Network Working Group O. Troan
Internet-Draft B. Volz
Updates: 3315,3633 (if approved) Cisco Systems, Inc.
Intended status: Standards Track M. Siodelski
Expires: April 5, 2015 ISC
October 2, 2014
Issues and Recommendations with Multiple Stateful DHCPv6 Options
draft-ietf-dhc-dhcpv6-stateful-issues-07.txt
Abstract
Dynamic Host Configuration Protocol for IPv6 (DHCPv6) was not written
with the expectation that additional stateful DHCPv6 options would be
developed. IPv6 Prefix Options for Dynamic Host Configuration
Protocol (DHCP) version 6 shoe-horned the new options for Prefix
Delegation into DHCPv6. Implementation experience of the CPE model
described in RFC 7084 has shown multiple issues with the DHCPv6
protocol in supporting multiple stateful options. This document
updates RFC 3315 and RFC 3633.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 5, 2015.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Handling of Multiple IA Options Types . . . . . . . . . . . . 4
4.1. Placement of Status Codes . . . . . . . . . . . . . . . . 5
4.2. Advertise Message . . . . . . . . . . . . . . . . . . . . 6
4.3. T1/T2 Timers . . . . . . . . . . . . . . . . . . . . . . 7
4.4. Renew and Rebind Messages . . . . . . . . . . . . . . . . 8
4.4.1. Renew Message . . . . . . . . . . . . . . . . . . . . 8
4.4.2. Rebind Message . . . . . . . . . . . . . . . . . . . 8
4.4.3. Updates to section 18.1.3 of RFC 3315 . . . . . . . . 9
4.4.4. Updates to Section 18.1.4 of RFC 3315 . . . . . . . . 10
4.4.5. Updates to Section 18.1.8 of RFC 3315 . . . . . . . . 11
4.4.6. Updates to Section 18.2.3 of RFC 3315 . . . . . . . . 14
4.4.7. Updates to Section 18.2.4 of RFC 3315 . . . . . . . . 15
4.4.8. Updates to RFC 3633 . . . . . . . . . . . . . . . . . 17
4.5. Confirm Message . . . . . . . . . . . . . . . . . . . . . 18
4.6. Decline Should Not Necessarily Trigger a Release . . . . 19
4.7. Multiple Provisioning Domains . . . . . . . . . . . . . . 19
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
6. Security Considerations . . . . . . . . . . . . . . . . . . . 19
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 19
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
8.1. Normative References . . . . . . . . . . . . . . . . . . 20
8.2. Informative References . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
1. Introduction
DHCPv6 [RFC3315] was not written with the expectation that additional
stateful DHCPv6 options would be developed. DHCPv6 Prefix Delegation
[RFC3633] shoe-horned the new options for Prefix Delegation into
DHCPv6. Implementation experience of the CPE model described in
[RFC7084] has shown issues with the DHCPv6 protocol in supporting
multiple stateful option types, in particular IA_NA (non-temporary
addresses) and IA_PD (delegated prefixes).
This document describes a number of problems encountered with
coexistence of the IA_NA and IA_PD option types and changes to the
DHCPv6 protocol specifications to address these problems.
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The intention of this work is to clarify and, where needed, modify
the DHCP protocol specification to support multiple IA option types
within a single DHCP session. However, as it is not possible to know
what future IA option types might be used for, this work is primarily
to clarify DHCP operation when IA_NA and IA_PD options are being
requested as per [RFC7084]. And, to provide a framework to support
new IA option types, assuming they are similar enough. Future
documents that define new IA option types will need to specify
whether they fit into this framework or define the DHCP operation for
the new and existing IA option types, as appropriate.
There are two general solutions to the problem of supporting multiple
IA option types. One is by using a separate DHCP session (separate
instances of the client state machine) per IA option type. While
conceptually simple, this approach has a number of issues: multiple
instances of the state machine in clients, additional DHCP protocol
traffic, 'collisions' between other configuration options, divergence
in that each IA option type specification specifies its 'own' version
of the DHCP protocol. The other is by using a single DHCP session
and state machine, which is the approach taken by this document (see
Section 4).
