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INTERNET-DRAFT J. Bound
DHC Working Group Digital Equipment Corp
Obsoletes: draft-ietf-dhc-dhcpv6-02.txt November 1995
Dynamic Host Configuration Protocol for IPv6 (DHCPv6)
draft-ietf-dhc-dhcpv6-03.txt
Status of this Memo
This document is a submission to the DHC Working Group of the
Internet Engineering Task Force (IETF). Comments should be submitted
to the dhcp-v6@bucknell.edu mailing list.
This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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To learn the current status of any Internet-Draft, please check the
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Distribution of this document is unlimited.
Abstract
This document is an Internet application protocol, for IP version 6
(IPv6), that specifies a client/server model for communications
between hosts to dynamically configure parameters for a network, and
autoconfigure addresses within a stateful model. This document
supports the model for IPv6 Stateless Address Autoconfiguration,
where there are clear integration points between stateless and
stateful address autoconfiguration for IPv6.
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Table of Contents:
1. Introduction.................................................3
1.1. Requirements...............................................3
2. Terminology and Definitions..................................4
2.1. IPv6 Terminology...........................................4
2.2. DHCPv6 Terminology.........................................6
3. Protocol Design Model........................................9
3.1. Design Goals...............................................9
3.2. Request/Response Model....................................10
3.3. Leased Address Model......................................11
3.3.1. Address Lifetimes.......................................11
3.3.2. Duplicate Address Detection.............................12
3.3.3. Releasing Infinite Lifetime Addresses...................13
3.4. DNS Host Name Autoregistration Model......................13
4. Request/Response Processing.................................13
4.1. Processing when Server Address is not Known...............14
4.2. Processing when Server Address is Known...................16
4.3. Retransmission and Configuation Variables.................16
5. Datagram and Field Definitions..............................18
5.1. Datagram..................................................18
5.2. Field Definitions.........................................19
6. Client/Server Message Formats...............................21
6.1. Client/Server UDP Ports, Multicast Group, and Addresses...21
6.2. Client DISCOVER and CONF-REQUEST Messages.................21
6.3. Server CONF-RESPONSE Message..............................23
6.4. Client ACCEPT Message.....................................24
6.5. Server SERVER-ACK Message.................................25
6.6. Client RELEASE Message....................................27
7. Relay-Agent Processing......................................28
8. Security Considerations.....................................29
Appendix A - Related Work in IPv6..............................29
Change History.................................................31
Acknowledgements...............................................33
References.....................................................33
Authors' Address...............................................34
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1. Introduction
DHCPv6 is an Internet application protocol, for IP version 6 (IPv6),
that specifies a client/server model for communications between hosts
to dynamically configure parameters for a network, and autoconfigure
addresses within a stateful model. DHCPv6 supports the model for
IPv6 Stateless Address Autoconfiguration [IPv6-ADDRCONF], where there
are clear integration points between stateless and stateful address
autoconfiguration for IPv6.
DHCPv6 uses a set of request/response messages to support a
transaction processing model where a commit to the data can be
verified by both the client and server. This affords DHCPv6 the
ability in the future to support dynamic updates to data located
within a sites network. In addition to the capability of verifying
commits to transactions a recovery mechanism is specified, should
commits need to be rolled back during the course of a DHCPv6
transaction being processed.
DHCPv6 supports optional configuration parameters and processing for
hosts through its companion document Options for the Dynamic Host
Configuration Protocol for IPv6 [DHCPv6-OPT].
The IPv6 Addressing Architecture [IPv6-ADDR] and IPv6 Stateless
Address Autoconfiguration specifications provide new functionality
not present in IP version 4 (IPv4). This new IPv6 functionality
provides inherent benefits to autoconfigure IPv6 addresses for nodes.
In addition the IETF DNS Working Group has defined a method to
support Dynamic Updates to DNS [DYN-UPD], which can be used by a node
to add, delete, and change node names dynamically.
DHCPv6 used several of the architecture principles from DHCPv4
[DHCP-v4], but it is beyond the scope of this document to contrast
and compare DHCPv6 with DHCPv4.
Section 2 provides definitions for terminology used throughout this
document. Section 3 provides a review of the protocol design model
parts that are inherent in the specification. Section 4 provides the
request/response model and interaction between the set of messages
and the semantics for those messages. Section 5 provides the
datagram packet format and field definitions for that datagram.
Section 6 provides the message formats and field contents for
processing the client and server messages. Section 7 provides the
specification of how relay-agents and servers interact with clients,
when the server is not on the same link as the client. Section 8
provides the security specifications that can be used to support
security in DHCPv6. Appendix A provides a summary of related work in
IPv6 that will help put DHCPv6 in the context of IPv6 for the reader,
and is not part of this specification, but here for information
purposes.
1.1. Requirements
Throughout this document, the words that are used to define the
significance of the particular requirements are capitalized. These
words are:
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o "MUST"
This word or the adjective "REQUIRED" means that the item is an
absolute requirement of this specification.
o "MUST NOT"
This phrase means the item is an absolute prohibition of this
specification.
o "SHOULD"
This word or the adjective "RECOMMENDED" means that there may
exist valid reasons in particular circumstances to ignore this
item, but the full implications should be understood and the case
carefully weighed before choosing a different course.
o "SHOULD NOT"
This phrase means that there may exist valid reasons in particular
circumstances when the listed behavior is acceptable or even
useful, but the full implications should be understood and the
case carefully weighted before implementing any behavior described
with this label.
o "MAY"
This word or the adjective "OPTIONAL" means that this item is
truly optional. One vendor may choose to include the item because
a particular marketplace requires it or because it enhances the
product, for example, another vendor may omit the same item.
2. Terminology and Definitions
Relevant terminology from the IPv6 Protocol [IPv6-SPEC], IPv6
Addressing Architecture, and IPv6 Stateless Address Autoconfiguration
will be provided, and then the DHCPv6 terminology.
