draft-ietf-savi-mix-02.txt   draft-ietf-savi-mix-03.txt 
SAVI J. Bi SAVI J. Bi
Internet-Draft G. Yao Internet-Draft G. Yao
Intended status: Standards Track Tsinghua Univ. Intended status: Standards Track Tsinghua Univ.
Expires: October 29, 2012 J. Halpern Expires: May 10, 2013 J. Halpern
Newbridge Newbridge
E. Levy-Abegnoli, Ed. E. Levy-Abegnoli, Ed.
Cisco Cisco
April 27, 2012 November 6, 2012
SAVI for Mixed Address Assignment Methods Scenario SAVI for Mixed Address Assignment Methods Scenario
draft-ietf-savi-mix-02 draft-ietf-savi-mix-03
Abstract Abstract
This document reviews how multiple address discovery methods can This document reviews how multiple address discovery methods can
coexist in a single SAVI device and collisions are resolved when the coexist in a single SAVI device and collisions are resolved when the
same binding entry is discovered by two or more methods. same binding entry is discovered by two or more methods.
Status of this Memo Status of this Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 29, 2012. This Internet-Draft will expire on May 10, 2013.
Copyright Notice Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
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modifications of such material outside the IETF Standards Process. modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling Without obtaining an adequate license from the person(s) controlling
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than English. than English.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . . 3 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Problem Scope . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Problem Scope . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Recommendations for preventing collisions . . . . . . . . . . . 4 4. Architecture . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Handing binding collisions . . . . . . . . . . . . . . . . . . 4 5. Security Perimeter in SAVI MIX . . . . . . . . . . . . . . . . 5
5.1. Same Address on Different Binding Anchors . . . . . . . . . 5 6. Recommendations for preventing collisions . . . . . . . . . . 6
5.1.1. Basic preference . . . . . . . . . . . . . . . . . . . 5 7. Handing binding collisions . . . . . . . . . . . . . . . . . . 7
5.1.2. Overwritten preference . . . . . . . . . . . . . . . . 5 7.1. Same Address on Different Binding Anchors . . . . . . . . 7
5.1.3. Multiple SAVI Device Scenario . . . . . . . . . . . . . 6 7.1.1. Basic preference . . . . . . . . . . . . . . . . . . . 7
5.2. Same Address on the Same Binding Anchor . . . . . . . . . . 6 7.1.2. Overwritten preference . . . . . . . . . . . . . . . . 7
6. Disscusion on Assumption Conflict . . . . . . . . . . . . . . . 6 7.1.3. Multiple SAVI Device Scenario . . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 7.2. Same Address on the Same Binding Anchor . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7 8. Security Considerations . . . . . . . . . . . . . . . . . . . 9
9. Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . 7 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 10. Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . 9
10.1. Informative References . . . . . . . . . . . . . . . . . . 8 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
10.2. Normative References . . . . . . . . . . . . . . . . . . . 8 11.1. Informative References . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8 11.2. Normative References . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction 1. Introduction
There are currently several documents [savi-fcfs], [savi-dhcp] and There are currently several documents [savi-fcfs], [savi-dhcp] and
[savi-send] that describe the different methods by which a switch can [savi-send] that describe the different methods by which a switch can
discover and record bindings between a node's layer3 address and a discover and record bindings between a node's layer3 address and a
binding anchor and use that binding to perform Source Address binding anchor and use that binding to perform Source Address
Validation. Each of these documents specifies how to learn on-link Validation. Each of these documents specifies how to learn on-link
addresses, based on the method used for their assignment, addresses, based on the method used for their assignment,
respectively: StateLess Autoconfiguration (SLAAC), Dynamic Host respectively: StateLess Autoconfiguration (SLAAC), Dynamic Host
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own entries. In the absence of reconciliation, each solution will own entries. In the absence of reconciliation, each solution will
reject packets sourced with an address it did not discovered. To reject packets sourced with an address it did not discovered. To
prevent addresses discovered by one solution to be filtered out by prevent addresses discovered by one solution to be filtered out by
another, the binding table should be shared by all the solutions. another, the binding table should be shared by all the solutions.
However this could create some conflict when the same entry is However this could create some conflict when the same entry is
discovered by two different methods: the purpose of this document is discovered by two different methods: the purpose of this document is
of two folds: provide recommendations and method to avoid conflicts, of two folds: provide recommendations and method to avoid conflicts,
and resolve conflicts if and when they happen. Collisions happening and resolve conflicts if and when they happen. Collisions happening
within a given solution are outside the scope of this document. within a given solution are outside the scope of this document.
