Routing Working Group M. Jethanandani Internet-Draft K. Patel Intended status: Informational Cisco Systems, Inc Expires: August 29, 2011 L. Zheng Huawei February 25, 2011 Analysis of BGP, LDP and MSDP Security According to KARP Design Guide draft-mahesh-bgp-ldp-msdp-analysis-00.txt Abstract This document analyzes BGP, LDP and MSDP according to guidelines set forth in section 4.2 of [draft-ietf-karp-design-guide]. 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/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on August 29, 2011. Copyright Notice Copyright (c) 2011 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Jethanandani, et al. Expires August 29, 2011 [Page 1] Internet-Draft BGP, LDP and MSDP Analysis February 2011 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Contributing Authors . . . . . . . . . . . . . . . . . . . 3 1.2. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 3 2. Current State of BGP, LDP and MSDP . . . . . . . . . . . . . . 4 2.1. LDP . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1.1. Spoofing attacks . . . . . . . . . . . . . . . . . . . 5 2.1.2. Privacy Issues . . . . . . . . . . . . . . . . . . . . 5 2.1.3. Denial of Service Attacks . . . . . . . . . . . . . . 6 2.2. MSDP . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3. Optimal State for BGP, LDP and MSDP . . . . . . . . . . . . . 7 3.1. LDP . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 4. Gap Analysis for BGP, LDP and MSDP . . . . . . . . . . . . . . 8 4.1. LDP . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 5. Security Requirements . . . . . . . . . . . . . . . . . . . . 10 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 7.1. Normative References . . . . . . . . . . . . . . . . . . . 12 7.2. Informative References . . . . . . . . . . . . . . . . . . 12 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13 Jethanandani, et al. Expires August 29, 2011 [Page 2] Internet-Draft BGP, LDP and MSDP Analysis February 2011 1. Introduction In March 2006 the Internet Architecture Board (IAB) in its "Unwanted Internet Traffic" workshop described an attack on core routing infrastructure as an ideal attack with the most amount of damage. It called for the tightening the security of the core routing infrastructure. This document performs the initial analysis of the current state of BGP, LDP and MSDP according to the requirements of [draft-ietf-karp-design-guide]. This draft builds on several previous analysis efforts into routing security. The OPSEC working group put together [draft-ietf-opsec-routing-protocols-crypto-issues] an analysis of cryptographic issues with routing protocols and draft-hartman-ospf-analysis-01 which has a analysis for OSPF. 1.1. Contributing Authors Anantha Ramaiah, Mach Chen 1.2. Abbreviations BGP - Border Gateway Protocol DoS - Denial of Service KARP - Key and Authentication for Routing Protocols KDF - Key Derivation Function KMP - Key Management Protocol LDP - Label Distribution Protocol LSR - Label Switch Routers MAC - Message Authentication Code MSDP - Multicast Source Distribution Protocol MD5 - Message Digest algorithm 5 OSPF - OPen Shortest Path First TCP - Tranmission Control Protocol UDP - User Datagram Protocol Jethanandani, et al. Expires August 29, 2011 [Page 3] Internet-Draft BGP, LDP and MSDP Analysis February 2011 2. Current State of BGP, LDP and MSDP This section describes the security mechanisms built into BGP, LDP and MSDP or in the underlying transport protocol. GTSM [RFC3682] describes a generalized Time to Live (TTL) security mechanism to protect a protocol stack from CPU-utilization based attacks. In addition, most vendors have their TCP based routing protocols do a access list check to permit packets only from known sources. These help preventing DoS attacks from unknown sources. TCP Robustness [RFC5961] recommends some TCP level mitigations against spoofing attacks targeted towards long lived routing protocol sessions. Session mode DoS attacks for LDP are the same attacks that TCP is vulnerable to such as SYN attacks. [To be updated] TCP MD5 [RFC2385] specifies a mechanism to protect BGP and other TCP sessions via the TCP MD5 option. TCP MD5 option provides a way for carrying an MD5 digest in a TCP segment. This digest acts like a signature for that segment, incorporating information known only to the connection end points. The MD5 key used to compute the digest is stored locally on the router. MD5 does not provide a generic mechanism to support Key roll-over. This option is used by routing protocols to provide for session level protection against the introduction of spoofed TCP segments into any existing TCP streams, in particular TCP Reset segments. However, the Message Authentication Codes (MACs) used by MD5 to compute the signature are considered to be too weak. TCP-AO [RFC5926] specifies a mechamism to protect BGP sessions and its data integrity using cryptographic authentication. In order to accomplish this funtion, it defines two MAC algorithms. It also defines two Key Derivation Functions (KDFs) used to create the traffic keys used by the newly defined and any future specified MACs. Cryptographic research suggests that both these MAC algorithms defined are fairly secured and are not known to be broken in any ways. In addition, there is no Key Management Protocol (KMP) used to manage the keys that are used for generating the Message Authentication Code (MAC). Most routers are configured with a static key that does not change over the life of the session. 