Internet DRAFT - draft-ietf-savi-mix
draft-ietf-savi-mix
SAVI J. Bi
Internet-Draft Tsinghua University
Intended status: Standards Track G. Yao
Expires: July 5, 2017 Tsinghua University/Baidu
J. Halpern
Ericsson
E. Levy-Abegnoli, Ed.
Cisco
January 1, 2017
SAVI for Mixed Address Assignment Methods Scenario
draft-ietf-savi-mix-15
Abstract
In networks that use multiple techniques for address assignment, the
spoofing of addresses assigned by each technique can be prevented
using the appropriate Source Address Validation Improvement (SAVI)
methods. This document reviews how multiple SAVI methods can coexist
in a single SAVI device and collisions are resolved when the same
binding entry is discovered by two or more methods.
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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This Internet-Draft will expire on July 5, 2017.
Copyright Notice
Copyright (c) 2017 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
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publication of this document. Please review these documents
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Problem Scope . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Architecture . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Recommendations for assignment separation . . . . . . . . . . 5
6. Resolving binding collisions . . . . . . . . . . . . . . . . 6
6.1. Same Address on Different Binding Anchors . . . . . . . . 6
6.1.1. Basic preference . . . . . . . . . . . . . . . . . . 6
6.1.2. Exceptions . . . . . . . . . . . . . . . . . . . . . 7
6.1.3. Multiple SAVI Device Scenario . . . . . . . . . . . . 8
6.2. Same Address on the Same Binding Anchor . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9
8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 9
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
10. Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . 9
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
11.1. Normative References . . . . . . . . . . . . . . . . . . 9
11.2. Informative References . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
There are currently several Source Address Validation Improvement
(SAVI) documents ([RFC6620], [RFC7513] and [RFC7219]) that describe
the different methods by which a switch can discover and record
bindings between a node's IP address and a binding anchor and use
that binding to perform source address validation. Each of these
documents specifies how to learn on-link addresses, based on the
technique used for their assignment, respectively: StateLess
Autoconfiguration (SLAAC), Dynamic Host Control Protocol (DHCP) and
Secure Neighbor Discovery (SeND). Each of these documents describes
separately how one particular SAVI method deals with address
collisions (same address, different binding anchor).
While multiple IP assignment techniques can be used in the same
layer-2 domain, this means that a single SAVI device might have to
deal with a combination or mix of SAVI methods. The purpose of this
document is to provide recommendations to avoid collisions and to
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review collisions handling when two or more such methods come up with
competing bindings.
2. Requirements Language
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 RFC 2119 [RFC2119].
3. Problem Scope
Three different IP address assignment techniques have been analyzed
for SAVI:
1. StateLess Address AutoConfiguration (SLAAC) - analyzed in SAVI-
FCFS[RFC6620]
2. Dynamic Host Control Protocol address assignment (DHCP) -
analyzed in SAVI-DHCP[RFC7513]
3. Secure Neighbor Discovery (SeND) address assignment, analyzed in
SAVI-SEND[RFC7219]
In addition, there is a fourth technique for managing (i.e.,
creation, management, deletion) a binding on the switch, referred to
as "manual". It is based on manual binding configuration. Because
how to manage manual bindings is determined by operators, there is
not a new SAVI method for manual addresses.
All combinations of address assignment techniques can coexist within
a layer-2 domain. A SAVI device MUST implement the corresponding
binding setup methods (referred to as a "SAVI method") for each such
technique that is in use if it is to provide Source Address
Validation.
SAVI methods are normally viewed as independent from each other, each
one handling its own entries. If multiple methods are used in the
same device without coordination, each method will attempt to reject
packets sourced with any addresses that method did not discover. To
prevent addresses discovered by one SAVI method from being filtered
out by another method, the SAVI binding table SHOULD be shared by all
the SAVI methods in use in the device. This in turn could create
some conflict when the same entry is discovered by two different
methods. The purpose of this document is of two folds: provide
recommendations and methods to avoid conflicts, and to resolve
conflicts when they happen. Collisions happening within a given
method are outside the scope of this document.
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4. Architecture
A SAVI device may implement and use multiple SAVI methods. This
mechanism, called SAVI-MIX, is proposed as a arbiter of the binding
generation algorithms from these multiple methods, generating the
final binding entries as illustrated in Figure 1. Once a SAVI method
generates a candidate binding, it will request SAVI-MIX to set up a
corresponding entry in the binding table. Then SAVI-MIX will check
if there is any conflict in the binding table. A new binding will be
generated if there is no conflict. If there is a conflict, SAVI-MIX
will determine whether to replace the existing binding or reject the
candidate binding based on the policies specified in Section 6.
As a result of this, the packet filtering in the SAVI device will not
be performed by each SAVI method separately. Instead, the table
resulting from applying SAVI-MIX will be used to perform filtering.
Thus the filtering is based on the combined results of the differents
SAVI mechanisms. It is beyond the scope of this document to describe
the details of the filtering mechanism and its use of the combined
SAVI binding table.