Note that while IA_TA (temporary addresses) options may be included
with other IA option type requests, these generally are not renewed
(there are no T1/T2 times) and have a separate life cycle from IA_NA
and IA_PD option types. DHCPv6 assigned temporary addresses also
have limited value when DHCPv6 is used for non-temporary address
assignment, as the privacy issues identified for IPv6 stateless
address assignment ([RFC4941]) do not apply to DHCPv6 assignments.
The changes described in this document are intended to be
incorporated in a new revision of the DHCPv6 protocol specification
([I-D.dhcwg-dhc-rfc3315bis]).
2. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
3. Terminology
In addition to the terminology defined in [RFC3315], [RFC3633], and
[RFC7227], the following terminology is used in this document:
Resource (allocable resource): A value (or a collection of values)
dynamically assigned to the client by
the server and being carried in the
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stateful options. Examples of
resources are an IPv6 address or an
IPv6 prefix. Information about the
resources is transported in stateful
options such as IA_NA, for addresses,
and IA_PD, for prefix delegations.
In the future, other types of
resources and stateful options may be
defined.
Identity association (IA): A collection of resources assigned to
a client. Each IA has an associated
IAID. A client may have more than
one IA assigned to it; for example,
one for each of its interfaces. Each
IA holds one type of IA option; for
example, an identity association for
non-temporary addresses (IA_NA) holds
non-temporary addresses. Throughout
this document, "IA" is used to refer
to an identity association without
identifying the type of resources in
the IA.
IA option types: This is used to generally mean an
IA_NA and/or IA_PD and may also
include IA_TA, as well as future IA
options.
Stateful options: Options that require dynamic binding
state per client on the server.
4. Handling of Multiple IA Options Types
DHCPv6 was written with the assumption that the only stateful options
were for assigning addresses. DHCPv6 PD describes how to extend the
DHCPv6 protocol to handle prefix delegation, but [RFC3633] did not
consider how DHCP address assignment and prefix delegation could co-
exist.
If a client requests multiple IA option types, but the server is
configured to only offer a subset of them, the client could react in
several ways. Reset the state machine and continue to send Solicit
messages, create separate DHCP sessions for each IA option type and
continue to Solicit for the unfulfilled IA options, or it could
continue with the single session, and include the unfulfilled IA
options in subsequent messages to the server.
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Proposed solution: the client should keep a single session with the
server and include the missing options in subsequent messages
(Request, Renew, and Rebind) to the server.
4.1. Placement of Status Codes
In Reply messages IA specific status codes (i.e., NoAddrsAvail,
NotOnlink, NoBinding, NoPrefixAvail) are encapsulated in the IA
option. In Advertise messages the Status Code option with the
NoAddrsAvail code is in the top-level. That makes sense when the
failure case is fatal. However, with the introduction of other
stateful option types, there may be cases where a server is not
willing to offer addresses, but is willing to offer other resources,
e.g. delegated prefixes.
Ideally the Status Code option for IA specific status codes should be
encapsulated in the IA option for all DHCP messages. This also makes
the NoAddrsAvail and NoPrefixAvail Status Code option placement for
Advertise messages identical to Reply messages.
In addition, how a server formats the Advertise message when
addresses are not available has been a point of some confusion and
implementations seem to vary (some strictly follow RFC 3315 while
others assumed it was encapsulated in the IA option as for Reply
messages).
Therefore, the proposed solution is:
Clients MUST be prepared to handle each of the following Advertise
messages formats when there are no addresses available (even when no
other IA option types were in the Solicit):
1. Advertise containing just a top-level Status Code option (of
NoAddrsAvail) and no IA_NAs/IA_TAs.
2. Advertise containing the IA_NAs and/or IA_TAs with encapsulated
Status Code option (of NoAddrsAvail) and no top-level Status Code
option.
3. Advertise containing a top-level Status Code option (of
NoAddrsAvail) and IA_NAs and/or IA_TAs with a Status Code option
(of NoAddrsAvail).
