Heuristics for Detecting ESP-NULL Packets
RFC 5879
Internet Engineering Task Force (IETF) T. Kivinen
Request for Comments: 5879 AuthenTec, Inc.
Category: Informational D. McDonald
ISSN: 2070-1721 Oracle Corporation
May 2010
Heuristics for Detecting ESP-NULL Packets
Abstract
This document describes a set of heuristics for distinguishing IPsec
ESP-NULL (Encapsulating Security Payload without encryption) packets
from encrypted ESP packets. These heuristics can be used on
intermediate devices, like traffic analyzers, and deep-inspection
engines, to quickly decide whether or not a given packet flow is
encrypted, i.e., whether or not it can be inspected. Use of these
heuristics does not require any changes made on existing IPsec hosts
that are compliant with RFC 4303.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc5879.
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RFC 5879 Heuristics for Detecting ESP-NULL May 2010
Copyright Notice
Copyright (c) 2010 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
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described in the Simplified BSD License.
Table of Contents
1. Introduction ....................................................3
1.1. Applicability: Heuristic Traffic Inspection and
Wrapped ESP ................................................4
1.2. Terminology ................................................4
2. Other Options ...................................................5
2.1. AH .........................................................5
2.2. Mandating by Policy ........................................6
2.3. Modifying ESP ..............................................6
3. Description of Heuristics .......................................6
4. IPsec Flows .....................................................7
5. Deep-Inspection Engine ..........................................9
6. Special and Error Cases .........................................9
7. UDP Encapsulation ..............................................10
8. Heuristic Checks ...............................................10
8.1. ESP-NULL Format ...........................................11
8.2. Self Describing Padding Check .............................12
8.3. Protocol Checks ...........................................14
8.3.1. TCP Checks .........................................15
8.3.2. UDP Checks .........................................16
8.3.3. ICMP Checks ........................................16
8.3.4. SCTP Checks ........................................17
8.3.5. IPv4 and IPv6 Tunnel Checks ........................17
9. Security Considerations ........................................17
10. References ....................................................18
10.1. Normative References .....................................18
10.2. Informative References ...................................18
Appendix A. Example Pseudocode ...................................20
A.1. Fastpath ..................................................20
A.2. Slowpath ..................................................23
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RFC 5879 Heuristics for Detecting ESP-NULL May 2010
1. Introduction
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