2.1. LDP Section 5 of LDP [RFC5036] states that LDP is subject to three different types of attacks. It talks about spoofing, protection of Jethanandani, et al. Expires August 29, 2011 [Page 4] Internet-Draft BGP, LDP and MSDP Analysis February 2011 privacy of label distribution and denial of service attacks. 2.1.1. Spoofing attacks Spoofing attack occur both during the discover phase and during the session communication phase. 2.1.1.1. Discovery exchanges using UDP Label Switching Routers (LSRs) indicate their willingness to establish and maintain LDP sessions by periodically sending Hello messages. Receipt of a Hello message serves to create a new "Hello adjacency", if one does not already exist, or to refresh an existing one. Unlike all other LDP messages, the Hello messages are sent using UDP not TCP. This means that they cannot benefit from the security mechanisms available with TCP. LDP [RFC5036] does not provide any security mechanisms for use with Hello messages except to note that some configuration may help protect against bogus discovery events. Spoofing a Hello packet for an existing adjacency can cause the adjacency to time out and that can result in termination of the associated session. This can occur when the spoofed Hello message specifies a small Hold Time, causing the receiver to expect Hello messages within this interval, while the true neighbor continues sending Hello messages at the lower, previously agreed to, frequency. Spoofing a Hello packet can also cause the LDP session to be terminated directly. This can occur when the spoofed Hello specifies a different Transport Address from the previously agreed one between neighbors. Spoofed Hello messages are observed and reported as real problem in production networks. 2.1.1.2. Session communication using TCP LDP like other TCP based routing protocols specifies use of the TCP MD5 Signature Option to provide for the authenticity and integrity of session messages. As stated above, some assert that MD5 authentication is now considered by some to be too weak for this application. A stronger hashing algorithm e.g SHA1, could be deployed to take care of the weakness. 2.1.2. Privacy Issues LDP provides no mechanism for protecting the privacy of label distribution. The security requirements of label distribution are similar to other routing protocols that need to distribute routing Jethanandani, et al. Expires August 29, 2011 [Page 5] Internet-Draft BGP, LDP and MSDP Analysis February 2011 information. 2.1.3. Denial of Service Attacks LDP is subject to Denial of Service (DoS) attacks both in its discovery mode as well as during the session mode. The discovery mode attack is similar to the spoofing attack except that when the spoofed Hello messages are sent with a high enough frequency, they can cause the adjacency to time out. 2.2. MSDP Similar to BGP and LDP, TCP MD5 [RFC2385] specifies a mechanism to protect TCP sessions via the TCP MD5 option. But with a weak MD5 authentication, TCP MD5 is considered too weak for this application. MSDP also advocates imposing a limit on number of source address and group addresses (S,G) that can be stored within the protocol and thereby mitigate state explosion due to any denial of service and other attacks. Jethanandani, et al. Expires August 29, 2011 [Page 6] Internet-Draft BGP, LDP and MSDP Analysis February 2011 3. Optimal State for BGP, LDP and MSDP The ideal state for BGP, LDP and MSDP protocols are when they can withstand any of the known types of attacks. Additionally, Key Management Protocol (KMP) for the routing sessions should help negotiate unique, pair wise random keys without administrator involvement. It should also negotiate Security Association (SA) parameter required for the session connection, including key life times. It should keep track of those lifetimes and negotiate new keys and parameters before they expire and do so without administrator involvement. In the event of a breach, the keys should be changed immediately. The DoS attacks for BGP, LDP and MSDP are attacks to the transport protocol, TCP in this case. TCP should be able to withstand any of DoS scenarios by dropping packets that are attack packets in a way that does not impact legitimate packets. The routing protocols should provide a mechanism to authenticate and validate the routing information carried within the payload. 3.1. LDP For the spoofing kind of attacks that LDP is vulnerable to during the discovery phase, it should be able to determine the authenticity of the neighbors sending the Hello message. There is currently no requirement to protect the privacy of label distribution as labels are carried in the clear like other routing information. Jethanandani, et al. Expires August 29, 2011 [Page 7] Internet-Draft BGP, LDP and MSDP Analysis February 2011 4. Gap Analysis for BGP, LDP and MSDP This section outlines the differences between the current state of the routing protocol and the desired state as outlined in section 4.2 of [draft-ietf-karp-design-guide]. It covers issues that are common to the three protocols leaving protocol specific issues to sub- sections. The session layer that runs on TCP needs to protect itself by running TCP LISTEN only on interfaces