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Versions: (draft-gont-opsec-ip-options-filtering) 00 01 02 03 04 05 06 07 RFC 7126

Operational Security Capabilities for                            F. Gont
IP Network Infrastructure (opsec)                 UTN-FRH / SI6 Networks
Internet-Draft                                               R. Atkinson
Intended status: BCP                                          Consultant
Expires: December 13, 2012                                  C. Pignataro
                                                                   Cisco
                                                           June 11, 2012


  Recommendations on filtering of IPv4 packets containing IPv4 options
              draft-ietf-opsec-ip-options-filtering-00.txt

Abstract

   This document document provides advice on the filtering of IPv4
   packets based on the IPv4 options they contain.  Additionally, it
   discusses the operational and interoperability implications of
   dropping packets based on the IP 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 December 13, 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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of



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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Terminology and Conventions Used in This Document  . . . .  3
   2.  IP Options . . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  General Security Implications of IP options  . . . . . . . . .  5
     3.1.  Processing Requirements  . . . . . . . . . . . . . . . . .  5
   4.  Advice on the Handling of Packets with Specific IP Options . .  5
     4.1.  End of Option List (Type = 0)  . . . . . . . . . . . . . .  5
     4.2.  No Operation (Type = 1)  . . . . . . . . . . . . . . . . .  6
     4.3.  Loose Source and Record Route (LSRR) (Type = 131)  . . . .  7
     4.4.  Strict Source and Record Route (SSRR) (Type = 137) . . . .  8
     4.5.  Record Route (Type = 7)  . . . . . . . . . . . . . . . . .  9
     4.6.  Stream Identifier (Type = 136) (obsolete)  . . . . . . . . 10
     4.7.  Internet Timestamp (Type = 68) . . . . . . . . . . . . . . 11
     4.8.  Router Alert (Type = 148)  . . . . . . . . . . . . . . . . 12
     4.9.  Probe MTU (Type = 11) (obsolete) . . . . . . . . . . . . . 13
     4.10. Reply MTU (Type = 12) (obsolete) . . . . . . . . . . . . . 13
     4.11. Traceroute (Type = 82) . . . . . . . . . . . . . . . . . . 14
     4.12. DoD Basic Security Option (Type = 130) . . . . . . . . . . 14
     4.13. DoD Extended Security Option (Type = 133)  . . . . . . . . 16
     4.14. Commercial IP Security Option (CIPSO) (Type = 134) . . . . 17
     4.15. VISA (Type = 142)  . . . . . . . . . . . . . . . . . . . . 19
     4.16. Extended Internet Protocol (Type = 145)  . . . . . . . . . 19
     4.17. Address Extension (Type = 147) . . . . . . . . . . . . . . 20
     4.18. Sender Directed Multi-Destination Delivery (Type = 149)  . 20
     4.19. Dynamic Packet State (Type = 151)  . . . . . . . . . . . . 21
     4.20. Upstream Multicast Pkt. (Type = 152) . . . . . . . . . . . 22
     4.21. Quick-Start (Type = 25)  . . . . . . . . . . . . . . . . . 22
     4.22. RFC3692-style Experiment (Types = 30, 94, 158, and 222)  . 23
     4.23. Other IP Options . . . . . . . . . . . . . . . . . . . . . 24
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 25
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 25
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 25
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 25
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 25
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 26
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29









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1.  Introduction

   This document document discusses the filtering of IPv4 packets based
   on the IPv4 options they contain.  Since various protocols may use
   IPv4 options to some extent, dropping packets based on the options
   they contain may have implications on the proper functioning of the
   protocol.  Therefore, this document attempts to discuss the
   operational and interoperability implications of such dropping.
   Additionally, it outlines what a network operator might do in a
   typical enterprise or Service Provider environments.

   We note that data seems to indicate that there is a current
   widespread practice of blocking IPv4 optioned packets.  There are
   various plausible approaches to minimize the potential negative
   effects of IPv4 optioned packets while allowing some options
   semantics.  One approach is to allow for specific options that are
   expected or needed, and a default deny.  A different approach is to
   deny unneeded options and a default allow.  Yet a third possible
   approach is to allow for end-to-end semantics by ignoring options and
   treating packets as un-optioned while in transit.  Experiments and
   currently-available data tends to support the first or third
   approaches as more realistic.  Some results of regarding the current
   state of affairs with respect to dropping packets containing IP
   options can be found in [MEDINA].

   We also note that while this document provides advice on dropping
   packets on a "per IP option type", not all devices may provide this
   capability with such granularity.  Additionally, even in cases in
   which such functionality is provided, the operator might want to
   specify a dropping policy with a coarser granularity (rather than on
   a "per IP option type" granularity), as indicated above.

   Finally, in scenarios in which processing of IP options by
   intermediate systems is not required, a widespread approach is to
   simply ignore IP options, and process the corresponding packets as if
   they do not contain any IP options.