4. Recommendations for preventing collisions 4. Architecture
A SAVI device may enable multiple SAVI methods. This mechanism,
called SAVI-MIX, is proposed as a layer between the binding
generation algorithems and the binding database which contains the
working binding entries Figure 1. SAVI methods, i.e., SAVI-FCFS,
SAVI-DHCP, SAVI-SEND, do not have exclusive binding tables. Once a
SAVI method generates a candidate binding, it will request SAVI-MIX
to set up a corresponding entry in the shared binding database, named
Binding DB. Then SAVI-MIX will check if there is any conflict in the
Binding DB. A new binding will be generated if there is no conflict.
If there is a conflict, SAVI-MIX will determine whether replace the
existing binding or reject the candidate binding based on the
policies specified in Section 7. Whether the candidate binding can
be install in the Binding DB will not be returned to the requesting
SAVI method.
Correspondingly, the packet filtering will not be performed by each
SAVI method separately. Instead, SAVI-MIX will perform filtering
based on the entries in the Binding DB.
+--------------------------------------------------------+
| |
| SAVI Device |
| |
| |
| +------+ +------+ +------+ |
| | SAVI | | SAVI | | SAVI | |
| | | | | | | |
| | FCFS | | DHCP | | SEND | |
| +------+ +------+ +------+ |
| | | | |
| | | | Candidate Binding |
| v v v |
| +------------------------------+ |
| | | |
| | SAVI-MIX | |
| | | |
| +------------------------------+ |
| | |
| v Final Binding |
| +--------------+ |
| | Binding | |
| | | |
| | Database | |
| +--------------+ |
| |
+--------------------------------------------------------+
Figure 1: SAVI-Mix Architecture
5. Security Perimeter in SAVI MIX
The perimeter of SAVI MIX is the union of the perimeter of each SAVI
method, as illustrated in Figure 2.
+-----------------+
| |
+----+ | +-----+ |
| | | | | |
| H1 | | |DHCP1| |
| | | | | |
| | | | | |
+----+ | +-----+ |
+-------|------------------------------+ | |
| | | |
| +---------+ +---------+ |
| | SAVI | | SAVI | |
| | |--------+ +--------| | |
| +---------+ | | +---------+ |
| | | |
| +-------------+ |
| | SWITCH-A | |
| | | |
| +-------------+ |
| | | |
| +---------+ | | +---------+ |
| | SAVI | | | | SAVI | |
| | |--------+ +--------| | |
| +---------+ +---------+ |
| | | |
| | +----------------------------|---------+
| | | |
| +----+ | +----+
| | | | | |
| | R1 | | | H2 |
| | | | | |
| | | | | |
| +----+ | +----+
| |
+-----------------+
Figure 2: SAVI-Mix Perimeter
6. Recommendations for preventing collisions
If each solution has a dedicated address space, collisions won't If each solution has a dedicated address space, collisions won't
happen. Using non overlapping address space across SAVI solutions is happen. Using non overlapping address space across SAVI solutions is
therefore recommended. To that end, one should: therefore recommended. To that end, one should:
1. DHCP/SLAAC: use non-overlapping prefix for DHCP and SLAAC. Set 1. DHCP/SLAAC: use non-overlapping prefix for DHCP and SLAAC. Set
the A bit in Prefix information option of Router Advertisement the A bit in Prefix information option of Router Advertisement
for SLAAC prefix. And set the M bit in Router Advertisement for for SLAAC prefix. And set the M bit in Router Advertisement for
DHCP prefix. For detail explanations on these bits, refer to DHCP prefix. For detail explanations on these bits, refer to
[rfc4861][rfc4862]. [rfc4861][rfc4862].
2. SeND/non-SeND: avoid mixed environment (where SeND and non-SeND 2. SeND/non-SeND: avoid mixed environment (where SeND and non-SeND
nodes are deployed) or separate the prefixes announced to SeND nodes are deployed) or separate the prefixes announced to SeND
and non-SenD nodes. One way to separate the prefixes is to have and non-SenD nodes. One way to separate the prefixes is to have
the router(s) announcing different (non-overlapping) prefixes to the router(s) announcing different (non-overlapping) prefixes to
SeND and to non-SeND nodes, using unicast Router Advertisements, SeND and to non-SeND nodes, using unicast Router Advertisements,
in response to SeND/non-SeND Router Solicit. in response to SeND/non-SeND Router Solicit.
