Internet DRAFT - draft-ietf-karp-threats-reqs
draft-ietf-karp-threats-reqs
KARP Working Group G. Lebovitz
Internet-Draft
Intended status: Informational M. Bhatia
Expires: June 22, 2013 Alcatel-Lucent
B. Weis
Cisco Systems
December 19, 2012
Keying and Authentication for Routing Protocols (KARP) Overview,
Threats, and Requirements
draft-ietf-karp-threats-reqs-07
Abstract
Different routing protocols employ different mechanisms for securing
protocol packets on the wire. While most already have some method
for accomplishing cryptographic message authentication, in many cases
the existing methods are dated, vulnerable to attack, and employ
cryptographic algorithms that have been deprecated. The "Keying and
Authentication for Routing Protocols" (KARP) effort aims to overhaul
and improve these mechanisms.
This document does not contain protocol specifications. Instead, it
defines the areas where protocol specification work is needed and a
set of requirements for KARP design teams to follow. RFC 6518,
"Keying and Authentication for Routing Protocols (KARP) Design
Guidelines" is a companion to this document; KARP design teams will
use them together to review and overhaul routing protocols. These
two documents reflect the input of both the IETF Security Area and
IETF Routing Area in order to form a mutually agreeable work plan.
This document has three main parts. The first part provides an
overview of the KARP effort. The second part lists the threats from
RFC 4593 (Generic Threats To Routing Protocols) that are in scope for
attacks against routing protocol transport systems. This includes
any mechanisms built into the routing protocols themselves, to
authenticate packets. The third part enumerates the requirements
that routing protocol specifications must meet when addressing those
threats for RFC 6518's "Work Phase 1", the update to a routing
protocol's existing transport security.
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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Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
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This Internet-Draft will expire on June 22, 2013.
Copyright Notice
Copyright (c) 2012 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
1.2. Requirements Language . . . . . . . . . . . . . . . . . . 8
2. KARP Effort Overview . . . . . . . . . . . . . . . . . . . . . 9
2.1. KARP Scope . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2. Incremental Approach . . . . . . . . . . . . . . . . . . . 10
2.3. Goals . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.4. Non-Goals . . . . . . . . . . . . . . . . . . . . . . . . 13
2.5. Audience . . . . . . . . . . . . . . . . . . . . . . . . . 14
3. Threats . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.1. Threat Sources . . . . . . . . . . . . . . . . . . . . . . 15
3.1.1. OUTSIDERS . . . . . . . . . . . . . . . . . . . . . . 15
3.1.2. Unauthorized Key Holder . . . . . . . . . . . . . . . 16
3.1.2.1. Terminated Employee . . . . . . . . . . . . . . . 17
3.1.3. BYZANTINE . . . . . . . . . . . . . . . . . . . . . . 17
3.2. Threat Actions In Scope . . . . . . . . . . . . . . . . . 18
3.3. Threat Actions Out of Scope . . . . . . . . . . . . . . . 19
4. Requirements for KARP Work Phase 1, the Update to a
Routing Protocol's Existing Transport Security . . . . . 21
5. Security Considerations . . . . . . . . . . . . . . . . . . . 27
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 29
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 30
8.1. Normative References . . . . . . . . . . . . . . . . . . . 30
8.2. Informative References . . . . . . . . . . . . . . . . . . 30
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 32
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1. Introduction
In March 2006 the Internet Architecture Board (IAB) held a workshop
on the topic of "Unwanted Internet Traffic". The report from that
workshop is documented in [RFC4948]. Section 8.1 of that document
states "A simple risk analysis would suggest that an ideal attack
target of minimal cost but maximal disruption is the core routing
infrastructure." Section 8.2 calls for "[t]ightening the security of
the core routing infrastructure." Four main steps were identified
for that tightening:
o Create secure mechanisms and practices for operating routers.
o Clean up the Internet Routing Registry repository (IRR), and
securing both the database and the access, so that it can be used
for routing verification.
o Create specifications for cryptographic validation of routing
message content.
o Secure the routing protocols' packets on the wire
The first bullet is being addressed in the OPSEC working group. The
second bullet should be addressed through liaisons with those running
the IRR's globally. The third bullet is being addressed in other
efforts within the IETF. For example, BGP message content validity
is being addressed in the SIDR working group.
This document addresses the last item in the list above, securing the
transmission of routing protocol packets on the wire. More
precisely, it focuses on securing the transport systems employed by
routing protocols, including any mechanisms built into the protocols
themselves to authenticate packets. This effort is referred to as
Keying and Authentication for Routing Protocols, or "KARP". KARP is
concerned with issues and techniques for protecting the messages
between directly communicating peers. This may overlap with, but is
strongly distinct from, protection designed to ensure that routing
information is properly authorized relative to the source of the
information. Such assurances are provided by other mechanisms and
are outside the scope of this document.
This document is one of two that together form the guidance and
instructions for KARP design teams working to overhaul routing
protocol transport security. The other document is the KARP Design
Guide [RFC6518].
This document does not contain protocol specifications. Instead, its
goal is to define the areas where protocol specification work is
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needed and to provide a set of requirements for KARP design teams to
follow as they update a routing protocol's existing transport
security (see[RFC6518], Section 4.1's "Work Phase 1").
This document has three main parts. The first part, found in Section
2, provides an overview of the KARP effort. Section 3 lists the
threats from [RFC4593], (Generic Threats To Routing Protocols), that
are in scope for per-packet authentication for routing protocol
transport systems. Therefore, this document does not contain a
complete threat model; it simply points to the parts of the governing
threat model that KARP design teams must address, and explicitly
states which parts are out of scope for KARP design teams. Section 4
enumerates the requirements that routing protocol specifications must
meet when addressing those threats related to KARP's "Work Phase 1",
the update to a routing protocol's existing transport security.
