DHCP Failover configuration.

Dear Team,
As per the requirement i've created 10 VLANs. and also configued HSRP for failover. Out of 10 Vlans we have configured DHCP for 2 VLANs in the active switch.
My concerns:
1. Do we have to configure DHCP in standby switch too?
2. If yes, is there any Active and Standby concept for DHCP?
Switch Model:
WS-C4506-E
Regards,
Vamsi Harish.T.
[email protected]

Hi,
The Host sends a DHCP broadcast request message to the Active Switch whenever it needs to assign and get an ip address based on the DHCP release confguration on the DHCP server or when the Hosts Got shut down. So yes there is a Concept here, the Concept is that the Active Switch will always get the DHCP request from the HOST. However, if the Active Switch fails, The HOSTS will be sending the DHCP broadcast request messages to the Standby Switch which becomes the Active one now, and if there is no DHCP service configured on the Standby Switch, then Hosts will fail to assign/Got an IP addresses. This Means both Active & Standby Switches should be configured with DHCP.
HTH
Mohamed

Similar Messages

DHCP Failover BINDING-ACK

Greetings,
Atm we have 2 Windows 2012 Servers been used as DHCP only.
Our configuration consists in one been active and the other on passive mode (Hot Stand-by)
They have been running fine for about 2 weeks. But right now we are getting an Error with the event id: 20291
Same error shows as:
A BINDING-ACK message with transaction id: 241305 was received for IP address: 166.xx.xx.xxx with reject reason: (Less critical binding information ) from partner server: xxxxx.corp for failover relationship: xxxx1.crop-xxxxx2.corp
In our best interest, i do want to know if anyone has experienced this sort of issues within their Dhcp Failover configuration.
Thank you.

Hi,
According to the description here, I would recommend you check if there is any conflicts between primary DHCP server and the partner server.
http://tools.ietf.org/html/draft-ietf-dhc-failover-12
You can search for “Less critical binding information” in the page.
Please Note: Since the web site is not hosted by Microsoft, the link may change without notice. Microsoft does not guarantee the accuracy of this information.

Unable to replicate reservation to DHCP failover cluster partner node

Hello.
After reading that whilst DHCP address leases are replicated automatically to DHCP failover cluster partner nodes, and that reservations aren't, I followed steps to right-click the scope from the server which features the specified reservation, and select
'Replicate Scope'. The status window detailing the progression of associated tasks shows that replication of reservations to my other node partner, failed. The error code returned was 20022, which states that the specified IP address is currently taken by
another client.
Why is this occurring? The other node I am trying to replicate to, is within the DHCP failover cluster, and so should be aware that the reservation I am trying to replicate is linked to the same device? Why am I unable to replicate the reservations?
Any help would be appreciated.
Many thanks.

Hi,
Based on my research,
DHCP Failover automatically synchronizes leases between failover partners in Windows server 2012 and Windows Server 2012 R2. However, configuration changes on one server in the failover relationship do not automatically get replicated
to the partner, you need to manually replicate by choosing the “Replicate Scope…”
or “Replicate Relationship…” option in DHCP Server.
In addition, for DHCP failover to function correctly, time must be kept synchronized between the two servers in a failover relationship. Please check if the time is synchronized between the two servers.
Besides, you can check the event log to see if any other related information exists.
Best regards,
Susie

DHCP Failover in Windows 2008 R2 and Windows 2012 R2 Environment

Hi Everyone,
We are trying to implement DHCP failover in our environment. Our IT Infrastructure consists of 4 – windows server 2008 R2 servers and 7 – Windows Server 2012 servers; 1 Main Office with 2 – DC’s and 9 branch/remote offices with one DNS server in every remote
office. All the DNS servers have 2 scopes defined on them for VOICE and Data with different Subnets.
What would be the best method to implement failover in 2008 R2 – Windows Failover Cluster or Split scope? And how to implement DHCP Failover in Windows Server 2012 R2?
Please let me know if you need more information.
Thank you for your help!
-kN

