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Question
Wednesday, October 23, 2019 3:33 AM
Hi,
I have a couple of questions for dhcp failover in windows server 2016.
1. For my hot standby mode which ip helper ip address should our network guys configure? Is it both the active and stadby dhcp servers or just the active dhcp server?
2. In Load balance mode which ip helper should the network guys configure? Is it both the active dhcp servers? I'm figuring our how the client machines decide to which server they would get the ip address
3. In a hot standby mode can I configure to choose which is the primary and standby server for each of my scope in a multiple scope setting?
That's all for now.
All replies (14)
Wednesday, October 23, 2019 4:53 AM ✅Answered
Hi Janus,
1. When you deploy DHCP failover, a single DHCP relay address might not be sufficient, since DHCP clients must always be able to communicate with both the primary DHCP server and the failover partner server
2. Same as answer 1.
3. Yes you should be able to do that.
You'll find all the information over at the official documentation here:
DHCP Failover Architecture
https://docs.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2012-r2-and-2012/dn338979(v%3Dws.11)
DHCP Failover Modes
/en-us/previous-versions/windows/it-pro/windows-server-2012-r2-and-2012/dn338976%28v%3dws.11%29
Best regards,
Leon
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Wednesday, October 23, 2019 6:17 AM ✅Answered
Hi ,
Thanks for your posting here.
**>>**For my hot standby mode which ip helper ip address should our network guys configure?
***>>*In Load balance mode which ip helper should the network guys configure?
I am a bit confused about IP helper. Did you mean DHCP relay agents? Please feel free to let me know if my understanding is wrong.
Relay agents are used to relay DHCP and BOOTP messages between clients and servers on different subnets.
If primary DHCP server and the failover partner server are located on a different subnet than DHCP clients, this requires at least two DHCP relay agents.
Here is an official documents talking bout how to configure Relay agents, you could have a look:
>>For my hot standby mode, Is it both the active and standby dhcp servers or just the active dhcp server?
In host standby mode, one of the two DHCP servers in the failover relationship is active at a time. If the active server goes offline, the other server (the standby server) takes over.
The active server for one subnet can be the standby for another, and a given server can be the active or standby server for multiple subnets.
>> In Load balance mode ,Is it both the active dhcp servers? I'm figuring our how the client machines decide to which server they would get the ip address**
Yes. In this mode, both servers are active at the same time.
The following blog explains details about how DHCP failover load-balancing mode handle the IP address pool, you could have a look:
DHCP Failover Load Balance Mode
**>>**In a hot standby mode can I configure to choose which is the primary and standby server for each of my scope in a multiple scope setting?
We can choose active or standby role when create new failover relationship, but we cannot change the standby and active mode in an existing DHCP failover relationship.
If you want to switch active and standby DHCP servers in existing failover relationship, we need to re-configure the DHCP failover to change it.
Hope this can help you, if you have anything unclear, please feel free to let me know.
Best Regards,
Candy
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Thursday, October 24, 2019 6:50 AM ✅Answered
Might try restarting the DHCP Server service.
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Wednesday, October 23, 2019 5:33 AM
Hi Leon,
So that would be a yes to add both the primary and failover dhcp server in the ip helper of the router?
Thanks!
Wednesday, October 23, 2019 5:34 AM
That’s right.
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Thursday, October 24, 2019 4:23 AM
Hi Candy,
By ip helper I mean the router configuration not the windows relay agent. I believe the relay agent term is used also for routers.
I tried experimenting dhcp1 as primary and dhcp2 as secondary. I disabled dhcp1 and true enough dhcp2 was able take the primary role and lease out ip address to my client machine. But when I enabled back dhcp1 my client machine is no longer able to get an IP address. Checking the state of dhcp1 it is already active and back to normal.
Did I miss something?
Thursday, October 24, 2019 4:33 AM
Did you run the following on your client:
Ipconfig /release
Ipconfig /renew
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Thursday, October 24, 2019 5:13 AM
Hi ,
Please first check the partnership on the two DHCP servers:
The ipconfig /all will show the current DHCP server on your client. I would suspect the current DHCP server on your client is DHCP2, as DHCP2 is changed to standby, then the client machine will not get the IP address.
As Leon said, please run the Ipconfig /release and Ipconfig /renew on the client to do a check.
Best Regards,
Candy
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Thursday, October 24, 2019 6:09 AM
Hi Guys,
I already ran release and renew several times and still I get the 169 ip address. Checking the relationship both the partner and the server state is normal.
This is the error that I get when I try to renew:
An error occurred while renewing interface Local Area Connection: unable to contact your DHCP server. Request has timed out.
An error occurred while releasing interface loopback pseudo-interface1: the system cannot find the file specified.
Thursday, October 24, 2019 6:32 AM
Could you describe in full step-by-step detail how you performed the failover test?
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Thursday, October 24, 2019 6:43 AM
Hi Leon,
I disabled the nic of the primary. Dhcp failover was successful. But when I turned It back on my client can no longer lease ip with ipconfig /release and ipconfig /renew command.
Thursday, October 24, 2019 8:11 AM
First I restarted the server and it worked. Then I tried restarting the service and still work.
I was wondering if the backup and restore process is the same as with no failover setup?
I have some scopes where in their main dhcp is dhcp1 with dhcp2 as secondary and some scopes have their main in dhcp2 with secondary in dhcp1. What would be my strategy in backing up? Will the backup include the configuration, ip leases and reservations? How about the restoration?
Thursday, October 24, 2019 8:22 AM
Hi ,
>>I was wondering if the backup and restore process is the same as with no failover setup?
I have some scopes where in their main dhcp is dhcp1 with dhcp2 as secondary and some scopes have their main in dhcp2 with secondary in dhcp1. What would be my strategy in backing up? Will the backup include the configuration, ip leases and reservations? How about the restoration?
Since this is a new question, I would suggest you post a new thread and we will continue to assist you.
Thanks for your understanding.
Best Regards,
Candy
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Thursday, October 24, 2019 8:38 AM
Okay. will post another thread.