("Work Phase 2", a framework and usage of a KMP, will be addressed in
a future document[s]).
This document uses the terminology "on the wire" to refer to the
information used by routing protocols' transport systems. This term
is widely used in IETF RFCs, but is used in several different ways.
In this document, it is used to refer both to information exchanged
between routing protocol instances, and to underlying protocols that
may also need to be protected in specific circumstances. Individual
protocol analysis documents will need to be more specific in their
use of this phrase.
1.1. Terminology
Within the scope of this document, the following words, when
beginning with a capital letter, or spelled in all capitals, hold the
meanings described immediately following each term. If the same word
is used uncapitalized, then it is intended to have its common English
definition.
Identifier
The type and value used by a peer of an authenticated message
exchange to signify who it is to another peer. The Identifier is
used by the receiver as an index into a table containing further
information about the peer that is required to continue processing
the message, for example a Security Association (SA) or keys.
Identity Authentication
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Once the identity is verified, then there must be a cryptographic
proof of that identity, that the peer really is who it asserts to
be. Proof of identity can be arranged among peers in a few ways,
for example symmetric and asymmetric pre-shared keys, or an
asymmetric key contained in a certificate. Certificates can be
used in ways that requires no additional supporting systems
external to the routers themselves. An example of this would be
using self signed certificates and a flat file list of "approved
thumbprints". The use of these different identity verification
mechanisms vary in ease of deployment, ease of ongoing management,
startup effort, security strength, and consequences from loss of
secrets from one part of the system to the rest of the system.
For example, they differ in resistance to a security breach, and
the effort required to recover in the event of such a breach. The
point here is that there are options, many of which are quite
simple to employ and deploy.
KDF (Key derivation function)
A KDF is a function in which an input key and other input data is
used to generate keying material that can be employed by
cryptographic algorithms. The key that is input to a KDF is
called a key derivation key. KDFs can be used to generate one or
more keys from either (i) a random or pseudorandom seed value or
(ii) result of the Diffie-Hellman exchange or (iii) a non-uniform
random source (e.g., from a non-deterministic random bit
generator) or (iv) a pre-shared key which may or may not be
memorable by a human.
KMP (Key Management Protocol)
A protocol to establish a shared symmetric key between a pair (or
among a group) of users. It determines how secret keys are made
available to the users and in some cases also determines how the
secret keys are generated. In some routing protocols traffic keys
are derived by the routing protocol from a master key. In this
case, KMP is responsible for the master key generation and for
determining when it should be renewed. In other cases, there are
only traffic keys (and no master key), and in such a case KMP is
responsible for the traffic key generation and renewal mechanism.
KMP Function
Any KMP used in the general KARP solution framework
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Peer Key
Keys that are used among peers as a basis for identifying one
another. These keys may or may not be connection-specific,
depending on how they were established, and what forms of identity
and identity authentication mechanism are used in the system. A
peer key generally would be provided by a KMP and would later be
used to derive fresh traffic keys.
PSK (Pre-Shared Key)
A key used to communicate with one or more peers in a secure
configuration. Always distributed out-of-band prior to a first
connection.
Replayed Messages
Replayed messages are genuine messages that have been re-sent by
an attacker. Messages may be replayed within a session (i.e.,
intra-session) or replayed from a different session (i.e., inter-
session). For non-TCP based protocols like OSPF [RFC2328], IS-IS
[RFC1195], etc., two routers are said to have a session up if they
are able to exchange protocol packets (i.e., the peers have an
adjacency). Messages replayed during an adjacency are intra-
session replays while message replayed between two peers who re-
establish an adjacency after a reboot or loss of connectivity are
inter-session replays.
Routing Protocol
When used with capital "R" and "P" in this document the term
refers the Routing Protocol for which work is being done to its
packets on the wire.
SA (Security Association)
A relationship established between two or more entities to enable
them to protect data they exchange. Examples of attributes that
may be associated with an SA include: Identifier, PSK, Traffic
Key, cryptographic algorithms, key lifetimes.
Threat Source
A threat source is a motivated, capable adversary.
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Traffic Key
The key (or one of a set of keys) used for protecting the routing
protocol traffic. A traffic key should not be a fixed value in a
device configuration. A traffic key should be known only to the
participants in a connection, so that a compromise of a stored key
(possibly available to a terminated or turned employee) does not
result in disclosure of traffic keys. If a server or other data
store is stolen or compromised, the attackers gain no access to
current traffic keys. They may gain access to key derivation
material, like a PSK, but not current traffic keys in use.
Additional terminology specific to threats are listed and defined
below in the Threats Section 3 section.
1.2. 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 RFC2119 [RFC2119].
When used in lower case, these words convey their typical use in
common language, and are not to be interpreted as described in
RFC2119 [RFC2119].
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2. KARP Effort Overview
2.1. KARP Scope
Three basic principles are possible to secure any piece of data as it
is transmitted over the wire: confidentiality, authenticity, and
integrity. The focus for the KARP working group will be message
authentication and message integrity only. This work explicitly
excludes, at this point in time, confidentiality. Non-repudiation is
also excluded as a goal at this time. Since the objective of most
routing protocols is to broadly advertise the routing topology,
routing protocol packets are commonly sent in the clear;
confidentiality is not normally required for routing protocols.
However, ensuring that routing peers are authentically identified,
and that no rogue peers or unauthenticated packets can compromise the
stability of the routing environment is critical, and thus in scope.
Confidentiality and non-repudiation may be addressed in future work.
OSPF [RFC5709], IS-IS [RFC5310], LDP [RFC5036], and RIP [RFC2453]
[RFC4822] already incorporate mechanisms for cryptographically
authenticating and integrity checking the messages on the wire.