Servers MUST return the Status Code option (of NoAddrsAvail)
encapsulated in an IA_NA/IA_TA options and not as a top-level Status
Code option (of NoAddrsAvail) when no addresses will be assigned (2
in the above list). This means that the Advertise response matches
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the Reply response with respect to the handling of the NoAddrsAvail
status.
Replace the following paragraph in RFC 3315, section 17.2.2:
If the server will not assign any addresses to any IAs in a
subsequent Request from the client, the server MUST send an
Advertise message to the client that includes only a Status
Code option with code NoAddrsAvail and a status message for
the user, a Server Identifier option with the server's DUID,
and a Client Identifier option with the client's DUID.
With:
If the server will not assign any addresses to an IA in a
subsequent Request from the client, the server MUST include
the IA in the Advertise message with no addresses in the IA
and a Status Code option encapsulated in the IA containing
status code NoAddrsAvail.
4.2. Advertise Message
[RFC3315] specifies that a client must ignore an Advertise message if
a server will not assign any addresses to a client. A client
requesting both IA_NA and IA_PD, with a server that only offers one
of them, is not supported in the current protocol specification.
Proposed solution: a client SHOULD accept Advertise messages, even
when not all IA option types are being offered. And, in this case,
the client SHOULD include the not offered IA option types in its
Request. A client SHOULD only ignore an Advertise message when all
IA options include no offered addresses or delegated prefixes. Note
that ignored messages MUST still be processed for SOL_MAX_RT and
INF_MAX_RT options as specified in [RFC7083].
Replace Section 17.1.3 of RFC 3315: (existing errata)
The client MUST ignore any Advertise message that includes a Status
Code option containing the value NoAddrsAvail, with the exception
that the client MAY display the associated status message(s) to the
user.
With (this includes the changes made by [RFC7083]):
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The client MUST ignore any Advertise message that contains no
addresses (IAADDR options encapsulated in IA_NA or IA_TA options)
and no delegated prefixes (IAPREFIX options encapsulated in IA_PD
options, see RFC 3633) with the exception that the client
MUST process an included SOL_MAX_RT option (RFC 7083), MUST
process an included INF_MAX_RT option (RFC 7083), and MAY
display any associated status message(s) to the user.
And, replace:
- The client MAY choose a less-preferred server if that server
has a better set of advertised parameters, such as the
available addresses advertised in IAs.
With:
- The client MAY choose a less-preferred server if that server
has a better set of advertised parameters, such as the
available options advertised in IAs.
It is important to note that the receipt of an Advertise message
without any addresses and delegated prefixes does not imply that the
client should restart the Solicit retransmissions timers. Doing so
would lead to a Solicit/Advertise storm.
4.3. T1/T2 Timers
The T1 and T2 times determine when the client will contact the server
to extend lifetimes of information received in an IA. How should a
client handle the case where multiple IA options have different T1
and T2 times?
In a multiple IA option type model, the T1/T2 times are protocol
timers, that should be independent of the IA options themselves. If
we were to redo the DHCP protocol from scratch the T1/T2 times should
be carried in a separate DHCP option.
Proposed solution: The server MUST set the T1/T2 times in all IA
options in a Reply or Advertise message to the same value. To deal
with the case where servers have not yet been updated to do that,
clients MUST use the shortest (explicit or implicit) T1/T2 times
(larger than 0), from the same IA option, in the Reply. T1/T2 times
from other IAs are ignored.
The following paragraph should be added to Section 18.2.1, 18.2.3,
and 18.2.4 of RFC 3315:
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The T1/T2 times set in each applicable IA option for a Reply MUST
be the same values across all IAs. The server MUST determine the
T1/T2 times across all of the applicable client's bindings in the
Reply. This facilitates the client being able to renew all of the
bindings at the same time.
4.4. Renew and Rebind Messages
This section presents issues with handling multiple IA option types
in the context of creation and processing the Renew and Rebind
messages. It also proposes relevant updates to the [RFC3315] and
[RFC3633].
4.4.1. Renew Message
The Renew message, as described in [RFC3315], allows a client to only
renew bindings assigned via a Request message.
