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Packet Staining
NSA tracks Google ads to find Tor users:
GCHQ packet staining of Tor users:
Versions: 00 01

6man Working Group                                           T. Macaulay
Internet-Draft                                               Bell Canada
Intended status: Standards Track                       February 14, 2012
Expires: August 17, 2012


IPv6 packet staining


Abstract This document specifies the application of security staining on an IPv6 datagrams and the minimum requirements for IPv6 nodes staining flows, IPv6 nodes forwarding stained packets and interpreting stains on flows. The usage of the packet staining destination option enables proactive delivery of security intelligence to IPv6 nodes such as firewalls and intrusion prevention systems, and end-points such servers, workstations, mobile and smart devices and an infinite array of as- yet-to-be-invented sensors and controllers. 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 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 17, 2012. Copyright Notice Copyright (c) 2012 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 ( in effect on the date of publication of this document. Please review these documents Macaulay Expires August 17, 2012 [Page 1]

Internet-Draft            IPv6 Packet Staining             February 2012

   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.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions used in this document  . . . . . . . . . . . . . .  3
   3.  Background . . . . . . . . . . . . . . . . . . . . . . . . . .  3
     3.1.  Packet Staining Benefits . . . . . . . . . . . . . . . . .  4
     3.2.  Implementation and support models  . . . . . . . . . . . .  5
     3.3.  Use cases  . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Requirements for staining IPv6 packets . . . . . . . . . . . .  6
   5.  Packet Stain Destination Option (PSDO) . . . . . . . . . . . .  7
   6.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  8
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   9.  Normative References . . . . . . . . . . . . . . . . . . . . .  9
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 10

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1. Introduction

From the viewpoint of the network layer, a flow is a sequence of packets sent from a particular source to a particular unicast, anycast, or multicast destination. From an upper layer viewpoint, a flow could consist of all packets in one direction of a specific transport connection or media stream. However, a flow is not necessarily 1:1 mapped to a transport connection. Traditionally, flow classifiers have been based on the 5-tuple of the source and destination addresses, ports, and the transport protocol type. However, as the growth of internetworked devices continues under IPv6, security issues associated with the reputation of the source of flows are becoming a critical criterion associated with the trust of the data payloads and the security of the destination end- points and the networks on which they reside. The usage of security reputational intelligence associated with the source address field and possibly the port and protocol [REF1] enables packet-by-packet IPv6 security classification, where the IPv6 header extensions in the form of Destination Options may be used to stain each packet with security reputation information such that the network routing is unaffected, but intermediate security nodes and endpoint devices can apply policy decisions about incoming information flows without the requirement to assemble and treat payloads at higher levels of the stack. IPv6 packet staining support consists of labeling datagrams with security reputation information through the addition of an IPv6 destination option in the packet header by packet manipulation devices (PMDs) in the carrier or enterprise network. This destination option may be read by in-line security nodes upstream from the packet destination, as well as by the destination nodes themselves.

2. Conventions used in this document

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 [RFC2119].

3. Background

Internet based threats in the form of both malicious software and the agents that control this software (organized crime, spys, hackitivits) have surpassed the abilities of signature-based security Macaulay Expires August 17, 2012 [Page 3]

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   systems; whether they be on the enterprise perimeter, within the
   corporate network, on the endpoint point or in-the-cloud (internet-
   based service).  Additionally, the sensitivity of IP network
   continues to grow as new generation of smart devices is appearing on
   the networks in the form of broadband mobile devices, legacy
   industrial control devices, and very low-power sensors.  This diverse
   collections of IP-based assets is coming to be known as the Internet
   of Things (IOT).

   In response to the accelerating threats, the security vendor
   community have integrated their products with proprietary forms of
   security reputation intelligence.  This intelligence is about IP
   addresses and domains which have been observed engaged in attack-
   behaviours such as inappropriate messaging and traffic volumes,
   domain management, Botnet command-and-control channel exchanges and
   other indicators of either compromise or malicious intent.  [REF 1]
   IP address may also end up on a security reputation list if they are
   identified as compromised through vendor-specific signature-based
   processes.  Security reputation intelligence from vendors is
   typically made available to perimeter and end-point products through
   proprietary, internet-based queries to vendor information bases.