Products with these mechanisms have been produced, code has been
written, and have been optimized for these existing security
mechanisms. Rather than turn away from these mechanisms, this
document aims to enhance them, updating them to modern and secure
levels.
Therefore, the scope of KARP's roadmap of work includes:
o Making use of existing routing protocol transport security
mechanisms, where they have been specified, and enhancing or
updating them as necessary for modern cryptographic best
practices. [RFC6518], Section 4.1 labels this KARP's "Work Phase
1."
o Developing a framework for using automatic key management in order
to ease deployment, lower cost of operation, and allow for rapid
responses to security breaches. [RFC6518], Section 4.1 labels
this KARP's "Work Phase 2."
o Specifying an automated key management protocol that may be
combined with Routing Protocol mechanisms. [RFC6518], Section 4.1
labels this KARP's "Work Phase 2."
Neither this document nor [RFC6518] contain protocol specifications.
Instead, they define the areas where protocol specification work is
needed and set a direction, a set of requirements, and priorities for
addressing that specification work.
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There are a set of threats to routing protocols that are considered
in-scope for KARP, and a set considered out-of- scope. These are
described in detail in the Threats (Section 3) section below.
2.2. Incremental Approach
This document also serves as an agreement between the Routing Area
and the Security Area about the priorities and work plan for
incrementally delivering the above work. The principle of "crawl,
walk, run" will be employed. Thus routing protocol authentication
mechanisms may not go immediately from their current state to a state
reflecting the best possible, most modern security practices. This
point is important as there will be times when the best-security-
possible will give way to vastly-improved-over-current-security-but-
admittedly-not-yet-best-security-possible, in order that incremental
progress toward a more secure Internet may be achieved. As such,
this document will call out places where agreement has been reached
on such trade offs.
Incremental steps will need to be taken for a few very practical
reasons. First, there are a considerable number of deployed routing
devices in operating networks that will not be able to run the most
modern cryptographic mechanisms without significant and unacceptable
performance penalties. The roadmap for any routing protocol MUST
allow for incremental improvements on existing operational devices.
Second, current routing protocol performance on deployed devices has
been achieved over the last 20 years through extensive tuning of
software and hardware elements, and is a constant focus for
improvement by vendors and operators alike. The introduction of new
security mechanisms affects this performance balance. The
performance impact of any incremental security improvement will need
to be weighed by the community, and introduced in such a way that
allows the vendor and operator community a path to adoption that
upholds reasonable performance metrics. Therefore, certain
specification elements may be introduced carrying the "SHOULD"
guidance, with the intention that the same mechanism will carry a
"MUST" in a future release of the specification. This approach gives
the vendors and implementors the guidance they need to tune their
software and hardware appropriately over time. Last, some security
mechanisms require the build out of other operational support
systems, and this will take time.
An example where these three reasons were at play in an incremental
improvement roadmap was seen in the improvement of BGP's [RFC4271]
security via the TCP Authentication Option (TCP-AO) [RFC5925] effort.
It would have been ideal, and reflected best common security
practice, to have a fully specified key management protocol for
negotiating TCP-AO's keying material, e.g., using certificates for
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peer authentication. However, in the spirit of incremental
deployment, the IETF first addressed issues like cryptographic
algorithm agility, replay attacks, and TCP session resetting in the
base TCP-AO protocol, and then later began work to layer key
management on top of it.
2.3. Goals
The goals and general guidance for the KARP work follow.
1. Provide authentication and integrity protection for messages on
the wire for existing routing protocols.
2. Define a path to incrementally improve security of the routing
infrastructure as explained in Section 2.2.
3. Ensure that the improved security solutions are deployable on
current routing infrastructure. This requires consideration of
the current state of processing power available on routers in the
network today.
4. Operational deployability - A solution's acceptability also will
be measured by how deployable the solution is by operator teams,
with consideration for their deployment processes and
infrastructures. Specifically, KARP design teams will try to
make these solutions fit as well as possible into current
operational practices and router deployment methodologies. Doing
so will depend heavily on operator input during KARP design
efforts. Hopefully, operator input will lead to a more
deployable solution, which will, in turn, lead to more production
deployments. Deployment of incrementally more secure routing
infrastructure in the Internet is the final measure of success.
We would like to see an increase in the number of respondents to
surveys such as [ISR2008] to report deploying the updated
authentication and integrity mechanisms in their networks, as
well as see a sharp rise in usage for the total percentage of
their network's routers.
Interviews with operators show several points about routing
security. First, according to [ISR2008], over 70% of operators
have deployed transport connection protection via TCP-MD5
[RFC3562] on their exterior Border Gateway Protocol (eBGP)
sessions. Over 55% also deploy TCP-MD5 on their interior Border
Gateway Protocol (iBGP) connections, and 50% make use of TCP-MD5
offered on some other internal gateway protocol (IGP). The same
survey states that "a considerable increase was observed over
previous editions of the survey for use of TCP MD5 with external
peers (eBGP), internal peers (iBGP) and MD5 extensions for IGPs."
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Though the data is not captured in the report, the authors
believe anecdotally that of those who have deployed TCP-MD5
somewhere in their network, only about 25-30% of the routers in
their network are deployed with the authentication enabled. None
report using IPsec [RFC4301] to protect the routing protocol, and
this was a decline from the few that reported doing so in the
previous year's report. Anecdotal evidence from operators using
MD5 shows that almost all report using one, manually-distributed
key throughout the entire network. These same operators report
that the single key has not been changed since it was originally
installed, sometimes five or more years ago. When asked why,
particularly for the case of protecting BGP sessions using TCP
MD5, the following reasons are often given:
A. Changing the keys triggers a TCP reset, and thus bounces the
links/adjacencies, undermining Service Level Agreements
(SLAs).
