Gilly2003 Posted September 30, 2015 Posted September 30, 2015 Hi, hoping someone can shed some light on this for me. Long story short I had to take down our primary domain controller (PDC is server 2008r2) because of a virus I have a secondary domain controller (replication of AD) which should of, or I would have assumed, kicked in to continue authenticating users. Now we have a short DHCP lease of 1 hour so naturally during the time there was no dhcp server as its a service on our PDC However i still thought servers and some devices would of still seen the default gateway especially if they were set to a static IP? Out of our 4 IT computers only one remained to be able to RDP to servers, but no internet connection and the other 3 couldn't do either. I cant work out why as it isnt set to a static IP... Maybe I need an explanation as to what a secondary/replicating domain controller actually does as the whole thing has confused me and I now don't know if what happened was correct or not.
win Posted September 30, 2015 Posted September 30, 2015 Make sure your secondary has taken over the fsmo role (no primary & secondary DCs now) Does your 'secondary' DC have the dhcp role installed? If not you need to install it asap. The secondary DC should have a static, the gateway should be on the static config. After that, your IT rooms will be able to get an IP address and gateway from the secondary DC
win Posted September 30, 2015 Posted September 30, 2015 Once sorted, you should setup another DC for replication. For 2008r2 do a search for split scope DHCP so if one DC fails, the other one will still give out IP addresses
Oaktech Posted September 30, 2015 Posted September 30, 2015 Also make sure your DNS has replicated successfully and has a full complement of working forward and reverse lookup zones. Is your second DC (not secondary, FSMO/PDC emulator here!) entered into the DHCP your machines have received as a valid source of DNS? - if it isn't, that could well explain your issues. I've never bothered with split scope, but I have configured a DHCP server on a second DC to be identical to the first DC but with the service set to manual. It takes seconds to bring the service in - I'd get on it with a new DHCP server post-haste!
Gilly2003 Posted September 30, 2015 Author Posted September 30, 2015 thanks win is there no way of replicating the dhcp service on both servers or is a "split scope" the best way we have a number of static IP's obviously for other servers, devices... so if I wasnt able to get our primary DC back up I wouldof had to manually put these static settings in to the new DHCP server
Gilly2003 Posted September 30, 2015 Author Posted September 30, 2015 okay forget the last reply then, didnt see your 3rd in time I cant run a split as our IP pool is typically running with only 20-25 free (on a good day) Yes the second DC is in the DNS records to be used if primary DNS is not available
sparkeh Posted September 30, 2015 Posted September 30, 2015 is there no way of replicating the dhcp service on both servers or is a "split scope" the best way Is there any scope for upgrading to Server 2012r2? It has DHCP failover which does exactly that.
Oaktech Posted September 30, 2015 Posted September 30, 2015 thanks win is there no way of replicating the dhcp service on both servers or is a "split scope" the best way we have a number of static IP's obviously for other servers, devices... so if I wasnt able to get our primary DC back up I wouldof had to manually put these static settings in to the new DHCP server There is no way of replicating a simple DHCP scope - well, not with an MS 2008 era DHCP server anyway. Split scope is the ticket for automatic resiliency. If it is possible to safely bring the broken DC up for a moment or two disconnected from the network you can create a backup of the DHCP config and import that into a new DHCP server to make life easier. Otherwise yes, manual is the thing I manually take a backup of my DHCP scope every so often and plonk it on a USB stick which sits in the safe with the DR procedure.
win Posted September 30, 2015 Posted September 30, 2015 As mentioned by others, server 2012r2 does dhcp replication, but with 2008r2 you're looking at split scopes. It could be a good time then to widen your subnet a little and add some extra IP addresses on your network. If you're using reserved MAC addresses for static IPs then yes it needs to be done manually. However, the easy way (not recommended though) is just to reserve a block of IPs in a range (not for dhcp allocation) and use a spreadsheet to keep track of which ones are used. Then you won't need to re-enter them. I have a split scope and one of the scopes is replicated - but that is probably overkill!
Gilly2003 Posted September 30, 2015 Author Posted September 30, 2015 well we have just yesterday signed off on a complete virtualisation project which will bring all our servers up to 2012r2 OS's I will keep this in mind I have got the primary DC back up and going thankfully after 7 hours of work but I just wasnt sure what all was meant to happen with the second DC when primary failed. Thanks for clearing it up guys much appreciated
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