1.1.  Terminology and Conventions Used in This Document

   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 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].





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2.  IP Options

   IP options allow for the extension of the Internet Protocol

   There are two cases for the format of an option:

   o  Case 1: A single byte of option-type.

   o  Case 2: An option-type byte, an option-length byte, and the actual
      option-data bytes.

   IP options of Case 1 have the following syntax:

   +-+-+-+-+-+-+-+-+- - - - - - - - -
   |  option-type  |  option-data
   +-+-+-+-+-+-+-+-+- - - - - - - - -

   The length of IP options of Case 1 is implicitly specified by the
   option-type byte.

   IP options of Case 2 have the following syntax:

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - -
   |  option-type  | option-length |  option-data
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - -

   In this case, the option-length byte counts the option-type byte and
   the option-length byte, as well as the actual option-data bytes.

   All current and future options except "End of Option List" (Type = 0)
   and "No Operation" (Type = 1), are of Class 2.

   The option-type has three fields:

   o  1 bit: copied flag.

   o  2 bits: option class.

   o  5 bits: option number.

   The copied flag indicates whether this option should be copied to all
   fragments in the event the packet carrying it needs to be fragmented:

   o  0 = not copied.

   o  1 = copied.

   The values for the option class are:



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   o  0 = control.

   o  1 = reserved for future use.

   o  2 = debugging and measurement.

   o  3 = reserved for future use.

   This format allows for the creation of new options for the extension
   of the Internet Protocol (IP).

   Finally, the option number identifies the syntax of the rest of the
   option.

   The "IP OPTION NUMBERS" registry [IANA-IP] contains the list of the
   currently assigned IP option numbers.


3.  General Security Implications of IP options

3.1.  Processing Requirements

   Router architectures can perform IP option processing in a slower
   path.  Unless protective measures are taken, this represents a
   potential Denial of Service (DoS) risk, as there is possibility for
   the option processing to overwhelm the router's CPU or the protocols
   processed in the router's slow path.  Additional considerations for
   protecting the router control plane from IP optioned packets can be
   found in [RFC6192].


4.  Advice on the Handling of Packets with Specific IP Options

   The following subsections contain a description of each of the IP
   options that have so far been specified, a discussion of possible
   interoperability implications if packets containing such options are
   dropped, and specific advice on whether to drop packets containing
   these options in a typical enterprise or Service Provider
   environment.

4.1.  End of Option List (Type = 0)

4.1.1.  Uses

   This option is used to indicate the "end of options" in those cases
   in which the end of options would not coincide with the end of the
   Internet Protocol Header.




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4.1.2.  Option Specification

   Specified in RFC 791 [RFC0791].

4.1.3.  Threats

   No security issues are known for this option, other than the general
   security implications of IP options discussed in Section 3.

4.1.4.  Operational and Interoperability Impact if Blocked

   Packets containing any IP options are likely to include an End of
   Option List.  Therefore, if packets containing this option are
   dropped, it is very likely that legitimate traffic is blocked.

4.1.5.  Advice

   Routers, security gateways, and firewalls SHOULD NOT drop packets
   containing this option.

4.2.  No Operation (Type = 1)

4.2.1.  Uses

   The no-operation option is basically meant to allow the sending
   system to align subsequent options in, for example, 32-bit
   boundaries.

4.2.2.  Option Specification

   Specified in RFC 791 [RFC0791].

4.2.3.  Threats

   No security issues are known for this option, other than the general
   security implications of IP options discussed in Section 3.

4.2.4.  Operational and Interoperability Impact if Blocked

   Packets containing any IP options are likely to include a No
   Operation option.  Therefore, if packets containing this option are
   dropped, it is very likely that legitimate traffic is blocked.

4.2.5.  Advice

   Routers, security gateways, and firewalls SHOULD NOT drop packets
   containing this option.




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4.3.  Loose Source and Record Route (LSRR) (Type = 131)

   RFC 791 states that this option should appear, at most, once in a
   given packet.  Thus, if a packet contains more than one LSRR option,
   it should be dropped, and this event should be logged (e.g., a
   counter could be incremented to reflect the packet drop).
   Additionally, packets containing a combination of LSRR and SSRR
   options should be dropped, and this event should be logged (e.g., a
   counter could be incremented to reflect the packet drop).

4.3.1.  Uses

   This option lets the originating system specify a number of
   intermediate systems a packet must pass through to get to the
   destination host.  Additionally, the route followed by the packet is
   recorded in the option.  The receiving host (end-system) must use the
   reverse of the path contained in the received LSRR option.

   The LSSR option can be of help in debugging some network problems.
   Some ISP (Internet Service Provider) peering agreements require
   support for this option in the routers within the peer of the ISP.

4.3.2.  Option Specification

   Specified in RFC 791 [RFC0791].

