Internet DRAFT - draft-ietf-dhc-dhcpv6-agentopt-delegate
draft-ietf-dhc-dhcpv6-agentopt-delegate
Network Working Group R. Droms
Internet-Draft
Intended status: Standards Track B. Volz
Expires: October 3, 2017 Cisco Systems
O. Troan
Cisco Systems, Inc.
April 1, 2017
DHCPv6 Relay Agent Assignment Notification (RAAN) Option
draft-ietf-dhc-dhcpv6-agentopt-delegate-05.txt
Abstract
The DHCP Relay Agent Assignment Notification (RAAN) option is sent
from a DHCP server to a DHCP relay agent to inform the relay agent of
IPv6 addresses that have been assigned or IPv6 prefixes that have
been delegated to DHCP clients.
Status of This Memo
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This Internet-Draft will expire on October 3, 2017.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language and Terminology . . . . . . . . . . . . 3
3. Option Semantics and Usage . . . . . . . . . . . . . . . . . 3
4. Relay Agent Behavior . . . . . . . . . . . . . . . . . . . . 4
5. Server Behavior . . . . . . . . . . . . . . . . . . . . . . . 4
6. Option Format . . . . . . . . . . . . . . . . . . . . . . . . 4
7. Encapsulating DHCP Options in the RAAN Option . . . . . . . . 5
7.1. IA Address Option . . . . . . . . . . . . . . . . . . . . 5
7.2. IA Prefix Option . . . . . . . . . . . . . . . . . . . . 6
8. Requesting Assignment Information from the DHCP Server . . . 6
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
10. Security Considerations . . . . . . . . . . . . . . . . . . . 6
11. Changes Log . . . . . . . . . . . . . . . . . . . . . . . . . 7
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
12.1. Normative References . . . . . . . . . . . . . . . . . . 8
12.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
The DHCP Relay Agent Assignment Notification (RAAN) option
encapsulates address and prefix options to indicate that an address
or prefix has been assigned. The option may also carry other
information required by the network element for configuration related
to the assigned address or prefix.
For example, a relay agent uses the RAAN option to learn when a
prefix that has been delegated through DHCP prefix delegation (PD) to
a DHCP client. The relay agent notifies the network element on which
it is implemented of the delegation information so the network
element can add routing information about the delegated prefix into
the routing infrastructure.
While the practice to date for DHCPv6 has been for the relay agents
to "snoop" the client's message (encapsulated in the received Relay
Message option, and which is forwarded to the client), this will no
longer be possible when clients and servers use
[I-D.ietf-dhc-sedhcpv6] to encrypt their communication.
Use of the RAAN option has another benefit in that the Reply to a
client's Release message, which does not have any useful information
for the relay agent about the addresses or delegated prefixes the
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client released, can now communicate this information in the RAAN
option to the relay agent.
2. Requirements Language and Terminology
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] when they
appear in ALL CAPS. When these words are not in ALL CAPS (such as
"should" or "Should"), they have their usual English meanings, and
are not to be interpreted as [RFC2119] key words.
The term "DHCP" in this document refers to DHCP for IPv6, as defined
in [RFC3315]. The terms "DHCP prefix delegation" and "DHCP PD" refer
DHCP for IPv6 prefix delegation, as defined in [RFC3633].
Additional terms used in the description of DHCP and DHCP prefix
delegation are defined in RFC 3315 and RFC 3633. In this document
"assigning" an IPv6 prefix is equivalent to "delegating" a prefix.
3. Option Semantics and Usage
The RAAN option carries information about assigned IPv6 addresses and
prefixes. It encapsulates IA Address options (RFC 3315) and/or IA
Prefix options (RFC 3633), and possibly other options that carry
other information related to the assigned IPv6 address or prefix.
The DHCP server is responsible for synchronizing any state created by
a node through the use of the RAAN option. For example, if a DHCP
server receives a Release message for a delegated prefix, it causes
the node to delete any state associated with that prefix by sending a
RAAN option containing an IA Prefix option with the released prefix
and a valid lifetime of zero.