In a multiple IA option type model, the Renew does not support the
ability for the client to renew one IA option type while requesting
bindings for other IA option types that were not available when the
client sent the Request.
Proposed solution: The client should continue with the IA options
received, while continuing to include the other IA options in
subsequent messages to the server. The client and server processing
need to be modified. Note that this change makes the server's IA
processing of Renew similar to the Request processing.
4.4.2. Rebind Message
In Section 4.4.1 it has been proposed that the client includes IA
options in a Renew message for the bindings it desires but has been
unable to obtain by sending a Request message, apart from the IA
options for the existing bindings.
At time T2, the client stops sending Renew messages to the server and
initiates the Rebind/Reply message exchange with any available
server. In this case, it should be possible to continue trying to
obtain new bindings using the Rebind message if the client failed to
get the response from the server to the Renew message.
The Rebind message, as described in [RFC3315] does not explicitly
specify what a server should do when an IA option which contains no
addresses is present.
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Proposed solution: The client should continue with the IA options
received and it MAY include additional IA options to request creation
of additional bindings.
4.4.3. Updates to section 18.1.3 of RFC 3315
Replace Section 18.1.3 of RFC 3315 with the following text:
To extend the valid and preferred lifetimes for the addresses
associated with an IA, the client sends a Renew message to the
server from which the client obtained the addresses in the IA
containing an IA option for the IA. The client includes IA Address
options in the IA option for the addresses associated with the IA.
The server determines new lifetimes for the addresses in the IA
according to the administrative configuration of the server. The
server may also add new addresses to the IA. The server may remove
addresses from the IA by setting the preferred and valid lifetimes
of those addresses to zero.
The server controls the time at which the client contacts the
server to extend the lifetimes on assigned addresses through the T1
and T2 parameters assigned to an IA.
At time T1 for an IA, the client initiates a Renew/Reply message
exchange to extend the lifetimes on any addresses in the IA.
If T1 or T2 had been set to 0 by the server (for an IA_NA) or there
are no T1 or T2 times (for an IA_TA) in a previous Reply, the
client may send a Renew or Rebind message, respectively, at the
client's discretion.
The client sets the "msg-type" field to RENEW. The client
generates a transaction ID and inserts this value in the
"transaction-id" field.
The client places the identifier of the destination server in a
Server Identifier option.
The client MUST include a Client Identifier option to identify
itself to the server. The client adds any appropriate options,
including one or more IA options.
The client includes an IA option with all addresses currently
assigned to the IA in its Renew message. The client also includes
IA options for all other bindings for which the client desires to
extend the lifetimes of addresses. The client MUST only include
addresses in the IA that the client obtained from the server and
are still valid (have non-zero lifetime).
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The client MAY include an IA option for each binding it desires but
has been unable to obtain. This IA option MUST NOT contain any
addresses. However, it MAY contain the IA Address option with IPv6
address field set to 0 to indicate the client's preference for the
preferred and valid lifetimes for any newly assigned addresses.
The client MUST include an Option Request option (see section 22.7)
to indicate the options the client is interested in receiving. The
client MAY include options with data values as hints to the server
about parameter values the client would like to have returned.
The client transmits the message according to section 14, using the
following parameters:
IRT REN_TIMEOUT
MRT REN_MAX_RT
MRC 0
MRD Remaining time until T2
The message exchange is terminated when time T2 is reached (see
section 18.1.4), at which time the client begins a Rebind message
exchange.
4.4.4. Updates to Section 18.1.4 of RFC 3315
Replace Section 18.1.4 of RFC 3315 with the following text:
At time T2 for an IA (which will only be reached if the server to
which the Renew message was sent at time T1 has not responded), the
client initiates a Rebind/Reply message exchange with any available
server.
The client constructs the Rebind message as described in 18.1.3
with the following differences:
- The client sets the "msg-type" field to REBIND.
- The client does not include the Server Identifier option in the
Rebind message.
