Internet DRAFT - draft-ietf-savi-framework
draft-ietf-savi-framework
Network Working Group Jianping Wu
Internet-Draft Jun Bi
Intended status: Informational Tsinghua Univ.
Expires: July 24, 2012 Marcelo Bagnulo
UC3M
Fred Baker
Cisco
Christian Vogt, Ed.
Ericsson
December 27, 2011
Source Address Validation Improvement Framework
draft-ietf-savi-framework-06
Abstract
Source Address Validation Improvement methods were developed to
prevent nodes attached to the same IP link from spoofing each other's
IP addresses, so as to complement ingress filtering with finer-
grained, standardized IP source address validation. This document is
a framework document, which describes and motivates the design of the
SAVI methods. Particular SAVI methods are described in other
documents.
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
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This Internet-Draft will expire on April 24, 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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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Deployment Options . . . . . . . . . . . . . . . . . . . . . . 6
4. Scalability Optimizations . . . . . . . . . . . . . . . . . . 8
5. Reliability Optimizations . . . . . . . . . . . . . . . . . . 10
6. Scenario with Multiple Assignment Methods . . . . . . . . . . 10
7. Prefix Configuration . . . . . . . . . . . . . . . . . . . . . 11
8. Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . 12
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
10. Security Considerations . . . . . . . . . . . . . . . . . . . 12
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
11.1. Informative References . . . . . . . . . . . . . . . . . 13
11.2. Normative References . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
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1. Introduction
Since IP source addresses are used by hosts and network entities to
determine the origin of a packet and as a destination for return
data, spoofing of IP source addresses can enable impersonation,
concealment, and malicious traffic redirection. Unfortunately, the
Internet architecture does not prevent IP source address spoofing
[draft-ietf-savi-threat-scope]. Since the IP source address of a
packet generally takes no role in forwarding the packet, it can be
selected arbitrarily by the sending host without jeopardizing packet
delivery. Extra methods are necessary for IP source address
validation, to augment packet forwarding with an explicit check of
whether a given packet's IP source address is legitimate.
IP source address validation can happen at different granularity:
Ingress filtering [BCP38] [BCP84], a widely deployed standard for IP
source address validation, functions at the coarse granularity of
networks. It verifies that the prefix of an IP source address routes
to the network from which the packet was received. An advantage of
ingress filtering is simplicity: the decision of whether to accept
or to reject an IP source address can be made solely based on the
information available from routing protocols. However, the
simplicity comes at the cost of not being able to validate IP source
addresses at a finer granularity, due to the aggregated nature of the
information available from routing protocols. Finer-grained IP
source address validation would ensure that source address
information is accurate, reduce the ability to launch denial-of-
service attacks, and help with localizing hosts and identify
misbehaving hosts. Partial solutions [BA2007] exist for finer-
grained IP source address validation, but are proprietary and hence
often unsuitable for corporate procurement.
The Source Address Validation Improvement method was developed to
complement ingress filtering with standardized IP source address
validation at the maximally fine granularity of individual IP
addresses: It prevents hosts attached to the same link from spoofing
each other's IP addresses. To facilitate deployment in networks of
various kinds, the SAVI method was designed to be modular and
extensible. This document describes and motivates the design of the
SAVI method.
2. Model
To enable network operators to deploy fine-grained IP source address
validation without a dependency on supportive functionality on hosts,
the SAVI method was designed to be purely network-based. A SAVI
instance enforces the hosts' use of legitimate IP source addresses
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according to the following three-step model:
1. Identify which IP source addresses are legitimate for a host,
based on monitoring packets exchanged by the host.
2. Bind a legitimate IP address to a link layer property of the
host's network attachment. This property, called a "binding
anchor", must be verifiable in every packet that the host sends,
and harder to spoof than the host's IP source address itself.
3. Enforce that the IP source addresses in packets match the binding
anchors to which they were bound.