5. Handing binding collisions 7. Handing binding collisions
In situations where collisions could not be avoided, two cases should In situations where collisions could not be avoided, two cases should
be considered: be considered:
1. The same address is bound on two different binding anchors by 1. The same address is bound on two different binding anchors by
different SAVI solutions. different SAVI solutions.
2. The same address is bound on the same binding anchor by different 2. The same address is bound on the same binding anchor by different
SAVI solutions. SAVI solutions.
5.1. Same Address on Different Binding Anchors 7.1. Same Address on Different Binding Anchors
This would typically occur in case assignment address spaces could This would typically occur in case assignment address spaces could
not be separated. For instance,overl an address is assigned by SLAAC not be separated. For instance,overl an address is assigned by SLAAC
on node X, installed in the binding table using SAVI-FCFS, anchored 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 to "anchor-X". Later, the same address is assigned by DHCP to node
Y, as a potential candidate in the same binding table, anchored to Y, as a potential candidate in the same binding table, anchored to
"anchor-Y". "anchor-Y".
5.1.1. Basic preference 7.1.1. Basic preference
The SAVI device must decide whom the address should be bound with The SAVI device must decide whom the address should be bound with
(anchor-X or anchor-Y in this example). Current standard documents (anchor-X or anchor-Y in this example). Current standard documents
of address assignment methods have implied the prioritization of address assignment methods have implied the prioritization
relationship (first-come). In the absence of any configuration or relationship (first-come). In the absence of any configuration or
protocol hint (see Section 5.1.2) the SAVI device should choose the protocol hint (see Section 7.1.2) the SAVI device should choose the
first-come entry, whether it was learnt from SLACC, SeND or DHCP. first-come entry, whether it was learnt from SLACC, SeND or DHCP.
5.1.2. Overwritten preference 7.1.2. Overwritten preference
There are two identified exceptions to the general prioritization There are two identified exceptions to the general prioritization
model, one of them being CGA addresses, another one controlled by the model, one of them being CGA addresses, another one controlled by the
configuration of the switch: configuration of the switch:
1. When CGA addresses are used, and a collision is detected, 1. When CGA addresses are used, and a collision is detected,
preference should be given to the anchor that carries the CGA preference should be given to the anchor that carries the CGA
credentials once they are verified, in particular the CGA credentials once they are verified, in particular the CGA
parameters and the RSA options. Note that if an attacker was parameters and the RSA options. Note that if an attacker was
trying to replay CGA credentials, he would then compete on the trying to replay CGA credentials, he would then compete on the
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from "method", the switch should defend the address by responding from "method", the switch should defend the address by responding
to the DAD message. It should not at this point install the to the DAD message. It should not at this point install the
entry into the binding table. It will simply prevent the node to entry into the binding table. It will simply prevent the node to
assign the address, and will de-facto prioritize the configured assign the address, and will de-facto prioritize the configured
anchor or configured assignment method for that address. This is anchor or configured assignment method for that address. This is
especially useful to protect well known bindings such as a static especially useful to protect well known bindings such as a static
address of a server over anybody, even when the server is down. 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- 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. DHCP over a binding for the same address, learnt from SAVI-FCFS.
5.1.3. Multiple SAVI Device Scenario 7.1.3. Multiple SAVI Device Scenario
A single SAVI device doesn't have the information of all bound A single SAVI device doesn't have the information of all bound
addresses on the perimeter. Therefore it is not enough to lookup addresses on the perimeter. Therefore it is not enough to lookup
local bindings to identify a collision. However, assuming DAD is local bindings to identify a collision. However, assuming DAD is
performed throughout the security perimeter for all addresses performed throughout the security perimeter for all addresses
regardless of the assignment method, then DAD response will inform regardless of the assignment method, then DAD response will inform
all SAVI devices about any collision. In that case, FCFS will apply all SAVI devices about any collision. In that case, FCFS will apply
the same way as in a single switch scenario. If the admin configured 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, on one the switches a prefix (or a single static binding) to defend,
the DAD response generated by this switch will also prevent the the DAD response generated by this switch will also prevent the
binding to be installed on other switches of the perimeter. binding to be installed on other switches of the perimeter.
5.2. Same Address on the Same Binding Anchor 7.2. Same Address on the Same Binding Anchor
A binding may be set up on the same binding anchor by multiple A binding may be set up on the same binding anchor by multiple
solutions. For example, if SAVI-FCFS and SAVI-DHCP are both enabled solutions. For example, if SAVI-FCFS and SAVI-DHCP are both enabled
on one SAVI device, a DHCP address be bound by both SAVI instances. on one SAVI device, a DHCP address be bound by both SAVI instances.