   This system of using proactive, security reputation intelligence has
   many benefits, but also several weakness and scaling challenges.
   Specifically, existing intelligence systems are:
   1.  subject to direct attack from the internet on distribution
       points, for instance
   2.  are proprietary to vendor devices
   3.  require fat-clients consuming both bandwidth and CPU, and
   4.  introduces flow latency while queries are sent, received and
   5.  introduces intelligence latency as reputation lists will be
       inevitably cached and only periodically refreshed given the
       number and range of vendor-specific processing elements

3.1. Packet Staining Benefits

In contrast to the challenges of current security reputation intelligence systems, packet staining has the following strengths 1. packet staining can occur transparently in the network, presenting no attack surface 2. packet staining uses standardized, public domain IPv6 capabilities 3. security rules can be easily applied in hardware or firmware 4. reading packet stains introduces little to no latency 5. near-real-time threat intelligence distribution systems can be implemented can be implemented out of band in PMDs using a standardized packet staining method allowing multiple Macaulay Expires August 17, 2012 [Page 4]

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       intelligence sources (vendor sources) to be aggregated and
       applied in an agnostic (cross-vendor) manner.

3.2. Implementation and support models

Packet staining may be accomplished by different entities including carriers, enterprises and third-party value-added service providers. Carriers or service providers may elect to implement staining centres at strategic locations in the network to provide value-added services on a subscription basis. Under this model, subscribers to a security staining service would see their traffic directed through a staining centre where Destination Options are added to the IPv6 headers and IPv4 traffic is encapsulated within IPv6 tunnels, with stained headers. Carriers or service providers may elect to stain all IPv6 traffic entering their network, and allow subscribers to process the stains at their own discretion. If such upstream, network-based staining services are inappropriate or unavailable, Enterprise data centre managers / cloud computing service providers may elect to deploy IPv6 staining at the perimeter into the internal network, tunnelling all IPv4 traffic, and allow data centre/cloud service users to process stains at their discretion. Enterprise may wish to deploy IPv6 on internal networks, and stain all internal traffic whereby security nodes and end-points may apply corporate security policy related to reputation.

3.3. Use cases

The following are example use-cases for a security technique based upon a packet staining system. Organization Perimeter Use-case Traffic to a subscriber is routed through a PMD in the carrier network configured to stain (apply Destination Options extensions) all packets to the subscriber (TM)s IP-range, which have entries in the threat intelligence information base. The PMD accesses the information base from a locally cached file or other method not defined in this draft. Packets from sources not in the information base pass through the PDM unchanged. Packets from sources in the information base have a Destinations Option added to the datagram header. The Destination Options contains reputation from the information base. The format of the destination option is discussed later in this draft. IPv6 perimeter devices such as firewalls, web proxies or security routers on the perimeter of the Macaulay Expires August 17, 2012 [Page 5]

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   subscriber network look for Destination Options on incoming packets
   with reputation stains.  If a stain is found, the perimeter device
   applies the organization policy associated with the reputation
   indicated by the stain.  For instance, drop the packet, quarantine
   the packet, issue alarms, or pass the packets and associated flow to
   specially hardened extra-net authentication systems, or do nothing.

   IPv4 support Use-case" IPv4 header fields and options are not
   suitable for packet staining; however, there is a clear security
   benefit to supporting IPv4 flows.  IPv4 traffic to a subscriber is
   routed through a PMD in the carrier network configured to encapsulate
   the IPv4 traffic in an IPv6 tunnel.  The PMD applies a stain
   (Destination Options extension) to the IPv6 tunnel as per the
   Perimeter Use-case above.  Subscriber perimeter devices such as
   firewalls, web proxies or security routers are configured to support
   both native IPv6 flows and IPv6 tunnels contain legacy IPv4 flows.
   Perimeter devices look for Destination Options on incoming IPv6
   packets with reputation stains.  If a stain is found, the perimeter
   device applies the organization policy associated with the reputation
   indicated by the stain to the IPv4 packet within the IPv6 tunnel.  In
   this manner IPv4 support may be transparent to end-users and

   IPv6 end-point use-case" IPv6 end-points may make use of reputation
   stains by processing Destination Options before engaging in any
   application level processing.  In the case of certain classes of
   smart device, remote and mobile sensors, reputation stains may be a
   critical form of security when other mitigations such as signature
   bases and firewalls are too power and processor intensive to support.

