Internet DRAFT - draft-ietf-dhc-pd-exclude
draft-ietf-dhc-pd-exclude
Dynamic Host Configuration (DHC) J. Korhonen, Ed.
Internet-Draft Nokia Siemens Networks
Updates: 3633 (if approved) T. Savolainen
Intended status: Standards Track Nokia
Expires: June 22, 2012 S. Krishnan
Ericsson
O. Troan
Cisco Systems, Inc
December 20, 2011
Prefix Exclude Option for DHCPv6-based Prefix Delegation
draft-ietf-dhc-pd-exclude-04.txt
Abstract
This specification defines an optional mechanism to allow exclusion
of one specific prefix from a delegated prefix set when using DHCPv6-
based prefix delegation. The new mechanism updates 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
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 22, 2012.
Copyright Notice
Copyright (c) 2011 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
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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 . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements and Terminology . . . . . . . . . . . . . . . . . 3
3. Problem Background . . . . . . . . . . . . . . . . . . . . . . 3
4. Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Prefix Delegation with Excluded Prefixes . . . . . . . . . 4
4.2. Prefix Exclude Option . . . . . . . . . . . . . . . . . . . 4
5. Delegating Router Solicitation . . . . . . . . . . . . . . . . 6
5.1. Requesting Router . . . . . . . . . . . . . . . . . . . . . 6
5.2. Delegating Router . . . . . . . . . . . . . . . . . . . . . 7
6. Requesting Router Initiated Prefix Delegation . . . . . . . . . 7
6.1. Requesting Router . . . . . . . . . . . . . . . . . . . . . 7
6.2. Delegating Router . . . . . . . . . . . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
10.1. Normative References . . . . . . . . . . . . . . . . . . . 9
10.2. Informative References . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
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1. Introduction
This specification defines an optional mechanism and the related
DHCPv6 option to allow exclusion of one specific prefix from a
delegated prefix set when using DHCPv6-based prefix delegation.
The prefix exclusion mechanism is targeted to deployments where
DHCPv6-based prefix delegation is used but a single aggregated route/
prefix has to represent one customer, instead of using one prefix for
the link between the delegating router and the requesting router and
another prefix for the customer network. The mechanism defined in
this specification allows a delegating router to use a prefix out of
the delegated prefix set on the link through which it exchanges
DHCPv6 messages with the requesting router, and is intended for use
in networks where each requesting router is on its own layer 2
domain.
2. Requirements 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].
3. Problem Background
DHCPv6 Prefix Delegation (DHCPv6-PD) [RFC3633] has an explicit
limitation described in Section 12.1 of [RFC3633] that a prefix
delegated to a requesting router cannot be used by the delegating
router. This restriction implies that the delegating router will
have two (non aggregatable) routes towards a customer, one for the
link between the requesting router and the delegating router, and one
for the customer site behind the requesting router.
There are architectures and link models, where a host (e.g. a mobile
router, also acting as a requesting router) always has a single (/64)
prefix configured on its uplink interface and the delegating router
is also requesting router's first hop router. Furthermore, it may be
required that the prefix configured on the uplink interface has to be
aggregatable with the delegated prefixes. This introduces a problem
in how to use DHCPv6-PD together with stateless [RFC4862] or stateful
[RFC3315] address autoconfiguration on a link, where the /64
advertised on the link is also part of the prefix delegated (e.g /56)
to the requesting router.
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4. Solution
4.1. Prefix Delegation with Excluded Prefixes
This specification defines a new DHCPv6 option, OPTION_PD_EXCLUDE
(TBD1), that is used to exclude exactly one prefix from a delegated
prefix. The OPTION_PD_EXCLUDE is included in the OPTION_IAPREFIX
IAprefix-options field. There can be at most one OPTION_PD_EXCLUDE
option in one OPTION_IAPREFIX option. The OPTION_PD_EXCLUDE option
allows prefix delegation where a requesting router is delegated a
prefix (e.g. /56) and the delegating router uses one prefix (e.g.
/64) on the link through which it exchanges DHCPv6 messages with the
requesting router with a prefix out of the same delegated prefix set.
A requesting router includes an OPTION_ORO option with the
OPTION_PD_EXCLUDE option code in a Solicit, Request, Renew, or Rebind
message to inform the delegating router about the support for the
prefix delegation functionality defined in this specification. A
delegating router may include the OPTION_PD_EXCLUDE option code in an
OPTION_ORO option in a Reconfigure message for indicating that the
requesting router should request OPTION_PD_EXCLUDE from the
delegating router.
