draft-ietf-dhc-dhcp-dns-07.txt   draft-ietf-dhc-dhcp-dns-08.txt 
Network Working Group Yakov Rekhter Network Working Group Yakov Rekhter
Internet Draft Cisco Systems Internet Draft Cisco Systems
Expiration Date: August 1998 February 1998 Expiration Date: September 1998 March 1998
Interaction between DHCP and DNS Interaction between DHCP and DNS
draft-ietf-dhc-dhcp-dns-07.txt draft-ietf-dhc-dhcp-dns-08.txt
1. Status of this Memo 1. Status of this Memo
This document is an Internet-Draft. Internet-Drafts are working This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas, documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts. working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
skipping to change at page 3, line 13 skipping to change at page 3, line 13
IP address(es). However, DHCP does not provide any mechanisms to IP address(es). However, DHCP does not provide any mechanisms to
update the DNS RRs that contain the information about mapping between update the DNS RRs that contain the information about mapping between
the host's FQDN and its IP address(es) (A and PTR RRs). Thus the the host's FQDN and its IP address(es) (A and PTR RRs). Thus the
information maintained by DNS for a DHCP client may be incorrect - a information maintained by DNS for a DHCP client may be incorrect - a
host (the client) could acquire its address by using DHCP, but the A host (the client) could acquire its address by using DHCP, but the A
RR for the host's FQDN wouldn't reflect the address that the host RR for the host's FQDN wouldn't reflect the address that the host
acquired, and the PTR RR for the acquired address wouldn't reflect acquired, and the PTR RR for the acquired address wouldn't reflect
the host's FQDN. the host's FQDN.
Dynamic DNS Updates [RFC2136] is a mechanism that enables DNS Dynamic DNS Updates [RFC2136] is a mechanism that enables DNS
information to be updated DNS over a network. information to be updated over a network.
The Dynamic DNS Update protocol can be used to maintain consistency The Dynamic DNS Update protocol can be used to maintain consistency
between the information stored in the A and PTR RRs and the actual between the information stored in the A and PTR RRs and the actual
address assignment done via DHCP. When a host with a particular FQDN address assignment done via DHCP. When a host with a particular FQDN
acquires its IP address via DHCP, the A RR associated with the host's acquires its IP address via DHCP, the A RR associated with the host's
FQDN would be updated (by using the Dynamic DNS Updates protocol) to FQDN would be updated (by using the Dynamic DNS Updates protocol) to
reflect the new address. Likewise, when an IP address gets assigned reflect the new address. Likewise, when an IP address gets assigned
to a host with a particular FQDN, the PTR RR associated with this to a host with a particular FQDN, the PTR RR associated with this
address would be updated (using the Dynamic DNS Updates protocol) to address would be updated (using the Dynamic DNS Updates protocol) to
reflect the new FQDN. reflect the new FQDN.
skipping to change at page 4, line 5 skipping to change at page 3, line 46
(1) DHCP client updates the A RR, DHCP server updates the PTR (1) DHCP client updates the A RR, DHCP server updates the PTR
RR RR
(2) DHCP server updates both the A and the PTR RRs (2) DHCP server updates both the A and the PTR RRs
One could observe that the only difference between these two cases is One could observe that the only difference between these two cases is
whether the FQDN to IP address mapping is updated by a DHCP client or whether the FQDN to IP address mapping is updated by a DHCP client or
by a DHCP server. The IP address to FQDN mapping is updated by a DHCP by a DHCP server. The IP address to FQDN mapping is updated by a DHCP
server in both cases. server in both cases.
The reason these two are important, while others are unlikely, has to
do with authority over the respective DNS RRs. A client may be given
authority over mapping it's own A RRs, or that may be restricted to a
server to prevent the client from listing arbitrary addresses. In
all cases, the only reasonable place for the authority over the PTR
RRs associated with the address is in the DHCP server that allocates
them.
5.1. Client FQDN Option 5.1. Client FQDN Option
To update the IP address to FQDN mapping a DHCP server needs to know To update the IP address to FQDN mapping a DHCP server needs to know
FQDN of the client to which the server leases the address. To allow FQDN of the client to which the server leases the address. To allow
the client to convey its FQDN to the server this document defines a the client to convey its FQDN to the server this document defines a
new option, called "Client FQDN". new option, called "Client FQDN".
The code for this option is 81. Its minimum length is 4. The code for this option is 81. Its minimum length is 4.
Code Len Flags RCODE1 RCODE2 Domain Name Code Len Flags RCODE1 RCODE2 Domain Name
skipping to change at page 5, line 14 skipping to change at page 5, line 19
MUST be originated following the procedures described in [RFC2136]. MUST be originated following the procedures described in [RFC2136].
A client that owns/maintains its own FQDN can choose to delegate the A client that owns/maintains its own FQDN can choose to delegate the
responsibility for updating the FQDN to IP address mapping for the responsibility for updating the FQDN to IP address mapping for the
FQDN and address(es) used by the client to the server. In order to FQDN and address(es) used by the client to the server. In order to
inform the server of this choice, the client MUST include the Client inform the server of this choice, the client MUST include the Client
FQDN option in the DHCPREQUEST message originated by the client. The FQDN option in the DHCPREQUEST message originated by the client. The
Flags field in the option MUST be set to 1. In this case, the client Flags field in the option MUST be set to 1. In this case, the client
MAY supply an FQDN in the Client FQDN option, or it MAY leave that MAY supply an FQDN in the Client FQDN option, or it MAY leave that
field empty as a signal to the server to determine an FQDN for the field empty as a signal to the server to determine an FQDN for the
client in a local to the server manner. client in any manner the server chooses.