on which its peers have been discovered or that are configured to expect sessions on. Also the use of access list can help protect the edge routers from attacks originating from outside the protected cloud. Inspite of this BGP, LDP and MDSP sessions are subject to spoofing and man in the middle attacks. While the MD5 option helps somewhat, without a KMP and a stronger MAC, these sessions are still vulnerable to attacks. TCP-AO [RFC5926]is a step towards correcting both the MAC weakness and KMP. For MAC it specifies two MAC algorithms that MUST be supported. Additional MACs can be added in the future. They are HMAC-SHA-1-96 as specified in HMAC [RFC2104] and AES-128-CMAC-96 as specified in [NIST-SP800-38B]. For KMP it requires that a Key Derivation Function (KDF) MUST be supported. They are KDF_HMAC-SHA1 and KDF_AES_128_CMAC. But this does not address the question of connectionless reset. [Need to add details about key rollover for manual keys and strategy for automatic keys here] There is a need to protect authenticity and validity of the routing/ label information that is carried in the payload of the sessions. However, we believe that is outside the scope of this document at this time and is being addressed by SIDR WG. Similar mechanisms could be used for intra-domain protocols. 4.1. LDP As described in LDP [RFC5036], the threat of spoofed Basic Hellos can be reduced by accepting Basic Hellos on interfaces that LSRs trust, and ignoring Basic Hellos not addressed to the "all routers on this subnet" multicast group. Spoofing attacks via Extended Hellos are potentially a more serious threat. An LSR can reduce the threat of spoofed Extended Hellos by filtering them and accepting Hellos from sources permitted by an access list. However, performing the filtering using access lists requires LSR resource, and the LSR is still vulnerable to the IP source address spoofing. Spoofing attacks Jethanandani, et al. Expires August 29, 2011 [Page 8] Internet-Draft BGP, LDP and MSDP Analysis February 2011 can be solved by being able to authenticate the Hello messages, and an LSR can be configured to only accept Hello messages from specific peers when authentication is in use. Jethanandani, et al. Expires August 29, 2011 [Page 9] Internet-Draft BGP, LDP and MSDP Analysis February 2011 5. Security Requirements This section describes requirements for BGP, LDP and MSFP security that should be met within the routing protocol. As with all routing protocols, they need protection from both on-path and off-path blind attacks. A better way to protect them would be with per-packet protection using a cryptographic MAC. Mechanisms are required in order to support key rollover. This should cover both manual and automatic key rollover. Multiple approaches could be used. However since the existing mechanisms provide a protocol field to identify the key as well as management mechanisms to introduce and retire new keys, focusing on the existing mechanism as a starting point is prudent. Replay protection is required. The replay mechanism needs to be sufficient to prevent an attacker from creating a denial of service or disrupting the integrity of the routing protocol by replaying packets. It is important that an attacker not be able to disrupt service by capturing packets and waiting for replay state to be lost. Jethanandani, et al. Expires August 29, 2011 [Page 10] Internet-Draft BGP, LDP and MSDP Analysis February 2011 6. Acknowledgements Jethanandani, et al. Expires August 29, 2011 [Page 11] Internet-Draft BGP, LDP and MSDP Analysis February 2011 7. References 7.1. Normative References [RFC2385] Heffernan, A., "Protection of BGP Sessions via the TCP MD5 Signature Option", RFC 2385, August 1998. [RFC5926] Lebovitz, G. and E. Rescorla, "Cryptographic Algorithms for the TCP Authentication Option (TCP-AO)", RFC 5926, June 2010. [draft-ietf-karp-design-guide] Lebovitz, G., "KARP Desgin Guidelines", September 2010. 7.2. Informative References [NIST-SP800-38B] Dworking, "Recommendation for Block Cipher Modes of Operation: The CMAC Mode for Authentication", May 2005. [RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed- Hashing for Message Authentication", RFC 2104, February 1997. [RFC3682] Gill, V., Heasley, J., and D. Meyer, "The Generalized TTL Security Mechanism (GTSM)", RFC 3682, February 2004. [RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway Protocol 4 (BGP-4)", RFC 4271, January 2006. [RFC5036] Andersson, L., Minei, I., and B. Thomas, "LDP Specification", RFC 5036, October 2007. [RFC5961] Ramaiah, A., Stewart, R., and M. Dalal, "Improving TCP's Robustness to Blind In-Window Attacks", RFC 5961, August 2010. [draft-ietf-opsec-routing-protocols-crypto-issues] Manral, "Issues with existing Cryptographic Protection Methods for Routing Protocols", September 2010. Jethanandani, et al. Expires August 29, 2011 [Page 12] Internet-Draft BGP, LDP and MSDP Analysis February 2011 Authors' Addresses Mahesh Jethanandani Cisco Systems, Inc 170 Tasman Drive San Jose, CA 95134 USA Phone: +1 (408) 527-8230 Email: mahesh@cisco.com Keyur Patel Cisco Systems, Inc 170 Tasman Drive San Jose, CA 95134 USA Phone: +1 (408) 526-7183 Email: keyupate@cisco.com Lianshu Zheng Huawei No. 3 Xinxi Road Beijing, 100085 China Phone: +86 (10) 82882008 Fax: Email: verozheng@huawei.com URI: Jethanandani, et al. Expires August 29, 2011 [Page 13]