B. For external peers, the difficulty of coordination with the
other organization is an issue. Once they find the correct
contact at the other organization (not always so easy), the
coordination function is serialized and on a per peer/AS
basis. The coordination is very cumbersome and tedious to
execute in practice.
C. Keys must be changed at precisely the same time, or at least
within 60 seconds (as supported by two major vendors) in order
to limit connectivity outage duration. This is incredibly
difficult to do, operationally, especially between different
organizations.
D. Key change is perceived as a relatively low priority compared
to other operational issues.
E. Lack of staff to implement the changes on a device-by-device
basis.
F. There are three use cases for operational peering at play
here: peers and interconnection with other operators, iBGP and
other routing sessions within a single operator, and operator-
to-customer devices. All three have very different
properties, and all are reported as cumbersome to manage
securely. One operator reported that the same key is used for
all customer premise equipment (CPE). The same operator
reported that if the customer mandated it, a unique key could
be created, although the last time this occurred it created
such an operational headache that the administrators now
usually tell customers that the option doesn't even exist, to
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avoid the difficulties. These customer-unique keys are never
changed, unless the customer demands so. The main threat here
is that a terminated employee from such an operator who had
access to the one (or several) keys used for authentication in
these environments could wage an attack. Alternatively, the
operator could offer the keys to others who would wage the
attack. In either case, the attacker could then bring down
many of the adjacencies, causing destabilization to the
routing system.
5. Whatever mechanisms KARP specifies need to be easier to deploy
than the current methods, and should provide obvious operational
efficiency gains along with significantly better security. This
combination of value may be enough to drive much broader
adoption.
6. Address the threats enumerated below in the "Threats" section
(Section 3) for each routing protocol. Not all threats may be
able to be addressed in the first specification update for any
one protocol. Roadmaps will be defined so that both the security
area and the routing area agree on how the threats will be
addressed completely over time.
7. Create a re-usable architecture, framework, and guidelines for
various IETF working groups who will address these security
improvements for various Routing Protocols. The crux of the KARP
work is to re-use the architecture, guidelines and the framework
as much as possible across relevant Routing Protocols. For
example, designers should aim to re-use the key management
protocol that will be defined for BGP, which will establish keys
for TCP-AO, for as many other routing protocols with similar
characteristics and properties as possible.
8. Bridge any gaps between IETF Routing and IETF Security Areas by
recording agreements on work items, roadmaps, and guidance from
the cognizant Area Directors and the Internet Architecture Board
(IAB).
2.4. Non-Goals
The following goals are considered out-of-scope for this effort:
o Confidentiality and non-repudiation of the packets on the wire.
Once this roadmap is realized, work on confidentiality may be
considered.
o Non-repudiation of the packets on the wire.
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o Message content validity (routing database validity). This work
is being addressed in other IETF efforts. For example, BGP
message content validity is being addressed in the SIDR working
group.
2.5. Audience
The audience for this document includes:
o Routing Area working group chairs and participants - These people
are charged with updated Routing Protocol specifications. Any and
all cryptographic authentication work on these specifications will
occur in Routing Area working groups, in close partnership with
the Security Area. Co-advisors from the Security Area may often
be named for these partnership efforts.
o Security Area reviewers of routing area documents - These people
are tasked by the Security Area Directors to perform reviews on
routing protocol specifications as they pass through working group
last call or IESG review. Their particular attention to the use
of cryptographic authentication and newly specified security
mechanisms for the routing protocols is appreciated. They also
help to ensure that incremental security improvements are being
made, in line with this roadmap.
o Security Area engineers - These people partner with routing area
authors/designers on the security mechanisms in routing protocol
specifications. Some of these security area engineers will be
assigned by the Security Area Directors, while others will be
interested parties in the relevant working groups.
o Operators - The operators are a key audience for this work, as the
work is considered to have succeeded only if operators deploy the
technology. It is anticipated that deployment will take place
only if operators perceive that the improved security offered by
the Routing Protocol updates warrant the complexity and cost of
deployment and operation. Conversely, the work will be considered
a failure if operators do not deploy it, either due to lack of
perceived value or due to perceived operational complexity. As a
result, the GROW and OPSEC WGs should be kept squarely in the loop
as well.
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3. Threats
This document uses the definition of "threat" from RFC4949 [RFC4949]:
"a potential for violation of security, which exists when there is a
circumstance, capability, action, or event that could breach security
and cause harm."
This section defines the threats that are in scope for the KARP
effort. It also lists those threats that are explicitly out of scope
for the KARP effort. Threats are discussed assuming that no
protection (i.e., message authentication and message integrity) has
been applied to routing protocol messages.
This document leverages the "Generic Threats to Routing Protocols"
model, [RFC4593]. Specifically, the threats below were derived by
reviewing [RFC4593], analyzing the KARP problem space relative to it,
and listing the threats that are applicable to the KARP design teams'
work. This document categorizes [RFC4593] threats into those in
scope and those out of scope for KARP. Each in-scope threat is
discussed below, and its applicability to the KARP problem space is
described. As such, the following text intentionally is not a
comprehensive threat analysis. Rather it describes the applicability
of the existing threat analysis [RFC4593] to KARP.
Note: terms from [RFC4593] appear capitalized below -- e.g.
OUTSIDERS -- so as to make explicit the term's origin, and to enable
rapid cross referencing to the source RFC.
For convenience, a terse definition of most [RFC4593] terms is
offered here. Those interested in a more thorough description of
routing protocol threat sources, motivations, consequences and
actions will want to read [RFC4593] before continuing here.
3.1. Threat Sources
3.1.1. OUTSIDERS
One of the threats that will be addressed in this roadmap are those
where the source is an OUTSIDER. An OUTSIDER attacker may reside
anywhere in the Internet, have the ability to send IP traffic to the
router, may be able to observe the router's replies, and may even
control the path for a legitimate peer's traffic. OUTSIDERS are not
legitimate participants in the routing protocol. The use of message
authentication and integrity protection specifically aims to identify
packets originating from OUTSIDERS.