This model allows SAVI functionality (a SAVI instance) to be located
anywhere on the link to which the hosts attach, hence enabling
different locations for a SAVI instance. One way to locate a SAVI
instance is in the hosts' default router. IP source addresses are
then validated in packets traversing the default router, yet the IP
source addresses in packets exchanged locally on the link may bypass
validation. Another way to locate a SAVI instance is in a switch
between the hosts and their default router. Thus, packets may
undergo IP source address validation even if exchanged locally on the
link.
The closer a SAVI instance is located to the hosts, the more
effective the SAVI method is. This is because each of the three
steps of the SAVI model can best be accomplished in a position close
to the host:
o Identifying a host's legitimate IP source addresses is most
efficient close to the host, because the likelihood that the
host's packets bypass a SAVI instance, and hence cannot be
monitored, increases with the topological distance between the
SAVI instance and the host.
o Selecting a binding anchor for a host's IP source address is
easiest close to the host, because many link layer properties are
unique for a given host only on a link segment directly attaching
to the host.
o Enforcing a host's use of a legitimate IP source address is most
reliable when pursued close to the host, because the likelihood
that the host's packets bypass a SAVI instance, and hence do not
undergo IP source address validation, increases with the
topological distance between the SAVI instance and the host.
The preferred location of SAVI instances is therefore close to hosts,
such as in switches that directly attach to the hosts whose IP source
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addresses are being validated.
Nevertheless, it is useful for SAVI mechanisms to be able to handle
situations where hosts are not directly attached to the SAVI-capable
device. For instance, deployments with both SAVI-capable and legacy
switches could be supported. In general, a SAVI solution needs to
specify how it deals with a number of deployment scenarios and
exceptional situations, including interaction with legacy devices,
hosts moving between wireless attachment points, network partitions,
and so on.
Besides, in the case of legacy switches, the security level is lower,
as there is no full protection for the hosts connected to the legacy
server.
3. Deployment Options
The model of the SAVI method, as explained in Section 2, is
deployment-specific in two ways:
o The identification of legitimate IP source addresses is dependent
on the IP address assignment method in use on a link, since it is
through assignment that a host becomes the legitimate user of an
IP source address.
o Binding anchors are dependent on the technology used to build the
link on which they are used, as binding anchors are link layer
properties of a host's network attachment.
To facilitate the deployment of the SAVI method in networks of
various kinds, the SAVI method is designed to support different IP
address assignment methods, and to function with different binding
anchors. Naturally, both the IP address assignment methods in use on
a link and the available binding anchors have an impact on the
functioning and the strength of IP source address validation. The
following two sub-sections explain this impact, and describe how the
SAVI method accommodates this.
3.1. IP Address Assignment Methods
Since the SAVI method traces IP address assignment packets, it
necessarily needs to incorporate logic that is specific to particular
IP address assignment methods. However, developing SAVI method
variants for each IP address assignment method is alone not
sufficient, since multiple IP address assignment methods may co-exist
on a given link. The SAVI method hence comes in multiple variants,
e.g. for links with DHCP [rfc2131] [rfc3315], Stateless Address
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Autoconfiguration [rfc4862] with or without Secure Neighbor Discovery
[rfc3971], IKEv2 [rfc5996] [rfc5739] [rfc5026] and combinations
thereof.
The reason to develop SAVI method variants for each single IP address
configuration method, in addition to the variant that handles all IP
address assignment methods, is to minimize the complexity of the
common case: many link deployments today either are constrained to a
single IP address assignment methods or, equivalently from the
perspective of the SAVI method, separate IP address assignment
methods into different IP address prefixes. The SAVI method for such
links can be simpler than the SAVI method for links with multiple IP
address assignment methods per IP address prefix.
3.2. Binding Anchors
The SAVI method supports a range of binding anchors:
o The IEEE extended unique identifier, EUI-48 or EUI-64, of a host's
interface.
o The port on an Ethernet switch to which a host attaches.
o The security association between a host and the base station on
wireless links.
o The combination of a host interface's link-layer address and a
customer relationship in cable modem networks.
o An ATM virtual channel, a PPP session identifier, or an L2TP
session identifier in a DSL network.
o A tunnel that connects to a single host, such as an IP-in-IP
tunnel, a GRE tunnel, or an MPLS label-switched path.
