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The DHCP Database

Guarding and also maintaining the DHCP database is vital for device administrators not only to carry out consistent performance, but likewise to minimization unscheduled downtime due to unexpected server or network snags.

The DHCP database is a dynamic database the stores the DHCP configuration information and also the lease data for clients that have leased an IP address from the DHCP server; this has DHCP options, border configuration, deal with leases, exclusion, and also reservations. By default, the adhering to DHCP database documents are stored in the %systemroot%\System32\Dhcp folder.

Dhcp.mdb – This is the DHCP server database file.

Dhcp.tmp – A temporary record that the DHCP database offers as a swap file during database index maintenance operations.

J50.log and also J50#####.log – These are logs of every database transactions. This logs may be supplied by the DHCP server for data recovery.


J50.chk – A checkpoint file that is to update every time data is written to the DHCP.mdb database file. This checkpoint file can be used during recovery to show where the recovery or replaying of data must begin.

Backup and Restore

By default, the DHCP database and also associated it is registered entries room backed up automatically at 60-minute intervals. There is no GUI to adjust the backup interval; however if you desire to adjust the default settings, you have the right to do for this reason in the complying with registry key:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\DHCPServer\Parameters

You have the right to also earlier up a DHCP database manually at any time. Over there is no need to stop the DHCP service to carry out a back-up of the database. The default course for the DHCP back-up is systemroot\System32\Dhcp\Backup. That is possible to modify this route in the server properties to allude to one more hard drive. Backing up the DHCP database end the network is not possible.

You can use the “restore” duty in the DHCP server console to regain the database. As soon as performing a restore, after ~ you choose the location, the DHCP service stops and also the database is restored. You should be a member of the administrators group or the DHCP administrators group to execute a DHCP database restore.

Reconciling scopes helps to resolve inconsistencies ~ above the DHCP database. The DHCP Server organization stores thorough IP attend to lease information in the DHCP database and review IP deal with lease information in the home windows Server registry. As soon as you convey the DHCP scopes, the information and an introduction entries are contrasted to verify inconsistencies. Throughout this process, the DHCP company may regain those inconsistent IP addresses come the initial clients, or that may set aside those IP addresses in the form of temporary appointments with duration same to the lease time assigned to the scope.

Using DHCP Relay Agents to provide DHCP service throughout multiple subnets.

DHCPv4 offers IP broadcasts and DHCPv6 offers multicasts; in both cases, DHCP servers are minimal to interaction within their IP subnet. If your organization has actually a huge number that subnets, you need to either deploy a DHCP server on every subnet or carry out DHCP service throughout multiple subnets by configuring DHCP relay.

Using DHCP relay means that you configure a DHCP relay agent on each subnet where a DHCP server is not present. A DHCP relay agent is a computer or router that listens for DHCPv4 broadcasts from DHCPv4 or DHCPv6 multicast indigenous DHCPv6 clients and then relays them come DHCP servers in different subnets. DHCPv4 and also DHCPv6 require separate DHCP relay configurations. In either instance however, you cannot deploy the DHCP relay agent ingredient on a windows Server that is running the DHCP service; the network deal with translation (NAT) routing protocol component with automatic addressing enabled, or Internet link sharing (ICS).


DHCP company Availability

Even though you may have the ability to service countless clients native a single DHCP server, that is a ideal practice come implement at least two DHCP servers to boost reliability and fault tolerance through the added benefit in some cases of configuring fill balancing to distribution the workload throughout multiple DHCP servers.

One feasible approach is come configure the DHCP organization using the windows Server 2012 cluster attribute or a third-party clustering solution. If one DHCP server fails, the DHCP organization can fail over to another DHCP server in the cluster. In this implementation, the DHCP servers have accessibility to a warehouse area network (SAN) where the DHCP database and also related files are stored.

To improve ease of access and pack balancing, there space two various other Windows Server 2012 DHCP indigenous solutions that room less complicated than deploying windows Server clusters; lock are break-up scopes and also DHCP Failover.

DHCP break-up Scopes

Split scope permits you to boost the fill balancing and fault yongin of the DHCP company by configuring two DHCP servers that serve the very same subnet without IP address overlapping. This feature is only obtainable for IPv4 and also cannot it is in configured ~ above IPv6 scopes.

Using a wizard-based configuration, girlfriend use 2 stand-alone DHCP servers to do a particular percentage of a scope’s IP addresses available on one DHCP server while the staying IP addresses room assigned come the second DHCP server. For this come work, each DHCP server is configured with the very same scope variety but with various exclusions within that range. The exclusions space necessary due to the fact that the DHCP servers do not share your lease database information. Each server have to be configured to assign just a subset that the obtainable IP deal with from a provided scope.

Let’s say the you have actually a border of 192.168.1.0 /24 and also you want to configure a break-up scope using two DHCP servers: DHCP1 and also DHCP2. You want to assign 70% of the IP addresses in the subnet to DHCP1 and the other 30% to DHCP2.

The DHCP scope might be configured together follows:


DHCP1 limit configuration:

Range: 192.168.1.1 come 192.168.1.254Exclusion: 192.168.1.178 come 192.168.1.254

DHCP2 border configuration:

Range: 192.168.1.1 to 192.168.1.254Exclusion: 192.168.1.1 to 192.168.1.177

As part of the split-scope implementation, you have to specify the 2nd DHCP server connected in the process. To run the Split-scope construction wizard top top DHCP1 enables you to allocate the IP attend to pool in the right proportion; the wizard immediately creates the scope and also the equivalent exclusions ~ above DHCP2. Girlfriend still need to activate the border on DHCP2 before its IP addresses become obtainable to DHCP client in the network. The figure listed below show the DHCP split-scope configuration wizard being run from DHCP1.

