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Versions: 00 01 02

opsec                                                            F. Gont
Internet-Draft                                    UTN-FRH / SI6 Networks
Intended status: Best Current Practice                            W. Liu
Expires: February 27, 2015                           Huawei Technologies
                                                               R. Bonica
                                                        Juniper Networks
                                                         August 26, 2014


 Recommendations on Filtering of IPv6 Packets Containing IPv6 Extension
                                Headers
               draft-gont-opsec-ipv6-eh-filtering-02.txt

Abstract

   This document provides advice on the filtering of IPv6 packets based
   on the IPv6 Extension Headers and the IPv6 options they contain.
   Additionally, it discusses the operational and interoperability
   implications of discarding packets based on the IPv6 Extension
   Headers and IPv6 options they contain.

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 February 27, 2015.

Copyright Notice

   Copyright (c) 2014 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



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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology and Conventions Used in This Document . . . . . .   3
     2.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Conventions . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  IPv6 Extension Headers  . . . . . . . . . . . . . . . . . . .   4
     3.1.  General Discussion  . . . . . . . . . . . . . . . . . . .   4
     3.2.  General Security Implications . . . . . . . . . . . . . .   5
     3.3.  Advice on the Handling of IPv6 Packets with Specific IPv6
           Extension Headers . . . . . . . . . . . . . . . . . . . .   5
     3.4.  Advice on the Handling of Packets with Unknown IPv6
           Extension Headers . . . . . . . . . . . . . . . . . . . .  13
   4.  IPv6 Options  . . . . . . . . . . . . . . . . . . . . . . . .  14
     4.1.  General Discussion  . . . . . . . . . . . . . . . . . . .  14
     4.2.  General Security Implications of IPv6 Options . . . . . .  14
     4.3.  Advice on the Handling of Packets with Specific IPv6
           Options . . . . . . . . . . . . . . . . . . . . . . . . .  14
     4.4.  Advice on the handling of Packets with Unknown IPv6
           Options . . . . . . . . . . . . . . . . . . . . . . . . .  24
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  25
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  25
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  25
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  26
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  26
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  28
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  29

1.  Introduction

   Recent studies (see e.g.[I-D.gont-v6ops-ipv6-ehs-in-real-world])
   suggest that there is widespread filtering of IPv6 packets that
   contain IPv6 Extension Headers (EHs).  While some operators
   "officially" filter packets that contain IPv6 extension headers, it
   is possible that some of the measured packet drops be the result of
   improper configuration defaults, or inappropriate advice in this
   area.

   This document discusses the filtering of IPv6 packets based on the
   IPv6 Extension Headers and the IPv6 options they contain.  Since
   various protocols may use IPv6 Extension Headers (possibly with IPv6
   options), discarding packets based on the IPv6 Extension Headers or
   IPv6 options they contain may have implications on the proper



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   functioning of such protocols.  Thus, this document attempts to
   discuss the operational and interoperability implications of such
   filtering policies, and provide advice in this area.  This document
   is similar in nature to [RFC7126], which addresses the same problem
   for the IPv4 case.

   Section 2 of this document specifies the terminology and conventions
   employed throughout this document.  Section 3 of this document
   discusses IPv6 extension headers and provides advice in the area of
   filtering IPv6 packets that contain such IPv6 Extension Headers.
   Section 4 of this document discusses IPv6 options and provides advice
   in the area of filtering IPv6 packets that contain such options.

2.  Terminology and Conventions Used in This Document

2.1.  Terminology

   The terms "fast path", "slow path", and associated relative terms
   ("faster path" and "slower path") are loosely defined as in Section 2
   of [RFC6398].

   The terms "permit" (allow the traffic), "drop" (drop with no
   notification to sender), and "reject" (drop with appropriate
   notification to sender) are employed as defined in [RFC3871].
   Throughout this document we also employ the term "discard" as a
   generic term to indicate the act of discarding a packet, irrespective
   of whether the sender is notified of such drops.

   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].

2.2.  Conventions

   This document assumes that nodes comply with the requirements in
   [RFC7045].  Namely (from [RFC7045]),

   o  If a forwarding node discards a packet containing a standard IPv6
      extension header, it MUST be the result of a configurable policy
      and not just the result of a failure to recognise such a header.

   o  The discard policy for each standard type of extension header MUST
      be individually configurable.

   o  The default configuration SHOULD allow all standard extension
      headers.





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   The advice provided in this document is only meant to guide an
   operator in configuring forwarding devices, and is *not* to be
   interpreted as advice regarding default configuration settings for
   network devices.  That is, this document provides advice with respect
   to operational configurations, but does not change the implementation
   defaults required by [RFC7045] and
   [draft-gont-6man-ipv6-opt-transmit].

   We recommend that a configuration option is made available to govern
   the processing of each IPv6 Extension Header type and each IPv6
   option type.  Such configuration options may include the following
   possible settings:

   o  Permit this IPv6 Extension Header or IPv6 Option type

   o  Drop (and log) packets containing this IPv6 Extension Header or
      option type

   o  Reject (and log) packets containing this IPv6 Extension Header or
      option type (where the packet drop is signaled with an ICMPv6
      error message)

   o  Rate-limit the processing of packets containing this IPv6
      Extension Header or option type

   o  Ignore this IPv6 Extension Header or option type (forwarding
      packets that contain them)

   We note that special care needs to be taken when devices log packet
   drops/rejects.  Devices should count the number of packets dropped/
   rejected, but the logging of drop/reject events should be limited so
   as to not overburden device resources.