The client transmits the message according to section 14, using the
following parameters:
IRT REB_TIMEOUT
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MRT REB_MAX_RT
MRC 0
MRD Remaining time until valid lifetimes of all addresses in
all IAs have expired
If all addresses for an IA have expired the client may choose to
include this IA without any addresses (or with only a hint for
lifetimes) in subsequent Rebind messages to indicate that the
client is interested in assignment of the addresses to this IA.
The message exchange is terminated when the valid lifetimes of all
addresses across all IAs have expired, at which time the client may
use a Solicit message to locate a new DHCP server and send a
Request for the expired IAs to the new server.
4.4.5. Updates to Section 18.1.8 of RFC 3315
Replace Section 18.1.8 of RFC 3315 with the following text:
Upon the receipt of a valid Reply message in response to a Solicit
(with a Rapid Commit option), Request, Confirm, Renew, Rebind or
Information-request message, the client extracts the configuration
information contained in the Reply. The client MAY choose to
report any status code or message from the status code option in
the Reply message.
If the client receives a Reply message with a Status Code
containing UnspecFail, the server is indicating that it was unable
to process the message due to an unspecified failure condition. If
the client retransmits the original message to the same server to
retry the desired operation, the client MUST limit the rate at
which it retransmits the message and limit the duration of the time
during which it retransmits the message.
When the client receives a Reply message with a Status Code option
with the value UseMulticast, the client records the receipt of the
message and sends subsequent messages to the server through the
interface on which the message was received using multicast. The
client resends the original message using multicast.
When the client receives a NotOnLink status from the server in
response to a Confirm message, the client performs DHCP server
solicitation, as described in section 17, and client-initiated
configuration as described in section 18. If the client receives
any Reply messages that do not indicate a NotOnLink status, the
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client can use the addresses in the IA and ignore any messages that
indicate a NotOnLink status.
When the client receives a NotOnLink status from the server in
response to a Request, the client can either re-issue the Request
without specifying any addresses or restart the DHCP server
discovery process (see section 17).
The client SHOULD perform duplicate address detection [17] on each
of the received addresses in any IAs, on which it has not performed
duplicate address detection during processing of any of the
previous Reply messages from the server. The client performs the
duplicate address detection before using the received addresses for
the traffic. If any of the addresses are found to be in use on the
link, the client sends a Decline message to the server for those
addresses as described in section 18.1.7.
If the Reply was received in response to a Solicit (with a Rapid
Commit option), Request, Renew or Rebind message, the client
updates the information it has recorded about IAs from the IA
options contained in the Reply message:
- Record T1 and T2 times. The client MUST use the shortest
(explicit or implicit) T1 and T2 times (larger than 0) from the
same IA option across all of the IA options to facilitate
initiating the renewal process for all bindings simultaneously.
T1/T2 times from other IAs are ignored.
- Add any new addresses in the IA option to the IA as recorded by
the client.
- Update lifetimes for any addresses in the IA option that the
client already has recorded in the IA.
- Discard any addresses from the IA, as recorded by the client,
that have a valid lifetime of 0 in the IA Address option.
- Leave unchanged any information about addresses the client has
recorded in the IA but that were not included in the IA from the
server.
Management of the specific configuration information is detailed in
the definition of each option in section 22.
The client examines the status code in each IA individually. If
the client receives a NoAddrsAvail, the client has received no
usable addresses in the IA.
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If the client finds no usable addresses in any IA, the client MAY
use the Information-request message to obtain other configuration
information only.
The client uses addresses and other information from any IAs that
do not contain a Status Code option with the NoAddrsAvail code.
For each IA for which the client receives NoAddrsAvail status code
the client has the following choices:
- The client includes the IA with no addresses in subsequent Renew
and Rebind messages sent to the server, to request creation of
the binding for the IA.
- Tries another server (perhaps restarting the DHCP server
discovery process).
When the client receives a Reply message in response to a Renew or
Rebind message, for each IA in the original Renew or Rebind
message, the client:
- Sends a Request message if the IA sent in the Renew or Rebind
contained addresses that the client is currently using and the
server responded with a NoBinding status code.