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+--------------------------------------------------------+
| |
| SAVI Device |
| |
| |
| +------+ +------+ +------+ |
| | SAVI | | SAVI | | SAVI | |
| | | | | | | |
| | FCFS | | DHCP | | SEND | |
| +------+ +------+ +------+ |
| | | | Binding |
| | | | setup |
| v v v requests |
| +------------------------------+ |
| | | |
| | SAVI-MIX | |
| | | |
| +------------------------------+ |
| | |
| v Final Binding |
| +--------------+ |
| | Binding | |
| | | |
| | Table | |
| +--------------+ |
| |
+--------------------------------------------------------+
Figure 1: SAVI-Mix Architecture
Each entry in the binding table will contain the following fields:
1. IP source address
2. Binding anchor[RFC7039]
3. Lifetime
4. Creation time
5. Binding methods: the SAVI method used for this entry.
5. Recommendations for assignment separation
If each address assignment technique uses a separate portion of the
IP address space, collisions won't happen. Using non overlapping
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address space across address assignment techniques, and thus across
SAVI methods is therefore recommended. To that end, one should:
1. DHCP and SLAAC: use non-overlapping prefix for DHCP and SLAAC.
Set the A bit in Prefix information option of Router
Advertisement for SLAAC prefix, and set the M bit in Router
Advertisement for DHCP prefix. For detail explanations on these
bits, refer to [RFC4861][RFC4862].
2. SeND and non-SeND: avoid mixed environment (where SeND and non-
SeND nodes are deployed) or separate the prefixes announced to
SeND and non-SenD nodes. One way to separate the prefixes is to
have the router(s) announcing different (non-overlapping)
prefixes to SeND and to non-SeND nodes, using unicast Router
Advertisements[RFC6085], in response to SeND/non-SeND Router
Solicit.
6. Resolving binding collisions
In situations where collisions can not be avoided by assignment
separation, two cases should be considered:
1. The same address is bound on two different binding anchors by
different SAVI methods.
2. The same address is bound on the same binding anchor by different
SAVI methods.
6.1. Same Address on Different Binding Anchors
This would typically occur in case assignment address spaces could
not be separated. For instance, an address is assigned by SLAAC on
node X, installed in the binding table using SAVI-FCFS, anchored to
"anchor-X". Later, the same address is assigned by DHCP to node Y,
and SAVI-DHCP will generate a candidate binding entry, anchored to
"anchor-Y".
6.1.1. Basic preference
If there is any manually configured binding, the SAVI device SHOULD
choose the manual configured binding acnhor.
For an address not covered by any manual bindings, the SAVI device
must decide to which binding anchor the address should be bound
(anchor-X or anchor-Y in this example). Current standard documents
of address assignment methods have implied the prioritization
relationship based on order in time, i.e., first-come first-served.
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o SLAAC: s5.4.5 of [RFC4862]
o DHCPv4: s3.1-p5 of [RFC2131]
o DHCPv6: s18.1.8 of [RFC3315]
o SeND: s8 of [RFC3971]
In the absence of any configuration or protocol hint (see
Section 6.1.2) the SAVI device SHOULD choose the first-come binding
anchor, whether it was learnt from SLAAC, SeND or DHCP.
6.1.2. Exceptions
There are two identified exceptions to the general prioritization
model, one of them being CGA addresses[RFC3971], another one
controlled by the configuration of the switch.
6.1.2.1. CGA preference
When CGA addresses are used, and a collision is detected, preference
should be given to the anchor that carries the CGA credentials once
they are verified, in particular the CGA parameters and the RSA
options. Note that if an attacker was trying to replay CGA
credentials, he would then compete on the base of "First-Come, First-
Served" (FCFS) principle.
6.1.2.2. configuration preference
For configuration driven exceptions, the SAVI device may allow the
configuration of a triplet ("prefix", "anchor", "method") or
("address", "anchor", "method"). The "prefix" or "address"
represents the address or address prefix to which this preference
entry applies. The "anchor" is the value of a known binding anchor
that this device expects to see using this address or addresses from
this prefix. The "method" is the SAVI method that this device
expects to use in validating address binding entries from the address
or prefix. At least one of "anchor" and "method" MUST be specified.
Later, if a DAD message [RFC4861] is received with the following
conditions verified:
1. The target in the DAD message does not exist in the binding table
2. The target is within the configured "prefix" (or equal to
"address")
3. The anchor bound to target is different from the configured
anchor, when specified
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4. The configured method, if any, is different from SAVI-FCFS
The switch SHOULD defend the address by responding to the DAD
message, with a NA message, on behalf of the target node. It SHOULD
NOT install the entry into the binding table. The DAD message SHOULD
be discarded and not forwarded. Forwarding it may cause other SAVI
devices to send additional defense NAs. SeND nodes in the network
MUST disable the option to ignore unsecured advertisements (see s8 of
[RFC3971]). If the option is enabled, the case is outside the scope
of this document. It is suggested to limit the rate of defense NAs
to reduce security threats to the switch. Or else, a malicious host
could consume the resource of the switch heavily with flooding DAD
messages.
This will simply prevent the node from assigning the address, and
will de-facto prioritize the configured anchor. It is especially
useful to protect well known bindings such as a static address of a
server over anybody, even when the server is down. It is also a way
to give priority to a binding learnt from SAVI-DHCP over a binding
for the same address, learnt from SAVI-FCFS.
