stratisphere Posted January 26, 2009 Posted January 26, 2009 Hi All, This is a fairly urgent problem so i'm hoping I can get some helpful tips here. Our network uses Win2k3 DHCP & DNS (both on the same server). The network configuration is 172.18.0.0/22 (Subnet of 255.255.252.0). We have DHCP set to hand out leases in the scope 172.18.1.10-172.18.2.250 Except when the lease's hit 172.18.1.254, it wont hand any new ones out and hand's out old ones. Meaning when the machine it did belong to connects, we get IP conflicts. I've checked everything I can think of but cant find anything wrong DHCP wise... it sucks cause everything is coming to a halt!!! We're only just having the problem now because we've started to add new machines to the network (bringing the total above the 172.18.1.x number available). Weirdest thing is, DHCP says that it's got ~ 50% free leases... so why isnt it handing any out in the 2.x range?! I'm thinking about altering the subnet to 255.255.0.0 to see if it resolves it... but obviously thats alot of work. Help please!!!
treetops Posted January 26, 2009 Posted January 26, 2009 Have all of the reverse lookup zones got a SOA (start of authority)? Also, since were spread over 3 DCs we have an NS record for each server in each.
james_yale Posted January 26, 2009 Posted January 26, 2009 Is the correct subnet mask definitely set on the server's network interface?
stratisphere Posted January 26, 2009 Author Posted January 26, 2009 Is the correct subnet mask definitely set on the server's network interface? Yup Hmm, i'll checkout the SOA stuff... may well be that!
stratisphere Posted January 26, 2009 Author Posted January 26, 2009 Nope:( all lookup zones have the correct SOA records
matt40k Posted January 26, 2009 Posted January 26, 2009 Try splitting it into two blocks. 172.18.1.1 - 172.18.1.254 172.18.2.1 - 172.18.2.254 then exclude 172.18.1.1 - 172.18.1.10 and 172.18.1.250 - 172.18.1.254 also 172.18.2.250 - 172.18.2.254
stratisphere Posted January 26, 2009 Author Posted January 26, 2009 2k3 DHCP wont allow me to add a second scope in the same subnet. It says "THe address range and mask conflict with an existing scope" Which is a downright lie
matt40k Posted January 26, 2009 Posted January 26, 2009 Won't you have to edit the scope first, then add the second?
stratisphere Posted January 26, 2009 Author Posted January 26, 2009 Did. Even took the brave/stupid/smart (delete as appropriate) move to delete the zone totally.
matt40k Posted January 26, 2009 Posted January 26, 2009 Gulp. Mmm... guessing it wants .24 subnet. Could try the one scope: 172.18.1.1 - 172.18.2.254 exclude 172.18.1.1 - 172.18.1.10 172.18.1.250 - 172.18.1.255 (or is it 4) 172.18.2.250 - 172.18.2.254 Wouldn't say about using .24 / 255.255.255.0. I'll let someone else say\try that - Don't like the whole issue of routing etc
stratisphere Posted January 26, 2009 Author Posted January 26, 2009 Well my current thoughts at the moment are to do one of the following: a) change the entire network subnet to 255.255.0.0 - But if DHCP wont give out leases in the same subnet for a /22 range... which this make any difference?! b) All of our switches support vlans... segregate our network and use vlans. Zone the entire school out and then give /24 subnets to each zone. (Problem is i've never really played with vlans... do i risk it?!) c) Just found out, even with DHCP being on a single range now of 1.1 to 1.250, it reports 92 addresses free... yet DHCP is still handing out addresses which are in use. Makes me think there's another problem somewhere. d) build up an old box as a linux machine and setup dhcpd on it and use that.
matt40k Posted January 26, 2009 Posted January 26, 2009 b) VLANs really is something for the summer holiday when no-one is using the system.
artsaudi Posted January 26, 2009 Posted January 26, 2009 We had similar situation before and after hours of troubleshooting we found out that one of our staff setup his own home router with DHCP service running in his classroom. It was a nightmare! 1
Tamarside Posted January 26, 2009 Posted January 26, 2009 OK, I'm curious here: why are you using 172.18.x.x and not 172.16.x.x?
stratisphere Posted January 26, 2009 Author Posted January 26, 2009 b) VLANs really is something for the summer holiday when no-one is using the system. Yeh but the lack of available leases is really stopping us from doing lots of things. I may stop behind either tonight or tomorrow and do it... if I cant find any other solution.
stratisphere Posted January 26, 2009 Author Posted January 26, 2009 OK, I'm curious here: why are you using 172.18.x.x and not 172.16.x.x? Because it was the original range our LEA gave us before we walled ourself off their network. Besides the range for private addresses is 172.16.0.0 - 172.31.255.255
contink Posted January 26, 2009 Posted January 26, 2009 We had similar situation before and after hours of troubleshooting we found out that one of our staff setup his own home router with DHCP service running in his classroom. It was a nightmare! You've just reminded me that a 3rd party tech installed a wireless router as part of a smartboard install around the time our DHCP started going whappy in one school. Of course, it looks like the dozy s*d didn't turn the internal DHCP off...
stratisphere Posted January 26, 2009 Author Posted January 26, 2009 172.18.0.3 Addresses from 172.18.0.1 - 172.18.0.254 are used for static stuff. E.g. servers etc
matt40k Posted January 26, 2009 Posted January 26, 2009 Include in the range and add it to the exclude block!!
tmcd35 Posted January 26, 2009 Posted January 26, 2009 d) build up an old box as a linux machine and setup dhcpd on it and use that. This sounds like a better plan than jumping in with VLANs too quickly IMHO. Although, before you do anything else, how meny Windows Servers do you have? Have you tried installing DHCP on another Windows Server and disabling from the existing server? Maybe the quickest/simplest of all solutions if you have the servers already set up.
matt40k Posted January 26, 2009 Posted January 26, 2009 Problem you have with linux is 1/ do you know how to admin linux beyond the first install and 2/ does the person after you know linux beyond the first install. Have to agree with tmcd35 about setting up another DHCP server then disabling the current. Assuming it gets that bad.
stratisphere Posted January 26, 2009 Author Posted January 26, 2009 More than half our servers are already linux... so linux isnt really an issue. To be honest, i'd use it over windows. But my main worry is obviously dhcp in windows links in with DNS and updates the records etc... not sure if dhcpd in linux would do that. Yeh, i'll give running dhcp on another server a try. I've just been sniffing broadcasts on the network and no such luck as far as a second dhcp server is concerned. I dont think thats the case anyway because new leases are coming up in DHCP... just not in the right range! Fully agree with planning VLANs; it's something we oughta look into though as we're going to be using wireless laptops soon and it'd be nice to minimise broadcast traffic (i know wireless ap's can disable broadcast, but it'd rather not disable it altogether as broadcast does have it's uses). Thanks for all your help so far guys, i'll give the second DHCP server a go. If that fails i'll setup a test linux one and see how it goes. (By the way, I will give you all thanks... just a bit busy at the moment! )
Polski Posted January 26, 2009 Posted January 26, 2009 The IP address conflicts, are they ACTUALLY conflicts or is this a DNS issue? Your IP lease will expire and a new IP address will be issued, but is the DNS record being updated? Is DNS scavenging being done? Obviously we have no idea just how many nodes your are trying to connect, but your address range should be 172.18.0.0 - 172.18.3.255, am I right? You have confirmed the the first 254 are reserved for static devices, leaving you with a possible 750 ish addresses free. Never dipped my toe this far into subnets, but had problems with IP address and DNS conficts before, so thought I would add my half penny worth.
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