KARP Working Group G. Lebovitz
Internet-Draft
Intended status: Informational M. Bhatia
Expires: November 11, 2012 Alcatel-Lucent
May 10, 2012
Keying and Authentication for Routing Protocols (KARP) Overview,
Threats, and Requirements
draft-ietf-karp-threats-reqs-05
Abstract
Different routing protocols exist and each employs its own mechanism
for securing the 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's Security Area and
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 protocols' transport systems, including any
mechanisms built into the routing protocols themselves, which
accomplish packet authentication. 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
Task Force (IETF). Note that other groups may also distribute
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working documents as Internet-Drafts. The list of current Internet-
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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 November 11, 2012.
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. Stolen Keys . . . . . . . . . . . . . . . . . . . . . 16
3.1.2.1. Terminated Employee . . . . . . . . . . . . . . . 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 the SIDR
working group.
This document addresses the last item in the list above, securing the
transmission of routing protocol packets on the wire, or rather
securing the routing protocols' transport systems, including any
mechanisms built into the routing protocols themselves which
accomplish packet authentication. 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 and
their contents 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
sources of information. Such assurances are provided by other
mechanisms and are outside the scope of this document and work that
relies on it.
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 tackle [RFC6518], Section 4.1's "Work Phase 1", the
update to a routing protocol's existing transport security.
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 routing protocols' transport systems' per packet
authentication. 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
usage."
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 to the right of 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 decided, 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
assymetric key containted 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 authentication
mechanisms vary in ease of deployment, ease of ongoing management,
startup effort, ongoing effort and management, 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 remediate the
whole system 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 (or derive) 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 truly random or pseudorandom seed
value or (ii) result of the Diffie-Hellman exchange or (iii) a
non-uniform random source 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
a group) of users. It determines how secret keys are generated
and made available to both the parties. If session or traffic
keys are being used, KMP is responsible for generating them and
determining when they should be renewed.
A KMP is helpful because it negotiates unique, random keys without
administrator involvement. It also negotiates, as mentioned
earlier, several of the SA parameters required for the secure
connection, including key life times. It keeps track of those
lifetimes, and negotiates new keys and parameters before they
expire, again, without administrator interaction. Additionally,
in the event of a security breach, changing KMP authentication
credentials will immediately cause a rekey to occur for the
Traffic Keys, and new Traffic Keys will be installed and used in
the current connection.
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KMP Function
Any actual KMP used in the general KARP solution framework
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 used in the system. A peer
key generally would be provided by a KMP that would later be used
to derive fresh traffic keys.
PRF
In cryptography, a pseudorandom function, abbreviated PRF, is a
collection of efficiently-computable functions which emulate a
random oracle in the following way: No efficient algorithm can
distinguish (with significant advantage) between a function chosen
randomly from the PRF family and a random oracle (a function whose
outputs are determined at random). Informally, a PRF takes a
secret key and a set of input values and produces random-seeming
output values for each input value.
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.
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
provide or enhance its peer authentication mechanisms.
SA (Security Association)
A relationship established between two or more entities to enable
them to protect data they exchange. Examples of items that may
exist in an SA include: Identifier, PSK, Traffic Key,
cryptographic algorithms, key lifetimes.
Traffic Key
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The key (or one of a set of keys) used for protecting the routing
protocol traffic. Since the traffic keys used in a particular
connection are not a fixed part of a device configuration no data
exists anywhere else in the operator's systems which can be
stolen, e.g. in the case of a terminated or turned employee. If a
server or other data store is stolen or compromised, the thieves
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.
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 services may be employed in order to secure any piece of
data as it is transmitted over the wire: confidentiality,
authenticity, or 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, privacy services. 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 our focus. Confidentiality and non-repudiation may be addressed
in future work.
OSPF [RFC5709], IS-IS [RFC5310], LDP [RFC5036], and RIP [RFC2453]
[RFC4822] already have existing mechanisms for cryptographically
authenticating and integrity checking the messages on the wire.
Products with these mechanisms have been produced, code has been
written, and both 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 exist, 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 the bits-on-the-wire 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
The work 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 one 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 step of 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, we 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 of existing routing protocols.
2. Define a path to incrementally improve security of the routing
infrastructure as explained in the earlier sections.
3. Ensure that the improved security solutions on currently running
routing infrastructure equipment are deployable. This begs the
consideration of the current state of processing power available
on routers in the network today.
4. Operational deployability - A solution's acceptability will also
be measured by how deployable the solution is by common operator
teams using common deployment processes and infrastructures.