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Figure 1

It is possible to configure a time hold-up on the DHCP2 server (see figure below). The delay in DHCP Offer enables DHCP2 to wait before responding come DHCP find requests indigenous DHCP clients, permitting the DHCP1 server to respond to and accept the DHCPOFFER first. In the occasion that DHCP1 becomes unavailable, DHCP2 can proceed distributing addresses until DHCP1 is obtainable to organization clients again.

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Figure 2

In our example, DHCP1 manages 70% of the IP addresses in the 192.168.1.0 /24 subnet. This may be a problem if DHCP1 fails and stays out of service for a prolonged period the time, due to the fact that DHCP2 is responsible only for 30% that the IP addresses within the scope and it could run the end of assignable IP addresses quickly.

Wouldn’t it be an excellent if DHCP2 could also manage the various other 70% of the attend to space? How about if both DHCP1 and also DHCP2 could manage 100% the the IP address variety within the limit in coordination through each other? This is now possible by configuring DHCP failover on home windows Server 2012.

DHCP Failover

DHCP failover allows two home windows Server 2012 DHCP servers to share a usual pool that IP addresses in which both servers can have accessibility to 100% the the IP address variety in a provided scope and either among them may assign IP addresses to network clients. Together the lease info is replicated between the servers, there is no danger of duplicate IP deal with distribution. Due to the fact that both DHCP servers are allowed to carry out IP addresses and also option construction to the same subnet or scope, the availability and redundancy of the DHCP organization is substantially improved.

There are some caveats precious mentioning prior to you get too excited about DHCP failover and try to implement the in your network. Windows Server 2012 permits just two DHCP servers because that failover; this feature applies to IPv4 scopes and subnets and there is no method to configure that on IPv6 scopes. A solitary DHCP server have the right to have multiple failover relationship with other DHCP servers, but each configuration need to be assigned a unique name for the tandem to work. DHCP failover is time-sensitive therefore time synchronization is critically important; a time difference between the partners higher than one minute will result in a crucial error and the failover procedure will stop.

DHCP failover have the right to be configured in two different modes: fill sharing or warm standby.

In Load Sharing mode (default) both DHCP servers carry out IP setups to clients concurrently. By configuring the load distribution ratio you recognize your concerns on exactly how the servers respond to IP configuration requests.

In Hot Standby mode girlfriend specify a major DHCP server that actively dispenses IP setups for the border or subnet and also a secondary DHCP server that will just distribute IP setups if the major server i do not care unavailable. You have to configure a percent of the IP address variety to be assigned come the standby server. This addresses are yielded during the maximum customer lead time (MCLT) interval if the major server is down. The second server takes manage of the whole IP variety after the MCLT term expires.

It is vital to remind you the whether you are configuring pack sharing or warm standby mode, the configured limit is still shared in between the two servers. In either case, if one server fails, the various other DHCP server will have the ability to manage the entirety pool the IP addresses because the lease information has been replicated all along.

Here space the procedures to configure DHCP failover:

In the DHCP console, right-click the IPv4 node, and also then click Configure Failover.

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Figure 3

In the Configure Failover Wizard, click Next. Any scope that you room configuring because that failover should not exist top top the partner DHCP server.

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Figure 4

On the Specify a companion server to usage for failover page, in the Partner Server box, go into the various other DHCP server hold name or IP Address.

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Figure 5

On the Create a brand-new failover relationship page, in the Relationship Name box, get in a unique name and review and/or configure these settings prior to clicking Next.Maximum client Lead Time (MCLT): This parameter identify the lot of time a DHCP server need to wait as soon as a companion is unavailable, before assuming manage of the deal with range. It likewise specifies the quantity of time for which a DHCP lease might be put in order by either failover peer without previously contacting the other.Mode: Load balance or standby. Pack balance provides the choice to entrust the pack balance percentage for every server. Warm standby enables you to set the role of the companion as active or standby and also to point out a portion of addresses to the standby server.State switchover interval: This option specifies the moment interval before a DHCP server is immediately transitioned to a “partner down” state when network interaction is interrupted and also the DHCP partner is no longer available. By default you need to manually move the standing of a DHCP Server to a “partner down” state making use of the DHCP Management console or PowerShell.Enable blog post Authentication: Use to enable or disable authentication of failover replication traffic in between servers.Shared Secret: Enter a password come authenticate the failover connection between servers.

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Figure 6

Click Finish, and also then click Close.

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Figure 7

After the wizard runs on DHCP1, we have the right to verify that the failover scope has actually been created and activated ~ above the DHCP2 server. (See figure below.)

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Figure 8

Here we have used the DHCP administration console come configure DHCP failover; that is possible to finish the same configuration making use of Windows PowerShell.

In this post we concentrated on the windows Server 2012 DHCP service performance and accessibility issues. Us reviewed the DHCP database maintenance, utilizing DHCP relay agents, and also the configuration alternatives to boost availability, fill balancing and fault tolerance.

This article was originally published by extreme School, a defense training agency that specialization in Cisco CCNA training.

See more: Deer Hunter 2: The Hunt Continues Pc Download Free Torrent, Deer Hunter Ii: The Hunt Continues (Pc, 1998)

If girlfriend would like to be informed when Wilfredo Lanz releases the next part of this article series please sign up come the WindowsNetworking.com genuine time post update newsletter.

If girlfriend would favor to review the very first part in this article series please walk to home windows Server 2012 DHCP (Part 1).