6.1.3. Multiple SAVI Device Scenario
A single SAVI device doesn't have the information of all bound
addresses on the perimeter. Therefore it is not enough to lookup
local bindings to identify a collision. However, assuming DAD is
performed throughout the security perimeter for all addresses
regardless of the assignment method, then DAD response will inform
all SAVI devices about any collision. In that case, "First-Come,
First- Served" will apply the same way as in a single switch
scenario. If the admin configured on one the switches a prefix (or a
single static binding) to defend, the DAD response generated by this
switch will also prevent the binding to be installed on other
switches of the perimeter. The SAVI MIX preferences of all the SAVI
devices in the same layer-2 domain should be consistent.
Inconsistent configurations may cause network breaks.
6.2. Same Address on the Same Binding Anchor
A binding may be set up on the same binding anchor by multiple
methods, typically SAVI-FCFS and SAVI-DHCP. If the binding lifetimes
obtained from the two methods are different, priority should be given
to 1) Manual configuration 2) SAVI-DHCP 3) SAVI-FCFS as the least
authoritative. The binding will be removed when the prioritized
lifetime expires, even if a less authoritative method had a longer
lifetime.
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7. Security Considerations
Combining SAVI methods (as in SAVI MIX) does not improve on or
eliminate the security considerations associated with each individual
SAVI method. Therefore, security considerations for each enabled
SAVI method should be addressed as described in that method's
associated RFC. Moreover, combining methods (as in SAVI MIX) has two
additional implications for security. First, it may increase
susceptibility to DoS attacks, because the SAVI binding setup rate
will be the sum of the rates of all enabled SAVI methods.
Implementers must take these added resource requirements into
account. Second, because SAVI MIX supports multiple binding
mechanisms, it potentially reduces the security level to that of the
weakest supported method, unless additional steps (e.g. requiring
non-overlapping address spaces for different methods) are taken.
8. Privacy Considerations
When implementing multiple SAVI methods, privacy considerations of
all methods apply cumulatively.
9. IANA Considerations
This memo asks the IANA for no new parameters.
10. Acknowledgment
Thanks to Christian Vogt, Eric Nordmark, Marcelo Bagnulo Braun, David
Lamparter, Scott G. Kelly and Jari Arkko for their valuable
contributions.
11. References
11.1. 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>.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, DOI 10.17487/RFC2131, March 1997,
<http://www.rfc-editor.org/info/rfc2131>.
[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>.
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[RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
"SEcure Neighbor Discovery (SEND)", RFC 3971,
DOI 10.17487/RFC3971, March 2005,
<http://www.rfc-editor.org/info/rfc3971>.
[RFC6085] Gundavelli, S., Townsley, M., Troan, O., and W. Dec,
"Address Mapping of IPv6 Multicast Packets on Ethernet",
RFC 6085, DOI 10.17487/RFC6085, January 2011,
<http://www.rfc-editor.org/info/rfc6085>.
[RFC6620] Nordmark, E., Bagnulo, M., and E. Levy-Abegnoli, "FCFS
SAVI: First-Come, First-Served Source Address Validation
Improvement for Locally Assigned IPv6 Addresses",
RFC 6620, DOI 10.17487/RFC6620, May 2012,
<http://www.rfc-editor.org/info/rfc6620>.
[RFC7219] Bagnulo, M. and A. Garcia-Martinez, "SEcure Neighbor
Discovery (SEND) Source Address Validation Improvement
(SAVI)", RFC 7219, DOI 10.17487/RFC7219, May 2014,
<http://www.rfc-editor.org/info/rfc7219>.
[RFC7513] Bi, J., Wu, J., Yao, G., and F. Baker, "Source Address
Validation Improvement (SAVI) Solution for DHCP",
RFC 7513, DOI 10.17487/RFC7513, May 2015,
<http://www.rfc-editor.org/info/rfc7513>.
11.2. Informative References
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007,
<http://www.rfc-editor.org/info/rfc4861>.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862,
DOI 10.17487/RFC4862, September 2007,
<http://www.rfc-editor.org/info/rfc4862>.
[RFC7039] Wu, J., Bi, J., Bagnulo, M., Baker, F., and C. Vogt, Ed.,
"Source Address Validation Improvement (SAVI) Framework",
RFC 7039, DOI 10.17487/RFC7039, October 2013,
<http://www.rfc-editor.org/info/rfc7039>.
Authors' Addresses
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Jun Bi
Tsinghua University
Network Research Center, Tsinghua University
Beijing 100084
China
EMail: junbi@tsinghua.edu.cn
Guang Yao
Tsinghua University/Baidu
Baidu Science and Technology Park, Building 1
Beijing 100193
China
EMail: yaoguang.china@gmail.com
Joel M. Halpern
Ericsson
EMail: joel.halpern@ericsson.com
Eric Levy-Abegnoli (editor)
Cisco Systems
Village d'Entreprises Green Side - 400, Avenue Roumanille
Biot-Sophia Antipolis 06410
France
EMail: elevyabe@cisco.com
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