KARP design teams will consider two specific use cases of OUTSIDERS:
those on-path, and those off-path.
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o On-Path - These attackers have control of a network resource or a
tap that sits along the path between two routing peers. A "Man-
in-the-Middle" (MitM) is an on-path attacker. From this vantage
point, the attacker can conduct either active or passive attacks.
An active attack occurs when the attacker places packets on the
network as part of the attack. One active MitM attack relevant to
KARP, an active wiretapping attack, occurs when the attacker
tampers with packets moving between two legitimate router peers in
such a way that both peers think they are talking to each other
directly, when in fact they are actually talking to the attacker.
Protocols conforming to this roadmap will use cryptographic
mechanisms to detect MitM attacks and reject packets from such
attacks (i.e. discard them as being not authentic). Passive on-
path attacks occur when the attacker silently gathers data and
analyses it to gain advantage. Passive activity by an on-path
attacker may lead to an active attack.
o Off-Path - These attackers sit on some network outside of that
over which runs the packets between two routing peers. The source
may be one or several hops away. Off-path attackers can launch
active attacks, such as SPOOFING or denial-of-service (DoS)
attacks, to name a few.
3.1.2. Unauthorized Key Holder
This threat source exists when an unauthorized entity somehow manages
to gain access to keying material. Using this material, the attacker
could send packets that pass the authenticity checks based on message
authentication codes (MACs). The resulting traffic might appear to
come from router A, destined to router B, and thus the attacker could
impersonate an authorized peer. The attacker could then adversely
affect network behavior by sending bogus messages that appear to be
authentic. The attack source possessing the unauthorized keys could
be on-path, off-path, or both.
The obvious mitigation for an unauthorized key holder is to change
the keys currently in use by the legitimate routing peers. This
mitigation can be either reactive or pro-active. Reactive mitigation
occurs when keys are changed only after one has discovered that the
previous keys fell into the possession of unauthorized users. The
reactive mitigation case is highlighted here in order to explain a
common operational situation where new keying material will need to
be put in place with little or no advanced warning. In such a case
new keys must be able to be installed and put into use very quickly,
and with little operational expense. Pro-active mitigation occurs
when an operator assumes that unauthorized possession will occur from
time to time without being discovered, and the operator moves to new
keying material in order to cut short an attacker's window of
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opportunity to use the stolen keys effectively.
KARP design teams can address this type of attack by creating
specifications that make it practical for the operator to quickly
change keys without disruption to the routing system, and with
minimal operational overhead. Operators can further mitigate threats
from unauthorized key holders by regularly changing keys.
3.1.2.1. Terminated Employee
A terminated employee is an important example of an "unauthorized key
holder". Staff attrition is a reality in routing operations, and so
regularly causes the potential for a threat source. The threat
source risk arises when a network operator who had been granted
access to keys ceases to be an employee. If new keys are deployed
immediately, the situation of a terminated employee can become an
"unauthorized key holder, pro-active" case, as described above,
rather than an "unauthorized key holder, reactive mitigation" case.
It behooves the operator to change the keys, to enforce the
revocation of authorization of the old keys, in order to minimize the
threat source's window of opportunity.
A terminated employee is a valid unauthorized key holder threat
source for KARP, and designs should address the associated threats.
For example,new keys must be able to be installed and made
operational in the routing protocols very quickly, with zero impact
to the routing system, and with little operational expense. The
threat actions associated with a terminated employee also motivate
the need to roll the keys quickly, also with little operational
expense.
3.1.3. BYZANTINE
According to [RFC4593] , Section 3.1.1.2, BYZANTINE "attackers are
faulty, misconfigured, or subverted routers, i.e., legitimate
participants in the routing protocol" whose messages cause routing to
malfunction.
[RFC4593] goes on to say that "[s]ome adversaries can subvert
routers, or the management workstations used to control these
routers. These Byzantine failures represent the most serious form of
attack capability in that they result in emission of bogus traffic by
legitimate routers."
[RFC4593] explains that "[d]eliberate attacks are mimicked by
failures that are random and unintentional. In particular, a
Byzantine failure in a router may occur because the router is faulty
in hardware or software or is misconfigured," and thus routing
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malfunctions unintentionally. Though not malicious, such occurrences
still disrupt network operation.
Whether faulty, misconfigured, or subverted, Byzantine routers have
an empowered position from which to provide believable yet bogus
routing messages that are damaging to the network.
3.2. Threat Actions In Scope
These THREAT ACTIONS are in scope for KARP:
o SPOOFING - when an unauthorized device assumes the identity of an
authorized one. Spoofing is special in that it can be used to
carry out other threat actions causing other threat consequences.
SPOOFING can be used, for example, to inject malicious routing
information that causes the disruption of network services.
SPOOFING can also be used to cause a neighbor relationship to form
that subsequently denies the formation of the relationship with
the legitimate router.
o DoS attacks
1. At the transport layer - This occurs when an attacker sends
packets aimed at halting or preventing the underlying protocol
over which the routing protocol runs. The attacker could use
SPOOFING, FALSIFICATION and INTERFERENCE (see below) to
produce the DoS attack. For example, BGP running over TLS
will still not solve the problem of being able to send a
spoofed TCP FIN or TCP RST and causing the BGP session to go
down. Since this attack depends on spoofing, operators are
encouraged to deploy proper authentication mechanisms to
prevent such attacks. Specification work should ensure that
Routing Protocols can operate over transport sub-systems in a
fashion that is resilient to such DoS attacks.
