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Difference between DHCP function within Failover Cluster and DHCP failover ? RRS feed

  • Question

  • Hi, 

    I noticed that with server 2012 there is a new function for DHCP Failover, so what's the difference between that vs creating a DHCP server under the Failover cluster manager? 

    Which one is preferred ? thanks

    Wednesday, October 24, 2012 10:07 PM

Answers

  • Hi,

    In Windows Server 2008 R2, there are two high availability options available for DHCP Server deployment. Each of these options is associated with some challenges.

    1. 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.
    2. 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).

    DHCP failover in Windows Server 2012 enables administrators to deploy a highly resilient DHCP service to support a large enterprise without the challenges above. The main goals of the feature are the following:

    • Provide DHCP service availability at all times on the enterprise network.
    • If a DHCP server is no longer reachable, the DHCP client is able to extend the lease on its current IP address by contacting another DHCP server on the enterprise network.

    The DHCP server failover feature provides the ability to have two DHCP servers provide IP addresses and option configuration to the same subnet or scope, providing for continuous availability of DHCP service to clients. The two DHCP servers replicate lease information between them, allowing one server to assume responsibility for servicing of clients for the entire subnet when the other server is unavailable. It is also possible to configure failover in a load-balancing configuration with client requests distributed between the two servers in a failover relationship.

    DHCP failover in Windows Server 2012 provides support for a maximum of two DHCP servers, and the failover relationship is limited to IPv4 scopes and subnets. Network nodes using Internet Protocol version 6 (IPv6) typically determine their own IPv6 address using stateless IP auto configuration. In this mode, the DHCP server delivers only the DHCP option configuration, and the server does not maintain any lease state information. A high availability deployment for stateless DHCPv6 is possible by simply setting up two servers with identical option configuration. Even in a stateful DHCPv6 deployment, the scopes do not run under high address utilization, which makes split scope a viable solution for high availability.

    Configure DHCP for Failover
    http://technet.microsoft.com/en-us/library/hh831385.aspx
    What's new in DHCP
    http://technet.microsoft.com/en-us/library/jj200226.aspx
    Ensuring High Availability of DHCP using Windows Server 2012 DHCP Failover
    http://blogs.technet.com/b/teamdhcp/archive/2012/06/28/ensuring-high-availability-of-dhcp-using-windows-server-2012-dhcp-failover.aspx


    Hope this helps!

    TechNet Subscriber Support

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    Lawrence

    TechNet Community Support

    • Marked as answer by OxYI Thursday, October 25, 2012 2:26 PM
    Thursday, October 25, 2012 5:25 AM

All replies

  • Hi,

    The Windows 2012 DHCP failover feature seems to be an improvement on the on the limitations of the DHCP service being setup in a windows cluster. A big problem with DHCP clusters and WFC's in general is the need for shared storage between the nodes in the cluster. With the new failover feature in 2012 shared storage for the nodes is not required.

    I have only reviewed this new option but I would deploy that and test going forward based on what I have read/seen so far.

    http://blogs.technet.com/b/teamdhcp/archive/2012/06/28/ensuring-high-availability-of-dhcp-using-windows-server-2012-dhcp-failover.aspx


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    Thursday, October 25, 2012 12:08 AM
  • Hi,

    In Windows Server 2008 R2, there are two high availability options available for DHCP Server deployment. Each of these options is associated with some challenges.

    1. 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.
    2. 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).

    DHCP failover in Windows Server 2012 enables administrators to deploy a highly resilient DHCP service to support a large enterprise without the challenges above. The main goals of the feature are the following:

    • Provide DHCP service availability at all times on the enterprise network.
    • If a DHCP server is no longer reachable, the DHCP client is able to extend the lease on its current IP address by contacting another DHCP server on the enterprise network.

    The DHCP server failover feature provides the ability to have two DHCP servers provide IP addresses and option configuration to the same subnet or scope, providing for continuous availability of DHCP service to clients. The two DHCP servers replicate lease information between them, allowing one server to assume responsibility for servicing of clients for the entire subnet when the other server is unavailable. It is also possible to configure failover in a load-balancing configuration with client requests distributed between the two servers in a failover relationship.

    DHCP failover in Windows Server 2012 provides support for a maximum of two DHCP servers, and the failover relationship is limited to IPv4 scopes and subnets. Network nodes using Internet Protocol version 6 (IPv6) typically determine their own IPv6 address using stateless IP auto configuration. In this mode, the DHCP server delivers only the DHCP option configuration, and the server does not maintain any lease state information. A high availability deployment for stateless DHCPv6 is possible by simply setting up two servers with identical option configuration. Even in a stateful DHCPv6 deployment, the scopes do not run under high address utilization, which makes split scope a viable solution for high availability.

    Configure DHCP for Failover
    http://technet.microsoft.com/en-us/library/hh831385.aspx
    What's new in DHCP
    http://technet.microsoft.com/en-us/library/jj200226.aspx
    Ensuring High Availability of DHCP using Windows Server 2012 DHCP Failover
    http://blogs.technet.com/b/teamdhcp/archive/2012/06/28/ensuring-high-availability-of-dhcp-using-windows-server-2012-dhcp-failover.aspx


    Hope this helps!

    TechNet Subscriber Support

    If you are TechNet Subscription user and have any feedback on our support quality, please send your feedback here.



    Lawrence

    TechNet Community Support

    • Marked as answer by OxYI Thursday, October 25, 2012 2:26 PM
    Thursday, October 25, 2012 5:25 AM
  • Can someone please  explain to me what IP Address Continuity is? I have been searching for the best way to have DHCP failover in 2008 R2. I found some script which claims to be 100/100. I found it somewhere on these boards. But, I'm trying to understand what is meant by ip address continuity and how it could impact clients or server if the primary goes down.Thank You
    • Edited by technet128 Wednesday, December 5, 2012 4:32 PM
    Wednesday, December 5, 2012 4:32 PM
  • IP address continuity means that when a client goes to renew a DHCP lease, if the client makes the request to the DHCP service that initially granted the address, the client will get the same address.  But, if that original DHCP server is down, and the DHCP server that responds is not sharing lease information with the original DHCP server, the client can get a new IP address.

    My philosophy is that if a machine needs a consistent address, it should be given a static address instead of relying on DHCP.  True clients, desktop, laptops, etc., tend not to require IP address continuity.  Print server, clusters, SQL servers, etc. are better handled by static addresses.  But any of them can work with DHCP addresses.  If you do not have continuity, clients might have cached stale information that could cause some delays in getting to the service.


    tim

    Wednesday, December 5, 2012 5:45 PM
  • so if I use a script that copies the DHCP database every couple of minutes and I import it on a backup DHCP server, will I have IP address continuity?

    Wednesday, December 5, 2012 9:16 PM
  • anyone?
    Monday, December 10, 2012 2:03 PM
  • technet128, Tim,

    IP address continuity means the client can continue to renew the _same_ IP address even if the original DHCP server which leases the IP address goes down. This is achieved in the DHCP failover feature in Windows Server 2012 by replication of lease information between 2 DHCP servers which are configured in a failover relationship. As both servers have identical lease information, the client can renew the lease from the other server even if the server even if the server which initially gave the lease has gone down.

    Monday, January 7, 2013 5:57 AM