- Tries to obtain the IA from another server (by restarting the
DHCP discovery process) if the client attempted to obtain a new
binding in the Renew or Rebind message by sending an IA without
any addresses and the server responded with NoBinding status
code.
- Follows the retransmission procedure for Renew/Rebind messages
as described in section 14 if the IA is not in the Reply
message.
- Otherwise accepts the information in the IA.
When the client receives a valid Reply message in response to a
Release message, the client considers the Release event completed,
regardless of the Status Code option(s) returned by the server.
When the client receives a valid Reply message in response to a
Decline message, the client considers the Decline event completed,
regardless of the Status Code option(s) returned by the server.
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4.4.6. Updates to Section 18.2.3 of RFC 3315
Replace Section 18.2.3 of RFC 3315 with the following text:
When the server receives a Renew message via unicast from a client
to which the server has not sent a unicast option, the server
discards the Renew message and responds with a Reply message
containing a Status Code option with the value UseMulticast, a
Server Identifier option containing the server's DUID, the Client
Identifier option from the client message, and no other options.
For each IA in the Renew message from a client, the server locates
the client's binding and verifies that the information in the IA
from the client matches the information stored for that client.
If the server finds the addresses in the IA for the client then the
server sends back the IA to the client with new lifetimes and, if
applicable, T1/T2 times. If the server is unable to extend the
lifetimes of an address in the IA, the server MAY choose not to
include the IA Address option for this address.
The server may choose to change the list of addresses and the
lifetimes of addresses in IAs that are returned to the client.
If the server finds that any of the addresses in the IA are not
appropriate for the link to which the client is attached, the
server returns the address to the client with lifetimes of 0.
For each IA for which the server cannot find a client entry, the
server has the following choices depending on the server's policy
and configuration information:
- If the server is configured to create new bindings as a result
of processing Renew messages, the server SHOULD create a binding
and return the IA with allocated addresses with lifetimes and,
if applicable, T1/T2 times and other information requested by
the client. The server MAY use values in the IA Address option
(if included) as a hint.
- If the server is configured to create new bindings as a result
of processing Renew messages, but the server will not assign any
addresses to an IA, the server returns the IA option containing
a Status Code option with the NoAddrsAvail status code and a
status message for a user.
- If the server does not support creation of new bindings for the
client sending a Renew message, or if this behavior is disabled
according to the server's policy or configuration information,
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the server returns the IA option containing a Status code option
with the NoBinding status code and a status message for a user.
The server constructs a Reply message by setting the "msg-type"
field to REPLY, and copying the transaction ID from the Renew
message into the transaction-id field.
The server MUST include a Server Identifier option containing the
server's DUID and the Client Identifier option from the Renew
message in the Reply message.
The server includes other options containing configuration
information to be returned to the client as described in section
18.2.
The T1/T2 times set in each applicable IA option for a Reply MUST
be the same values across all IAs. The server MUST determine the
T1/T2 times across all of the applicable client's bindings in the
Reply. This facilitates the client being able to renew all of the
bindings at the same time.
4.4.7. Updates to Section 18.2.4 of RFC 3315
Replace Section 18.2.4 of RFC 3315 with the following text:
When the server receives a Rebind message that contains an IA
option from a client, it locates the client's binding and verifies
that the information in the IA from the client matches the
information stored for that client.
If the server finds the addresses in the IA for the client and the
server determines that the addresses in the IA are appropriate for
the link to which the client's interface is attached according to
the server's explicit configuration information, the server SHOULD
send back the IA to the client with new lifetimes and, if
applicable, T1/T2 times. If the server is unable to extend the
lifetimes of an address in the IA, the server MAY choose not to
include the IA Address option for this address.
If the server finds the client entry for the IA and any of the
addresses are no longer appropriate for the link to which the
client's interface is attached according to the server's explicit
configuration information, the server returns the addresses to the
client with lifetimes of 0.