   URL-specific stains" it is a common occurrence to see large public
   content portals with millions of users sharing dozens of addresses.
   Frequently, malicious content will be loaded to such sites.  This
   content represents a very small fraction of the otherwise legitimate
   content on the site, which may be under the direct control of
   entirely separate entities .  Degrading the reputation of IP
   addresses used by these large portals based on a very small amount of
   content is problematic.  For such sites, reputation stains should
   have the ability to include the URL of malicious content, such that
   the reputation of the only specific portions of these large portals
   is degraded according to threat evidence, rather than the entire IP
   address, CIDR block, ASN or domain name.

4. Requirements for staining IPv6 packets

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   1.  The default behaviour of a security node MUST be to leave a
       packet unchanged (apply no stain).
   2.  Reputation stains may be inserted or overwritten by security
       nodes in the path.
   3.  Reputation stains may not be applied by the sender/source of the
   4.  The reputation staining mechanism needs to be visible to all
       stain-aware nodes on the path.
   5.  The mechanism needs to be able to traverse nodes that do not
       understand the reputation stains.  This is required to ensure
       that packet-staining can be incrementally deployed over the
   6.  The presence of the reputation staining mechanism should not
       significantly alter the processing of the packet by nodes, unless
       policy is explicitly configured.  This is required to ensure that
       stained packets do not face any undue delays or drops due to a
       badly chosen mechanism.
   7.  A PMD should be able to distinguish a trusted stain from an
       untrusted stain, through mechanism such as digital signatures or
       intrinsic trust among network elements.
   8.  A staining node MAY apply more specific and selective staining
       services according to subscriptions.  Staining nodes SHOULD
       support different reputation taxonomies to support different
       subscribers and/or interoperability with other staining entities,
       and have the ability to stain flows to different subscriber
       sources according to different semantics.

5. Packet Stain Destination Option (PSDO)

The Packet Stain Destination Option (PSDO) is a destination option that can be included in IPv6 datagrams that are inserted by PMDs in order to inform packet staining aware nodes on the path, or endpoints, that the PSDO has an alignment requirement of (none). 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option Type | Option Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |S|U| Stain Data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: Packet Stain Destination Option Layout Macaulay Expires August 17, 2012 [Page 7]

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   Option Type

      8-bit identifier of the type of option. The option identifier
      for the reputation stain option will be allocated by the IANA.

   Option Length

      8-bit unsigned integer.  The length of the option (excluding
      the Option Type and Option Length fields).

   S Bit

      When this bit is set, the reputation stain option has been signed.

   U Bit

      When this bit is set, the reputation stain option contains a
      malicious URL.

   Stain Data

      Contains the staining data.

6. Acknowledgements

The author wishes to achknowledge the guidance and support of Suresh Krishnan from Ericsson's Montreal lab. The author also wishes to credit Chris Mac-Stoker from NIKSUN for his substantial contributions to the early stages of the packet staining concept.

7. Security Considerations

Some implementation may elect to no apply digital signature to reputation stains in the Destination Option, in which case the stain is not protected in any way, even if IPsec authentication [RFC4302] is in use. Therefore an unsigned reputation stain can be forged by an on-path attacker. Implementers are advised that any en-route change to an unsigned security reputation stain value is undetectable. Therefore packet staining use the Destination Options extension without digital signatures requires intrinsic trust among the network elements and the PMD, and the destination node or intervening security nodes such as firewalls or IDS services. For this reason, receiving nodes MAY need to take account of the network from which the stained packet was received. For instance, a multi- homed organization may have some service providers with staining Macaulay Expires August 17, 2012 [Page 8]

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   services and others that do not.  A receiving node SHOULD be able to
   distinguish which source from which stains are expected.  A receiving
   node SHOULD by default ignore any reputation stains from sources
   (networks or devices) that have not been specifically configured as

   The reputation intelligence of IP source addresses, ASNs, CIDR blocks
   and domains is fundamental to the application of reputation stains
   within packet headers.  Such reputation information can be seeded
   from a variety of open and closed sources.  Poorly managed or
   compromised intelligence information bases can result in denial of
   service against legitimate IP addresses, and allow malicious entities
   to appear trustworthy.  Intelligence information bases themselves may
   be compromised in a variety of ways; for instance the raw information
   feeds may be corrupted with erroneous information, alternately the
   intelligence reputation algorithms could be flawed in design or
   corrupted such that they generate false reputation scores.  Therefore
   seed intelligence SHOULD be sourced and monitored with demonstratable
   diligence.  Similarly, reputation algorithms should be protected from
   unauthorized change with multi-layered access controls.