Hi,
if you can choose between 2008 R2 and 2012 R2 than go with 2012 R2 it is easy to create a DHCP failover there. Actually that is one of the new features of Windows 2012.
With Server 2012 you setup your fist DHCP server with the scopes you want to setup. Than you install the second 2012 server with DHCP role and authorized. If you have done this you going back to your first server, where you already configured your scopes.
Now right click onto the scope you want to setup for failover and select 'Configure Failover'. You can than set it up as kind of split scope (Load balance Mode) or as real fail over setup (Hot Standby). In Load balance Mode you can configure the balance of
IP addresses between the both servers, like primary has 60% IP addresses and secondary has 40%.
With Server 2008 R2 the easiest configuration is split scope. But here it depends how many IP leases you will max have and if you can absorb if one of the server is going down. Lets say you have 50 DHCP leases max, than sure, set it up as split scope. But
if you have 200 DHCP clients, than I would go with failover cluster. At the end it depends on your environment.
Sven

DHCP Failover, one DHCP Server Partners Supnet is deactivated, Clients losing network connectivity for 3 sec. after renewing they IP Adress

Hello,
currently we are using two W2K12R2 DHCP server configured in "load balance Mode". On DHCP1 the IP-scope with failover partnership to DHCP2 is deactivated. DHCP2 is working fine. Now we register that 50 percent of our clients (W2K8R2 application
server) losing the network connectivity for 3 sec. after rereleasing they IP-Address. On DHCP2 servers eventlog we receive a lot of
BINDING ACK reject events 20291 and 20292 for these IP addresses entries.
These 3 sec. of loosing they Network connectivity is our big Problem because the Client application (W2K8R2 application server) cannot handle these timeout. It looks like a
DISCOVER-OFFER-REQUEST-NAK cycle that are described here:
http://blogs.technet.com/b/teamdhcp/archive/2014/02/26/dhcp-failover-patch-to-address-a-reservation-issue-and-another-issue-related-to-failover-partner-not-accepting-state-transition-from-bad-address-gt-active-has-been-released.aspx#pi47623=2
there is a solution to prevent the 3 sec network failure?
Rgds

Hi Steffen,
Have you applied KB2919355 in the server?
If issue persists, please check the detailed information about the event. It will tell us why does the server send the NAK.
Best Regards.
Steven Lee Please remember to mark the replies as answers if they help and unmark them if they provide no help. If you have feedback for TechNet Support, contact [email protected]

Removing DHCP failover removes DNS A records

We are running a windows 2012 r2 domain with 4 DCs all configured as DNS servers. One of the DCs is also our DHCP server. We configured a second dhcp server in January and joined it in failover mode. It was fine for a couple weeks, but then we got spammed
with 20291 and 20292 errors. We decided to remove the failover relationship and unauthorize the second dhcp server which we did without any errors. However when we rebooted the original dhcp server, we immediately lost over 30 A records in dns, mostly printers,
and we found that the dns server ip addresses on the nics of the dhcp server were changed to invalid addresses. Is there anything known that could explain this behavior? Otherwise the server seems to be working fine, and diagnostics (dcdiag, repadmin, event
log) are not showing any errors.

Hi,
Was the second DHCP server also a DC? Which kind of DHCP Failover Modes did you used?
Based on my experience, a DHCP server can register and update DNS PTR and address A resource records on behalf of its DHCP-enabled clients. I assume the lost A
records may be due to the IP address of the DNS server was changed. Did you configure a static DNS server in the DNS settings on the DHCP server? I assume that you select "Obtain DNS server address automatically" as if you define a DNS
server, it won't be changed after reboot.
In general, it would be better to point the preferred/secondary DNS server to the DC instead of obtaining the DNS server address automatically.
Besides, for event ID 20291, you can refer to the KB below:
http://support.microsoft.com/kb/2955135
Best regards,
Susie
Please remember to mark the replies as answers if they help and unmark them if they provide no help. If you have feedback for TechNet Subscriber Support, contact [email protected]

DHCP failover not working

I am attempting to implement DHCP failover using load balancing with an Essentials and a Standard server. I have everything configured and working but I am facing an issue.
If I try to start the DHCP services on the Essentials server and the DHCP services on the Standard server are already started it will not start and I get error 1053 The DHCP/BINL service has encountered another server on this network with IP Address, 192.168.1.3,
belonging to the domain: . in the event log on the Essentials serve.
Any ideas why this is?