   Finally, we note that when discarding packets, it is generally
   desirable that the sender be signaled of the packet drop, since this
   is of use for trouble-shooting purposes.  However, throughout this
   document (when recommending that packets be discarded) we generically
   refer to the action as "discard" without specifying whether the
   sender is signaled of the packet drop.

3.  IPv6 Extension Headers

3.1.  General Discussion

   IPv6 [RFC2460] Extension Headers allow for the extension of the IPv6
   protocol.  Since both IPv6 Extension Headers and upper-layer
   protocols share the same namespace ("Next Header" registry/
   namespace), [RFC7045] identifies which of the currently assigned



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   Internet Protocol numbers identify IPv6 Extension Headers vs. upper-
   layer protocols.  This document discusses the filtering of packets
   based on the IPv6 Extension Headers (as specified by [RFC7045]) they
   contain.

      NOTE: [RFC7112] specifies that non-fragmented IPv6 datagrams and
      IPv6 First-Fragments MUST contain the entire IPv6 header chain
      [RFC7112].  Therefore, intermediate systems can always enforce the
      filtering policies discussed in this document, or resort to simply
      discarding the offending packets when they fail to comply with the
      requirements in [RFC7112].

3.2.  General Security Implications

   Depending on the specific device architecture, IPv6 packets that
   contain IPv6 Extension Headers may cause the corresponding packets to
   be processed on the slow path, and hence may be leveraged for the
   purpose of Denial of Service (DoS) attacks [Cisco-EH] [FW-Benchmark].

   Operators are urged to consider IPv6 Extension Header filtering and
   IPv6 options handling capabilities of different devices as they make
   deployment decisions in future.

3.3.  Advice on the Handling of IPv6 Packets with Specific IPv6
      Extension Headers

3.3.1.  IPv6 Hop-by-Hop Options (Protocol Number=0)

3.3.1.1.  Uses

   The Hop-by-Hop Options header is used to carry optional information
   that should be examined by every node along a packet's delivery path.

3.3.1.2.  Specification

   This Extension Header is specified in [RFC2460], and its processing
   rules have been updated by [RFC7045].  At the time of this writing,
   the following options have been specified for the Hop-by-Hop Options
   extension header:

   o  Type 0x05: Router Alert [RFC2711]

   o  Type 0xC2: Jumbo Payload [RFC2675]

   o  Type 0x63: RPL Option [RFC6553]

   o  Type 0x08: SMF_DPD [RFC6621]




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   o  Type 0x6D: MPL Option [I-D.ietf-roll-trickle-mcast]

   o  Type 0xEE: IPv6 DFF Header [RFC6971]

   o  Type 0x26: Quick-Start [RFC4782]

   o  Type 0x07: CALIPSO [RFC5570]

3.3.1.3.  Specific Security Implications

   Since this Extension Header should be processed by all intermediate-
   systems en route, it can be leveraged to perform Denial of Service
   attacks against the network infrastructure.

3.3.1.4.  Operational and Interoperability Impact if Blocked

   Discarding packets containing a Hop-by-Hop Option extension header
   would break any of the protocols that rely on it for proper
   functioning.  For example, it would break RSVP [RFC2205] and
   multicast deployments, and would cause IPv6 jumbograms to be
   discarded.

3.3.1.5.  Advice

   The recommended configuration for the processing of these packets
   depends on the features and capabilities of the underlying platform.
   On platforms that allow forwarding of packets with HBH Options on the
   fast path, we recommend that packets with a HBH Options extension
   header be forwarded as normal (for instance, [RFC7045] allows for
   implementations to ignore the HBH Options extension header when
   forwarding packets).  Otherwise, on platforms in which processing of
   packets with a IPv6 HBH Options extension header is carried out in
   the slow path, and an option is provided to rate-limit these packets,
   we recommend that this option be selected.  Finally, when packets
   containing a HBH Options extension header are processed in the slow-
   path, and the underlying platform does not have any mitigation
   options available for attacks based on these packets, we recommend
   that such platforms discard packets containing IPv6 HBH Options
   extension headers.

   Finally, we note that, for obvious reasons, RPL (Routing Protocol for
   Low-Power and Lossy Networks) [RFC6550] routers must not discard
   packets based on the presence of an IPv6 Hop-by-Hop Options Extension
   Header.







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3.3.2.  Routing Header for IPv6 (Protocol Number=43)

3.3.2.1.  Uses

   The Routing header is used by an IPv6 source to list one or more
   intermediate nodes to be "visited" on the way to a packet's
   destination.

3.3.2.2.  Specification

   This Extension Header is specified in [RFC2460].  [RFC2460]
   originally specified the Routing Header Type 0, which has been later
   obsoleted by [RFC5095].

   At the time of this writing, the following Routing Types have been
   specified:

   o  Type 0: Source Route (DEPRECATED) [RFC2460] [RFC5095]

   o  Type 1: Nimrod (DEPRECATED)

   o  Type 2: Type 2 Routing Header [RFC6275]

   o  Type 3: RPL Source Route Header [RFC6554]

   o  Types 4-252: Unassigned

   o  Type 253: RFC3692-style Experiment 1 [RFC4727]

   o  Type 254: RFC3692-style Experiment 2 [RFC4727]

   o  Type 255: Reserved

3.3.2.3.  Specific Security Implications

   The security implications of RHT0 have been discussed in detail in
   [Biondi2007] and [RFC5095].

