DHCPv6 Information-Refresh Time Option

DHCPv6 Stateless Clients obtain configuration data from DHCP Server, by sending Information-request messages. The configuration data typically has no associated lifetime, hence there is no information telling a host when to refresh its configuration information. DHCPv6 Information-Refresh time option (Option 32), specified in RFC-4242 allows stateless clients to refresh configuration data periodically. The information refresh time specifies an upper bound for how long a client should wait, before refreshing the configuration information received from DHCP Server. This option has particular reference in very dynamic environments like the periodic change of address of infrastructure servers like DNS.

Windows Server 2008 R2 DHCP Server Behaviour:

Microsoft DHCP Server allows the administrator to configure Information Refresh time option at server or scope level from MMC or command-line using netsh. The minimum value of Refresh time that can be configured for option 32 is 600 seconds (IRT_MINIMUM). A value of 0xffffffff for Refresh time is considered infinite time and indicates that the client should never refresh its options.

The DHCP Server includes Information-Refresh time option in Reply message, if this option is requested in ORO of Information-Request message received from client.

Windows7 DHCP Client Behaviour:

DHCPv6 client in stateless mode includes option 32 in ORO of information request messages sent to Server. DHCP Server responds back with Reply that includes configuration data and Information refresh time (if option 32 is configured on Server). DHCPv6 client sends Information Request message to update configuration data, whenever Information-Refresh time expires.

In case, if reply from Server does not include option 32, then client uses 86400 seconds (IRT_DEFAULT) as Information-Refresh time value. In case if client receives 0xffffffff as Information-Refresh time value, then client would not refresh configuration data at all, unless there is some trigger like movement to a new network etc. In case Information refresh time expires and the server does not respond to Information-request messages, then client continues to use configuration data and refresh time that is previously received from Server.

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