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].
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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
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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
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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
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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
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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.
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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.
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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
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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.
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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.
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6. Acknowledgements
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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.
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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:
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