If the server cannot find a client entry for the IA, the IA
contains addresses and the server determines that the addresses in
the IA are not appropriate for the link to which the client's
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interface is attached according to the server's explicit
configuration information, the server MAY send a Reply message to
the client containing the client's IA, with the lifetimes for the
addresses in the IA set to 0. This Reply constitutes an explicit
notification to the client that the addresses in the IA are no
longer valid. In this situation, if the server does not send a
Reply message it silently discards the Rebind message.
Otherwise, for each IA for which the server cannot find a client
entry, the server has the following choices depending on the
server's policy and configuration information:
- If the server is configured to create new bindings as a result
of processing Rebind messages (also see the note about the
Rapid Commit option below), the server SHOULD create a binding
and return the IA with allocated addresses with lifetimes and,
if applicable, T1/T2 times and other information requested by
the client. The server MAY use values in the IA Address option
(if included) as a hint.
- If the server is configured to create new bindings as a result
of processing Rebind messages, but the server will not assign
any addresses to an IA, the server returns the IA option
containing a Status Code option with the NoAddrsAvail status
code and a status message for a user.
- If the server does not support creation of new bindings for the
client sending a Rebind message, or if this behavior is
disabled according to the server's policy or configuration
information, the server returns the IA option containing a
Status Code option with the NoBinding status code and a status
message for a user.
When the server creates new bindings for the IA it is possible
that other servers also create bindings as a result of receiving
the same Rebind message. This is the same issue as in the
Discussion under the Rapid Commit option, see section 22.14.
Therefore, the server SHOULD only create new bindings during
processing of a Rebind message if the server is configured to
respond with a Reply message to a Solicit message containing the
Rapid Commit option.
The server constructs a Reply message by setting the "msg-type"
field to REPLY, and copying the transaction ID from the Rebind
message into the transaction-id field.
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The server MUST include a Server Identifier option containing the
server's DUID and the Client Identifier option from the Rebind
message in the Reply message.
The server includes other options containing configuration
information to be returned to the client as described in section
18.2.
The T1/T2 times set in each applicable IA option for a Reply MUST
be the same values across all IAs. The server MUST determine the
T1/T2 times across all of the applicable client's bindings in the
Reply. This facilitates the client being able to renew all of the
bindings at the same time.
4.4.8. Updates to RFC 3633
Replace Section 12.1:
Each prefix has valid and preferred lifetimes whose durations are
specified in the IA_PD Prefix option for that prefix. The
requesting router uses Renew and Rebind messages to request the
extension of the lifetimes of a delegated prefix.
With:
Each prefix has valid and preferred lifetimes whose durations are
specified in the IA_PD Prefix option for that prefix. The
requesting router uses Renew and Rebind messages to request the
extension of the lifetimes of a delegated prefix.
The requesting router MAY include IA_PD options without any
prefixes, i.e. without IA Prefix option or with IPv6 prefix field
of IA Prefix option set to 0, in a Renew or Rebind message to
obtain bindings it desires but has been unable to obtain. The
requesting router MAY set the prefix-length field of the IA Prefix
option as a hint to the server.
Replace Section 12.2:
The delegating router behaves as follows when it cannot find a
binding for the requesting router's IA_PD:
With:
For the Renew or Rebind, if the IA_PD contains no prefixes, i.e.
contains no IA Prefix option or the IPv6 prefix field in the IA
Prefix option is set to 0, the delegating router MAY assign
prefixes to the IA_PD according to the delegating router's
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explicit configuration information. In this case, when the server
assigns new prefixes to the IA_PD, the server MAY use the value in
the prefix-length field of the IA Prefix option as a hint for the
length of the prefixes being assigned.
The delegating router behaves as follows when it cannot find a
binding for the requesting router's IA_PD containing prefixes:
4.5. Confirm Message
The Confirm message, as described in [RFC3315], is specific to
address assignment. It allows a server without a binding to reply to
the message, under the assumption that the server only needs
knowledge about the prefix(es) on the link, to inform the client that
the address is likely valid or not. This message is sent when e.g.
the client has moved and needs to validate its addresses. Not all
bindings can be validated by servers and the Confirm message provides
for this by specifying that a server that is unable to determine the
on-link status MUST NOT send a Reply.