3.3.2.4.  Operational and Interoperability Impact if Blocked

   Blocking packets containing a RHT0 or RTH1 has no operational
   implications.  However, blocking packets employing other routing
   header types will break the protocols that rely on them.








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3.3.2.5.  Advice

   Intermediate systems should discard packets containing a RHT0 or
   RHT1.  As required by [RFC7045], packets containing standardised and
   undeprecated Routing Headers should be permitted.

3.3.3.  Fragment Header for IPv6 (Protocol Number=44)

3.3.3.1.  Uses

   This Extension Header provides the fragmentation functionality for
   IPv6.

3.3.3.2.  Specification

   This Extension Header is specified in [RFC2460].

3.3.3.3.  Specific Security Implications

   The security implications of the Fragment Header range from Denial of
   Service attacks (e.g. based on flooding a target with IPv6 fragments)
   to information leakage attacks
   [I-D.ietf-6man-predictable-fragment-id].

3.3.3.4.  Operational and Interoperability Impact if Blocked

   Blocking packets that contain a Fragment Header will break any
   protocol that may rely on fragmentation (e.g., the DNS [RFC1034]).

3.3.3.5.  Advice

   Intermediate systems should permit packets that contain a Fragment
   Header.

3.3.4.  Encapsulating Security Payload (Protocol Number=50)

3.3.4.1.  Uses

   This extension Header is employed for the IPsec suite [RFC4303].

3.3.4.2.  Specification

   This extension header is specified in [RFC4303].








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3.3.4.3.  Specific Security Implications

   Besides the general implications of IPv6 Extension Headers, this
   extension header could be employed to potentially perform a DoS
   attack at the destination system by wasting CPU resources in
   validating the contents of the packet.

3.3.4.4.  Operational and Interoperability Impact if Blocked

   Discarding packets that employ this extension header would break
   IPsec deployments.

3.3.4.5.  Advice

   Intermediate systems should permit packets containing the
   Encapsulating Security Payload extension header.

3.3.5.  Authentication Header (Number=51)

3.3.5.1.  Uses

   The Authentication Header can be employed for provide authentication
   services in IPv4 and IPv6.

3.3.5.2.  Specification

   This Extension Header is specified in [RFC4302].

3.3.5.3.  Specific Security Implications

   Besides the general implications of IPv6 Extension Headers, this
   extension header could be employed to potentially perform a DoS
   attack at the destination system by wasting CPU resources in
   validating the contents of the packet.

3.3.5.4.  Operational and Interoperability Impact if Blocked

   Discarding packets that employ this extension header would break
   IPsec deployments.

3.3.5.5.  Advice

   Intermediate systems should permit packets containing an
   Authentication Header.







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3.3.6.  Destination Options for IPv6 (Protocol Number=60)

3.3.6.1.  Uses

   The Destination Options header is used to carry optional information
   that needs be examined only by a packet's destination node(s).

3.3.6.2.  Specification

   This Extension Header is specified in [RFC2460].  At the time of this
   writing, the following options have been specified for this extension
   header:

   o  Type 0x04: Tunnel Encapsulation Limit [RFC2473]

   o  Type 0xC9: Home Address [RFC6275]

   o  Type 0x8B: ILNP Nonce [RFC6744]

   o  Type 0x8C: Line-Identification Option [RFC6788]

3.3.6.3.  Specific Security Implications

   No security implications are known, other than the general
   implications of IPv6 extension headers.

3.3.6.4.  Operational and Interoperability Impact if Blocked

   Discarding packets that contain a Destination Options header would
   break protocols that rely on this EH type for conveying information,
   including protocols such as ILNP [RFC6740] and Mobile IPv6 [RFC6275],
   and IPv6 tunnels that employ the Tunnel Encapsulation Limit option.

3.3.6.5.  Advice

   Intermediate systems should permit packets that contain a Destination
   Options Header.

3.3.7.  Mobility Header (Number=135)

3.3.7.1.  Uses

   The Mobility Header is an extension header used by mobile nodes,
   correspondent nodes, and home agents in all messaging related to the
   creation and management of bindings in Mobile IPv6.






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3.3.7.2.  Specification

   This Extension Header is specified in [RFC6275].

3.3.7.3.  Specific Security Implications

   TBD.

3.3.7.4.  Operational and Interoperability Impact if Blocked

   Discarding packets containing this extension header would break
   Mobile IPv6.

3.3.7.5.  Advice

   Intermediate systems should permit packets containing this extension
   header.

3.3.8.  Host Identity Protocol (Protocol Number=139)

3.3.8.1.  Uses

   This extension header is employed with the Host Identity Protocol
   (HIP), an experimental protocol that allows consenting hosts to
   securely establish and maintain shared IP-layer state, allowing
   separation of the identifier and locator roles of IP addresses,
   thereby enabling continuity of communications across IP address
   changes.

3.3.8.2.  Specification

   This extension Header is specified in [RFC5201].

3.3.8.3.  Specific Security Implications

   TBD.

3.3.8.4.  Operational and Interoperability Impact if Blocked

   Discarding packets that contain the Host Identity Protocol would
   break HIP deployments.