In a network of this size there is little need for multiple or failover DHCP servers. With a lease time in the one week category the chances that the server will be off line at the same time that clients need to renew are pretty slim. Should
the server simply be unavailable you can turn the DHCP on the router, or, as you intend, on the second server.
Larry Struckmeyer[SBS-MVP]
Larry, I am not sure I find this to be the case -- that rarely will the server be off at the same time clients need to renew. I volunteer support to a local non profit. Sadly, it's not uncommon for the Essentials server to not come up cleanly
after a Microsoft Update or a power outage. With DHCP not available on the WSE2012 server, employees who come in and fire up their laptops will in some cases hit the lease expiration. I'll get a phone call, and now there will be two frustrated
people. :-)
I *could* return to letting the router handle DHCP, but I've read too many times on technet and social forums the rather forceful recommendations by microsoft people that an Essentials served network should have DHCP running on the server.
I feel I'm stuck between a rock and a hard place. The strong recommendation from microsoft is to always serve BOTH DHCP and DNS from a WSE server. However, there appears to be no DHCP failover option for WSE, which will make my users unhappy
(and strain my volunteerism!).
Thoughts?
I've tried to research whether WSE will allow a router to act as a failover in hot standby mode, but haven't succeeded. (I'll then need to find a router that supports hot standby in a WSE environment.)
(I realize I am quite late to this thread. Hopefully that's not a problem.)
Steve

DHCP Failover feature in Windows 2012

I am planning to configure DHCP on windows 2012 failover (Load balanced)mode.Just want to confirm two things:
1.How will the DCHP address be assigned to clients incase the DHCP Servers loose communication between them.
2.Regarding IP helpers that i need to put onto my network switches would it be Ips for both the server or does configuration of failover feature uses single IP (as is used in cluster config)

Hi,
Sorry for the delay. I think we need to get more people monitoring this forum :)
Your questions are answered in documentation here:
http://technet.microsoft.com/en-us/library/dn338978.aspx.
From DHCP Failover Modes:
In load balancing mode, when a DHCP server loses contact with its failover partner it will begin granting leases to all DHCP clients. If it receives a lease renewal request from a DHCP client that is assigned to its failover partner, it will temporarily
renew the same IP address lease for the duration of the MCLT. If it receives a request from a client that was not previously assigned a lease, it will grant a new lease from its free IP address pool until this is exhausted, and then it will begin using the
free IP address pool of its failover partner. If the DHCP server enters a partner down state, it will wait for the MCLT duration and then assume responsibility for 100% of the IP address pool.
From DHCP Failover Architecture:
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. If both DHCP servers are located on a different subnet
than DHCP clients, this requires at least two DHCP relay agents. For example:
ip helper-address 10.0.1.1
ip helper-address 10.0.1.2
In this example, both DHCP servers are on the same subnet (10.0.1.0/24). The primary DHCP server’s IP address is 10.0.1.1 and 10.0.1.2 is the IP address for the failover partner server. If both DHCP servers are located on the same subnet, you can also configure
the subnet broadcast address (ex: 10.0.1.255) as a single DHCP relay. The use of a subnet broadcast address as a single DHCP relay is not possible if DHCP servers are located on separate subnets.
-Greg

DHCP Failover / Migrate DHCP Server to another Machine

We have DHCP Server Installed in Domain Controller with Windows Server 2008 R2 Based OS.
I have Checked that there is no way to make the DHCP Failover in Server 2008 R2.
Can anyone help me to get some level of Failover in DHCP?
or
If I want to migrate the DHCP to Server 2012 what is the Best Practice?