There is no conflict if the binding is valid in all the solutions. There is no conflict if the binding is valid in all the solutions.
However, the binding lifetimes of different solutions can be However, the binding lifetimes of different solutions can be
different. If one SAVI instance changes the state of a binding to different. If one SAVI instance changes the state of a binding to
invalid on lifetime expires, conflict will happen. invalid on lifetime expires, conflict will happen.
The solution proposed is to keep a binding as long as possible. A The solution proposed is to keep a binding as long as possible. A
binding is kept until it has been required to be removed by all the binding is kept until it has been required to be removed by all the
solutions that ever set up it. solutions that ever set up it.
6. Disscusion on Assumption Conflict 8. Security Considerations
Different assumptions are made as the basis of solutions. The
assumptions of each solution specified which entity is the origin of
the trust. Indeed, the binding between address and binding anchor is
actually the derivative of the assumptions based on the principles of
binding set up. The conflict in identifier field of address is
specified in the above sections. This section specifies the conflict
in prefix field from different assumptions.
SAVI FCFS and SAVI DHCP trust routers to get the legitimate prefixes
for local link; however, only RADV validated by SEND is trusted by
SAVI SEND. In this solution, if any SAVI solution regards a prefix
to be valid, the prefix is valid for the whole mechanism.
7. Security Considerations
As described in [savi-framework], this solution cannot strictly As described in [savi-framework], this solution cannot strictly
prevent spoofing. There are two scenarios in which spoofing can prevent spoofing. There are two scenarios in which spoofing can
still happen: still happen:
1. The binding anchor is spoofable. if the binding anchor is 1. The binding anchor is spoofable. if the binding anchor is
spoofable, e.g., plain MAC address, an attacker can use forged spoofable, e.g., plain MAC address, an attacker can use forged
binding anchor to send packet which will not be regarded as binding anchor to send packet which will not be regarded as
spoofing by SAVI device. Indeed, using binding anchor that can spoofing by SAVI device. Indeed, using binding anchor that can
be easily spoofed is dangerous. An attacker can use the binding be easily spoofed is dangerous. An attacker can use the binding
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2. The binding anchor is shared by more than one host. If the 2. The binding anchor is shared by more than one host. If the
binding anchor is shared by more than one host, they can spoof binding anchor is shared by more than one host, they can spoof
the addresses of each other. For example, a number of hosts can the addresses of each other. For example, a number of hosts can
attach to the same switch port of a SAVI device through a hub. attach to the same switch port of a SAVI device through a hub.
The SAVI device cannot distinguish packets from different hosts The SAVI device cannot distinguish packets from different hosts
and thus the spoofing between them will not be detected. This and thus the spoofing between them will not be detected. This
problem can be solved through not sharing binding anchor between problem can be solved through not sharing binding anchor between
hosts. hosts.
8. IANA Considerations 9. IANA Considerations
This memo asks the IANA for no new parameters. This memo asks the IANA for no new parameters.
Note to RFC Editor: This section will have served its purpose if it Note to RFC Editor: This section will have served its purpose if it
correctly tells IANA that no new assignments or registries are correctly tells IANA that no new assignments or registries are
required, or if those assignments or registries are created during required, or if those assignments or registries are created during
the RFC publication process. From the authors' perspective, it may the RFC publication process. From the authors' perspective, it may
therefore be removed upon publication as an RFC at the RFC Editor's therefore be removed upon publication as an RFC at the RFC Editor's
discretion. discretion.
9. Acknowledgment 10. Acknowledgment
Thanks to Christian Vogt, Eric Nordmark, Marcelo Bagnulo Braun and Thanks to Christian Vogt, Eric Nordmark, Marcelo Bagnulo Braun and
Jari Arkko for their valuable contributions. Jari Arkko for their valuable contributions.
This document was generated using the xml2rfc tool. This document was generated using the xml2rfc tool.
10. References 11. References
10.1. Informative References
11.1. Informative References
[rfc2119] Bradner, S., "Key words for use in RFCs to Indicate [rfc2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, BCP 14, Match 1997. Requirement Levels", RFC 2119, BCP 14, Match 1997.
10.2. Normative References 11.2. Normative References
[rfc4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, [rfc4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007. September 2007.
[rfc4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless [rfc4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007. Address Autoconfiguration", RFC 4862, September 2007.
[savi-dhcp] [savi-dhcp]
Bi, J., Wu, J., Yao, G., and F. Baker, "SAVI Solution for Bi, J., Wu, J., Yao, G., and F. Baker, "SAVI Solution for
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