3.3.8.5.  Advice

   Intermediate systems should permit packets that contain a Host
   Identity Protocol extension header.





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3.3.9.  Shim6 Protocol (Protocol Number=140)

3.3.9.1.  Uses

   This extension header is employed by the Shim6 [RFC5533] Protocol.

3.3.9.2.  Specification

   This Extension Header is specified in [RFC5533].

3.3.9.3.  Specific Security Implications

   TBD.

3.3.9.4.  Operational and Interoperability Impact if Blocked

   Discarding packets that contain this extension header will break
   Shim6.

3.3.9.5.  Advice

   Intermediate systems should permit packets containing this extension
   header.

3.3.10.  Use for experimentation and testing (Protocol Numbers=253 and
         254)

3.3.10.1.  Uses

   These IPv6 extension headers are employed for performing
   RFC3692-Style experiments (see [RFC3692] for details).

3.3.10.2.  Specification

   These Extension Headers are specified in [RFC3692] and [RFC4727].

3.3.10.3.  Specific Security Implications

   The security implications of these extension headers will depend on
   their specific use.

3.3.10.4.  Operational and Interoperability Impact if Blocked

   For obvious reasons, discarding packets that contain these extension
   headers limits the ability to perform legitimate experiments across
   IPv6 routers.





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3.3.10.5.  Advice

   Intermediate systems should discard packets containing these
   extension headers.  Only in specific scenarios in which RFC3692-Style
   experiments are to be performed should these extension headers be
   permitted.

3.4.  Advice on the Handling of Packets with Unknown IPv6 Extension
      Headers

   We refer to IPv6 extension headers that have not been assigned an
   Internet Protocol Number by IANA (and marked as such) in
   [IANA-PROTOCOLS] as "unknown IPv6 extension headers".

3.4.1.  Uses

   New IPv6 extension headers may be specified as part of future
   extensions to the IPv6 protocol.

   Since IPv6 Extension Headers and Upper-layer protocols employ the
   same namespace, it is impossible to tell whether an unknown "Internet
   Protocol Number" is being employed for an IPv6 Extension Header or an
   Upper-Layer protocol.

3.4.2.  Specification

   The processing of unknown IPv6 extension headers is specified in
   [RFC2460] and [RFC7045].

3.4.3.  Specific Security Implications

   For obvious reasons, it is impossible to determine specific security
   implications of unknown IPv6 extension headers.

3.4.4.  Operational and Interoperability Impact if Blocked

   As noted in [RFC7045], discarding unknown IPv6 extension headers may
   slow down the deployment of new IPv6 extension headers and transport
   protocols.  The corresponding IANA registry ([IANA-PROTOCOLS] should
   be monitored such that filtering rules are updated as new IPv6
   extension headers are standardized.

   We note that since IPv6 extension headers and upper-layer protocols
   share the same numbering space, discarding unknown IPv6 extension
   headers may result in packets encapsulating unknown upper-layer
   protocols being discarded.





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3.4.5.  Advice

   Intermediate systems should discard packets containing unknown IPv6
   extension headers.

4.  IPv6 Options

4.1.  General Discussion

   The following subsections describe specific security implications of
   different IPv6 options, and provide advice regarding filtering
   packets that contain such options.

4.2.  General Security Implications of IPv6 Options

   The general security implications of IPv6 options are closely related
   to those discussed in Section 3.2 for IPv6 Extension Headers.
   Essentially, packets that contain IPv6 options might need to be
   processed by an IPv6 router's general-purpose CPU,and hence could
   present a DDoS risk to that router's general-purpose CPU (and thus to
   the router itself).  For some architectures, a possible mitigation
   would be to rate-limit the packets that are to be processed by the
   general-purpose CPU (see e.g.  [Cisco-EH]).

4.3.  Advice on the Handling of Packets with Specific IPv6 Options

   The following subsections contain a description of each of the IPv6
   options that have so far been specified, a discussion of possible
   interoperability implications if packets containing such options are
   discarded, and specific advice regarding whether packets containing
   these options should be permitted.

4.3.1.  Pad1 (Type=0x00)

4.3.1.1.  Uses

   This option is used when necessary to align subsequent options and to
   pad out the containing header to a multiple of 8 octets in length.

4.3.1.2.  Specification

   This option is specified in [RFC2460].

4.3.1.3.  Specific Security Implications

   None.





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4.3.1.4.  Operational and Interoperability Impact if Blocked

   Discarding packets that contain this option would potentially break
   any protocol that relies on IPv6 extension headers.

4.3.1.5.  Advice

   Intermediate systems should not discard packets based on the presence
   of this option.

4.3.2.  PadN (Type=0x01)

4.3.2.1.  Uses

   This option is used when necessary to align subsequent options and to
   pad out the containing header to a multiple of 8 octets in length.

4.3.2.2.  Specification

   This option is specified in [RFC2460].

4.3.2.3.  Specific Security Implications

   Because of the possible size of this option, it could be leveraged as
   a large-bandwidth covert channel.

4.3.2.4.  Operational and Interoperability Impact if Blocked

   Discarding packets that contain this option would potentially break
   any protocol that relies on IPv6 extension headers.

4.3.2.5.  Advice

   Intermediate systems should not discard IPv6 packets based on the
   presence of this option.