2.1. IPv6 Terminology
IP - Internet Protocol Version 6 (IPv6). The terms
IPv4 and IPv6 are used only in contexts where
necessary to avoid ambiguity.
node - A device that implements IPv6.
router - A node that forwards IPv6 packets not explicitly
addressed to itself.
host - Any node that is not a router.
upper-layer - A protocol layer immediately above IP. Examples are
transport protocols such as TCP and UDP, control
protocols such as ICMP, routing protocols such as
OSPF, and internet or lower-layer protocols being
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"tunneled" over (e.g. encapsulated in) IP such as
IPX, Appletalk, or IP itself.
link - A communication facility or medium over which nodes
can communicate at the link layer, i.e., the layer
immediately below IPv6. Examples are Ethernet
(simple or bridged); PPP links, X.25, Frame Relay,
or ATM networks; and internet (or higher) layer
"tunnels", such as tunnels over IPv4 or IPv6 itself.
neighbors - Nodes attached to the same link.
interface - A node's attachment to the link.
address - An IP layer identifier for an interface or a set
of interfaces.
packet - An IP header plus payload.
communication
- Any packet exchange between nodes that requires
that the address of each node used in the exchange
remain the same for the duration of the packet
exchange. Examples are a TCP connection or UDP
request/response.
unicast address
- An identifier for a single interface. A packet sent
to a unicast address is delivered to the interface
identified by that address.
multicast address
- An identifier for a set of interfaces (typically
belonging to different nodes). A packet sent to a
multicast address is delivered to all interfaces
identified by that address.
link-layer identifier
- a link-layer identifier for an interface. Examples
include IEEE 802 addresses for Ethernet links,
and E.164 addresses for ISDN links.
link-local address
- An address having link-only scope that can be used
to reach neighboring nodes attached to the same link.
All interfaces have a link-local address.
preferred address
- An address assigned to an interface whose use by
upper layer protocols is unrestricted. Preferred
addresses may be used as the source or destination
address of packets sent from or to the interface.
deprecated address
- An address assigned to an interface whose use is
discouraged, but not forbidden. A deprecated
address should no longer be used as a source address
in new communications. but packets sent to a
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deprecated address are delivered as expected.
A deprecated address may continue to be used as a
source address for the duration of existing
communications.
valid address
- A preferred or deprecated address. A valid address
may appear as the source or destination address of a
packet, and the internet routing system is expected to
be able to deliver packets sent to a valid address.
invalid address
- An address that is not assigned to any interface. A
valid address becomes invalid when its valid
lifetime expires. Invalid addresses should not appear
as the source or destination of a packet.
preferred lifetime
- The length of time that a valid address is preferred.
When the preferred lifetime expires, the address
becomes deprecated.
valid lifetime
- The length of time the address remains in the valid
state. The valid lifetime MUST be greater than or
equal to the preferred lifetime. When the valid
lifetime expires, the address becomes invalid.
interface token
- A link-dependent identifier for an interface that
is (at least) unique per link. Stateless Address
Autoconfiguration combines an interface token with
a prefix to form an address. From an address
autoconfiguration perspective, an interface token
is a bit string of known length. The exact length
of an interface token and the way it is created is
defined in a separate link-specific document that
covers issues related to the transmission of IP
over a particular link type (e.g., [IPv6-ETHER]).
In many cases the token will be the same as the
link-layer address.
2.2. DHCPv6 Terminology
configuration parameters
- Is any parameter that can be used by a node to
configure their network environment so the node can
communicate on a link or on an internet.
client - A client is a host that initiates requests on a link
to obtain: addresses, dynamic updates to DNS, or
other configuration parameters.
server - A server is a node that responds to requests from
clients on a link to provide: addresses, dynamic
updates to DNS, or other configuration parameters.
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relay-agent - A relay-agent is a node that listens on a link for
client requests, and then forwards the packet to a
server on the network. The server will respond back
to the relay-agent, who will forward the response to
the client on the relay-agents link.
message-type - The message-type defines the DHCPv6 protocol type for
this packet.
message-flag - The message-flag defines an optional processing
notification for DHCPv6. The message-flag can also
be used by the Options for DHCPv6 specification.
error-code - The error-code specifies errors from a client or
server. The error-code can also be used by the
Options for DHCPv6 specification.
total-addresses
- The total-addresses specifies the total number of
addresses being provided from a server to a client.
For each address there is a preferred and valid
lifetime.
completed-transaction
- A completed-transaction is a communications exchange
between a client and server, using the required set
of DHCPv6 request/response message-types, where the
final response message in the request/response set
has been received by the client and by the server.
transaction-ID
- The transaction-ID is an integer identifier specified
by the client and is used by the client and server as
a transaction identifier to define the set of
request/response messages between the client and
server, for a clients interface token.
client-link address
- The client-link address specifies the clients
link-local address. The client-link address
is used by a relay-agent to respond to a client
on a link, after receiving a server response.
server address
- The server address specifies the address for the
server responding to a client.
gateway address
- The gateway address specifies the address of the
relay-agent for a server, which may be multiple
relay-agent hops away from the original relay-agent.
client address
- The client address specifies an address from a
server to be used by a client.
binding - A binding in DHCPv6 is an N-tuple that a client
and server MUST maintain in DHCPv6 for a
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completed-transaction, where N is the number of
configuration parameters for a client. An
implementation MUST support at least a 5-tuple
binding consisting of a clients interface token,
client address, preferred lifetime and valid
lifetime for each client address, and the
transaction-ID.
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3. Protocol Design Model
This section is provided for implementors to understand the DHCPv6
protocol design model from an architectural perspective. Any
conceptual models presented in this specification that provide
implementation examples are not a requirement of the DHCPv6 protocol.
3.1. Design Goals
The following list gives general design goals for DHCPv6.
