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

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 working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/.

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This Internet-Draft will expire on October 15, 2011.

Copyright Notice

Copyright (c) 2011 IETF Trust and the persons identified as the document authors. All rights reserved.

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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 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

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

6.2. Informative References

Author's Address

Table of Contents

• 1. Introduction
• 2. Current State and Gap Analysis
• 3. Security Considerations
• 4. IANA Considerations
• 5. Acknowledgements
• 6. References
• 6.1. Normative References
• 6.2. Informative References
• Author's Address