   The value of reputation stains will be directly proportional to the
   trustworthiness, reliability and reputation of the intelligence
   source itself.  Operators of security nodes SHOULD have defined and
   auditable methods upon which they select and manage the source of
   reputation intelligence and the packet staining infrastructure

8. IANA Considerations

This document defines a new IPv6 destination option for carrying security reputation packet stains. IANA is requested to assign a new destination option type (TBA1) in the Destination Options registry maintained at 1) Signed Security Reputation Option, 2) Unsigned Security Reputation Option 3) Signed Security Reputation Option with malicious URL 4) Unsigned Security Reputation Option with malicious URL The act bits for this option need to be 10 and the chg bit needs to be 0.

9. Normative References

[REF1] Macaulay, T., "Upstream Intelligence: anatomy, architecture, case studies and use-cases.", Information Assurance Newsletter, DOD , Aug to Feburary 2010 to 2011. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Macaulay Expires August 17, 2012 [Page 9]

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              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998.

Author's Address

   Tyson Macaulay
   Bell Canada
   160 Elgin Floor 5
   Ottawa, Ontario


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Related previous work:


Network Working Group                                        S. Bellovin
Request for Comments: 3514                            AT&T Labs Research
Category: Informational                                     1 April 2003


The Security Flag in the IPv4 Header

Status of this Memo This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2003). All Rights Reserved. Abstract Firewalls, packet filters, intrusion detection systems, and the like often have difficulty distinguishing between packets that have malicious intent and those that are merely unusual. We define a security flag in the IPv4 header as a means of distinguishing the two cases.

1. Introduction

Firewalls [CBR03], packet filters, intrusion detection systems, and the like often have difficulty distinguishing between packets that have malicious intent and those that are merely unusual. The problem is that making such determinations is hard. To solve this problem, we define a security flag, known as the "evil" bit, in the IPv4 [RFC791] header. Benign packets have this bit set to 0; those that are used for an attack will have the bit set to 1.

1.1. Terminology

The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this document, are to be interpreted as described in [RFC2119].

2. Syntax

The high-order bit of the IP fragment offset field is the only unused bit in the IP header. Accordingly, the selection of the bit position is not left to IANA. Bellovin Informational [Page 1]

RFC 3514          The Security Flag in the IPv4 Header      1 April 2003

   The bit field is laid out as follows:


   Currently-assigned values are defined as follows:

   0x0  If the bit is set to 0, the packet has no evil intent.  Hosts,
        network elements, etc., SHOULD assume that the packet is
        harmless, and SHOULD NOT take any defensive measures.  (We note
        that this part of the spec is already implemented by many common
        desktop operating systems.)

   0x1  If the bit is set to 1, the packet has evil intent.  Secure
        systems SHOULD try to defend themselves against such packets.
        Insecure systems MAY chose to crash, be penetrated, etc.

3. Setting the Evil Bit

There are a number of ways in which the evil bit may be set. Attack applications may use a suitable API to request that it be set. Systems that do not have other mechanisms MUST provide such an API; attack programs MUST use it. Multi-level insecure operating systems may have special levels for attack programs; the evil bit MUST be set by default on packets emanating from programs running at such levels. However, the system MAY provide an API to allow it to be cleared for non-malicious activity by users who normally engage in attack behavior. Fragments that by themselves are dangerous MUST have the evil bit set. If a packet with the evil bit set is fragmented by an intermediate router and the fragments themselves are not dangerous, the evil bit MUST be cleared in the fragments, and MUST be turned back on in the reassembled packet. Intermediate systems are sometimes used to launder attack connections. Packets to such systems that are intended to be relayed to a target SHOULD have the evil bit set. Some applications hand-craft their own packets. If these packets are part of an attack, the application MUST set the evil bit by itself. In networks protected by firewalls, it is axiomatic that all attackers are on the outside of the firewall. Therefore, hosts inside the firewall MUST NOT set the evil bit on any packets. Bellovin Informational [Page 2]

RFC 3514          The Security Flag in the IPv4 Header      1 April 2003

   Because NAT [RFC3022] boxes modify packets, they SHOULD set the evil
   bit on such packets.  "Transparent" http and email proxies SHOULD set
   the evil bit on their reply packets to the innocent client host.