2. Using the authentication mechanism - This includes an attacker
causing INTERFERENCE, which is inhibiting the exchanges of
legitimate routers. The attack is often perpetrated by
sending packets that confuse or overwhelm a security mechanism
itself. An example is initiating an overwhelming load of
spoofed routing protocol packets that contain a MAC (i.e,
INSERTING MESSAGES), so that the receiver needs to spend the
processing cycles to check the MAC, only to discard the
spoofed packet, consuming substantial CPU resources. Other
types of INTERFERENCE include: REPLAYING OUT-DATED PACKETS,
CORRUPTING MESSAGES, and BREAKING SYNCHRONIZATION.
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o FALSIFICATION - an action whereby an attacker sends false routing
information. This document is only targeting FALSIFICATION from
OUTSIDERS as may occur from tampering with packets in flight, or
sending entirely false messages. FALSIFICATION from BYZANTINES
(see the Threats Out of Scope section below) are not addressed by
the KARP effort.
o Brute Force Attacks Against Password/Keys - This includes either
online or offline attacks where attempts are made repeatedly using
different keys/passwords until a match is found. While it is
impossible to make brute force attacks on keys completely
unsuccessful, proper design can make such attacks much harder to
succeed. For example, current guidance for the security strength
of an algorithm with a particular key length should be deemed
acceptable for a period of 10 years. (Section 10 of [SP.800-131A]
is one source for guidance). Using per session keys is another
widely used method for reducing the number of brute force attacks
as this would make it difficult to guess the keys.
3.3. Threat Actions Out of Scope
BYZANTINE sources -- be they faulty, misconfigured, or subverted --
are out of scope for this roadmap. KARP works to cryptographically
ensure that received routing messages originated from authorized
peers, and that the message was not altered in transit. Formation of
a bogus message by a valid and authorized peer falls outside the KARP
scope. Any of the attacks described in the above section
(Section 3.2) that may be levied by a BYZANTINE source are therefore
also out of scope, e.g. FALSIFICATION from BYZANTINE sources, or
unauthorized message content by a legitimate authorized peer.
In addition, these other attack actions are out of scope for this
work:
o SNIFFING (passive wiretapping) - passive observation of route
message contents in flight. Data confidentiality, as achieved by
data encryption, is the common mechanism for preventing SNIFFING.
While useful, especially to prevent the gathering of data needed
to perform an off-path packet injection attack, data encryption is
out-of-scope for KARP.
o INTERFERENCE due to:
A. NOT FORWARDING PACKETS - cannot be prevented with
cryptographic authentication. Note: If sequence numbers with
sliding windows are used in the solution (as is done, for
example, in BFD [RFC5880]), a receiver can at least detect the
occurrence of this attack.
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B. DELAYING MESSAGES - cannot be prevented with cryptographic
authentication. Note: Timestamps can be used to detect
delays.
C. DENIAL OF RECEIPT (non-repudiation) - cannot be prevented with
cryptographic authentication
D. UNAUTHORIZED MESSAGE CONTENT - the work of the IETF's SIDR
working group
(http://www.ietf.org/html.charters/sidr-charter.html).
E. DoS attacks not involving the routing protocol. For example,
a flood of traffic that fills the link ahead of the router, so
that the router is rendered unusable and unreachable by valid
packets is NOT an attack that KARP will address. Many such
examples could be contrived.
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4. Requirements for KARP Work Phase 1, the Update to a Routing
Protocol's Existing Transport Security
The KARP Design Guide [RFC6518], Section 4.1 describes two distinct
work phases for the KARP effort. This section addresses requirements
for the first work phase only, "Work Phase 1", the update to a
routing protocol's existing transport security. "Work Phase 2", a
framework and usage of a KMP, will be addressed in a future
document(s).
The following list of requirements SHOULD be addressed by a KARP Work
Phase 1 security update to any Routing Protocol (according to section
4.1 of the KARP Design Guide [RFC6518]document). IT IS RECOMMENDED
that any Work Phase 1 security update to a Routing Protocol contain a
section of the specification document that describes how each of the
following requirements are met. It is further RECOMMENDED that
justification be presented for any requirements that are NOT
addressed.
1. Clear definitions of which elements of the transmitted data
(frame, packet, segment, etc.) are protected by an
authentication/integrity mechanism
2. Strong cryptographic algorithms, as defined and accepted by the
IETF security community, MUST be specified. The use of non-
standard or unpublished algorithms MUST be avoided.
3. Algorithm agility for the cryptographic algorithms used in the
authentication MUST be specified, and protocol specifications
MUST be clear how new algorithms are specified and used within
the protocol. This requirement exists because research
identifying weaknesses in cryptographic algorithms can cause the
security community to reduce confidence in some algorithms.
Breaking a cipher isn't a matter of if, but when it will occur.
Having the ability to specify alternate algorithms (algorithm
agility) within the protocol specification to support such an
event is essential. Additionally, more than one algorithm MUST
be specified. Mandating support for two algorithms (i.e., one
mandatory to implement algorithm and one or more backup
algorithms to guide transition) provides both redundancy, and a
mechanism for enacting that redundancy.
4. Secure use of PSKs, offering both operational convenience and a
baseline level of security, MUST be specified.
5. Routing Protocols (or the transport or network mechanism
protecting routing protocols) SHOULD be able to detect and
reject replayed intra-session and inter-session messages.
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Packets captured from one session MUST NOT be able to be re-sent
and accepted during a later session (i.e., inter-session
replay). Additionally, replay mechanisms MUST work correctly
even in the presence of routing protocol packet prioritization
by the router.
There is a specific case of replay attack combined with spoofing
that must be addressed. Several routing protocols (e.g., OSPF
[RFC2328], IS-IS [RFC1195], BFD [RFC5880], RIP [RFC2453], etc.),
require all speakers to share the same authentication and
message association key on a broadcast segment. It is important
that an integrity check associated with a message fail if an
attacker has replayed the message with a different origin.