Hello,
There is no big challenge for configuring DHCP failover in Windows 2008 platform. Kindly go through with this link for configuring DHCP failover. I am sure it will help you to completing your task.
1> Step-by-Step: Configure DHCP for Failover
http://technet.microsoft.com/en-us/library/hh831385.aspx
2> DHCP Step-by-Step Guide: Demonstrate DHCP Failover – Clustering in a Test Lab
http://technet.microsoft.com/en-us/library/ee405263(v=ws.10).aspx
Process of Migration DHCP Server 2008R2 to Windows 2012
• Firstly, you can disable the DHCP role in Windows Server 2008 R2. However, if the Windows Server 2012 is down, the clients cannot renew their IP lease duration and obtain IP address.
Therefore, it is recommended to leave the DHCP role in Windows Server 2008 R2 and deploy high availability. Windows Server 2012 brings the new feature: DHCP failover. However it requires both DHCP Servers are Windows Server 2012. Consider another Server
is Windows Server 2008 R2, we have to choose one of the following:
>> DHCP in a Windows failover cluster. This option places the DHCP server in a cluster with an additional server configured with the DHCP service that assumes the load if the primary DHCP server fails. The clustering deployment option uses
a single shared storage. This makes the storage a single point of failure, and requires additional investment in redundancy for storage. In addition, clustering involves relatively complex setup and maintenance.
>> Split scope DHCP. Split scope DHCP uses two independent DHCP servers that share responsibility for a scope. Typically 70% of the addresses in the scope are assigned to the primary server and the remaining 30% are assigned to the backup server.
If clients cannot reach the primary server then they can get an IP configuration from the secondary server. Split scope deployment does not provide IP address continuity and is unusable in scenarios where the scope is already running at high utilization of
address space, which is very common with Internet Protocol version 4 (IPv4).
More references:
Step-by-Step: Configure DHCP for Failover (Windows
Server 2012)
How
to configure split-scope using wizard
DHCP
Step-by-Step Guide: Demonstrate DHCP Split Scope with Delay on a Secondary Server in a Test Lab
DHCP
Step-by-Step Guide: Demonstrate DHCP Failover – Clustering in a Test Lab
If you need snap shot of migration then follow these links.
http://blogs.technet.com/b/canitpro/archive/2013/04/29/step-by-step-migration-of-dhcp-from-windows-server-2003-to-windows-server-2012.aspx
http://www.mehrban.net/migrating-dhcp-from-windows-2008-to-windows-2012
Deepak Kotian.
MCP, MCTS, MCITP Exchange 2010 Ent. Administrator
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DHCP failover from 2003 to 2012?

I know 2012 has some new DHCP failover features built in but our DC's are still 2003. :(
I'm looking for suggestions / options on how to handle this scenario. Upgrading all of the DC's isn't an option at the moment.

Hi,
The question is a little broad. How many 2012 servers are you planning to introduce and are all your DCs also DHCP servers? Are you upgrading in place or migrating to new hardware? If some DHCP servers are not also DCs I would focus on these first.
See this topic for some suggestions about how to migrate the configuration once you are ready:
Migrate to DHCP Failover.
If all your DHCP servers are also DCs I suggest adding a 2012 server to the environment and making it only a DHCP server, then add this DHCP server to your existing domain. Keep in mind that adding a 2012 server or 2012 R2 server to a 2003 domain will automatically
update the schema. I don't know if this will have any consequences for your environment - probably not - but I wanted to make you aware that this will happen.
-Greg

DHCP Failover strategy

Hi.
I would like to configure a DCHP server failover on Windows 7.
On a part I have a windows 2008 R2 server which currently leases adresses. I recently had a crash of this server.
In order to insure avaibility of dhcp on the next crash, I whish install a DHCP server freeware and configure a script powershell to start dhcp on failover of the first one.
An other tip is to split the pool of leasing. Is it possible to do it with a windows 7 software?
Thanks a lot for your help.

Hi,
The Windows DHCP server on 2008R2 platform support the following DHCP high ability method:
DHCP in a Windows failover cluster.
Split scope DHCP
The related KB:
Understand and Deploy DHCP Failover
http://technet.microsoft.com/en-us/library/dn338978.aspx
Hope this helps.
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DHCP Failover Address Leases

Just implemented 2012 DHCP Failover using the Hot-Standy model. I set the Maximum Client Lead Time to 1 hour.
My clients are getting the initial lease with an expiration of 1 hour. Then after the hour, they disappear from DHCP and DNS but they still have the address. Any ideas?

I am also having a similar issue after implementing DHCP Failover. I configured it with default settings (1 our MCLT, 8 day leases, %5 IP reserve). I tested the fail over and it worked. Clients received new addresses from the standby. I then started the
DHCP service on the primary and all seemed well. However, a short time later about a dozen hosts seem to have lost their DNS A records.
These machines have DHCP leases that began before the failover was tested and expire days after. They did not actually ever attempt to renew DHCP at this time (to my knowledge). I think this may be a bug or somehow related to the DNS configuration on the
scope. It is currently set to "Always update" and I may change to Dynamically update if requested, and test failover again.