4.3.3.  Jumbo Payload (Type=0XC2)

4.3.3.1.  Uses

   The Jumbo payload option provides the means of specifying payloads
   larger than 65535 bytes.

4.3.3.2.  Specification

   This option is specified in [RFC2675].





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4.3.3.3.  Specific Security Implications

   TBD.

4.3.3.4.  Operational and Interoperability Impact if Blocked

   Discarding packets based on the presence of this option will cause
   IPv6 jumbograms to be discarded.

4.3.3.5.  Advice

   Intermediate systems should discard packets that contain this option.
   An operator should permit this option only in specific scenarios in
   which support for IPv6 jumbograms is desired.

4.3.4.  RPL Option (Type=0x63)

4.3.4.1.  Uses

   The RPL Option provides a mechanism to include routing information
   with each datagram that an RPL router forwards.

4.3.4.2.  Specification

   This option is specified in [RFC6553].

4.3.4.3.  Specific Security Implications

   TBD.

4.3.4.4.  Operational and Interoperability Impact if Blocked

   This option is meant to be employed within an RPL instance.  As a
   result, discarding packets based on the presence of this option (e.g.
   at an ISP) will not result in interoperability implications.

4.3.4.5.  Advice

   Non-RPL routers should discard packets that contain an RPL option.

4.3.5.  Tunnel Encapsulation Limit (Type=0x04)

4.3.5.1.  Uses

   The Tunnel Encapsulation Limit option can be employed to specify how
   many further levels of nesting the packet is permitted to undergo.





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4.3.5.2.  Specification

   This option is specified in [RFC2473].

4.3.5.3.  Specific Security Implications

   TBD.

4.3.5.4.  Operational and Interoperability Impact if Blocked

   Discarding packets based on the presence of this option could result
   in tunnel traffic being discarded.

4.3.5.5.  Advice

   Intermediate systems should not discard packets based on the presence
   of this option.

4.3.6.  Router Alert (Type=0x05)

4.3.6.1.  Uses

   The Router Alert option [RFC2711] is typically employed for the RSVP
   protocol [RFC2205] and the MLD protocol [RFC2710].

4.3.6.2.  Specification

   This option is specified in [RFC2711].

4.3.6.3.  Specific Security Implications

   Since this option causes the contents of the packet to be inspected
   by the handling device, this option could be leveraged for performing
   DoS attacks.

4.3.6.4.  Operational and Interoperability Impact if Blocked

   Discarding packets that contain this option would break RSVP and
   multicast deployments.

4.3.6.5.  Advice

   Intermediate systems should discard packets that contain this option.
   Only in specific environments where support for RSVP or similar
   protocols is desired should this option be permitted.






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4.3.7.  Quick-Start (Type=0x26)

4.3.7.1.  Uses

   This IP Option is used in the specification of Quick-Start for TCP
   and IP, which is an experimental mechanism that allows transport
   protocols, in cooperation with routers, to determine an allowed
   sending rate at the start and, at times, in the middle of a data
   transfer (e.g., after an idle period) [RFC4782].

4.3.7.2.  Specification

   This option is specified in [RFC4782], on the "Experimental" track.

4.3.7.3.  Specific Security Implications

   Section 9.6 of [RFC4782] notes that Quick-Start is vulnerable to two
   kinds of attacks:

   o  attacks to increase the routers' processing and state load, and,

   o  attacks with bogus Quick-Start Requests to temporarily tie up
      available Quick-Start bandwidth, preventing routers from approving
      Quick-Start Requests from other connections.

   We note that if routers in a given environment do not implement and
   enable the Quick-Start mechanism, only the general security
   implications of IP options (discussed in Section 4.2) would apply.

4.3.7.4.  Operational and Interoperability Impact if Blocked

   The Quick-Start functionality would be disabled, and additional
   delays in TCP's connection establishment (for example) could be
   introduced.  (Please see Section 4.7.2 of [RFC4782].)  We note,
   however, that Quick-Start has been proposed as a mechanism that could
   be of use in controlled environments, and not as a mechanism that
   would be intended or appropriate for ubiquitous deployment in the
   global Internet [RFC4782].

4.3.7.5.  Advice

   Intermediate systems should not discard IPv6 packets based on the
   presence of this option.








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4.3.8.  CALIPSO (Type=0x07)

4.3.8.1.  Uses

   This option is used for encoding explicit packet Sensitivity Labels
   on IPv6 packets.  It is intended for use only within Multi-Level
   Secure (MLS) networking environments that are both trusted and
   trustworthy.

4.3.8.2.  Specification

   This option is specified in [RFC5570].

4.3.8.3.  Specific Security Implications

   Presence of this option in a packet does not by itself create any
   specific new threat.  Packets with this option ought not normally be
   seen on the global public Internet.

4.3.8.4.  Operational and Interoperability Impact if Blocked

   If packets with this option are discarded or if the option is
   stripped from the packet during transmission from source to
   destination, then the packet itself is likely to be discarded by the
   receiver because it is not properly labeled.  In some cases, the
   receiver might receive the packet but associate an incorrect
   sensitivity label with the received data from the packet whose
   CALIPSO was stripped by an intermediate router or firewall.
   Associating an incorrect sensitivity label can cause the received
   information either to be handled as more sensitive than it really is
   ("upgrading") or as less sensitive than it really is ("downgrading"),
   either of which is problematic.