When a DHCP server sends this option to a relay agent, it MUST
include all addresses and prefixes assigned to the client on the link
to which the option refers at the time the option is sent.
Examples of use:
o Populate an ACL with an assigned IPv6 address if the network
security policy requires limiting IPv6 forwarding to devices that
have obtained an address through DHCP.
o Inject routing information into a routing infrastructure about a
delegated prefix on behalf of a requesting router.
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4. Relay Agent Behavior
A relay agent that wants information from the server in a RAAN option
includes an ORO requesting the RAAN option in its Relay-Forw message.
A relay agent may do this for any relayed message, regardless of the
message type or the message contents.
When a relay agent receives a Relay-Reply message containing a RAAN
option, the relay agent may forward that option data to the node in
which the relay agent is instantiated. If no RAAN option is included
in the Relay-Reply, the relay agent MUST NOT assume anything with
regard to RAAN data and MUST NOT forward any indication to the node
in which the relay agent is instantiated.
If a node creates state based on the information included in this
option, it MUST remove that state when the lifetime as specified in
the option expires.
One concern with the RAAN option is that messages from the DHCP
server may be received (or processed) out of order. But this concern
is no different than that for the "snooping" which has been used by
relay agents for many years (both in DHCPv4 and DHCPv6).
Implementers should be aware of this and should consider making use
of Leasequery ([RFC5007]) to resolve conflicts.
5. Server Behavior
When a server is responding to a request and the ORO contains an RAAN
option, the server SHOULD include a RAAN option with all of the
addresses and prefixes that have been (or are being assigned) to the
client. If no addresses or prefixes are assigned, the server SHOULD
send a RAAN option with no addresses or prefixes.
If the DHCP server does include this option in a Relay-Reply message,
it MUST include it in the option area of the Relay-Reply message sent
to the relay agent intended as the recipient of the option.
If the message received from the client contains no Client Identifier
option or the server is otherwise unable to identify the client or
the client's link (perhaps because of missing or invalid data in the
request), the server MUST NOT include a RAAN option in the response.
6. Option Format
The RAAN option has the following format:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| option-code | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. encapsulated-options .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Relay Agent Assignment Notification Option Format
option-code OPTION_AGENT_NOTIFY (TBD).
option-len Length of encapsulated options, in octets.
encapsulated-options DHCP options to be delivered by the relay agent
Assignment Notification option.
7. Encapsulating DHCP Options in the RAAN Option
The contents of options encapsulated in the RAAN option are
interpreted according to the use of those options in the node on
which the relay agent is implemented. For the purposes of address
and prefix assignment, the uses of the DHCP IA Address and IA Prefix
options are defined in this document.
Note that the contents of these options are not necessarily the same
as in the corresponding options sent to the DHCP client.
7.1. IA Address Option
The fields in an IA Address option (OPTION_IAADDR, option code 5) are
used as follows:
IPv6 address The IPv6 address assigned in this DHCP message
preferred-lifetime Not used by the relay agent; the server SHOULD
set this field to the preferred-lifetime of the
corresponding IA Address options in the message
to be forwarded to the client
valid-lifetime The lifetime of the information carried in this
IA Address option, expressed in units of
seconds; if the valid-lifetime is 0, the
information is no longer valid
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IAaddr-options Not used by the relay agent; the server SHOULD
set this field to the IAaddr-options of the
corresponding IA Address option in the message
to be forwarded to the client
7.2. IA Prefix Option
The fields in an IA Prefix option (OPTION_IAPREFIX, option code 28)
are used as follows:
preferred-lifetime Not used by the relay agent; the server SHOULD
set this field to the preferred-lifetime of the
corresponding IA Prefix options in the message
to be forwarded to the client
valid-lifetime The lifetime of the information carried in this
IA Prefix option, expressed in units of seconds;
if the valid-lifetime is 0, the information is
no longer valid
prefix-length Length for this prefix in bits
IPv6-prefix The IPv6 prefix assigned in this DHCP message
IAprefix-options Not used by the relay agent; the server SHOULD
set this field to the IAprefix-options of the
corresponding IA Prefix option in the message to
be forwarded to the client
8. Requesting Assignment Information from the DHCP Server
If a relay agent requires the DHCP server to provide information
about assigned addresses and prefixes, it MUST include an Option
Request option, requesting the Assignment Notification option, as
described in section 22.7 of RFC 3315.