Specifically, we will try to make these solutions fit as well as
possible into current operational practices and router
deployment. This will be heavily influenced by operator input,
to ensure that what we specify can -- and, more importantly, will
-- be deployed once specified and implemented by vendors.
Deployment of incrementally more secure routing infrastructure in
the Internet is the final measure of success. Measurably, we
would like to see an increase in the number of surveyed
respondents who report deploying the updated authentication and
integrity mechanisms in their networks, as well as a sharp rise
in usage for the total percentage of their network's routers.
Interviews with operators show several points about routing
security. First, over 70% of operators have deployed transport
connection protection via TCP-MD5 [RFC3562] on their exterior
Border Gateway Protocol (eBGP) [ISR2008] sessions. Over 55% also
deploy TCP-MD5 on their interior Border Gateway Protoco (iBGP
connections, and 50% make use of TCP-MD5 offered on some other
internal gateway protocol (IGP). The 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." 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,
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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. From our personal conversations with operators, of those
using MD5, 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. 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 avoid the difficulties.
These customer-unique keys are never changed, unless the
customer demands so. The main threat at play here is that a
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terminated employee from such an operator who had access to
the one (or several) keys used for authentication in these
environments could easily 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 and
threat protection. 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's TCP-AO key establishment
for as many other routing protocols as possible.
8. Bridge any gaps between IETF's Routing and 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 two goals are considered out-of-scope for this effort:
o Confidentiality of the packets on the wire. Once this roadmap is
realized, we may revisit work on privacy.
o Message content validity (routing database validity). This work
is being addressed in other IETF efforts, like SIDR.
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2.5. Audience
The audience for this document includes:
o Routing Area working group chairs and participants - These people
are charged with updates to the Routing Protocol specifications.
Any and all cryptographic authentication work on these
specifications will occur in Routing Area working groups, with
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 delegated by the Security Area Directors to perform reviews on
routing protocol specifications as they pass through working group
last call or IESG review. They will pay particular attention to
the use of cryptographic authentication and newly specified
security mechanisms for the routing protocols. They will 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, presumably due to a perception of significantly
improved security value coupled with relative similarity to
deployment complexity and cost. Conversely, the work will be
considered a failure if the operators do not care to deploy it,
either due to lack of value or perceived (or real) over-
complexity of operations. As a result, the GROW and OPSEC WGs
should be kept squarely in the loop as well.
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3. Threats
In this document we will use the definition of "threat" as defined in
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.
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 simply 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 below text intentionally does not constitute
a self-standing, complete threat analysis, but rather describes the
applicability of the existing threat analysis [RFC4593]relevant 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 sources have control of a network resource or a
tap that sits along the path of packets between the 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
actually 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 only. Protocols conforming to this
roadmap will use cryptographic mechanisms to detect MitM attacks
and reject packets from such attacks (i.e. treat them as 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 often eventually lead to an
active attack.
o Off-Path - These sources 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. Stolen Keys
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 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 stolen keys could be on-
path, off-path, or both.
The obvious mitigation for stolen keys 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 having discovered that the previous
keys fell into the possession of unauthorized users. The stolen
keys, reactive mitigation case is highlighted here in order to
explain a common operational situation where new keying material will
become necessary 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
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keying material in order to cut short, or make nonexistent, an
attacker's window of opportunity to use the stolen keys effectively.
In KARP, we can address the attack source with stolen keys 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
the stolen keys case by habitually changing keys.
3.1.2.1. Terminated Employee
A terminated employee is an important example of a "stolen keys"
threat source to consider. 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 a "stolen keys, pro-active" case, as described above,
rather than a "stolen keys, reactive" case.
On one hand, terminated employees could be considered INSIDERS rather
than OUTSIDERS, because at one point in time they were authorized to
have the keys. On the other hand, they aren't really a BYZANTINE
attacker, which is defined to be an attack from an INSIDER, a
legitimate router. Further, once terminated, the authorization
granted to the terminated employee regarding the keys is revoked. If
they maintain possession of the keys they are acting in an
unauthorized way. If they go on to use those keys to launch an
attack they are definitely acting in an unauthorized way. In this
way the terminated employee becomes an OUTSIDER at the point of
termination, they cease to be legitimate participants in the routing
system. 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.
Regardless of whether one considers a terminated employee an
"insider" or an OUTSIDER, it is important to consider them a threat
source, study the use case, and address the threats therein. In such
a case within the KARP context, 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 source of the terminated employee and/or the detected-
stolen-keys drives the requirement for quick and easy key rollover.
The threat actions associated with these sources are mitigated if the
operator has mechanisms in place (both inherent in the protocol, as
well as built into their management systems) that allow them to roll
the keys quickly with minimal impact to the routing system, at low
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operational cost.