   Some hosts scan other hosts in a fashion that can alert intrusion
   detection systems.  If the scanning is part of a benign research
   project, the evil bit MUST NOT be set.  If the scanning per se is
   innocent, but the ultimate intent is evil and the destination site
   has such an intrusion detection system, the evil bit SHOULD be set.

4. Processing of the Evil Bit

Devices such as firewalls MUST drop all inbound packets that have the evil bit set. Packets with the evil bit off MUST NOT be dropped. Dropped packets SHOULD be noted in the appropriate MIB variable. Intrusion detection systems (IDSs) have a harder problem. Because of their known propensity for false negatives and false positives, IDSs MUST apply a probabilistic correction factor when evaluating the evil bit. If the evil bit is set, a suitable random number generator [RFC1750] must be consulted to determine if the attempt should be logged. Similarly, if the bit is off, another random number generator must be consulted to determine if it should be logged despite the setting. The default probabilities for these tests depends on the type of IDS. Thus, a signature-based IDS would have a low false positive value but a high false negative value. A suitable administrative interface MUST be provided to permit operators to reset these values. Routers that are not intended as as security devices SHOULD NOT examine this bit. This will allow them to pass packets at higher speeds. As outlined earlier, host processing of evil packets is operating- system dependent; however, all hosts MUST react appropriately according to their nature.

5. Related Work

Although this document only defines the IPv4 evil bit, there are complementary mechanisms for other forms of evil. We sketch some of those here. For IPv6 [RFC2460], evilness is conveyed by two options. The first, a hop-by-hop option, is used for packets that damage the network, such as DDoS packets. The second, an end-to-end option, is for packets intended to damage destination hosts. In either case, the Bellovin Informational [Page 3]

RFC 3514          The Security Flag in the IPv4 Header      1 April 2003

   option contains a 128-bit strength indicator, which says how evil the
   packet is, and a 128-bit type code that describes the particular type
   of attack intended.

   Some link layers, notably those based on optical switching, may
   bypass routers (and hence firewalls) entirely.  Accordingly, some
   link-layer scheme MUST be used to denote evil.  This may involve evil
   lambdas, evil polarizations, etc.

   DDoS attack packets are denoted by a special diffserv code point.

   An application/evil MIME type is defined for Web- or email-carried
   mischief.  Other MIME types can be embedded inside of evil sections;
   this permit easy encoding of word processing documents with macro
   viruses, etc.

6. IANA Considerations

This document defines the behavior of security elements for the 0x0 and 0x1 values of this bit. Behavior for other values of the bit may be defined only by IETF consensus [RFC2434].

7. Security Considerations

Correct functioning of security mechanisms depend critically on the evil bit being set properly. If faulty components do not set the evil bit to 1 when appropriate, firewalls will not be able to do their jobs properly. Similarly, if the bit is set to 1 when it shouldn't be, a denial of service condition may occur.

8. References

[CBR03] W.R. Cheswick, S.M. Bellovin, and A.D. Rubin, "Firewalls and Internet Security: Repelling the Wily Hacker", Second Edition, Addison-Wesley, 2003. [RFC791] Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981. [RFC1750] Eastlake, D., 3rd, Crocker, S. and J. Schiller, "Randomness Recommendations for Security", RFC 1750, December 1994. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998. Bellovin Informational [Page 4]

RFC 3514          The Security Flag in the IPv4 Header      1 April 2003

   [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
             (IPv6) Specification", RFC 2460, December 1998.

   [RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network
             Address Translator (Traditional NAT)", RFC 3022, January

9. Author's Address

Steven M. Bellovin AT&T Labs Research Shannon Laboratory 180 Park Avenue Florham Park, NJ 07932 Phone: +1 973-360-8656 EMail:

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