The various binding anchors differ significantly in the security they
provide. IEEE extended unique identifiers, for example, fail to
render a secure binding anchor because they can be spoofed with
little effort. And switch ports alone may be insufficient because
they may connect to more than a single host, such as in the case of
concatenated switches.
Given this diversity in the security provided, one could define a set
of possible binding anchors, and leave it up to the administrator to
choose one or more of them. Such a selection of binding anchors
would, of course, have to be accompanied by an explanation of the
pros and cons of the different binding anchors. In addition, SAVI
devices may have a default binding anchor depending on the lower
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layers. Such a default could be to use switch ports when available,
and MAC addresses otherwise. Or to use MAC addresses, and switch
ports in addition if available.
4. Scalability Optimizations
The preference to locate a SAVI instance close to hosts implies that
multiple SAVI instances must be able to co-exist in order to support
large links. Although the model of the SAVI method is independent of
the number of SAVI instances per link, co-existence of multiple SAVI
instances without further measures can lead to higher-than-necessary
memory requirements: since a SAVI instance creates bindings for the
IP source addresses of all hosts on a link, bindings are replicated
if multiple SAVI instances co-exist on the link. High memory
requirements, in turn, increase the cost of a SAVI instance. This is
problematic in particular for SAVI instances that are located on a
switch, since it may significantly increase the cost of such a
switch.
To reduce memory requirements for SAVI instances that are located on
a switch, the SAVI method enables the suppression of binding
replication on links with multiple SAVI instances. This requires
manual disabling of IP source address validation on switch ports that
connect to other switches running a SAVI instance. Each SAVI
instance is then responsible for validating IP source addresses only
on those ports to which hosts attach either directly, or via switches
without a SAVI instance. On ports towards other switches running a
SAVI instance, IP source addresses are not validated. The switches
running SAVI instances thus form a "protection perimeter". The IP
source addresses in packets passing the protection perimeter are
validated by the ingress SAVI instance, but no further validation
takes place as long as the packets remain within, or leave the
protection perimeter.
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..............
protection perimeter --> : +--------+ :
+---+ +---+ : | SAVI | :
| A | | B | <-- hosts : | switch | :
+---+ +---+ : +--------+ :
...|......|.............................: | :
: +--------+ +--------+ +--------+ :
: | SAVI |----------| legacy | | SAVI | :
: | switch | | switch |----------| switch | :
: +--------+ +--------+ +--------+ :
: | ...............................|........:
: +--------+ : +--------+
: | SAVI | : | legacy |
: | switch | : | switch |
: +--------+ : +--------+
:............: | |
+---+ +---+
hosts --> | C | | D |
+---+ +---+
Figure 1: Protection perimeter concept
Figure 1 illustrates the concept of the protection perimeter. The
figure shows a link with six switches, of which four, denoted "SAVI
switch", run a SAVI instance. The protection perimeter created by
the four SAVI instances is shown as a dotted line in the figure. IP
source address validation is enabled on all switch ports on the
protection perimeter, and it is disabled on all other switch ports.
Four hosts, denoted A through D in the figure, attach to the
protection perimeter.
In the example of figure Figure 1, the protection perimeter
encompasses one of the legacy switches, located in the middle of the
depicted link topology. This enables a single, unpartitioned
protection perimeter. A single protection perimeter minimizes memory
requirements for the SAVI instances because every binding is kept
only once, namely, by the SAVI instance that attaches to the host
being validated. Excluding the legacy switch from the protection
perimeter would result in two smaller protection perimeters to the
left and to the right of the depicted link topology. The memory
requirements for the SAVI instances would then be higher: since IP
source address validation would be activated on the two ports
connecting to the legacy switch, the SAVI instances adjacent to the
legacy switch would replicate all bindings from the respectively
other protection perimeter. The reason why it is possible to include
the legacy switch in the protection perimeter is because the depicted
link topology guarantees that packets cannot enter the protection
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perimeter via this legacy switch. Without this guarantee, the legacy
switch would have to be excluded from the protection perimeter in
order to ensure that packets entering the protection perimeter
undergo IP source address validation.