3.2. Threat Actions In Scope
These ATTACK ACTIONS are in scope for KARP:
o SPOOFING - when an unauthorized device assumes the identity of an
authorized one. 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 at the transport layer - This is an example of
SPOOFING. It can also be an example of FALSIFICATION and
INTERFERENCE (see below). It occurs when an attacker sends
spoofed packets aimed at halting or preventing the underlying
protocol over which the routing protocol runs. 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.
o FALSIFICATION - an action whereby an attacker sends false routing
information. To falsify the routing information, an attacker has
to be either the originator or a forwarder of the routing
information. FALSIFICATION may occur by an ORIGINATOR, or a
FORWARDER, and may involve OVERCLAIMING, MISCLAIMING, or
MISTATEMENT of network resource reachability. We must be careful
to remember that in this work we are 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 INTERFERENCE - when an attacker inhibits the exchanges by
legitimate routers. The types of INTERFERENCE addressed by this
work include:
A. ADDING NOISE
B. REPLAYING OUT-DATED PACKETS
C. INSERTING MESSAGES
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D. CORRUPTING MESSAGES
E. BREAKING SYNCHRONIZATION
F. Changing message content
o DoS attacks using the authentication mechanism - This includes an
attacker 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, so that
the receiver needs to spend the processing cycles to check the
MAC, only to discard the spoofed packet, consuming substantial CPU
resources. Another example is when an attacker sends an
overwhelming load of keying protocol initiations from bogus
sources.
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, the key length should be sufficiently long
so that covering the entire space of possible keys is improbable
using computational power expected to be available 10 years out or
more. 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
Threats from BYZANTINE sources -- faulty, misconfigured, or subverted
routers, i.e., legitimate participants in the routing protocol -- are
out of scope for this roadmap. Any of the attacks described in the
above section (Section 2.1) that may be levied by a BYZANTINE source
are therefore also out of scope, e.g. FALSIFICATION, 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 observation of route message contents in
flight. Data privacy, 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.
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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 IPsec's ESP [RFC4303]and BFD [RFC5880], a receiver
can at least detect the occurrence of this attack.
B. DELAYING MESSAGES - cannot be prevented with cryptographic
authentication. Note: Timestamps can be used to detect
delays.
C. DENIAL OF RECEIPT - 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
below 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 the
authentication 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 SHOULD BE avoided.
3. Algorithm agility for the cryptographic algorithms used in the
authentication MUST be specified, i.e. more than one algorithm
MUST be specified and it MUST be clear how new algorithms MAY be
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. Mandating two algorithms
provides both a redundancy, and a mechanism for enacting that
redundancy when needed. Further, the mechanism MUST describe
the generic interface for new cryptographic algorithms to be
used, so that implementers can use algorithms other than those
specified, and so that new algorithms may be specified and
supported in the future.
4. Secure use of PSKs, offering both operational convenience and a
baseline level of security, MUST be specified.
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5. Routing protocols (or the transport or network mechanism
protecting routing protocols) should be able to detect and
reject replayed messages. 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.
Packets captured from one session must not be able to be re-sent
and accepted during a later session. Additionally, replay
mechanisms must work correctly even in the presence of routing
protocol packet prioritization by the router.
A. There is a specific case of replay attack combined with
spoofing that must be addressed. In several routing
protocols (e.g., OSPF [RFC2328], IS-IS [RFC1195], BFD
[RFC5880], RIP [RFC2453], etc.), all speakers share the same
key (K) on a broadcast segment. The ability to run a MAC
operation with K is used for identity validation, and
(currently) no other identity validation check is performed.
Assume there are four routers using authentication on a LAN,
R1 - R4. Also assume attacker "Z", who is NOT a legitimate
neighbor, is observing and recording packets on the same LAN
segment. Z captures a packet from R1, and changes the
source IP, spoofing it to that of R2, then sends the packet
on the LAN. Z does not have K, but in this case it does not
matter because R1 already performed the MAC operation, and Z
simply re-uses that MAC. R3 and R4 will process the packet
as if coming from R2, the MAC check will return valid, and
they will update their route tables accordingly. R3 and R4
have confirmed that the MAC was created by someone holding
K, but not that it was actually sent by R2. This is a well
known attack with known solutions. Some string must be
added into the MAC operation that uniquely identifies the
sender. Said string must also be located in the packet such
that if that string were to be altered after the MAC
operation, it would be detected by the receiver. Examples
of solutions used in other protocols include sequence
numbers with sliding acceptance windows, time stamps, IP
header info (SRC, DST), unique identifiers which are
temporarily bound to an IP Address.