6. A change of security parameters MUST force a change of session
traffic keys. The specific security parameters for the various
routing protocols will differ, and will be defined by each
protocols design team. Some examples may include: master key,
key lifetime, cryptographic algorithm, etc. If one of these
configured parameters changes, then a new session traffic key
MUST immediately be established using the updated parameters.
The routing protocol security mechanisms MUST support this
behavior.
7. Security mechanisms MUST specify a means to affect intra-session
re-keying without disrupting a routing session. This should be
accomplished without data loss, if possible. Keys may need to
be changed periodically based on policy, or when an
administrator who had access to the keys leaves an organization.
A re-keying mechanism enables the operators to execute the
change without productivity loss.
8. Re-keying SHOULD be supported in such a way that it can occur
during a session without the peer needing to use multiple keys
to validate a given packet. The rare exception will occur if a
routing protocol's design team can find no other way to re-key
and still adhere to the other requirements in this section. The
specification SHOULD include a key identifier, which allows
receivers to choose the correct key (or determine that they are
not in possession of the correct key).
9. New mechanisms MUST resist DoS attacks described as in-scope in
Section 3.2. Routers protect the control plane by implementing
mechanisms to reject completely or rate limit traffic not
required at the control plane level (i.e., unwanted traffic).
Typically line rate packet filtering capabilities look at
information at the IP and transport (TCP or UDP) headers, but do
not include higher layer information. Therefore the new
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mechanisms shouldn't hide nor encrypt the information carried in
the IP and transport layers in control plane packets.
10. Mandatory cryptographic algorithms and mechanisms MUST be
specified for each routing protocol security mechanism.
Further, the protocol specification MUST define default security
mechanism settings for all implementations to use when no
explicit configuration is provided. To understand the need for
this requirement, consider the case where a routing protocol
mandates 3 different cryptographic algorithms for a MAC
operation. If company A implements algorithm 1 as the default
for this protocol, while company B implements algorithm 2 as the
default, then two operators who enable the security mechanism
with no explicit configuration other than a PSK will experience
a connection failure. It is not enough that each implementation
implement the 3 mandatory algorithms; one default must further
be specified in order to gain maximum out-of-the-box
interoperability.
11. For backward compatibility reasons, manual keying MUST be
supported.
12. The specification MUST consider and allow for future use of a
KMP.
13. The authentication mechanism in a Routing Protocol MUST be
decoupled from the key management system used. The
authentication protocol MUST include a specification for
agreeing on keying material. This will accommodate both manual
keying and the use of KMPs.
14. Convergence times of the Routing Protocols SHOULD NOT be
materially affected. Changes in the convergence time will be
immediately and independently verifiable by convergence
performance test beds already in use (e.g. those maintained by
router vendors, service providers, and researchers). An
increase in convergence time in excess of 5% is likely to be
considered to have materially affected convergence by network
operators. A number of other facts can also change convergence
over time (e.g., speed of processors used on individual routing
peers, processing power increases due to Moore's law,
implementation specifics), and the effect of an authentication
mechanism on Routing Protocols will need to take these into
account by implementors. Protocol designers should consider the
impact on convergence times as a function of both the total
number of protocol packets that must be exchanged and the
required computational processing of individual messages in the
specification, understanding that the operator community's
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threshold for increase of convergence times is very low, as
stated above.
15. The changes to or addition of security mechanisms SHOULD NOT
cause a refresh of route advertisements or cause additional
route advertisements to be generated.
16. Router implementations provide prioritized treatment for certain
protocol packets. For example, OSPF HELLO packets and ACKs are
prioritized for processing above other OSPF packets. The
security mechanism SHOULD NOT interfere with the ability to
observe and enforce such prioritization. Any effect on such
priority mechanisms MUST be explicitly documented and justified.
Replay protection mechanisms provided by the routing protocols
MUST work even if certain protocol packets are offered
prioritized treatment.
17. The Routing Protocol MUST send minimal information regarding the
authentication mechanisms and associated parameters in its
protocol packets. This keeps the Routing Protocols as clean and
focused as possible, and loads security negotiations into the
KMP as much as possible. Another reason is to avoid exposing
any security negotiation information unnecessarily to possible
attackers on the path.
18. Routing Protocols that rely on the IP header (or information
separate from routing protocol payload) to identify the neighbor
that originated the packet, MUST either protect the IP header or
provide some other means to authenticate the neighbor.
[RFC6039] describes some attacks that motivate this requirement.
19. Every new KARP-developed security mechanisms MUST support
incremental deployment. It will not be feasible to deploy a new
Routing Protocol authentication mechanism throughout a network
instantaneously. Indeed, it may not actually be feasible to
deploy such a mechanism to all routers in a large autonomous
system (AS) in a bounded timeframe. Proposed solutions MUST
support an incremental deployment method that benefits those who
participate. Because of this, there are several requirements
that any proposed KARP mechanism should consider.
A. The Routing Protocol security mechanism MUST enable each
router to configure use of the security mechanism on a per-
peer basis where the communication is peer-to-peer
(unicast).
B. Every new KARP-developed security mechanism MUST provide
backward compatibility with respect to message formatting,
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transmission, and processing of routing information carried
through a secure and non-secure security environment.
Message formatting in a fully secured environment MAY be
handled in a non-backward compatible fashion though care
must be taken to ensure that routing protocol packets can
traverse intermediate routers that don't support the new
format.
C. In an environment where both secured and non-secured routers
are interoperating, a mechanism MUST exist for secured
systems to identify whether a peer intended the messages to
be secured.
D. In an environment where secured service is in the process of
being deployed, a mechanism MUST exist to support a
transition free of service interruption (caused by the
deployment per se).
20. The introduction of mechanisms to improve routing security may
increase the processing performed by a router. Since most of
the currently deployed routers do not have hardware to
accelerate cryptographic operations, these operations could
impose a significant processing burden under some circumstances.
