Migrating DHCP from to another server that already has DHCP and get “Error while importing option “6.” “This option conflicts with the existing option “” An Internal Error Occurred.”

Hello Everyone,

Need to dig up an old issue briefly. The last time I tried to migrate a DHCP scope to an existing DHCP server (authorized and servicing scopes, but not in the same range as the ones being migrated over) I got an error “Error while importing option 6. This option conflicts with the existing option". Apparently this is the case because the already existing server added the entries for 006 DNS Server and 015 DNS Domain Name when it was installed/authorized. At the time the best recommendation I could find was to delete those two entries from the DHCP server options and then run the import (obviously DHCP scope would be exported from the source server) again. The last time I got around it because I had a server we could move the DHCP to that never had DHCP before and thus no previous entries existed. This time I have to move it to an existing DHCP server. However, I would like to understand what is the risk of deleting those two entries and has anyone ever done that step?

The other option would be to export only the v4 aspect of the scope since (as far as I understand it) the option for exporting specific scopes is split into v4 and v6 subcommands. So running something like this: netsh dhcp server v4 export c:\dhcp "192.168.1.0" might work because including the v4 portion of the command allows for the export of a single scope.  This also gets around the "class conflicts with an existing class" error message that is returned when you try to import an entire scope on a server that already has DHCP configured. Many thanks in advance for all insights/input as always. Cheers!
Laszlo DenesAsked:
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Thomas UCommented:
Hi Lazslo

On a Windows DHCP Server? You want to delete 015 and 006? you can...just make sure that your DHCP Server has the correct entries after the import. You can delete them, import and then recreate them if they are wrong or not there anymore.

BUT!

I dont really understand everything you want/have. So. you have an existing DHCP server that actually serves IP adresses in the network for its subnet and everything?
Is the range you want to import already there or you just want to get rid of an old DHCP but want to migrate/move the dhcp to another server which is already dhcp for a different subnet?
regards
Thomas
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Laszlo DenesAuthor Commented:
Get rid of old DHCP (it is a DC that we are decommissioning) and move to existing DHCP server.
Scopes are 100% different on both so no scope overlap at all.
Want to export DHCP scopes from server1 (the DC) and import into server2 (a member server that has other DHCP scopes).
Would those two values not just be recreated (presumably) when I do the import, since that is what it complained about, i.e. that they are already there. I don't want to delete them, but that seems to be the only way to import or the ipv4 scope only as noted above.
Grüezi ;-)
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Thomas UCommented:
how much work would it be to just recreate the scope manually? on a weekend, so all the clients get a fresh IP on monday morning?
on the old dhcp set the lease time to 1 day (if not already) a week beforehand.

Never seen such a massive config which cannot be created within a few dozen minutes by hand, right?

Grüezi ebefalls ;)
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Laszlo DenesAuthor Commented:
Not much, but we are 24/7 hospital so no weekend and I have been asked to migrate it.
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Thomas UCommented:
hm...how about set the leasetime to as little as possible, then prepare the scope on the new server, but not activating it. then point zero deactivate activate..

But maybe this could be very feasible for you:
https://technet.microsoft.com/de-de/library/jj590659(v=wps.630).aspx
https://docs.microsoft.com/en-us/powershell/module/dhcpserver/import-dhcpserver?view=win10-ps

You can actually export / import only the scope from a dhcp to a dhcp. with powershell, but needs a server 2012 at minimum..

I dont know..how many clients are we talking about? maybe its best if you try what you initially wanted by export/import the scope with netsh: http://pipe2text.com/?page_id=1498
delete DNS options first, import and recreate it or use the imported if its the same.
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Laszlo DenesAuthor Commented:
Thanks. Appreciate the links, but was also hoping to resolve the question around deleting the
006 DNS Server and 015 DNS Domain Name
because that was the same issue I had last time and this time I cannot ignore it.
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Thomas UCommented:
Dont bite on the two options 006 DNS and 015 DNS. Its safe to delete and recreate them.
If you backup the whole DHCP Server (only the service not the whole Server its installed) you are very safe anyway, because restore can be done anytime, if its within a few minutes (it can happen if a client gets a new IP in that very moment, but hey, whats the possibility, even then a simple ipconfig /renew or ipconfig /release then /renew solves it.)

DHCP is quite a "dumb" service. I have never have had any problems with it manipulation entries.
Backup everything: https://technet.microsoft.com/en-us/library/ff621490.aspx
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Laszlo DenesAuthor Commented:
Thanks
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Steve KnightIT ConsultancyCommented:
Easiest option IMO is to use DUMP not EXPORT command, that gives you a text file that you can edit before importing with all scopes and options etc. intact

I explain more in link below including a way using temporary reservations for how to effectively bring over existing leases without any delay

http://scripts.dragon-it.co.uk/links/dhcp-scope-move-export-backup

The options you mention are server options so apply to all scopes.  If you use the DUMP option you can remove those two entries from the text file and use EXEC to import.  Alternatively just delete and re-add them having notes what they contain.  Would take a minute maybe.

If it is only one subnet and haven't got any reservations etc. then I would just create the same scope,

For actualy change over many different methods but I'd normally look to set the lease time on the old to be low or ideally set an exclusion range if your number of free addresses allows it so that over next few days / hours those addresses are now free.  On the new server put the opposite exclusion of range on the scope and it can start giving out addresses.  Disable scope on the old machine, once the old server leases have (mainly) expired remove the exclusion from the new server and turn the old one off..

i.e. Old server : 10.0.0.1/24   say excluded 10.0.0.1 to 10.0.0.10 and 10.0.0.250 to 10.0.0.254.  Add exclusion for 10.0.0.120 to 10.0.0.249
On new server set it up the same but add exclusion for 10.0.0.11 to 10.0.0.119 to start with.

Make sure the new server has conflict checking turned on so it pings the address before giving it out if you haven't already.

Steve
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Laszlo DenesAuthor Commented:
Thank you everyone.
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Windows Server 2008

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