4.3.8.5.  Advice

   Intermediate systems that do not operate in Multi-Level Secure (MLS)
   networking environments should discard packets that contain this
   option.

4.3.9.  SMF_DPD (Type=0x08)

4.3.9.1.  Uses

   This option is employed in the (experimental) Simplified Multicast
   Forwarding (SMF) for unique packet identification for IPv6 I-DPD, and
   as a mechanism to guarantee non-collision of hash values for
   different packets when H-DPD is used.




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4.3.9.2.  Specification

   This option is specified in [RFC6621].

4.3.9.3.  Specific Security Implications

   TBD.

4.3.9.4.  Operational and Interoperability Impact if Blocked

   TBD.

4.3.9.5.  Advice

   TBD.

4.3.10.  Home Address (Type=0xC9)

4.3.10.1.  Uses

   The Home Address option is used by a Mobile IPv6 node while away from
   home, to inform the recipient of the mobile node's home address.

4.3.10.2.  Specification

   This option is specified in [RFC6275].

4.3.10.3.  Specific Security Implications

   TBD.

4.3.10.4.  Operational and Interoperability Impact if Blocked

   Discarding IPv6 packets based on the presence of this option will
   break Mobile IPv6.

4.3.10.5.  Advice

   Intermediate systems should not discard IPv6 packets based on the
   presence of this option.

4.3.11.  Endpoint Identification (Type=0x8A)

4.3.11.1.  Uses

   The Endpoint Identification option was meant to be used with the
   Nimrod routing architecture [NIMROD-DOC], but has never seen
   widespread deployment.



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4.3.11.2.  Specification

   This option is specified in [NIMROD-DOC].

4.3.11.3.  Specific Security Implications

   TBD.

4.3.11.4.  Operational and Interoperability Impact if Blocked

   None.

4.3.11.5.  Advice

   Intermediate systems should discard packets that contain this option.

4.3.12.  ILNP Nonce (Type=0x8B)

4.3.12.1.  Uses

   This option is employed by Identifier-Locator Network Protocol for
   IPv6 (ILNPv6) for providing protection against off-path attacks for
   packets when ILNPv6 is in use, and as a signal during initial
   network-layer session creation that ILNPv6 is proposed for use with
   this network-layer session, rather than classic IPv6.

4.3.12.2.  Specification

   This option is specified in [RFC6744].

4.3.12.3.  Specific Security Implications

   TBD.

4.3.12.4.  Operational and Interoperability Impact if Blocked

   Discarding packets that contain this option will break INLPv6
   deployments.

4.3.12.5.  Advice

   Intermediate systems should not discard packets based on the presence
   of this option.








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4.3.13.  Line-Identification Option (Type=0x8C)

4.3.13.1.  Uses

   This option is used by an Edge Router to identify the subscriber
   premises in scenarios where several subscriber premises may be
   logically connected to the same interface of an Edge Router.

4.3.13.2.  Specification

   This option is specified in [RFC6788].

4.3.13.3.  Specific Security Implications

   TBD.

4.3.13.4.  Operational and Interoperability Impact if Blocked

   Since this option is meant to be employed in Router Solicitation
   messages, discarding packets based on the presence of this option at
   intermediate systems will result in no interoperability implications.

4.3.13.5.  Advice

   Intermediate devices should discard packets that contain this option.

4.3.14.  Deprecated (Type=0x4D)

4.3.14.1.  Uses

   No information has been found about this option type.

4.3.14.2.  Specification

   No information has been found about this option type.

4.3.14.3.  Specific Security Implications

   No information has been found about this option type, and hence it
   has been impossible to perform the corresponding security assessment.

4.3.14.4.  Operational and Interoperability Impact if Blocked

   Unknown.







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4.3.14.5.  Advice

   Intermediate systems should discard packets that contain this option.

4.3.15.  MPL Option (Type=0x6D)

4.3.15.1.  Uses

   This option is used with the Multicast Protocol for Low power and
   Lossy Networks (MPL), that provides IPv6 multicast forwarding in
   constrained networks.

4.3.15.2.  Specification

   This option is specified in [I-D.ietf-roll-trickle-mcast], and is
   meant to be included only in Hop-by-Hop Option headers.

4.3.15.3.  Specific Security Implications

   TBD.

4.3.15.4.  Operational and Interoperability Impact if Blocked

   TBD.

4.3.15.5.  Advice

   TBD.

4.3.16.  IP_DFF (Type=0xEE)

4.3.16.1.  Uses

   This option is employed with the (Experimental) Depth-First
   Forwarding (DFF) in Unreliable Networks.

4.3.16.2.  Specification

   This option is specified in [RFC6971].

4.3.16.3.  Specific Security Implications

   TBD.








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4.3.16.4.  Operational and Interoperability Impact if Blocked

   TBD.

4.3.16.5.  Advice

   TBD.

4.3.17.  RFC3692-style Experiment (Types = 0x1E, 0x3E, 0x5E, 0x7E, 0x9E,
         0xBE, 0xDE, 0xFE)

4.3.17.1.  Uses

   These options can be employed for performing RFC3692-style
   experiments.  It is only appropriate to use these values in
   explicitly configured experiments; they must not be shipped as
   defaults in implementations.

4.3.17.2.  Specification

   Specified in RFC 4727 [RFC4727] in the context of RFC3692-style
   experiments.