Thus proposed solutions SHOULD be evaluated carefully with
regard to the processing burden they may impose, since
deployment may be impeded if network operators perceive that a
solution will impose a processing burden which either incurs
substantial capital expense, or threatens to degrade router
performance.
21. New authentication and security mechanisms should not rely on
systems external to the routing system (the equipment that is
performing forwarding) in order for the routing system to be
secure. In order to ensure the rapid initialization and/or
return to service of failed nodes it is important to reduce
reliance on these external systems to the greatest extent
possible. Proposed solutions SHOULD NOT require connections to
external systems, beyond those directly involved in peering
relationships, in order to return to full service. It is
however acceptable for the proposed solutions to require post
initialization synchronization with external systems in order to
fully synchronize security associations.
If authentication and security mechanisms rely on systems
external to the routing system, then there MUST be one or more
options available to avoid circular dependencies. It is not
acceptable to have a routing protocol (e.g., unicast routing)
depend upon correct operation of a security protocol that, in
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turn, depends upon correct operation of the same instance of
that routing protocol (i.e., the unicast routing). However, it
is acceptable to have operation of a routing protocol (e.g.,
multicast routing) depend upon operation of a security protocol,
which depends upon an independent routing protocol (e.g.,
unicast routing). Similarly it would be okay to have the
operation of a routing protocol depend upon a security protocol,
which in turn uses an out of band network to exchange
information with remote systems.
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5. Security Considerations
This document is mostly about security considerations for the KARP
efforts, both threats and requirements for addressing those threats.
More detailed security considerations were placed in the Security
Considerations section of the KARP Design Guide [RFC6518]document.
The use of a group key between a set of Routing Protocol peers has
special security considerations. Possession of the group key itself
is used for identity validation, and no other identity check is used.
Under these conditions an attack exists where one peer masquerades as
a neighbor by using the neighbor's source IP address. This type of
attack has been well documented in the group keying problem space,
and it's non-trivial to solve. Solutions exist within the group
keying realm, but they come with significant increases in complexity
and computational intensity.
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6. IANA Considerations
This document has no actions for IANA.
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7. Acknowledgements
The majority of the text for version -00 of this document was taken
from "Roadmap for Cryptographic Authentication of Routing Protocol
Packets on the Wire", draft-lebovitz-karp-roadmap, authored by
Gregory M. Lebovitz.
Brian Weis provided significant assistance in handling the many
comments that came back during IESG review, including making textual
edits directly to the XML. For his extensive efforts he was added as
an author on -07.
We would like to thank the following people for their thorough
reviews and comments: Brian Weis, Yoshifumi Nishida, Stephen Kent,
Vishwas Manral, Barry Leiba, Sean Turner, Uma Chunduri.
Author Gregory M. Lebovitz was employed at Juniper Networks, Inc. for
much of the time he worked on this document, though not at the time
of its publishing. Thus Juniper sponsored much of this effort.
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8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4593] Barbir, A., Murphy, S., and Y. Yang, "Generic Threats to
Routing Protocols", RFC 4593, October 2006.
[RFC4948] Andersson, L., Davies, E., and L. Zhang, "Report from the
IAB workshop on Unwanted Traffic March 9-10, 2006",
RFC 4948, August 2007.
8.2. Informative References
[ISR2008] McPherson, D. and C. Labovitz, "Worldwide Infrastructure
Security Report", October 2008,
<http://www.arbornetworks.com/dmdocuments/ISR2008_US.pdf>.
[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, December 1990.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
[RFC2453] Malkin, G., "RIP Version 2", STD 56, RFC 2453,
November 1998.
[RFC3562] Leech, M., "Key Management Considerations for the TCP MD5
Signature Option", RFC 3562, July 2003.
[RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
Protocol 4 (BGP-4)", RFC 4271, January 2006.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, December 2005.
[RFC4822] Atkinson, R. and M. Fanto, "RIPv2 Cryptographic
Authentication", RFC 4822, February 2007.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2",
RFC 4949, August 2007.
[RFC5036] Andersson, L., Minei, I., and B. Thomas, "LDP
Specification", RFC 5036, October 2007.
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[RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
and M. Fanto, "IS-IS Generic Cryptographic
Authentication", RFC 5310, February 2009.
[RFC5709] Bhatia, M., Manral, V., Fanto, M., White, R., Barnes, M.,
Li, T., and R. Atkinson, "OSPFv2 HMAC-SHA Cryptographic
Authentication", RFC 5709, October 2009.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, June 2010.
[RFC5925] Touch, J., Mankin, A., and R. Bonica, "The TCP
Authentication Option", RFC 5925, June 2010.
[RFC6039] Manral, V., Bhatia, M., Jaeggli, J., and R. White, "Issues
with Existing Cryptographic Protection Methods for Routing
Protocols", RFC 6039, October 2010.
[RFC6518] Lebovitz, G. and M. Bhatia, "Keying and Authentication for
Routing Protocols (KARP) Design Guidelines", RFC 6518,
February 2012.
[SP.800-131A]
Barker, E. and A. Roginsky, "Transitions: Recommendation
for Transitioning the Use of Cryptographic Algorithms and
Key Lengths", United States of America, National Institute
of Science and Technology, NIST Special Publication
800-131A, January 2011.
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Authors' Addresses
Gregory Lebovitz
Aptos, California 95003
USA
Email: gregory.ietf@gmail.com
Manav Bhatia
Alcatel-Lucent
Bangalore,
India
Phone:
Email: manav.bhatia@alcatel-lucent.com
Brian Weis
Cisco Systems
170 W. Tasman Drive
San Jose, California 95134-1706
USA
Phone:
Email: bew@cisco.com
URI: http://www.cisco.com
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