Server 2012 R2 DHCP Failover - Hot Standby clients not renewing with standby server

In my test network I have a pair of Server 2012 R2 DHCP servers setup for Hot Standby and they will successfully service a client request for a new request.
What I am seeing is that when I test failover the clients will not renew with the Standby server. I have to release first and then renew.
When both DHCP servers are up the state is normal and replication of configuration from the Active to Standby is working. As far as I can tell it is configured correctly.
MaxClientLeadTime is 10 minutes.
StateSwitchInterval is 10 minutes.
AutoStateTransition is set to True.
Adding that manual renews fail with a message stating that it was unable to contact the dhcp server. However if I wait for the lease to expire/auto-renew the dhcp server does indeed change to the standby. Once the primary server comes back up and the state
returns to normal I am able to manually renew.
thanks in advance

Hi,
For test, we let the active DHCP down and the standby DHCP server will take place. But when we renew an IP, client send unicast to the former DHCP
server. That’s why the first request failed.
At 7/8 of the scope lease time, the client moves into a REBINDING state and broadcasts a lease renewal request.
For more information please refer to:
DHCP Failover Examples
http://technet.microsoft.com/en-us/library/dn338973.aspx
Hope this helps.

DHCP Failover Server 2012

Hi,
I have a Problem with DHCP Failover in Windows Server 2012
We configured 2 Windows Server 2012 with DHCP Role and created a Scope with loadbalancing algorithm.
The Problem is, that the two DHCP Servers Show different statistic Information. DHCP 1 has 254 addresses and 218 in use. DHCP Server 2 has 254 addressses and 187 in use.
We found situations when one DHCP Server has no available IP addresses and the other one has about 40% available addresses.
Why do the Servers have different available address spaces ? We have one scope with one class c net, 254 addresses.
Our Szenario is with this config not high available, cause of sometimes running out of IP addresses on one DHCP Server.
Thanks for help
Björn
Björn Schiemann LemonTec IT Systems KG htttp://www.lemontec.de

Hi Bjoern,
Would you please provide us your detailed load balance configurations.
In load-balance mode of operation both the servers respond to client requests. Here’s how the servers ensure the distribution of client requests between themselves:
Each DHCP server on receiving the client request calculates hash of the MAC address in the client request as per hashing algorithm specified in RFC 3074. Each server hashes any MAC address
to a value between 1 and 256. If the load distribution ratio between the 2 servers is left at the default of 50:50; and if the hash of the MAC address falls between 1 and 128 then the first server will respond to the client request else if the hash is any
value between 129 and 256, the other server responds to the client. This ensures that only one server responds for a specific client. If the load distribution ratio has been changed by the admin to a different value, the distribution of hash buckets would
be in that proportion. The admin does not need to configure the MAC addresses on any server configuration a-priori.
Quote from DHCP Failover Load Balance Mode
http://blogs.technet.com/b/teamdhcp/archive/2012/08/06/dhcp-failover-load-balancing-mode.aspx
In addition, I notice that you have a Class C network for the scope, why does each DHCP server have 254 IP address available?
Thanks.
Jeremy Wu
TechNet Community Support

Windows 2012 DHCP Failover "Lost contact with partner"

We have stood up a pair of Windows 2012 DHCP servers and configured DHCP failover (in Load Balancing mode) as per the Microsoft Technet article. The two servers are on the same subnet, and time is in sync between them. Almost immediately after
configuring scopes to failover, one node loses contact with the other, and the alternate node goes to failover mode "Recover".
We have restarted both servers and services. Both DHCP servers show as available. Clicking "Replicate Failover Scopes" completes successfully with no errors, and the only two warnings in the Event Log are about credentials for Dynamic
DNS updates and a dynamic IPv6 address (which we don't use at all.)
How come they can replicate, but have "lost contact"; and how do we get the one out of "Recover" mode?

You should see Recover state only if one of the DHCP server actually went down and came back up. In this case the server which comes back up would be in Recover state but will transition to Recover_Wait state and come back to Normal after it syncs it
leases. This should be relatively quickly. Did your servers continue to remain in the Lost Contact...\Recover state for long.
Did you see any events in the DHCP Server admin channel
Microsoft\Windows\DHCP Server\Admin.
You can also enable AuditLogs (Microsoft\Windows\DHCP
Server\AuditLogs) which logs all the server to server messages. You can enable the log by right clicking on
Microsoft\Windows\DHCP Server. View->Show Analytical and Debug Logs. This will show the
Microsoft\Windows\DHCP Server\AuditLogs in event viewer. You can then right click and enable the log and see if there are any failures
being logged there.

DHCP Failover configuration.

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