can download tools to do this. Similarly, I'd check to see if there are any new devices on your network, maybe they are causing the problem.

 

Thanks.

[abillybob]

Thankyou guys for all your answers. I think I may have found the problem. I think anyway.....

 

It seems the second domain controller is running a DHCP Server role also, I have removed the role and restarted the server - Fingers crossed.

[sonofsanta]

Running DHCP on both servers is usually a good idea, in case something happens to one of them, but when you set up your address pool on both, you need to make sure to exclude half the range on each so they don't clash - sounds like he forgot to do this.

 

For example: your address range is 192.168.0.1 to 192.168.0.254. You add this as an address range on both your servers, DC1 and DC2.

 

But on DC1 you set an exclusion range of 192.168.0.128-192.168.0.254, and on DC2 you set an exclusion range of 192.168.0.1-192.168.0.127. That way, DC1 will only hand out addresses in the first half of the range, and DC2 will only hand out addresses in the second half - they'll never fight over one address.

 

Why do it? Because if DC2 fell over and was going to take a couple of days to bring back up, clients who had received their address from DC2 wouldn't be able to renew. It's then straightforward to take the exclusion range off DC1 so that it provides addresses from the whole pool. It's also some basic load balancing.

[abillybob]

Thankyou @sonofsanta that was very informative. I will do this then The server is also has WDS installed. If my memory is right don't I have to tick something to say it's a DHCP server as well so that WDS will work correctly?

[sonofsanta]

Thankyou @sonofsanta that was very informative. I will do this then The server is also has WDS installed. If my memory is right don't I have to tick something to say it's a DHCP server as well so that WDS will work correctly?

 

Don't use WDS, so can't help you there I'm afraid

[sted]

Thankyou @sonofsanta that was very informative. I will do this then The server is also has WDS installed. If my memory is right don't I have to tick something to say it's a DHCP server as well so that WDS will work correctly?

 

in wds console tab it out till you see your servers name on the right. Right click it and select properties. Go to the dhcp tab and tick both boxes

[abillybob]

Don't use WDS, so can't help you there I'm afraid

 

No problem Thankyou for your help anyway, I'm sure someone else will know the answer to that!

 

in wds console tab it out till you see your servers name on the right. Right click it and select properties. Go to the dhcp tab and tick both boxes

 

Oh... and there we go! Haha Love EduGeek cheers @sted!

[tmcd35]

Thankyou @sonofsanta that was very informative. I will do this then The server is also has WDS installed. If my memory is right don't I have to tick something to say it's a DHCP server as well so that WDS will work correctly?

 

In your DHCP server options, Option's 66 and 67 should be set. 66, boot server host name, should be the IP address of your WSUS server, and 67 should be the boot image file location on that server. Alas, we're using SCCM so our boot image is different, can't give you the details from my DHCP. Can't remember what it should be.

 

I think option 67 is the important one if DHCP and WSUS is on the same server - from memory.

[3s-gtech]

Since Server 2012, if both DHCP servers are running it, you can cluster DHCP. This is the best option, and is very easy to set up. If this wasn't done, then that's a fail.

[sted]

In your DHCP server options, Option's 66 and 67 should be set. 66, boot server host name, should be the IP address of your WSUS server, and 67 should be the boot image file location on that server. Alas, we're using SCCM so our boot image is different, can't give you the details from my DHCP. Can't remember what it should be.

 

I think option 67 is the important one if DHCP and WSUS is on the same server - from memory.

 

you dont actually HAVE to set them its not a bad idea but it will work quite happily without this. Though adding them does give you a bit more security so nobody can dump a second pxe server on your network and have pcs pick that up (ive also found its nesescary with some toshiba laptops IF dhcp and wds/mdt arnt on the same server

[Ergo_Computing_IS_Support]

As mentioned above, Server 2012 now supports DHCP clustering/failover which has been long overdue, but now its here it works really well.

 

Splitting scopes over multiple DHCP servers always felt like a bodge but now it seamless and very easy to set up. We always implement it now.