4.3.17.3.  Specific Security Implications

   The specific security implications will depend on the specific use of
   these options.

4.3.17.4.  Operational and Interoperability Impact if Blocked

   For obvious reasons, discarding packets that contain these options
   limits the ability to perform legitimate experiments across IPv6
   routers.

4.3.17.5.  Advice

   Intermediate systems should discard packets that contain these
   options.  Only in specific environments where RFC3692-style
   experiments are meant to be performed should these options be
   permitted.

4.4.  Advice on the handling of Packets with Unknown IPv6 Options

   We refer to IPv6 options that have not been assigned an IPv6 option
   type in the corresponding registry ([IANA-IPV6-PARAM]) as "unknown
   IPv6 options".





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4.4.1.  Uses

   New IPv6 options may be specified as part of future protocol work.

4.4.2.  Specification

   The processing of unknown IPv6 options is specified in [RFC2460].

4.4.3.  Specific Security Implications

   For obvious reasons, it is impossible to determine specific security
   implications of unknown IPv6 options.

4.4.4.  Operational and Interoperability Impact if Blocked

   Discarding unknown IPv6 options may slow down the deployment of new
   IPv6 options.  As noted in [draft-gont-6man-ipv6-opt-transmit], the
   corresponding IANA registry ([IANA-IPV6-PARAM] should be monitored
   such that IPv6 option filtering rules are updated as new IPv6 options
   are standardized.

4.4.5.  Advice

   Enterprise intermediate systems that process the contents of IPv6
   extension headers should discard packets that contain unknown
   options.  Other intermediate systems that process the contents of
   IPv6 extension headers should permit packets that contain unknown
   options.

5.  IANA Considerations

   This document has no actions for IANA.

6.  Security Considerations

   This document provides advice on the filtering of IPv6 packets that
   contain IPv6 Extension Headers (and possibly IPv6 options).
   Discarding such packets can help to mitigate the security issues that
   arise from the use of different IPv6 Extension Headers and options.

7.  Acknowledgements

   The authors of this document would like to thank (in alphabetical
   order) Mikael Abrahamsson, Brian Carpenter, Mike Heard, and Donald
   Smith, for providing valuable comments on earlier versions of this
   document.





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   This document borrows some text an analysis from [RFC7126], authored
   by Fernando Gont, Randall Atkinson, and Carlos Pignataro.

8.  References

8.1.  Normative References

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, November 1987.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2205]  Braden, B., Zhang, L., Berson, S., Herzog, S., and S.
              Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
              Functional Specification", RFC 2205, September 1997.

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

   [RFC2473]  Conta, A. and S. Deering, "Generic Packet Tunneling in
              IPv6 Specification", RFC 2473, December 1998.

   [RFC2675]  Borman, D., Deering, S., and R. Hinden, "IPv6 Jumbograms",
              RFC 2675, August 1999.

   [RFC2710]  Deering, S., Fenner, W., and B. Haberman, "Multicast
              Listener Discovery (MLD) for IPv6", RFC 2710, October
              1999.

   [RFC2711]  Partridge, C. and A. Jackson, "IPv6 Router Alert Option",
              RFC 2711, October 1999.

   [RFC3692]  Narten, T., "Assigning Experimental and Testing Numbers
              Considered Useful", BCP 82, RFC 3692, January 2004.

   [RFC4302]  Kent, S., "IP Authentication Header", RFC 4302, December
              2005.

   [RFC4303]  Kent, S., "IP Encapsulating Security Payload (ESP)", RFC
              4303, December 2005.

   [RFC4304]  Kent, S., "Extended Sequence Number (ESN) Addendum to
              IPsec Domain of Interpretation (DOI) for Internet Security
              Association and Key Management Protocol (ISAKMP)", RFC
              4304, December 2005.





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   [RFC4727]  Fenner, B., "Experimental Values In IPv4, IPv6, ICMPv4,
              ICMPv6, UDP, and TCP Headers", RFC 4727, November 2006.

   [RFC4782]  Floyd, S., Allman, M., Jain, A., and P. Sarolahti, "Quick-
              Start for TCP and IP", RFC 4782, January 2007.

   [RFC5095]  Abley, J., Savola, P., and G. Neville-Neil, "Deprecation
              of Type 0 Routing Headers in IPv6", RFC 5095, December
              2007.

   [RFC5201]  Moskowitz, R., Nikander, P., Jokela, P., and T. Henderson,
              "Host Identity Protocol", RFC 5201, April 2008.

   [RFC5533]  Nordmark, E. and M. Bagnulo, "Shim6: Level 3 Multihoming
              Shim Protocol for IPv6", RFC 5533, June 2009.

   [RFC5570]  StJohns, M., Atkinson, R., and G. Thomas, "Common
              Architecture Label IPv6 Security Option (CALIPSO)", RFC
              5570, July 2009.

   [RFC6275]  Perkins, C., Johnson, D., and J. Arkko, "Mobility Support
              in IPv6", RFC 6275, July 2011.

   [RFC6398]  Le Faucheur, F., "IP Router Alert Considerations and
              Usage", BCP 168, RFC 6398, October 2011.

   [RFC6550]  Winter, T., Thubert, P., Brandt, A., Hui, J., Kelsey, R.,
              Levis, P., Pister, K., Struik, R., Vasseur, JP., and R.
              Alexander, "RPL: IPv6 Routing Protocol for Low-Power and
              Lossy Networks", RFC 6550, March 2012.