The delegating router includes the prefix in the OPTION_PD_EXCLUDE
option that is excluded from the delegated prefix set. The
requesting router MUST NOT assign the excluded prefix to any of its
downstream interfaces.
4.2. Prefix Exclude Option
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_PD_EXCLUDE | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| prefix-len | IPv6 subnet ID (1 to 16 octets) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Prefix Exclude Option
o option-code: OPTION_PD_EXCLUDE (TBD1).
o option-len: 1 + length of IPv6 subnet ID in octets. A valid
option-len is between 2 and 17.
o prefix-len: The length of the excluded prefix in bits. The
prefix-len MUST be between 'OPTION_IAPREFIX prefix-length'+1 and
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128.
o IPv6 subnet ID: A variable length IPv6 subnet ID up to 128 bits.
The IPv6 subnet ID contains prefix-len minus 'OPTION_IAPREFIX prefix-
length' bits extracted from the excluded prefix starting from the bit
position 'OPTION_IAPREFIX prefix-length'. The extracted subnet ID
MUST be left shifted to start from a full octet boundary, i.e. left
shift of 'OPTION_IAPREFIX prefix-length' mod 8 bits. The subnet ID
MUST be zero padded to the next full octet boundary.
The encoding of the IPv6 subnet ID can be expressed in a C-like
pseudo code as shown below:
uint128_t p1; // the delegated IPv6 prefix
uint128_t p2; // the excluded IPv6 prefix
uint16_t a; // the OPTION_IAPREFIX prefix-length
uint8_t b; // the excluded IPv6 prefix length
uint8_t s;
// sanity checks
s = 128-a; // size of non-prefix bits
assert(b>a); // b must be at least a+1
assert(p1>>s == p2>>s); // p1 and p2 must share a common
// prefix of 'a' bits
// calculate the option content
uint16_t c = b-a-1; // the IPv6_subnet_ID_length-1 in bits
uint16_t d = (c/8)+1; // the IPv6_subnet_ID_length in octets
uint128_t p = p2<<a; // p is the IPv6 subnet ID that has the
// common p1 prefix left shifted out to
// a full octet boundary (trailing bits
// are zeroed)
// populate the option
uint8_t* id = &OPTION_PD_EXCLUDE.IPv6_subnet_ID;
OPTION_PD_EXCLUDE.option_len = d+1;
OPTION_PD_EXCLUDE.prefix_len = b;
while (d-- > 0) {
*id++ = p>>120;
p <<= 8;
}
The OPTION_PD_EXCLUDE option MUST only be included in the
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OPTION_IAPREFIX IAprefix-options [RFC3633] field.
Any prefix excluded from the delegated prefix MUST be contained in
OPTION_PD_EXCLUDE options within the corresponding OPTION_IAPREFIX.
The prefix included in the OPTION_PD_EXCLUDE option share the same
preferred-lifetime and valid-lifetime as the delegated prefix in the
encapsulating OPTION_IAPREFIX option.
The prefix in the OPTION_PD_EXCLUDE option MUST be part of the
delegated prefix in the OPTION_IAPREFIX. For example, the requesting
router has earlier been assigned a 2001:db8:dead:beef::/64 prefix by
the delegating router, and the delegated prefix in the
OPTION_IAPREFIX is 2001:db8:dead:bee0::/59. In this case, 2001:db8:
dead:beef::/64 is a valid prefix to be used in the OPTION_PD_EXCLUDE
option. The OPTION_PD_EXCLUDE option would be encoded as follows:
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_PD_EXCLUDE | 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 64 |0|1|1|1|1|0|0|0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
^ ^
| |
| +- 3 zero padded bits follow
|
+- using C syntax: 0xef << (59 % 8)
Note: 59 mod 8 = 3
5. Delegating Router Solicitation
The requesting router locates and selects a delegating router in the
same way as described in Section 11 [RFC3633]. This specification
only describes the additional steps required by the use of
OPTION_PD_EXCLUDE option.
5.1. Requesting Router
If the requesting router implements the solution described in
Section 4.1 then the requesting router SHOULD include the
OPTION_PD_EXCLUDE option code in the OPTION_ORO option in Solicit
messages.
Once receiving Advertise message, the requesting router uses the
prefix(es) received in OPTION_PD_EXCLUDE in addition to the
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advertised prefixes to choose the delegating router. Requesting
router MUST proceed to Prefix Delegation procedure described in
Section 6.1. If Advertise message did not include OPTION_PD_EXCLUDE
option, then the requesting router MUST fall back to normal [RFC3633]
Section 11.1 behavior.