5. Reliability Optimizations
The explicit storage of legitimate IP addresses in the form of
bindings implies that failure to create a binding, or the premature
removal of bindings, can lead to loss of legitimate packets. There
are three situations in which this can happen:
o Legitimate IP address configuration packets, which should trigger
the creation of a binding in a SAVI instance, are lost before
reaching the SAVI instance.
o A SAVI instance loses a binding, for example, due to a restart.
o The link topology changes, resulting in hosts to communicate
through SAVI instances that do not have a binding for those hosts'
IP addresses.
To limit the disruption that missing bindings for legitimate IP
addresses can have, the SAVI method includes a mechanism for reactive
binding creation based on regular packets. This mechanism
supplements the proactive binding creation based on IP address
configuration packets. Reactive binding creation occurs when a SAVI
instances recognizes excessive drops of regular packets originating
from the same IP address. The SAVI instance then verifies whether
said IP address is unique on the link. How the verification is
carried out depends on the IP address configuration method that the
SAVI instance supports: the SAVI method variant for Stateless
Address Autoconfiguration and for Secure Neighbor Discovery verifies
an IP address through the Duplicate Address Detection procedure. The
SAVI method variant for DHCP verifies an IP address through a DHCP
Lease Query message exchange with the DHCP server. If verification
indicates that the IP address is unique on the link, the SAVI
instance creates a binding for the IP address. Otherwise, no binding
is created, and packets sent from the IP address continue to be
dropped. These reliability issues should be addressed in all the
SAVI protocols describing particular SAVI methods.
6. Scenario with Multiple Assignment Methods
While multiple assignment methods can be used on the same link, the
SAVI device may have to deal with a mix of binding discovery methods.
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If the address prefix used for each assignment method is different,
mix scenario can handle the same as scenario with only one assignment
method. If different address assignment methods are used to assign
addresses from the same prefix, additional considerations are needed
because one binding mechanism may create a binding violating an
existing binding from another binding mechanism, e.g., binding from
SAVI-FCFS [savi-fcfs] may violate binding from SAVI-DHCP [savi-dhcp].
Thus, the collision between different SAVI mechanisms in mix scenario
must be handled in case more than one address assignment method is
used to assign addresses from the same prefix.
Prioritization relationship between different address assignment
methods is used as the basis to solve possible collisions. Current
standard documents of address assignment methods have implied the
prioritization relationship in general cases. However, considering
in some scenarios, default prioritization level may not be quite
suitable. Configurable prioritization level should be supported in a
document of SAVI solution for the mix scenario.
7. Prefix Configuration
Before setting up a host-level granularity binding, it is important
to configure correct prefixes on the SAVI device. This document
suggests set 3 prefix configuration mechanisms at SAVI device:
o Manual Prefix Configuration: The allowed prefix scope of IPv4
Addresses, IPv6 static addresses, IPv6 addresses assigned by
SLAAC, and IPv6 addresses assigned by DHCPv6 can be set manually
at SAVI device. FE80::/64 is always a feasible prefix in IPv6.
o Prefix Configuration by RA Snooping: The allowed prefix scope of
IPv6 static addresses and IPv6 addresses assigned by Stateless
Address Autoconfiguration (SLAAC) can be set at SAVI device
through snooping RA message at SAVI device.
o Prefix Configuration by DHCP Prefix Delegation (DHCP-PD) Snooping:
The allowed prefix scope of IPv6 static addresses, IPv6 addresses
assigned by SLAAC, and IPv6 addresses assigned by DHCPv6 can be
set through snooping DHCP-PD message at SAVI device.
If some of the prefix scopes is set to have no prefix, it implies
corresponding address assignment method is not allowed in the
network.
There is no need to explicitly present these prefix scopes, but these
restrictions should be used as premier check in binding set up.