6. A change of security parameters REQUIRES, and even forces, 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.
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7. Intra-session re-keying which occurs without a break or
interruption to the current routing session, and, if possible,
without data loss, MUST be specified. Keys need to be changed
periodically, for operational confidentiality (e.g. when an
administrator who had access to the keys leaves an organization)
and for entropy purposes, and a re-keying mechanism enables the
operators to execute the change without productivity loss.
8. Efficient re-keying SHOULD be provided. The specification
SHOULD support rekeying during a session without needing to try/
compute multiple keys on a given packet. The rare exception
will occur if a routing protocols design team can find no other
way to re-key and still adhere to the other requirements in this
section.
9. New mechanisms must resist DoS attacks described as in-scope in
Section 3.2. Routers protect the control plane by implementing
mechanisms to filter 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 or below the IP and transport (TCP or UDP)
headers, but do not include higher layer information. Therefore
the new 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 a routing protocol. 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. Architecture of the specification SHOULD consider and allow for
future use of a KMP.
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13. The authentication mechanism in the Routing Protocol MUST be
decoupled from the key management system used. It MUST be
obvious how the keying material was obtained, and the process
for obtaining the keying material MUST exist outside of the
Routing Protocol. This will allow for the various key
generation methods, like manual keys and KMPs, to be used with
the same Routing Protocol mechanism.
14. Convergence times of the Routing Protocols SHOULD NOT be
materially affected. "Materially" is defined here as anything
greater than a 5% increase in convergence time. Changes in the
convergence time will be immediately verifiable by convergence
performance test beds already in use by most router vendors and
service providers. Note that convergence is different than boot
time. Also note that convergence time has a lot to do with the
speed of processors used on individual routing peers, and this
processing power increases by Moore's law over time, meaning
that the same route calculations and table population routines
will decrease in duration over time. Therefore, this
requirement should be considered only in terms of total number
of protocol packets that must be exchanged, and less for the
computational intensity of processing any one message.
Alternatively this can be simplified by saying that the new
mechanisms should only result in a minimal increase in the
number of routing protocol packets passed between the peers.
15. The changes to or addition of security mechanisms SHOULD NOT
cause a refresh of route advertisements or cause additional
route advertisments 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. Routing protocols MUST only send minimal information regarding
the authentication mechanisms and the parameters in its protocol
packets. One reason for this is to keep the Routing Protocols
as clean and focused as possible, and load security negotiations
into the future KMP as much as possible. Another reason is to
avoid exposing any security negotiation information
unnecessarily to possible attackers on the path.
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18. Routing protocols that rely on the IP header (or information
seperate 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 are based on this.
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. It also may not be possible to deploy such a
mechanism to all routers in a large autonomous system (AS) at
one time. Proposed solutions MUST support an incremental
deployment method that provides some benefit for 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 in the message formatting,
transmission, and processing of routing information carried
through a mixed 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 systems
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
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solution will impose a processing burden which either incurs
substantial capital expense, or threatens to destabilize
routers.
21. Given the number of routers that would require the new
authentication mechanisms in a typical ISP deployment, solutions
can increase their appeal by minimizing the burden imposed on
all routers in favor of confining significant work loads to a
relatively small number of devices. Optional features or
increased assurance that engenders more pervasive processing
loads MAY be made available for deployments where the additional
resources are economically justifiable.
22. 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
function. 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 the security information.
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
turn, depends upon correct operation of the same instance of
that routing protocol (i.e., the unicast routing). However, it
is okay 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.
Spoofing by a Legitimate Neighbor - In several routing protocols (e.g
OSPF) all speakers share the same key, a group key, on a broadcast
segment. 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 neighbor (E.g. Router 1, or
R1) can masquerade as a different neighbor, R2, by sending spoofed
packets using R2 as the source IP address. When other neighbors, R3
and R4, receive these packets, they will calculate the MAC
successfully, and process its contents as if it originated from R2.
SPOOFING this way, the attacker can succeed in several different
types of attacks, including FALSIFICATION and INTERFERENCE. The
source of such an attack is a BYZANTINE actor, since the attack
originates from a legitimate actor in the routing system, and such
sources are out of scope for KARP. This type of attack has been well
documented in the group keying problem space, and it's non-trivial to
solve. The common method used to prevent this type of attack is to
use a unique key for each sender rather than a group key. Other
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.
We would like to thank the following people for their thorough
reviews and comments: Brian Weis, Yoshifumi Nishida, Stephen Kent,
Vishwas Manral.
Author Gregory M. Lebovitz was employed at Juniper Networks, Inc. for
the majority 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.
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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
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