DHCPv6 should be a mechanism rather than a policy. DHCPv6 must
allow local system administrators control over configuration
parameters where desired; e.g., local system administrators should
be able to enforce local policies concerning allocation and access
to local resources where desired.
Hosts should require no manual configuration. Each host should be
able to discover appropriate local configuration parameters
without user intervention, and incorporate those parameters into
its own configuration.
Networks should require no hand configuration for individual
hosts. Under normal circumstances, the network manager should not
have to enter any per-host configuration parameters.
DHCPv6 should not require a server on each link. To allow for
scale and economy, DHCPv6 must work across relay agents.
A DHCPv6 client must be prepared to receive multiple responses to
a request for configuration parameters. Some installations may
include multiple, overlapping DHCPv6 servers to enhance
reliability and increase performance.
DHCPv6 must coexist with statically configured, non-participating
hosts and with existing network protocol implementations.
DHCPv6 should as much as possible be compatible with IPv6
Stateless Address Autoconfiguration.
DHCPv6 must support the requirements of automated renumbering of
IPv6 addresses.
DHCPv6 servers should be able to support Dynamic Updates to DNS
[DYN-UPD].
It is NOT a design goal of DHCPv6 to specify a server to server
protocol.
It is NOT a design goal of DHCPv6 to specify how a server
configuration parameter database is maintained or determined.
The following list gives design goals specific to the transmission of
the network layer parameters.
Guarantee that any specific network address will not be in use by
more than one host at a time.
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Guarantee that client addresses that are not provided by DHCPv6
will not be added to a servers configuration parameter database or
the servers binding for a clients interface token.
Retain host configuration parameters across client reboots. A
client should, whenever possible, be assigned the same
configuration parameters in response to a request.
Retain host configuration across server reboots, and, whenever
possible, a host should be assigned the same configuration
parameters despite restarts of the DHCPv6 mechanism,
Allow automatic assignment of configuration parameters to new
hosts to avoid hand configuration for new hosts.
Support fixed or permanent allocation of configuration parameters
to specific hosts.
3.2. Request/Response Model
DHCPv6 uses a message-type to define whether the packet originated
from a DHCPv6 server or client. The set of packets used to complete
a DHCPv6 transaction are defined as the request and response set.
The message types are as follows:
01 DISCOVER
The DISCOVER message is a DHCPv6 multicast packet from a client
to locate and request configuration parameters on a network,
when the client does not know the servers address.
02 CONF-REQUEST
The CONF-REQUEST is an IPv6 unicast packet from a client to a
server, when the client knows the IPv6 unicast address of a
server, to request configuration parameters on a network.
03 CONF-RESPONSE
The CONF-RESPONSE is an IPv6 unicast packet from a server in
response to a client DISCOVER or CONF-REQUEST, which provides
the requested configuration parameters.
04 ACCEPT
The ACCEPT is a client response to a server CONF-RESPONSE. When
the client used DISCOVER to locate a server and request
configuration parameters on a network, the ACCEPT should be
sent using the DHCPv6 multicast address, which also serves to
inform other servers that responded to the DISCOVER they were
not selected. When the client used CONF-RESPONSE to request
configuration parameters from a server whose address was known,
the ACCEPT should be sent as an IPv6 unicast packet. The
ACCEPT is also an implied acknowledgment to the server selected
that the client has received the servers configuration
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parameters from the CONF-RESPONSE.
05 SERVER-ACK
The SERVER-ACK is an IPv6 unicast packet sent by a server to
inform a client that it received an ACCEPT. The SERVER-ACK is
used by the server to inform the client it has received an
acknowledgment that the client has received the configuration
parameters from the server, and denotes a completed-transaction
to a server. The server at that point MUST commit its bindings
and any updates it may do for the client. The SERVER-ACK for
the client denotes a completed-transaction. The client at that
point MUST commit its bindings.
06 RELEASE
The RELEASE is used by the client for two reasons:
1. To inform the server that the client did not receive the
SERVER-ACK required to complete the client transaction,
and the server should delete that binding and any
updates it may have done on behalf of the client.
2. To inform the server that the client is releasing a
particular address or set of addresses, even though the
lifetimes for those addresses may not have become
invalid.
The processing and algorithms for the request/response set of
message-types will be discussed in section 4.0.
3.3. Leased Address Model
The leased address model specifies a set of lifetimes associated with
addresses returned by the server. These lifetimes are meant to
support site renumbering, and are completely compatible with the
leasing model in IPv6 Stateless Address Autoconfiguration.
The DHCPv6 philosophy is that the client has the responsibility to
renew a lease for an address that is about to expire, or request a
new address or the same address before the lease actually expires.
If the client does not request a new lease for an address, the server
MUST assume the client does not want a new lease for that address.
The server MAY provide that address to another client requesting an
address, after all other addresses available to the server have been
exhausted.
3.3.1. Address Lifetimes
An address returned to a client has a preferred and valid lifetime.
The lifetimes represent the lease for addresses provided to the
client, from the server.
The client MAY request a value for the lifetimes returned by a
server, but the client MUST use the lifetimes provided by the server
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response.
When an address for a client interface becomes deprecated the
processing of the lease MUST be as follows:
When the preferred lifetime of an address expires, the clients
address becomes a deprecated address. A deprecated address can be
used as a source address in new communications and existing
communications. But a deprecated address means the node will soon
have an address whose valid lifetime will expire, when this
happens the address cannot be used in any communications.
An address is a deprecated until its valid lifetime expires at
which point the address becomes an invalid address. An invalid
address MUST NOT be used as a source address in outgoing
communications, and MUST NOT be recognized as a valid destination
address for incoming communications.
Once an address is deprecated an implementation SHOULD request a
new lease or address for that interface.
If the clients preferred lifetime is zero for an address the address
is immediately deprecated.