A client that delegates the responsibility for updating the FQDN to A client that delegates the responsibility for updating the FQDN to
IP address mapping to a server MAY not receive any indications IP address mapping to a server MAY not receive any indications
(either positive or negative) from the server whether the server was (either positive or negative) from the server whether the server was
able to perform the update. In this case the client SHOULD use DNS able to perform the update. In this case the client SHOULD use DNS
query to check whether the mapping is updated. query to check whether the mapping is updated.
A client MUST set the RCODE1 and RCODE2 fields in the Client FQDN A client MUST set the RCODE1 and RCODE2 fields in the Client FQDN
option to 0 when sending the option. option to 0 when sending the option.
skipping to change at page 5, line 38 skipping to change at page 5, line 43
[RFC2136]) associated with the leased address before sending DHCP [RFC2136]) associated with the leased address before sending DHCP
RELEASE message. RELEASE message.
5.3. DHCP Server behavior 5.3. DHCP Server behavior
When a server receives a DHCPREQUEST message from a client, if the When a server receives a DHCPREQUEST message from a client, if the
message contains the Client FQDN option, and the server replies to message contains the Client FQDN option, and the server replies to
the message with a DHCPACK message, the server SHOULD originate an the message with a DHCPACK message, the server SHOULD originate an
update for the PTR RR (associated with the address leased to the update for the PTR RR (associated with the address leased to the
client). The update MUST be originated following the procedures client). The update MUST be originated following the procedures
described in Section 5.4. The server MAY originate the update before described in Section 5.4. The server MAY complete the update before
the server sends the DHCPACK message to the client. In this case the the server sends the DHCPACK message to the client. In this case the
RCODE from the update [RFC2136] MUST be carried to the client in the RCODE from the update [RFC2136] MUST be carried to the client in the
RCODE1 field of the Client FQDN option in the DHCPACK message and the RCODE1 field of the Client FQDN option in the DHCPACK message and the
RCODE2 field MUST be set to 0. Alternatively, the server MAY send the RCODE2 field MUST be set to 0. Alternatively, the server MAY send the
DHCPACK message to the client without waiting for the update to be DHCPACK message to the client without waiting for the update to be
completed. In this case the RCODE1 field of the Client FQDN option completed. In this case the RCODE1 field of the Client FQDN option
in the DHCPACK message MUST be set to 255, and the RCODE2 field MUST in the DHCPACK message MUST be set to 255, and the RCODE2 field MUST
be set to 0. The choice between the two alternatives is a local to a be set to 0. The choice between the two alternatives is a local to a
DHCP server matter. DHCP server matter.
skipping to change at page 7, line 7 skipping to change at page 7, line 11
FQDN from a DHCP server (as part of a normal DHCP transaction), then FQDN from a DHCP server (as part of a normal DHCP transaction), then
the server MAY be configured to update both A and PTR RRs. The the server MAY be configured to update both A and PTR RRs. The
updates MUST be originated following the procedures described in updates MUST be originated following the procedures described in
Section 5.4. Section 5.4.
If a server originates updates for both the A and PTR RRs, then the If a server originates updates for both the A and PTR RRs, then the
order in which the updates are generated is not significant. order in which the updates are generated is not significant.
If a server detects that a lease on an address that the server leases If a server detects that a lease on an address that the server leases
to a client expires, the server SHOULD delete the PTR RR associated to a client expires, the server SHOULD delete the PTR RR associated
with the address. In addition, if the client authorized the server to with the address. In addition, if the A RR (of the client) was
update its A RR, the server SHOULD also delete the A RR. The deletion initially updated by the server, the server SHOULD also delete the A
MUST follow the procedures described in [RFC2136]. RR. The deletion MUST follow the procedures described in [RFC2136].
If a server terminates a lease on an address prior to the lease If a server terminates a lease on an address prior to the lease
expiration time, the server SHOULD delete the PTR RR associated with expiration time, the server SHOULD delete the PTR RR associated with
the address. In addition, if the client (that leased the address) the address. In addition, if the server (that leased the address)
authorized the server to update its A RR, the server SHOULD also initially updated the A RR (of the client), the server SHOULD also
delete the A RR. The deletion MUST follow the procedures described in delete the A RR. The deletion MUST follow the procedures described in
[RFC2136]. [RFC2136].
5.4. Procedures for performing DNS updates 5.4. Procedures for performing DNS updates
When a DHCP server needs to update the PTR RR for a particular IP When a DHCP server needs to update the PTR RR for a particular IP
address, the server just adds a new PTR RR for that address. address, the server just adds a new PTR RR for that address.
When a DHCP server needs to update the A RR for a particular FQDN, When a DHCP server needs to update the A RR for a particular FQDN,
the server first has to delete all the A RRs associated with that the server first has to delete all the A RRs associated with that
 End of changes. 

This html diff was produced by rfcdiff 1.23, available from http://www.levkowetz.com/ietf/tools/rfcdiff/