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The dynamic update algorithm differs depending on the type of client network
adapter engaging in the dynamic update process. The following three scenarios will
be examined:
• DHCP client
• Statically configured client
• RAS client
DHCP Client
When a Windows 2000 DHCP client bootstraps, it negotiates the dynamic update
procedure with a DHCP server. By default, the DHCP client always proposes that it
update the A resource record, while the DHCP server updates the PTR resource
record.
The Windows 2000 DHCP server can be configured to “Update DNS server
according to client request” (default setting), or ”Always update forward and reverse
look-ups.”
If the DHCP server is configured to Always update forward and reverse lookups, it
will update both A and PTR RRs itself regardless of the DHCP client’s request.
If the DHCP server is disabled to perform dynamic updates, the DHCP client will
attempt to update both A and PTR RRs itself.
At expiration of the IP address lease, these records must be removed from the
appropriate zones. Dynamic cleanup requires that the records are deleted by the
registering computer(s)—in this case the DHCP client or server or both—that
created them. Thus, if the machine that created an A or PTR resource record is
disconnected from the network before the lease expiration, the corresponding
resource records may become stale. Since the DHCP server is the owner of the IP
address it is encouraged that DHCP servers perform PTR records registration when
possible.
Mixed Environment
It is possible that a Windows 2000 DHCP client will try to negotiate the dynamic
update procedure with the Windows NT 4.0 DHCP server (or any other DHCP
server that doesn’t support DNS dynamic updates). Since the Windows NT 4.0
DHCP server does not support dynamic updates, the Windows 2000 DHCP client
will have to update both the A and PTR RRs itself.
In the reverse situation, with down-level clients (for example, Windows 95,
Windows 98, and Windows NT 4.0), the Windows 2000 DHCP server after
negotiation of a lease with a client, will register both the A and PTR records in DNS,
if the ”Do updates for down-level DHCP clients” option is selected in a configuration
of the DHCP server.
DHCP Server Considerations
In addition, when the DHCP client’s lease expires, the DHCP server will remove the
Windows 2000 White Paper
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