Implementors of DHCPv6 would find it beneficial to coordinate the use
of the preferred lifetime and valid lifetime for layers below the
DHCPv6 application layer with their implementation of Stateless
Address Autoconfiguration. It is suggested that implementations use
the same modules to configure addresses for stateless and stateful
address autoconfiguration. Implementors might want to consider an
option to stop all new communications for a deprecated address, to
support a very robust renumbering strategy, but this cannot be the
default behavior.
3.3.2. Duplicate Address Detection
DHCPv6 clients MUST support Duplicate Address Detection as specified
in IPv6 Stateless Address Autoconfiguration. This will provide a high
guarantee that DHCPv6 client addresses are not duplicated on a link.
It is an option for a server to inform the client it does not have to
perform Duplicate Address Detection by the server setting a value of
01 in the message-flag in client responses. In this case it is
assumed that the server implementation is providing the guarantee
that the client addresses returned are unique on the link. It is
implementation defined how a server verifies the uniqueness of client
addresses on a link.
A conceptual model of an implementation for DHCPv6 duplicate address
detection is that the client DHCPv6 module, which supports updating
the network interfaces for a host, would use the same application
configuration interface for DHCPv6 as is used for IPv6 Stateless
Address Autoconfiguration on an IPv6 conforming implementation. An
implementation can integrate and reuse the same modules in the
network operating system kernel to spawn duplicate address detection,
address lifetime processing, and the processing of deprecated and
invalid addresses for existing and new connections.
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3.3.3. Releasing Infinite Lifetime Addresses
DHCPv6 specifies no behavior which would require a client to listen
for asynchronous messages from servers on a well known UDP port. The
reason for this is that minimal implementations may not be able to
support such a feature in a client. But DHCPv6 does permit the
client to request an infinite lease for addresses. The problem in
this case is that though the server has permitted an infinite lease
for a client it may later be required that the client give up that
lease or the addresses, for some organizational reason.
This specification leaves it as implementation defined how this
problem is solved in a DHCPv6 network environment.
One solution to the problem is to define an SNMP MIB for DHCPv6
clients that when set by a network management agent causes a client
to revalidate all of its addresses with the DHCPv6 server or issue a
RELEASE to the server.
3.4. DNS Host Name Autoregistration Model
It is important that DHCPv6 provide a server implementation set of
options for Dynamic Updates to DNS (DYNDNS), to support the
autoregistration of addresses to names in IPv6. DYNDNS SHOULD be
supported as a set of options in DHCPv6 as specified in the Options
for DHCPv6 specification. The minimum requirements to support DYNDNS
in DHCPv6 are as follows:
1. Clients SHOULD be able to request or change names for
addresses.
2. Servers SHOULD be able to provide names for addresses
provided to a client.
3. If servers support DYNDNS then they MUST support the
following:
a) Create, Update, and Delete of IPv6 AAAA Records
[IPv6-DNS] as specified in DYNDNS [DYN-UPD].
b) Create, Update, and Delete of IPv6 IP6.INT Domain PTR
records for any IPv6 AAAA addresses defined in a client
DYNDNS request, or that the server automatically generated
for a client.
4. Request/Response Processing
The request/response processing for DHCPv6 is transaction based and
uses a best-effort set of messages to guarantee a completed-
transaction. The case where the client does not know the servers
address is depicted, and then the case where the client does know the
servers address is depicted. Then the timeout and retransmission
guidelines and configuration variables are discussed.
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4.1. Processing when Server Address is not Known
The processing for the DHCPv6 request/response model when the client
does not know the server address is as follows:
Server Client Server
(not selected) (selected)
v v v
| | |
| Begin Transaction |
| | |
| _____________ | _____________ |
| DISCOVER | DISCOVER |
| (DHCPv6 Multicast) |
| | |
Determine Client Configuration | Determine Client Configuration
| (Unicast) |
| ___________ | ____________ |
| CONF-RESPONSE | CONF-RESPONSE |
| | |
| Collects replies |
| | |
| Selects configuration |
| | |
| _____________ | _____________ |
| ACCEPT | ACCEPT |
| (DHCPv6 Multicast) |
| | |
| | Commits Client Bindings
| | (Unicast)
| | |
| | _____________ |
| | SERVER-ACK |
| | |
| Transaction Complete |
| Client commits Bindings |
| | |
| IF the Client did not |
| receive the SERVER-ACK |
| delete the Bindings |
| (Unicast) |
| | |
| | _____________ |
| | RELEASE |
| | |
| | Server deletes the Bindings
| | and rolls back any updates that
| | that may have been done for the
| | client.
| | |
v v v
DHCPv6 uses the UDP [RFC-768] protocol to communicate between clients
and servers. UDP is not reliable, but DHCPv6 must provide some
reliabilty between clients and servers. The network trade-off is
time versus the reliability that the completed set of
request/response messages were received by both the client and the
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server to define a completed-transaction.
The request/response set is always started by a client either with a
DISCOVER when the client does not know the servers address, or a
CONF-REQUEST when the client does know the servers address. The
second message is from the server and is the CONF-RESPONSE. The
client then acknowledges the servers CONF-RESPONSE with an ACCEPT.
At this point in the flow all data has been received and additional
messages are defined to insure the transaction is completed, and to
provide a method of recovery if either the client or server do not
receive the messages to complete the transaction.
The server after receiving the ACCEPT sends a SERVER-ACK, which is an
acknowledgment to the client the server has received the clients
ACCEPT. At that point the time vs reliability trade-off in DHCPv6 is
for the server to commit its bindings, and perform any updates as a
result of the client messages (e.g. Update DNS). If the client
receives the SERVER-ACK, then the client can commit its bindings.
But if the client does not receive the SERVER-ACK then it should send
the server a RELEASE to inform the server that any bindings should be
deleted and any updates for the client should be rolled back. The
client RELEASE provides the final recovery check in the DHCPv6
request/response set to complete a transaction.
Retransmission of messages is discussed in section 4.3.