   [RFC6553]  Hui, J. and JP. Vasseur, "The Routing Protocol for Low-
              Power and Lossy Networks (RPL) Option for Carrying RPL
              Information in Data-Plane Datagrams", RFC 6553, March
              2012.

   [RFC6554]  Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6
              Routing Header for Source Routes with the Routing Protocol
              for Low-Power and Lossy Networks (RPL)", RFC 6554, March
              2012.

   [RFC6621]  Macker, J., "Simplified Multicast Forwarding", RFC 6621,
              May 2012.

   [RFC6740]  Atkinson,, RJ., "Identifier-Locator Network Protocol
              (ILNP) Architectural Description", RFC 6740, November
              2012.




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   [RFC6744]  Atkinson,, RJ., "IPv6 Nonce Destination Option for the
              Identifier-Locator Network Protocol for IPv6 (ILNPv6)",
              RFC 6744, November 2012.

   [RFC6788]  Krishnan, S., Kavanagh, A., Varga, B., Ooghe, S., and E.
              Nordmark, "The Line-Identification Option", RFC 6788,
              November 2012.

   [RFC6971]  Herberg, U., Cardenas, A., Iwao, T., Dow, M., and S.
              Cespedes, "Depth-First Forwarding (DFF) in Unreliable
              Networks", RFC 6971, June 2013.

   [RFC7045]  Carpenter, B. and S. Jiang, "Transmission and Processing
              of IPv6 Extension Headers", RFC 7045, December 2013.

   [RFC7112]  Gont, F., Manral, V., and R. Bonica, "Implications of
              Oversized IPv6 Header Chains", RFC 7112, January 2014.

   [draft-gont-6man-ipv6-opt-transmit]
              Gont, F., Liu, W., and R. Bonica, "Transmission and
              Processing of IPv6 Options", IETF Internet Draft, work in
              progress, August 2014.

8.2.  Informative References

   [Biondi2007]
              Biondi, P. and A. Ebalard, "IPv6 Routing Header Security",
              CanSecWest 2007 Security Conference, 2007,
              <http://www.secdev.org/conf/IPv6_RH_security-csw07.pdf>.

   [Cisco-EH]
              Cisco Systems, , "IPv6 Extension Headers Review and
              Considerations", Whitepaper. October 2006,
              <http://www.cisco.com/en/US/technologies/tk648/tk872/
              technologies_white_paper0900aecd8054d37d.pdf>.

   [FW-Benchmark]
              Zack, E., "Firewall Security Assessment and Benchmarking
              IPv6 Firewall Load Tests", IPv6 Hackers Meeting #1,
              Berlin, Germany. June 30, 2013,
              <http://www.ipv6hackers.org/meetings/ipv6-hackers-1/zack-
              ipv6hackers1-firewall-security-assessment-and-
              benchmarking.pdf>.

   [I-D.gont-v6ops-ipv6-ehs-in-real-world]
              Gont, F., Linkova, J., Chown, T., and W. Will, "IPv6
              Extension Headers in the Real World", draft-gont-v6ops-
              ipv6-ehs-in-real-world-00 (work in progress), August 2014.



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   [I-D.ietf-6man-predictable-fragment-id]
              Gont, F., "Security Implications of Predictable Fragment
              Identification Values", draft-ietf-6man-predictable-
              fragment-id-01 (work in progress), April 2014.

   [I-D.ietf-roll-trickle-mcast]
              Hui, J. and R. Kelsey, "Multicast Protocol for Low power
              and Lossy Networks (MPL)", draft-ietf-roll-trickle-
              mcast-09 (work in progress), April 2014.

   [IANA-IPV6-PARAM]
              Internet Assigned Numbers Authority, "Internet Protocol
              Version 6 (IPv6) Parameters", December 2013,
              <http://www.iana.org/assignments/ipv6-parameters/
              ipv6-parameters.xhtml>.

   [IANA-PROTOCOLS]
              Internet Assigned Numbers Authority, "Protocol Numbers",
              2014, <http://www.iana.org/assignments/protocol-numbers/
              protocol-numbers.xhtml>.

   [NIMROD-DOC]
              Nimrod Documentation Page, ,
              "http://ana-3.lcs.mit.edu/~jnc/nimrod/", .

   [RFC3871]  Jones, G., "Operational Security Requirements for Large
              Internet Service Provider (ISP) IP Network
              Infrastructure", RFC 3871, September 2004.

   [RFC7126]  Gont, F., Atkinson, R., and C. Pignataro, "Recommendations
              on Filtering of IPv4 Packets Containing IPv4 Options", BCP
              186, RFC 7126, February 2014.

Authors' Addresses

   Fernando Gont
   UTN-FRH / SI6 Networks
   Evaristo Carriego 2644
   Haedo, Provincia de Buenos Aires  1706
   Argentina

   Phone: +54 11 4650 8472
   Email: fgont@si6networks.com
   URI:   http://www.si6networks.com







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   Will(Shucheng) Liu
   Huawei Technologies
   Bantian, Longgang District
   Shenzhen  518129
   P.R. China

   Email: liushucheng@huawei.com


   Ronald P. Bonica
   Juniper Networks
   2251 Corporate Park Drive
   Herndon, VA  20171
   US

   Phone: 571 250 5819
   Email: rbonica@juniper.net


































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