9. IANA Considerations
IANA is requested to assign an option code from the "DHCPv6 and
DHCPv6 options" registry http://www.iana.org/assignments/
dhcpv6-parameters to OPTION_AGENT_NOTIFY.
10. Security Considerations
Security issues related to DHCP are described in RFC 3315 and RFC
3633.
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The RAAN option may be used to mount a denial of service attack by
causing a node to incorrectly populate an ACL or incorrectly
configure routing information for a delegated prefix. This option
may also be used to insert invalid prefixes into the routing
infrastructure or add invalid IP addresses to ACLs in nodes.
Communication between a server and a relay agent, and communication
between relay agents, can be secured through the use of IPSec, as
described in [I-D.ietf-dhc-relay-server-security].
11. Changes Log
If this section is included in the document when it is submitted for
publication, the RFC Editor is requested to remove it.
Changes in rev -01:
o Added section describing use of "Server Reply Sequence Number"
option to allow resequencing of out-of-order messages.
Changes in rev -02:
o Made editorial change in section 1: s/the appropriate routing
protocols/the routing infrastructure/
o Updated first paragraph in Section 3 to allow multiple IA
Address options and/or IA Prefix options
o Renamed section 3 to "Options Semantics and Usage"
o Added paragraph to section "Option Semantics and Usage"
requiring that the DHCP server must include all addresses/
prefixes for the client (on that link) in the RAAN option
o Added list of use cases to section "Option Semantics and Usage"
o Added section "Relay Agent Behavior"
o Added section "Server Behavior"; moved second paragraph of
section "Option Semantics and Usage" to "Server Behavior"
o Updated reference to draft-ietf-dhc-dhcpv6-srsn-option-00
o Clarified descriptions of various option fields in section
"Encapsulating DHCP options in the RAAN Option"
Changes in rev -03: refreshed after expiration.
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Changes in rev -04: all references to the "Server Reply Sequence
Number" option were removed from the draft.
Changes in rev -05:
o Converted the -04 text version to xml.
o Updated introduction to add motivation for option because of
[I-D.ietf-dhc-sedhcpv6], and also Reply to Release "snooping"
issues.
o Updated security considerations to reference IPsec document
([I-D.ietf-dhc-relay-server-security]).
12. References
12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
C., and M. Carney, "Dynamic Host Configuration Protocol
for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
2003, <http://www.rfc-editor.org/info/rfc3315>.
[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633,
DOI 10.17487/RFC3633, December 2003,
<http://www.rfc-editor.org/info/rfc3633>.
12.2. Informative References
[I-D.ietf-dhc-relay-server-security]
Volz, B. and Y. Pal, "Security of Messages Exchanged
Between Servers and Relay Agents", draft-ietf-dhc-relay-
server-security-04 (work in progress), March 2017.
[I-D.ietf-dhc-sedhcpv6]
Li, L., Jiang, S., Cui, Y., Jinmei, T., Lemon, T., and D.
Zhang, "Secure DHCPv6", draft-ietf-dhc-sedhcpv6-21 (work
in progress), February 2017.
[RFC5007] Brzozowski, J., Kinnear, K., Volz, B., and S. Zeng,
"DHCPv6 Leasequery", RFC 5007, DOI 10.17487/RFC5007,
September 2007, <http://www.rfc-editor.org/info/rfc5007>.
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Authors' Addresses
Ralph Droms
Email: rdroms.ietf@gmail.com
Bernie Volz
Cisco Systems, Inc.
1414 Massachusetts Ave
Boxborough, MA 01719
USA
Email: volz@cisco.com
Ole Troan
Cisco Systems, Inc.
Oslo
Norway
Email: otroan@cisco.com
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