DHCP Server 2012 IPv6 Scope Full Monitor

Summary

Internet Protocol v6 (IPv6) addresses are leased by the Dynamic Host Configuration Protocol IPv6 (DHCPv6) server to its clients. Each lease has an expiration date, which the client must renew if it is going to continue to use that IPv6 address. The DHCPv6 server cannot issue leases to clients if the number of available IP addresses in the scope is insufficient.

Causes

DHCP has determined that a scope is nearing capacity. If the scope becomes full, the DHCP server cannot lease additional IP addresses. Client computers that cannot obtain new leases from the DHCP server will not have network connectivity

Resolutions

Resolution: Extend DHCP scopes, reduce lease times, or decrease cleanup interval

If the DHCP server does not have IP addresses available to provide to the requesting client, then the request fails, and the client might not be able to communicate with other computers on the network. When this occurs, consider the following possible solutions:

• Use scope extension to expand the address range for the current scope.

• Reduce the lease duration and decrease the cleanup interval. This can help to speed the reclaiming of expired scope IP addresses.

Extend the DHCP scopes

If you already have a DHCP scope and the Start Address and End Address do not currently include all addresses for your specific subnet, you can increase the number of addresses in the scope by extending the Start Address or End Address in the scope properties.

To perform these procedures, you must be a member of the Administrators group, or you must have been delegated the appropriate authority.

To increase the number of addresses available to clients:

• At the DHCP server, click Start, point to Administrative Tools, and then click DHCP.

• In the console tree, right-click the scope you want to extend, and then click Properties.

• Change Start IP Address and End IP Address to extend the scope.

Reduce the lease duration

To perform these procedures, you must be a member of the Administrators group, or you must have been delegated the appropriate authority.

To reduce the lease duration:

• At the DHCP server, click Start, point to Administrative Tools, and then click DHCP.

• In the DHCP console tree, right-click the scope you want to configure, and then click Properties.

• On the General tab, under Lease duration for DHCP clients, type the new lease duration.

Decrease the cleanup interval

To perform these procedures, you must be a member of the Administrators group, or you must have been delegated the appropriate authority.

To use a Netsh command to set the cleanup interval time:

• At the DHCP server, click Start, click Run, type cmd, and then press ENTER.

• Type netsh dhcp set databasecleanupinterval "NewInterval" (where "NewInterval" is the amount of time in minutes between DHCP database cleanups).

Example

In the following example, this command sets the database cleanup interval to 10,080 minutes (every seven days).

netsh dhcp set databasecleanupinterval 10080

Resolution: Take no action

A DHCP client might decline an address from the server if:

• A reservation is already assigned to another media access control (MAC) address.

• Static IP addresses on the network are put under exclusion ranges.

This condition should resolve itself, but if it persists, you can reconfigure reservations or exclusion ranges on the DHCP server.

Reconfigure client reservations

Client reservations allow you to reserve a specific IP address for permanent use by a DHCP client. Typically, reservations are used if the client has an IP address that was assigned by using another method for TCP/IP configuration.

Reservation IP addresses cannot be modified. If you want to change the IP address of a reservation, delete the reservation, and then re-create it with the new IP address.

To perform these procedures, you must be a member of the Administrators group, or you must have been delegated the appropriate authority.

To delete the reservation and then re-create it with the new IP address:

• At the DHCP server, click Start, point to Administrative Tools, and then click DHCP.

• In the DHCP console tree, click Reservations.

• In the details pane, select the reserved client for which you want to change the IP address.

• To delete the current reservation, on the Action menu, click Delete.

• Add a new reservation in DHCP that uses the new IP address for the client.

Reconfigure exclusion ranges

To prevent address conflicts, the scopes that you define must exclude the IP addresses of devices that you statically configure, such as DHCP servers. By setting exclusion ranges, an administrator can exclude IP address ranges within a scope so that those addresses are not offered to DHCP clients. When you create a new scope, immediately exclude IP addresses of the existing statically-configured computers. Excluded IP addresses can be active on your network, but only when these IP addresses are manually configured or distributed as reserved IP addresses.

To perform these procedures, you must be a member of the Administrators group, or you must have been delegated the appropriate authority.

To reconfigure exclusion ranges:

• At the DHCP server, click Start, point to Administrative Tools, and then click DHCP.

• In the DHCP console tree, expand the scope you want to configure.

• Select and right-click Address Pool under the appropriate scope.

• Select New Exclusion Range.

• In the Add Exclusion dialog box, type the starting and ending IP addresses of the exclusion range, and then click Add.