The ACCEPT in the flow above is a multicast packet which serves an
overloaded function, to respond to the selected server, and to inform
other servers on the network the client is not selecting them.
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4.2. Processing when Server Address is Known
The processing for the DHCPv6 request/response model when the client
does knows the server address is as follows (all packets are
Unicast):
Client Server
v v v
| | |
| Begin Transaction |
| | |
| | _____________ |
| | CONF-REQUEST |
| | |
| | Determine Client Configuration
| | |
| | ____________ |
| | CONF-RESPONSE |
| | |
| | _____________ |
| | ACCEPT |
| | |
| | Commits Client Bindings
| | |
| | _____________ |
| | SERVER-ACK |
| | |
| Transaction Complete |
| Client commits Bindings |
| | |
| IF the Client did not |
| receive the SERVER-ACK |
| | |
| | _____________ |
| | RELEASE |
| | |
| | Server deletes the Bindings
| | and rolls back any updates that
| | that may have been done for the
| | client.
| | |
v v v
The processing above is the same as was discussed in 4.1, except the
CONF-REQUEST is used by the client to request configuration parameters
from the server, and the CONF-REQUEST and ACCEPT are unicast packets.
4.3. Retransmission and Configuation Variables
Configuration variables for a DHCPv6 implementation that MUST be
configurable by a client or server are as follows:
Retranstimer - The time in seconds that a DHCPv6 client or server
should wait before retransmitting a message.
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Default: 3 seconds.
Maxretrans - The maximum retransmissions that a DHCPv6 client
or server should retransmit, before logging a
DHCPv6 System Error to the user.
Default: 3 retransmissions.
The problem with retransmissions occurs when they are continually
received by a client or server (e.g. duplicate bindings or updates).
To support informing a client or server that a retransmission is
being done a second set of message-types are supported in DHCPv6 as
follows:
20 - DISCOVER-Retrans
21 - CONF-REQUEST-Retrans
22 - CONF-RESPONSE-Retrans
23 - ACCEPT-Retrans
24 - SERVER-ACK-Retrans
25 - RELEASE-Retrans
When a client or server retransmits a DHCPv6 packet at the
application layer over UDP, they MUST change the message-type to the
same message-type with the Retrans suffix.
A response to a retransmission SHOULD be a duplicate of a previous
response to the client or server. It is implementation defined how
this is accomplished.
One method of retransmitting duplicates in an implementation
conceptually is to use the 5-Tuple binding for a client or server to
search for a previous response. At a minimum the client interface
token and transaction-ID will be present in all messages; hence a
binding can be searched (whether committed or in process) to verify
if a previous response has been sent.
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5. Datagram and Field Definitions
5.1. Datagram
DHCPv6 Datagram
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| msg-type | msg-flag | error-code | total-addrs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RESERVED | transaction-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| interface token |
| (8 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| server address |
| (16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| gateway address |
| (16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| client-link address |
| (16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| preferred lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| valid lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| client address |
| (16 octets) |
| (can be multiple addresses and lifetimes present) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| options (variable number and length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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5.2. Field Definitions
All fields in the datagram MUST be initialized to binary zeroes by
both the client and server messages unless otherwise noted in Section
6.
msg-type - 1 octet integer value (message-type)
Value Description
01 DISCOVER
02 CONF-REQUEST
03 CONF-RESPONSE
04 ACCEPT
05 SERVER-ACK
06 RELEASE
07-19 RESERVED
20 DISCOVER-Retrans
21 CONF-REQUEST-Retrans
22 CONF-RESPONSE
23 ACCEPT-Retrans
24 SERVER-ACK-Retrans
25 RELEASE-Retrans
26-255 RESERVED
msg-flag - 1 octet integer value (message-flag)
Value Description
01 Server - Duplicate Address Detection not Required.
02-255 RESERVED
error-code - 1 octet integer value
Value Description
01 Server - Addresses are not available at this time.
02 Server - Address not known by the Server
03-255 RESERVED
total-addrs - 1 octet integer value (total-addresses)
RESERVED - 2 octets Reserved for future use.
transaction-ID - 2 octets integer value
interface token - 8 octets link-dependent identifier
server address - 16 octets address
gateway address - 16 octets address
client-link address - 16 octets link-local address
preferred lifetime - 4 octets integer value in seconds
valid lifetime - 4 octets integer value in seconds
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client address - 16 octets address
options - variable number of octets [DHCPv6-OPT]
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6. Client/Server Message Formats
6.1. Client/Server UDP Ports, Multicast Group, and Addresses
A client MUST transmit all messages over UDP using UDP Server Port 547.
A server or relay-agent MUST transmit all messages over UDP using UDP
Client Port 546.
A client MUST receive all messages over UDP using UDP Client Port 546.
A server or relay-agent MUST receive all messages over UDP using UDP
Server Port 547.
A server or relay-agent MUST join the DHCPv6 Server/Relay-Agent
multicast group well-known multicast address FF02:0:0:0:0:0:1:0.
Servers on the same link as the client MUST use the source address in
the IPv6 header from the client as the destination address in the
servers response packet. Servers that respond to relay-agents and
relay-agent processing are discussed in section 7.
In the cases where a client or server must retransmit messages the
msg-type codes in this section are used as stated in section 4.3 with
the values that represent the Retrans suffix for the msg-types.
6.2. Client DISCOVER and CONF-REQUEST Messages
msg-type:
If the client does not know the server address or wants to locate a new
server to receive configuration parameters the client sets the msg-type
to DISCOVER. In this case the client MUST use as the destination
IP address the DHCPv6 Server/Relay-Agent multicast address
FF02:0:0:0:0:0:1:0.
If the client knows the server address the client sets the msg-type to
CONF-REQUEST. In this case the client MUST use as the destination
IP address the server address.
msg-flag:
Set to binary zeroes.
error-code:
Set to binary zeroes.
total-addrs:
Set to the number of addresses the client is requesting.
transaction-ID:
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Set to an integer value.
interface token:
Set to a unique link dependent identifier for the clients interface.
server address:
Set to binary zeroes for DISCOVER.