[tmcd35]

you dont actually HAVE to set them its not a bad idea but it will work quite happily without this. Though adding them does give you a bit more security so nobody can dump a second pxe server on your network and have pcs pick that up (ive also found its nesescary with some toshiba laptops IF dhcp and wds/mdt arnt on the same server

 

I can't remember the details, but I'm 99.999% certain one of them had to be set if both DHCP and WDS were on the same server. Alas it's been a long while since I set it up last. It only stuck in my mind because every time I do it I setup both those options anyway even though my DHCP is a separate standalone server. Not strickly required in my case, but best practice.

 

Now my memories being exercised a bit, I think one of the two check boxes in WDS you pointed @abillybob to above actually mentions one of those two DHCP Options (I'm gonna swear blind it's 67).

[abillybob]

Ok so hell broke loose this morning. Came in and the entire network was down. PANIC PANIC PANIC.

But now it seems to be fixed I re-built DHCP server from scratch and it all seems ok again now. Only issue is since doing that client machines can't resolve names such as 'Domain Controller' to an IP address instead it gives me what looks like an ipv6 address

 

So I'm not sure what's going on can anyone help me resolve this as I don't even know where to start!

 

Im guessing it has something to do with DNS.... and this is embarrassing but I have never setup a DNS server *sigh*

Edited November 27, 2014 by abillybob

[sted]

have you got option 6 on your dhcp server set to your dns server(s) ip(s)?

have you got option 15 set to domain.local

 

it looks like its defaulting to using ipv6 routing (not necessarily a bad thing) but it looks like dhcp isnt working right

 

what do you get if you run ipconfig /all on a workstation?

 

dns is usually pretty stable and hard to kill

 

also try ping whatever -4 see if that returns an ipv4 address

[Ergo_Computing_IS_Support]

Hello,

 

What method are you using to resolve device names? e.g. are you pinging them? or using nslookup?

 

Also, in DNS Manager, what type of records have got stored? Are they A records (IPv4) or AAAA records (IPv6)?

 

When you setup your new DHCP scope(s), did you enable DNS dynamic updates?

 

In the DNS Manager check the server properties and check and see what interfaces the server is listening on.

[tmcd35]

Do all devices show valid IP addresses if you do ipconfig \all on them, with correct subnet, gateway and dns? If so it's most likely a case that the OS on both client and server supports IPv6 and IPv6 is enabled on both their NICs. That being the case if you do a ping or nslookup you may find it uses IPv6 in preference unless you specifically disable it's use on the NICs. It should be nothing to worry about.

 

If you want to force IPv4 then disable IPv6 on the NICs. So long as IPConfig is reporting correctly and DNS is correctly configured, if you disable IPv6 on your servers NIC then the client will have no choice but to communicate the good old fashioned way.

[3s-gtech]

Be wary disabling IPv6 on DCs, it causes some weirdness to do with lookups and connecting to the directory.

[abillybob]

Hmmmm ok - thank you all although this is all very strange all seems to be working now and just started working on its own if I try to ping 'Domain' it resolves the IP, although after having a look at DHCP Address Leases it says BAD_Address by a lot of the IP's again. Also for example when setting up a reservation for a computer to use 10.150.6.125 (not real IP address has been changed) the client machine won't be able to obtain that IP and says something is already using that IP address on the network even though I don't get a reply when pinging 10.150.6.125, When I do ping that address it says:

Reply from '10.150.4.3': Destination host unreachable

 

Am I going mad here or should it say

Reply from '10.150.6.125': Destination host unreachable

 

Grrrr, so confused right now it's unreal!

[Ergo_Computing_IS_Support]

Reply from 10.150.4.3: destination host unreachable is correct, as 10.150.4.3 will be the IP address of the device from which you are running the command.

 

Its also worth noting that the os firewall may deny ping responses and therefore it may not respond.

 

Thanks.

[cullingsh]

If it can't ping 10.150.6.125, it won't say reply from 10.150.6.125: Destination host unreachable as it can't find it to get a reply from it. The address may be your ip, a router, switch etc which is feedback that it can't be found.

[abillybob]

Ok its just me being dumb then Haha thank you guys!