Conflict Resolution

To provide a measure of protection against unintentional changes of DNS data, the DHCP server can first check the record set to verify that it matches the client that originally inserted the record. This process provides assurance that the updates are from the same client. that originally triggered the creation of the record. These security checks are based upon inserting a cryptographic hash of the client identification (mac address, client id or DUID) into a DNS DHCID record and then verifying that value before updating. You can configure the DHCP server to update records only after passing verification or without any type of verification. When using verification you can adjust the way DHCP handles updates to require more or less stringent verification requirements.

Your specific requirements might benefit from less-stringent verification of the DHCID, or might require skipping verification entirely. Verification checks might cause complications in some specific cases described below:

Mobility: The DHCID is unique to each client and is usually based on the MAC address or DUID of the interface. Devices such as laptops that connect to both wired and wireless networks have different MAC addresses or DUIDs and different DHCID values for each interface. In this scenario, after either one of the network interfaces inserts a DNS record, updates are allowed from that interface only. This results in a disruption of service for DDNS updates when roaming between wired and wireless networks.
Migration: The second problem occurs during migration from non-ISC based systems to ISC systems. For example, if the user is migrating from a Microsoft-based system, the clients have A or AAAA and PTR records in the DDNS updates. As a result, new DDNS updates fail after the migration.
Mixed Environments: The final problem occurs in mixed ISC and non-ISC environments. For example, assume that both Microsoft and ISC DHCP servers update DNS records on the appliance. In a mixed environment, since the Microsoft DHCP server does not insert the DHCID, DDNS updates from ISC-based systems fail while updates from the Microsoft DHCP server are committed into the database.

Universal DDI offers four modes to handle DDNS updates as described in the DDNS Update Verification Mode table :

Mode	If a Record at Lease Grant	Then DHCID Record at Lease Grant	Lease Grant Action	Lease Expire Action

Mode	If a Record at Lease Grant	Then DHCID Record at Lease Grant	Lease Grant Action	Lease Expire Action
Update DNS if DHCID values match	Exists	Must match	Delete A or AAAA, DHCID if exists Add A or AAAA Add PTR	Delete A or AAAA, DHCID if DHCID matches and no other A or AAAA RRs Delete PTR
	No A or AAAA record	No check	Add A or AAAA. Add DHCID Add PTR
Update DNS if DHCID record exists (match not required)	Exists	Must exist	Delete A or AAAA. Add DHCID. Add A or AAAA. Add PTR	Delete A or AAAA if DHCID exists and no other A or AAAA RRs Delete PTR
	No A or AAAA record	No check	Add A or AAAA Add DHCID Add PTR
Update DNS and add or update DHCID records	Exists	No check	Delete A or AAAA DHCID if exists Add A or AAAA Add DHCID Add PTR	Delete A or AAAA DHCID if DHCID matches and no other A or AAAA RRs Delete PTR
	No A or AAAA record	No check	Add A or AAAA Add DHCID Add PTR
Update DNS without checking for or creating DHCID records	Exists	No check	Delete A or AAAA Add A or AAAA Add PTR	Delete A or AAAA Delete PTR
	No A or AAAA record	No check	Add A or AAAA Add PTR

If you are migrating from NIOS, the equivalent DDNS update verification modes are as follows:

DHCID Update Mode (Universal DDI)	DDNS Update Method (NIOS)

DHCID Update Mode (Universal DDI)	DDNS Update Method (NIOS)
Update DNS if DHCID values match	Standard ISC
Update DNS if DHCID record exists (match not required)	Check TXT only
Update DNS and add or update DHCID records	ISC Transitional
Update DNS without checking for or creating DHCID records	No TXT record

If you are migrating from NIOS to Universal DDI, ensure that the DDNS Update Method in NIOS is configured as Standard so that DHCID records are created.