Set to server address for CONF-REQUEST.
gateway address:
Set to binary zeroes.
client-link address:
Set to the clients link-local address for the link on which the client
transmitted the packet.
preferred lifetime:
Set to binary zeroes if the client is not requesting a lifetime.
Set to the number of seconds the client wants for the lifetime.
Set to all 1's (oxffffffff) if the client wants an infinite lifetime.
The client must provide a preferred lifetime for each address
requested.
valid lifetime:
Set to binary zeroes if the client is not requesting a lifetime.
Set to the number of seconds the client wants for the lifetime.
Set to all 1's (oxffffffff) if the client wants an infinite lifetime.
The client must provide a valid lifetime for each address
requested. The valid lifetime must be greater than or equal to the
preferred lifetime.
client address:
Set to binary zeroes if the client is not requesting a renewal for an
existing address it received from a server.
Set to an address the client previously received from a server when the
client is requesting a new set of lifetimes for the address.
A client MUST NOT provide a server with an address that was not given
to the client by a server. DHCPv6 does not permit a server to create
leases for manual configured addresses, or update leases for addresses
created by IPv6 Stateless Address Autoconfiguration.
options:
See Options for DHCPv6 specification [DHCPv6-OPT].
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6.3. Server CONF-RESPONSE Message
msg-type:
Set msg-type to CONF-RESPONSE.
msg-flag:
Set to 01 if the server knows addresses provided are verified to be
unique, otherwise set to binary zeroes.
error-code:
Set to 01 if the server cannot provide any addresses to the client at
this time.
Set to 02 if the server detects an address from the client it did not
provide to the client.
total-addrs:
Set to the number of addresses the server is returning the client.
transaction-ID:
Set to the value the client provided in the DISCOVER or CONF-REQUEST
msg-type.
interface token:
Set to a unique link dependent identifier for the clients interface as
provided in the clients DISCOVER or CONF-REQUEST msg-type.
server address:
The address of the server responding.
gateway address:
Set to the same value that existed when the server received the packet.
client-link address:
Set to the same value that existed when the server received the packet.
preferred lifetime:
Set to the value requested by the client or the value required by the
server.
valid lifetime:
Set to the value requested by the client or the value required by the
server.
The valid lifetime MUST be greater than or equal to the preferred
lifetime.
client address:
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Set to an address provided by the server if the client is not attempting
to renew existing addresses, meaning the address fields from the client
have a value of binary zeroes.
If the error-code is set to 02 the server will only return the addresses
that the server can verify were provided by the server. If no addresses
could be verified the total-addrs field, lifetimes, and client address
will be set to binary zeroes. In the case as far as the server is
concerned the DHCPv6 transaction is completed and the server will not
expect a client ACCEPT message to its CONF-RESPONSE message.
options:
See Options for DHCPv6 specification [DHCPv6-OPT].
6.4. Client ACCEPT Message
msg-type:
Set msg-type to ACCEPT.
If the client sent a DISCOVER to request configuration parameters on the
link, then the client should use as the IP destination address the DHCPv6
Server/Relay-Agent multicast address FF02:0:0:0:0:0:1:0.
If the client sent a CONF-REQUEST to request configuration parameters on
the link, then the client should use as the IP destination address the server
address in the CONF-RESPONSE from the server.
If the client sees an error-code of 02 and the total-addrs field is
zero, the server cannot process any of the addresses requested and the
client should not send an ACCEPT to the server. If the client sees an
error-code of 02 and total-addrs does not equal zero it means the server
dropped addresses that it could not locate requested by the client.
msg-flag:
Set to binary zeroes.
error-code:
Set to binary zeroes.
total-addrs:
Set to 1.
transaction-ID:
Set to the integer value that the client used on its initial DISCOVER or
CONF-REQUEST msg-type to the server.
interface token:
Set to the unique link dependent identifier for the clients interface
that was used for the clients initial DISCOVER or CONF-REQUEST msg-type
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to the server.
server address:
Set to the address provided by the servers CONF-RESPONSE.
gateway address:
Set to binary zeroes.
client-link address:
Set to the clients link-local address for the link on which the client
transmitted the packet.
preferred lifetime:
Set to the first or only preferred lifetime returned for an address by
the server.
valid lifetime:
Set to the first or only valid lifetime returned for an address by the
server.
The valid lifetime MUST be greater than or equal to the preferred
lifetime.
client address:
Set to the first or only address provided by the server.
If the client did receive more than one address and lifetime, it MUST
store this data in an implementation defined manner, so that it can
issue a complete RELEASE for all addresses provided from the server
CONF-RESPONSE, if necessary later. But the ACCEPT does not need to carry
all those addresses to acknowledge the servers CONF-RESPONSE packet in
an ACCEPT.
options:
No options are present.
6.5. Server SERVER-ACK Message
msg-type:
Set msg-type to SERVER-ACK.
If the client sent the ACCEPT to acknowledge a servers CONF-RESPONSE
message on the DHCPv6 Server/Relay-Agent multicast address
FF02:0:0:0:0:0:1:0, the server MUST look at the server address in the
packet to determine if the ACCEPT is for them or not.
If the message is not for a particular server then this is an indirect
message to that particular server the client is not accepting them as
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their server for this transaction, and MUST NOT send a SERVER-ACK to the
clients ACCEPT.
msg-flag:
Set to binary zeroes.
error-code:
Set to binary zeroes.
total-addrs:
Set to 1.
transaction-ID:
Set to the integer value that the client used on its initial DISCOVER or
CONF-REQUEST msg-type to the server.
interface token:
Set to the unique link dependent identifier for the clients interface
that was used for the clients initial DISCOVER or CONF-REQUEST msg-type
to the server.
server address:
Set to the servers address.
gateway address:
Set to the same value that existed when the server received the packet.
client-link address:
Set to the same value that existed when the server received the packet.
preferred lifetime:
Set to the value provided by the client.
valid lifetime:
Set to the value provided by the client.