Note: Confirm has a specific meaning and does not overload Renew/
Rebind. It also is lower processing cost as the server does NOT need
to extend lease times or otherwise send back other configuration
options.
The Confirm message is used by the client to verify that it has not
moved to a different link. For IAs with addresses, the mechanism
used to verify if a client has moved or not, is by matching the
link's on-link prefix(es) (typically a /64) against the prefix-length
first bits of the addresses provided by the client in the IA_NA or
IA_TA IA-types. As a consequence Confirm can only be used when the
client has an IA with address(es) (IA_NA or IA_TA).
A client MUST have a binding including an IA with addresses to use
the Confirm message. A client with IAs with addresses as well as
other IA-types MAY, depending on the IA-type, use the Confirm message
to detect if the client has moved to a different link. A client that
does not have a binding with an IA with addresses MUST use the Rebind
message instead.
IA_PD requires verification that the server has the binding for the
IAs. In that case a client MUST use the Rebind message in place of
the Confirm message and it MUST include all of its bindings, even
address IAs.
Note that Section 18.1.2 of RFC 3315 states that a client MUST
initiate a Confirm when it may have moved to a new link. This is
relaxed to a SHOULD as a client may have determined whether it has or
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has not moved using other techniques, such as described in [RFC6059].
And, as stated above, a client with delegated prefixes, MUST send a
Rebind instead of a Confirm.
4.6. Decline Should Not Necessarily Trigger a Release
Some client implementations have been found to send a Release message
for other bindings they may have received after they determine a
conflict and have correctly sent a Decline message for the
conflicting address(es).
It is recommended that a client SHOULD NOT send a Release message for
other bindings it may have received just because it sent a Decline
message. The client should retain the non-conflicting bindings.
4.7. Multiple Provisioning Domains
This document has assumed that all DHCP servers on a network are in a
single provisioning domain and thus should be "equal" in the service
that they offer. This was also assumed by [RFC3315] and [RFC3633].
One could envision a network where the DHCP servers are in multiple
provisioning domains, and it may be desirable to have the DHCP client
obtain different IA types from different provisioning domains. How a
client detects the multiple provisioning domains and how it would
interact with the multiple servers in these different domains is
outside the scope of this document.
5. IANA Considerations
This specification does not require any IANA actions.
6. Security Considerations
There are no new security considerations pertaining to this document.
7. Acknowledgements
Thanks to many people that contributed to identify the issues in this
document, including Ralph Droms, John, Brzozowski, Ted Lemon, Hemant
Singh, Wes Beebee, Gaurau Halwasia, Bud Millword, Tim Winters, and
Rob Shakir.
8. References
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8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633,
December 2003.
[RFC7083] Droms, R., "Modification to Default Values of SOL_MAX_RT
and INF_MAX_RT", RFC 7083, November 2013.
8.2. Informative References
[I-D.dhcwg-dhc-rfc3315bis]
Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
Richardson, M., Jiang, S., and T. Lemon, "Dynamic Host
Configuration Protocol for IPv6 (DHCPv6) bis", draft-
dhcwg-dhc-rfc3315bis-02 (work in progress), July 2014.
[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, September 2007.
[RFC6059] Krishnan, S. and G. Daley, "Simple Procedures for
Detecting Network Attachment in IPv6", RFC 6059, November
2010.
[RFC7084] Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic
Requirements for IPv6 Customer Edge Routers", RFC 7084,
November 2013.
[RFC7227] Hankins, D., Mrugalski, T., Siodelski, M., Jiang, S., and
S. Krishnan, "Guidelines for Creating New DHCPv6 Options",
BCP 187, RFC 7227, May 2014.
Authors' Addresses
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Ole Troan
Cisco Systems, Inc.
Philip Pedersens vei 20
N-1324 Lysaker
Norway
Email: ot@cisco.com
Bernie Volz
Cisco Systems, Inc.
1414 Massachusetts Ave
Boxborough, MA 01719
USA
Email: volz@cisco.com
Marcin Siodelski
ISC
950 Charter Street
Redwood City, CA 94063
USA
Email: msiodelski@gmail.com
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