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When SAVI is partially deployed, binding may fail as RA messages and
DHCP-PD can be spoofed. So it is recommended that Manual Prefix
Configuration is used unless SAVI gets fully deployed.
8. Acknowledgment
The authors would like to thank the SAVI working group for a thorough
technical discussion on the design and the framework of the SAVI
method, as captured in this document, in particular Erik Nordmark,
Guang Yao, Eric Levy-Abegnoli, and Alberto Garcia. Thanks also to
Torben Melsen for reviewing this document.
This document was generated using the xml2rfc tool.
9. IANA Considerations
This memo asks the IANA for no new parameters.
Note to RFC Editor: This section will have served its purpose if it
correctly tells IANA that no new assignments or registries are
required, or if those assignments or registries are created during
the RFC publication process. From the authors' perspective, it may
therefore be removed upon publication as an RFC at the RFC Editor's
discretion.
10. Security Considerations
This document only discusses the possible methods to mitigate the
usage of forged IP addresses. Some such methods may rely on
cryptographic methods, but not all do. As a result, it is generally
not possible to prove address ownership in any strong sense. If
binding anchor is not exclusive for each IP address, or is without
strong security, addresses can still be forged. Besides, the binding
may not accord with the address management requirement, which can be
more specified for each client. However, given no new protocol is
introduced, the improvements are still acceptable. If there is
requirement the usage of IP address must be of strong security, the
only way is using cryptographic based authentication.
11. References
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11.1. Informative References
[BA2007] Baker, F., "Cisco IP Version 4 Source Guard", IETF
Internet draft (work in progress), November 2007.
[BCP38] Paul, P. and D. Senie, "Network Ingress Filtering:
Defeating Denial of Service Attacks which employ IP Source
Address Spoofing", RFC 2827, BCP 38, May 2000.
[BCP84] Baker, F. and P. Savola, "Ingress Filtering for Multihomed
Networks", RFC 3704, BCP 84, March 2004.
11.2. Normative References
[draft-ietf-savi-threat-scope]
McPherson, D., Baker, F., and J. Halpern, "SAVI Threat
Scope", draft-ietf-savi-threat-scope-04 (work in
progress), March 2011.
[rfc2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, 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.
[rfc3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
Neighbor Discovery (SEND)", RFC 3971, March 2005.
[rfc4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007.
[rfc5026] Giaretta, G., Kempf, J., and V. Devarapalli, "Mobile IPv6
Bootstrapping in Split Scenario", RFC 5026, October 2007.
[rfc5739] Eronen, P., Laganier, J., and C. Madson, "IPv6
Configuration in Internet Key Exchange Protocol Version 2
(IKEv2)", RFC 5739, February 2010.
[rfc5996] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,
"Internet Key Exchange Protocol Version 2 (IKEv2)",
RFC 5996, September 2010.
[savi-dhcp]
Bi, J., Wu, J., Yao, G., and F. Baker, "SAVI Solution for
DHCP", draft-ietf-savi-dhcp-07 (work in progress),
November 2010.
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[savi-fcfs]
Nordmark, E., Bagnulo, M., and E. Levy-Abegnoli, "FCFS-
SAVI: First-Come First-Serve Source-Address Validation for
Locally Assigned Addresses", draft-ietf-savi-fcfs-05 (work
in progress), October 2010.
Authors' Addresses
Jianping Wu
Tsinghua University
Computer Science, Tsinghua University
Beijing 100084
China
Email: jianping@cernet.edu.cn
Jun Bi
Tsinghua University
Network Research Center, Tsinghua University
Beijing 100084
China
Email: junbi@tsinghua.edu.cn
Marcelo Bagnulo
Universidad Carlos III de Madrid
Avenida de la Universidad 30
Leganes, Madrid 28911
Spain
Email: marcelo@it.uc3m.es
Fred Baker
Cisco Systems
Santa Barbara, CA 93117
United States
Email: fred@cisco.com
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Christian Vogt (editor)
Ericsson
200 Holger Way
San Jose, CA 95134
United States
Email: christian.vogt@ericsson.com
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