The valid lifetime MUST be greater than or equal to the preferred
lifetime.
client address:
Set to the address provided by the client.
At this point the server MUST commit the configuration parameters
provided to the client from the servers CONF-RESPONSE.
options:
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No options are present.
6.6. Client RELEASE Message
msg-type:
Set msg-type to RELEASE.
If the client had sent an ACCEPT to the server and received a SERVER-ACK
for that message then the client MUST commit the configuration
parameters provided by the servers CONF-RESPONSE and a RELEASE message
is not required. But if the client did not receive a SERVER-ACK
in response to the clients ACCEPT, then the client MUST issue a RELEASE
to the server.
If the client no longer needs an address or has been notified to return
an address to the server, then the client SHOULD issue a RELEASE to the
server.
msg-flag:
Set to binary zeroes.
error-code:
Set to binary zeroes.
total-addrs:
Set to the total number of addresses the client is releasing. In the
case of a RELEASE where the client did not receive the SERVER-ACK this
value MUST equal the total number of addresses for the servers
CONF-RESPONSE.
transaction-ID:
Set to the integer value that the client used on its initial DISCOVER or
CONF-REQUEST msg-type to the server.
interface token:
Set to the unique link dependent identifier for the clients interface
that was used for the clients initial DISCOVER or CONF-REQUEST msg-type
to the server.
server address:
Set to binary zeroes.
gateway address:
Set to binary zeroes.
client-link address:
Set to the clients link-local address for the link on which the client
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transmitted the packet.
preferred lifetime:
Set to the valid lifetime returned for an address by the server.
valid lifetime:
Set to the valid lifetime returned for an address by the server.
The valid lifetime MUST be greater than or equal to the preferred
lifetime.
client address:
Set to the address provided by the server.
The client will return the number of addresses and associated lifetimes
provided in the servers CONF-RESPONSE.
options:
No options are present.
7. Relay-Agent Processing
The relay-agent MUST use UDP DHCPv6 Server Port 547 as the UDP port to
accept client responses in an implementation.
The relay-agent MUST join the DHCP Server/Relay-Agent multicast group
well-known multicast address FF02:0:0:0:0:0:1:0.
When a DHCPv6 Relay-Agent hears a request from a DHCPv6 Client it MUST:
If the gateway address is NOT zero then the relay-agent MUST:
Put the relay-agents IP address in the gateway address field of
the clients request packet.
All relay-agents MUST:
Put their relay-agent address as the source address for the IP
header.
Put the next relay-agent or known server address as the
destination address in the IP header.
Forward the packet to the to the next hop relay-agent or
known server.
When the remote server receives the client request from the relay-agent
it will know its a remote client request (not on the servers link),
because there is a gateway address in the request. So servers MUST
verify the gateway address is not zero, to determine if the clients request
is from a remote link.
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The server responds as specified in section 6.0, but uses the
gateway address as the destination address in the IP header.
When the relay-agent receives the remote servers response, it MUST
forward the packet to the client, by using the client-link address as
the source address for the IP Header.
8. Security Considerations
Security for DHCPv6 can be used as specified in [IPv6-SA], [IPv6-AUTH],
and [IPv6-ESP], which are implementation requirements for IPv6.
Appendix A - Related Work in IPv6
The related work in IPv6 that would best serve an implementor to study
is the IPv6 Specification [IPv6-SPEC], the IPv6 Addressing Architecture
[IPv6-ADDR], IPv6 Stateless Address Autoconfiguration [IPv6-ADDRCONF],
IPv6 Neighbor Discovery Processing [IPv6-ND], and Dynamic Updates to DNS
[DYN-UPD]. These specifications afford DHCPv6 to build upon the IPv6
work to provide both robust stateful autoconfiguration and
autoregistration of DNS Host Names.
The IPv6 Specification provides the base architecture and design of
IPv6. A key point for DHCPv6 implementors to understand is that IPv6
requires that every link in the internet have an MTU of 576 octets or
greater (in IPv4 the requirement is 68 octets). This means that a
UDP datagram of 536 octets will always pass through an internet (less 40
octets for the IPv6 header), as long as there are no IP options prior to
the UDP datagram in the packet. But, IPv6 does not support
fragmentation at routers and fragmentation must take place end-to-end
between hosts. If a DHCPv6 implementation needs to send a packet
greater than 536 octets it can either fragment the UDP datagram in UDP
or use Path MTU Discovery [IPv6-SPEC] to determine the size of the
packet that will traverse a network path. It is implementation defined
how this is accomplished in DHCPv6.
The IPv6 Addressing Architecture Specification provides the address
scope that can be used in an IPv6 implementation, and the various
configuration architecture guidelines for network designers of the IPv6
address space. Two advantages of IPv6 is that multicast addressing is well
defined and nodes can create link-local addresses during initialization
of the nodes environment. This means that a host immediately can configure
an IPv6 address at initialization for an interface, before communicating in
any manner on the link. The host can then use a well-known multicast address
to begin communications to discover neighbors on the link, or as was
discussed in the specification to locate a DHCPv6 server or relay-agent.
The IPv6 Stateless Address Autoconfiguration Specification (addrconf)
defines how a host can autoconfigure addresses based on neighbor discovery
router advertisements, and the use of a validation lifetime to support
renumbering of addresses on the Internet. In addition the addrconf
specification defines the protocol interaction for a host to begin stateless
or stateful autoconfiguration. DHCPv6 is one vehicle to perform stateful
autoconfiguration. Compatibility with addrconf is a design goal of DHCPv6
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where possible.
