Network Working Group M. Bhatia
Internet-Draft Alcatel-Lucent
Intended status: Standards Track April 14, 2011
Expires: October 16, 2011
Analysis of Protocol Independent Multicast Sparse Mode (PIM-SM)
Security According to KARP Design Guide
draft-bhatia-karp-pim-gap-analysis-00
Abstract
This document analyzes Protocol Independent Multicast Sparse Mode
(PIM-SM) according to the guidelines set forth in the KARP Design
Guide.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Status of this Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on October 16, 2011.
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1. Introduction
This document performs the initial analysis of the current state of
Protocol Independent Multicast Sparse Mode (PIM-SM) [RFC4601]
according to the requirements of [I-D.ietf-karp-design-guide]
[RFC5796] describes mechanisms to authenticate the PIM-SM link-local
messages using the IP security (IPsec) Encapsulating Security Payload
(ESP) [RFC4303] or (optionally) the Authentication Header (AH)
[RFC4302] .
This document specifies manual key management as mandatory to
implement, i.e., that all implementations MUST support, and provides
the necessary structure for an automated key management protocol that
the PIM routers may use.
However, some gaps remain between the current state and the
requirements for manually keyed routing security expressed in the
[I-D.ietf-karp-threats-reqs] document. This document explores these
gaps and proposes directions for addressing the gaps.
2. Current State and Gap Analysis
[RFC5796] describes how IPsec can be used to secure and authenticate
PIM-SM protocol packets. It mandates the use of manual keying and
optionally provides support for an automated group key management
mechanism. However, it leaves the procedures for implementing
automated group key management to other documents and does not
discuss how this can be done.
[RFC5796] uses manually configured keys, rather than some automated
key management protocol , since no suitable key management mechanism
is available at this time. This is because PIM-SM adjacencies are
formed on a one-to-many basis and most key management mechanisms are
designed for a one-to-one communication model. Since [RFC5796] uses
manual keying it clearly states that it provides no protection
against both inter-session and intra-session replay attacks. This
can be exploited in several ways.
Since multiple PIM-SM routers can exist on a single link, it would be
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worth noting that setting up IPsec Security Associations (SAs)
manually can be a very tedious process. The routers might not even
support IPsec, rendering automatic key negotiation either impractical
(in those platforms where an extra license has to be obtained for
using IPsec) or infeasible (in those platforms where IPsec support is
not available at all).
While I don't yet see a need to prioritize certain PIM-SM packets
over the others, it should be noted that this would be extremely
difficult to achieve since PIM-SM uses IPsec for its security and
authentication.
[RFC4601] requires all PIM-SM routers to configure an IPsec Security
Association (SA) when sending PIM Register packets to each Rendezous
Point (RP). This can become highly unscalable as the number of RPs
increase or in case of Anycast-RP [RFC4610] deployment where each
PIM-SM router close to the source will need to establish IPsec
tunnels to all PIM-SM routers in the Anycast-RP set.
Similarly, the Security Policy Database at each Rendezvous Point
should be configured to choose an SA to use when sending Register-
Stop messages. Because Register-Stop messages are unicast to the
destination DR, a different SA and a potentially unique SPI are
required for each DR.
In order to simplify the management problem, [RFC4601] suggests using
the same authentication algorithm and authentication parameters,
regardless of the sending RP and regardless of the destination DR.
While this alleviates the management problem by some extent it still
requires a unique SA on each DR which can result in a significant
scaling issue as the size of the PIM-SM network grows.
In order to encourage deployment of PIM-SM security, an
authentication option is required that does not have the deployment
challenges of IPsec. We thus need an authentication mechanism
alternate to IPsec as part of the first phase of the KARP design
guide where we secure the routing protocols using manual keying.
The new mechanism should work for both the Unicast and Multicast
PIM-SM routing exchanges. It should also provide both inter-session
and intra-session replay protection that has been spelled out in the
[I-D.ietf-karp-threats-reqs] document.
3. Security Considerations
TBD
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4. IANA Considerations
This document places no new request to IANA
5. Acknowledgements
I would like to thank Stig Venaas and Bill Atwood for reviewing and
providing feedback on this draft.
6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
"Protocol Independent Multicast - Sparse Mode (PIM-SM):
Protocol Specification (Revised)", RFC 4601, August 2006.
[RFC5796] Atwood, W., Islam, S., and M. Siami, "Authentication and
Confidentiality in Protocol Independent Multicast Sparse
Mode (PIM-SM) Link-Local Messages", RFC 5796, March 2010.
6.2. Informative References
[I-D.ietf-karp-design-guide]
Lebovitz, G. and M. Bhatia, "Keying and Authentication for
Routing Protocols (KARP) Design Guidelines",
draft-ietf-karp-design-guide-02 (work in progress),
March 2011.
[I-D.ietf-karp-threats-reqs]
Lebovitz, G., Bhatia, M., and R. White, "The Threat
Analysis and Requirements for Cryptographic Authentication
of Routing Protocols' Transports",
draft-ietf-karp-threats-reqs-01 (work in progress),
October 2010.
[RFC4302] Kent, S., "IP Authentication Header", RFC 4302,
December 2005.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, December 2005.
[RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
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RFC 4306, December 2005.
[RFC4610] Farinacci, D. and Y. Cai, "Anycast-RP Using Protocol
Independent Multicast (PIM)", RFC 4610, August 2006.
Author's Address
Manav Bhatia
Alcatel-Lucent
India
Email: manav.bhatia@alcatel-lucent.com
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