5.2. Delegating Router
If the OPTION_ORO option in the Solicit message includes the
OPTION_PD_EXCLUDE option code, then the delegating router knows that
the requesting router supports the solution defined in this
specification. If the Solicit message also contains an IA_PD option,
the delegating router can delegate to the requesting router a prefix
which includes the prefix already assigned to the requesting router's
uplink interface. The delegating router includes the prefix
originally or to be assigned to the requesting router in the
OPTION_PD_EXCLUDE option within the OPTION_IAPREFIX IAprefix-option
in the Advertise message.
If the OPTION_ORO option in the Solicit message does not include the
OPTION_PD_EXCLUDE option code, then the delegating router MUST fall
back to normal [RFC3633] Section 11.2 behavior.
If the OPTION_ORO option in the Solicit message includes the
OPTION_PD_EXCLUDE option code but the delegating router does not
support the solution described in this specification, then the
delegating router acts as specified in [RFC3633]. The requesting
router MUST in this case also fall back to normal [RFC3633] behavior.
6. Requesting Router Initiated Prefix Delegation
The procedures described in the following sections are aligned with
Section 12 of [RFC3633]. In this specification we only describe the
additional steps required by the use of OPTION_PD_EXCLUDE option.
6.1. Requesting Router
The requesting router behavior regarding the use of the
OPTION_PD_EXCLUDE option is more or less identical to step described
in Section 5.1. The only difference really is different used DHCPv6
messages. The requesting router SHOULD include the OPTION_PD_EXCLUDE
option code in the OPTION_ORO option in DHCPv6 messages as described
in Section 22.7 of [RFC3315].
The requesting router uses a Release message to return the delegated
prefix(es) to a delegating router. The prefix(es) to be released
MUST be included in the IA_PDs along with the excluded prefix
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included in the OPTION_PD_EXCLUDE option. The requesting router MUST
NOT use the OPTION_PD_EXCLUDE option to introduce additional excluded
prefix in the Release message that it originally got a valid binding
for.
The requesting router must create sink routes for the delegated
prefixes minus the excluded prefixes. This may be done by creating
sink routes for delegated prefixes and more specific routes for the
excluded prefixes.
6.2. Delegating Router
The delegating router behavior regarding the use of the
OPTION_PD_EXCLUDE option is more or less identical to step described
in Section 5.2. The only difference really is DHCPv6 messages used
to carry the OPTION_PD_EXCLUDE option.
The delegating router may mark any prefix(es) in IA_PD Prefix options
in a Release message from a requesting router as 'available'
excluding the prefix included in the OPTION_PD_EXCLUDE options. If
the Release message contains 'new' excluded prefix in any
OPTION_PD_EXCLUDE option, the delegating router MUST send a Reply
message with Status Code set to NoBinding for that IA_PD option.
7. Security Considerations
Security considerations in DHCPv6 are described in Section 23 of
[RFC3315], and for DHCPv6 Prefix Delegation in Section 12 of
[RFC3633].
8. IANA Considerations
A new DHCPv6 Option Code is reserved from DHCPv6 registry for DHCP
Option Codes.
OPTION_PD_EXCLUDE is set to TBD1
9. Acknowledgements
Authors would like to thank Ralph Droms, Frank Brockners, Ted Lemon,
Julien Laganier, Fredrik Garneij, Sri Gundavelli, Mikael Abrahamsson,
Behcet Sarikaya, Jyrki Soini, Deng Hui, Stephen Jacob, Hemant Singh,
Gaurav Halwasia, Lorenzo Colitti and Tomasz Mrugalski for their
valuable comments and discussions.
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10. References
10.1. 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.
10.2. Informative References
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007.
Authors' Addresses
Jouni Korhonen (editor)
Nokia Siemens Networks
Linnoitustie 6
FI-02600 Espoo
Finland
Email: jouni.nospam@gmail.com
Teemu Savolainen
Nokia
Hermiankatu 12 D
FI-33720 Tampere
Finland
Email: teemu.savolainen@nokia.com
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Suresh Krishnan
Ericsson
8400 Decarie Blvd.
Town of Mount Royal, QC
Canada
Email: suresh.krishnan@ericsson.com
Ole Troan
Cisco Systems, Inc
Oslo
Norway
Email: ot@cisco.com
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