IPv6 Neighbor Discovery (ND) is the node discovery protocol in IPv6
(replaces and enhances functions of IPv4 ARP Model). To truly
understand IPv6 and addrconf it is strongly recommended that
implementors understand IPv6 ND.
Dynamic Updates to DNS is a specification that supports the
dynamic update of DNS records for both IPv4 and IPv6. DHCPv6 can use
the dynamic updates to DNS to now integrate addresses and name space to
not only support autoconfiguration, but also autoregistration in IPv6.
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Change History
Changes from July 95 to November 95 Drafts:
Refined request/response codes and processing to support transaction
processing model.
Permit multiple addresses and lifetimes in a request and response.
Moved Dynamic Updates to DNS as an Option to be defined in that
specification.
Settled on using UDP as it supports DHCP client server model as opposed
to TCP which has overhead for this model.
Reformatted specification to support analysis, packet formats, and
processing in their own sections to make it easier for implementors to
read.
Removed address count as it is not necessary for synchronization.
Added error-code, msg-flag, and total-addrs fields.
Made transaction-ID 2 octets.
Updated terminology to coordinate with IPv6 Stateless Address
Autoconfiguration.
Added more implementation notes.
Moved IPv6 Related Work to an Appendix.
Fixed various bugs in the spec from DHC WG input.
Added Security reference pointers.
Removed options format, which will be in the options spec.
Added retransmission configuration variables, msg-types, and logic.
Changes from March 95 to July 95 Drafts:
Used integer values instead of bit values for type and code fields.
Used message-type and message-code fields and rely on looking at
the fields in the datagram instead of multiple over-lapping
request/response codes.
Added address-count field processing to be specified by the
client as opposed to the server, and the processing for when
client and server address-counts become disjoint.
Added Requirements wording for MUST, SHOULD, MAY, etc.
Added Design Goals section.
Redefined transaction-ID and interface-token.
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Added Client/Server Binding definition and processing
section to handle those bindings.
Added more terminology, definitions, and rationale.
Added model to support Dynamic Updates to DNS for Host Names.
Reduced the request/response model to 3 packets by not doing
a server confirm to a clients confirm to a servers response.
Added model to support like lifetime fields for lease
management to coordinate with IPv6 Stateless Address
Autoconfiguration.
Added model and processing definitions for future DHCPv6 Options
Specification.
Added gateway-address and client-link-address for relay-agent
processing.
Removed excessive use of the acronym DHCPv6 for section titles
and when referencing clients and servers.
Added Draft ***Open Issues*** Section for review by the DHC Working
Group.
Added Change History.
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Acknowledgements
The DHC Working Group for their time and input into the specification.
A special thanks for the consistent input, ideas, and review by (in
alphabetical order) Brian Carpenter, Ralph Droms, Thomas Narten, Jack
Mccann, Charlie Perkins, Yakov Rekhter, Matt Thomas, Sue Thomson, and
Phil Wells.
The author would also like to thank Steve Deering and Bob Hinden,
who have consistently taken the time to discuss the more complex
parts of the IPv6 specifications.
The author MUST also thank his employer for the opportunity and funding
to work on DHCPv6 and IPv6 in general as an individual in the IETF.
References
[DHCPv6-OPT]
C. Perkins, "Options for the Dynamic Host Configuration
Protocol for IPv6 (ODHCPv6)" Internet Draft, November 1995
<draft TBD>
[IPv6-SPEC]
S. Deering and R. Hinden, "Internet Protocol Version 6
[IPv6] Specification" Internet Draft, June 1995
<draft-ietf-ipngwg-ipv6-spec-02.txt>
[IPv6-ADDR]
R. Hinden, S. Deering, Editors, "IP Version 6 Addressing Architecture"
Internet Draft, June 1995
<draft-ietf-ipngwg-ipv6-addr-arch-03.txt>
[IPv6-ADDRCONF]
S. Thomson, T. Narten, "IPv6 Stateless Address Autoconfiguration"
Internet Draft, November 1995
<draft-ietf-addrconf-ipv6-auto-05.txt>
[IPv6-ND]
T. Narten, E. Nordmark, and W. A. Simpson, "IPv6 Neighbor Discovery"
Internet Draft, September 1995
<draft-ietf-ipngwg-discovery-02.txt>
[IPv6-DNS]
S. Thompson and C. Huitema, "DNS Extensions to support IP
version 6", Internet Draft, March 1995
<draft-ietf-ipngwg-dns-00.txt>
[RFC-1034]
P. Mockapetris, "Domain Names - implementation and specification"
STD-13, 11/01/87
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[RFC-1035]
P. Mockapetris, "Domain Names - concepts and facilities"
STD-13, 11/01/87
[DYN-UPD]
S. Thomson, Y. Rekhter, J. Bound, "Dynamic Updates in the Domain
Name System (DNS)" Internet Draft, March 1995
<draft-ietf-dnsind-dynDNS-01.txt>
[RFC-768]
J. Postel, "User Datagram Protocol"
STD-6, 08/28/80.
[DHCP-v4]
R. Droms, "Dynamic Host Configuration Protocol"
RFC 1541 Proposed Standard, October 1993
[IPv6-Ether]
M. Crawford, "A Method for the Transmission of IPv6 Packets over
Ethernet Networks", Internet Draft, October 1995
<draft-ietf-ipngwg-ethernet-ntwrks-01.txt>
[IPv6-SA]
R. Atkinson, "Security Architecture for the Internet Protocol"
RFC 1825, August 1995
[IPv6-AUTH]
R. Atkinson, "IP Authentication Header"
RFC 1826, August 1995
[IPv6-ESP]
R. Atkinson, "IP Encapsulating Security Payload (ESP)"
RFC 1827, August 1995
Authors' Address
Jim Bound
Digital Equipment Corporation
110 Spitbrook Road, ZKO3-3/U14
Nashua, NH 03062
Phone: (603) 881-0400
Email: bound@zk3.dec.com
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