Network Working Group S. Krishnan
Internet-Draft Ericsson
Intended status: Standards Track November 11, 2007
Expires: May 14, 2008
Carrying DHCP options over Neighbor Discovery Messages
draft-krishnan-intarea-ra-dhcp-00
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Copyright (C) The IETF Trust (2007).
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Abstract
DHCP options are used to convey network and host configuration
information to the hosts attached to a network. Some networks may
wish to configure their routers to advertise these same pieces of
information, and might use IPv6 Router Advertisements do distribute
these parameters. This document defines a generic neighbor discovery
option for carrying DHCP options. This option is carried over IPv6
Router Advertisements.
Table of Contents
1. Requirements notation . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Justification . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6. DHCP Container(DHCPC) Option . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
8. Security Considerations . . . . . . . . . . . . . . . . . . . 11
9. Acknowledgmentes . . . . . . . . . . . . . . . . . . . . . . . 12
10. Normative References . . . . . . . . . . . . . . . . . . . . . 13
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 14
Intellectual Property and Copyright Statements . . . . . . . . . . 15
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1. Requirements notation
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].
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2. Introduction
Router Advertisements (RAs) as defined in [RFC2461] are used to
deliver configuration information that is common to several nodes in
the same network. The router advertisements are usually multicasted
to all nodes in a given network in order to be scalable. The
configuration information is contained in Neigbor Discovery (ND)
options. DHCP [RFC3315] is used for delivering addressing
information and other related configuration information to single
clients when they request it. Since there are two mechanisms for
delivering common configuration information to a given node,
configuration parameters need to be defined under two varying option
formats. This leads to duplication of work needed to standardize
these options and additional implementation complexity on hosts in
order to process these option variants. In order to prevent this
duplication, this document proposes a neighbor discovery option that
can be used to directly carry any relevant DHCP option.
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3. Justification
Recently there has been interest in doing more of DHCP work using
Neighbor Discovery (Router Advertisement) messages. This is mainly
to accomodate environments where DHCP is not available and the only
way of convey configuration information is through RAs. Since DHCP
options cannot be carried in RAs this leads to duplicate
standardization efforts to develop ND options for options already
developed for DHCP. For example consider [RFC5006] that redefines a
DNS server address option for RAs that has been defined long ago for
DHCP. Not only does this waste valuable time in redundant
standardization effort, it also complicates client implementations
that need to be able to parse and understand tho incompatible option
formats. It also takes away valuable code points away from the
neighbor discovery message types (8 bit value). Thus it make sense
to define a DHCP carrier option for neighbor discovery messages so
that we can reuse DHCP options as necessary without coming up with
new neighbor discovery options.
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4. Applicability
It is possible to carry any DHCP option using the DHCPC option.
However, this does not always make sense since there are DHCP options
that are client specific and hence are not uniform across all the
hosts in the network. The DHCPC option SHOULD NOT be used to carry
DHCP options that are client specific. This option can be carried in
any neighbor discovery messages.
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5. Operation
After a node receives a neighbor discovery that contains a DHCPC
option it needs to verify if the DHCPC option length is at least 1 (8
octets). If it is not, the node MUST NOT process the DHCPC option
any further and SHOULD log an error message locally. Otherwise it
needs to process the embedded DHCP options one at a time as it would
if it had received them through a DHCP message. It is entirely
possible that the code for processing these options is shared between
the neighbor discovery based delivery and DHCP based delivery of
these options.
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6. DHCP Container(DHCPC) Option
The DHCPC option in Neighbor Discovery messages is used to carry
complete DHCP options. There can be more than DHCP option contained
in a DHCPC option. The number of contained DHCP options is not
explicitly mentioned in the DHCPC. The receiving node MUST process
all the contained options
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPT1_code | OPT1_len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPT1_data |
| (OPT1_len octets) |
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTn_code | OPTn_len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTn_data |
| (OPTn_len octets) |
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
8-bit identifier of the type of option. The option identifier
for the DHCPC option will be allocated by the IANA.
Option Length
8-bit unsigned integer. The length of the option (including
the type and length fields) in units of 8 octets. The value
0 is considered invalid.
OPT1_code
16-bit unsigned integer. The DHCPv6 option code of the first
DHCP option that is carried in the DHCPC option.
OPT1_len
16-bit unsigned integer. The length of the option data of the
first included DHCP option (excluding the OPT1_code and the
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OPT1_len fields)
OPT1_Data
The data field of the first included neighbor discovery
option. The contents of this field are determined by the type
of the option.
OPT1_code
16-bit unsigned integer. The DHCPv6 option code of the first
DHCP option that is carried in the DHCPC option.
OPT1_len
16-bit unsigned integer. The length of the option data of the
first included DHCP option (excluding the OPT1_code and the
OPT1_len fields)
OPT1_Data
The data field of the first included neighbor discovery
option. The contents of this field are determined by the type
of the option.
Figure 1: DHCPC layout
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7. IANA Considerations
This document defines a new IPv6 neighbor discovery option for
carrying DHCP options. IANA is requested to assign the a new
neighbor discovery option type in the registry maintained at
http://www.iana.org/assignments/icmpv6-parameters
<TBA> DHCP Carrier Option [RFC-krishnan-intarea-ra-dhcp-00.txt]
The option type 26 is recommended as it is the first unused option
type at the time of writing this draft.
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8. Security Considerations
The mechanism described in this document provides a method by which
one or more DHCP options can be carried using IPv6 Router
Advertisement messages. The neighbor discovery messages containing
the DHCPC option may be intercepted, modified or replayed in order to
communicate false configuration data to the client hosts. In order
to prevent these kinds of attacks, it is recommended that SEND
[RFC3971] be used.
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9. Acknowledgmentes
The author would like to thank Jari Arkko for his detailed review and
comments on the earlier versions of this document.
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10. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2461] Narten, T., Nordmark, E., and W. Simpson, "Neighbor
Discovery for IP Version 6 (IPv6)", RFC 2461,
December 1998.
[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.
[RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
Neighbor Discovery (SEND)", RFC 3971, March 2005.
[RFC5006] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli,
"IPv6 Router Advertisement Option for DNS Configuration",
RFC 5006, September 2007.
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Author's Address
Suresh Krishnan
Ericsson
8400 Decarie Blvd.
Town of Mount Royal, QC
Canada
Phone: +1 514 345 7900 x42871
Email: suresh.krishnan@ericsson.com
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