4.3.3.  Threats

   The LSRR option has well-known security implications.  Among other
   things, the option can be used to:

   o  Bypass firewall rules

   o  Reach otherwise unreachable internet systems

   o  Establish TCP connections in a stealthy way

   o  Learn about the topology of a network

   o  Perform bandwidth-exhaustion attacks

   Of these attack vectors, the one that has probably received least
   attention is the use of the LSRR option to perform bandwidth
   exhaustion attacks.  The LSRR option can be used as an amplification
   method for performing bandwidth-exhaustion attacks, as an attacker
   could make a packet bounce multiple times between a number of systems
   by carefully crafting an LSRR option.




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      This is the IPv4-version of the IPv6 amplification attack that was
      widely publicized in 2007 [Biondi2007].  The only difference is
      that the maximum length of the IPv4 header (and hence the LSRR
      option) limits the amplification factor when compared to the IPv6
      counter-part.

   Additionally, some implementations have been found to fail to include
   proper sanity checks on the LSRR option, thus leading to security
   issues.

      [Microsoft1999] is a security advisory about a vulnerability
      arising from improper validation of the Pointer field of the LSRR
      option.

   Finally, we note that some systems were known for providing a system-
   wide toggle to enable support for this option for those scenarios in
   which this option is required.  However, improper implementation of
   such system-wide toggle caused those systems to support the LSRR
   option even when explicitly configured not to do so.

      [OpenBSD1998] is a security advisory about an improper
      implementation of such a system-wide toggle in 4.4BSD kernels.

4.3.4.  Operational and Interoperability Impact if Blocked

   Network troubleshooting techniques that may employ the LSRR option
   (such as ping or traceroute) would break.  Nevertheless, it should be
   noted that it is virtually impossible to use the LSRR option for
   troubleshooting, due to widespread dropping of packets that contain
   such option.

4.3.5.  Advice

   Routers, security gateways, and firewalls SHOULD, by default, drop IP
   packets that contain an LSRR option.

4.4.  Strict Source and Record Route (SSRR) (Type = 137)

4.4.1.  Uses

   This option allows the originating system to specify a number of
   intermediate systems a packet must pass through to get to the
   destination host.  Additionally, the route followed by the packet is
   recorded in the option, and the destination host (end-system) must
   use the reverse of the path contained in the received SSRR option.

   This option is similar to the Loose Source and Record Route (LSRR)
   option, with the only difference that in the case of SSRR, the route



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   specified in the option is the exact route the packet must take
   (i.e., no other intervening routers are allowed to be in the route).

   The SSSR option can be of help in debugging some network problems.
   Some ISP (Internet Service Provider) peering agreements require
   support for this option in the routers within the peer of the ISP.

4.4.2.  Option Specification

   Specified in RFC 791 [RFC0791].

4.4.3.  Threats

   The SSRR option has the same security implications as the LSRR
   option.  Please refer to Section 4.3 for a discussion of such
   security implications.

4.4.4.  Operational and Interoperability Impact if Blocked

   Network troubleshooting techniques that may employ the SSRR option
   (such as ping or traceroute) would break.  Nevertheless, it should be
   noted that it is virtually impossible to use the SSR option for
   trouble-shooting, due to widespread dropping of packets that contain
   such option.

4.4.5.  Advice

   Routers, security gateways, and firewalls SHOULD, by default, drop IP
   packets that contain an SSRR option.

4.5.  Record Route (Type = 7)

4.5.1.  Uses

   This option provides a means to record the route that a given packet
   follows.

4.5.2.  Option Specification

   Specified in RFC 791 [RFC0791].

4.5.3.  Threats

   This option can be exploited to map the topology of a network.
   However, the limited space in the IP header limits the usefulness of
   this option for that purpose.





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4.5.4.  Operational and Interoperability Impact if Blocked

   Network troubleshooting techniques that may employ the RR option
   (such as ping with the RR option) would break.  Nevertheless, it
   should be noted that it is virtually impossible to use such
   techniques due to widespread dropping of packets that contain RR
   options.

4.5.5.  Advice

   Routers, security gateways, and firewalls SHOULD drop IP packets
   containing a Record Route option.

4.6.  Stream Identifier (Type = 136) (obsolete)

   The Stream Identifier option originally provided a means for the 16-
   bit SATNET stream Identifier to be carried through networks that did
   not support the stream concept.

   However, as stated by Section 3.2.1.8 of RFC 1122 [RFC1122] and
   Section 4.2.2.1 of RFC 1812 [RFC1812], this option is obsolete.
   Therefore, it must be ignored by the processing systems.  See also
   Section 5.

   RFC 791 states that this option appears at most once in a given
   datagram.  Therefore, if a packet contains more than one instance of
   this option, it should be dropped, and this event should be logged
   (e.g., a counter could be incremented to reflect the packet drop).

4.6.1.  Uses

   This option is obsolete.  There is no current use for this option.

4.6.2.  Option Specification

   Specified in RFC 791 [RFC0791], and obsoleted in RFC 1122 [RFC1122]
   and RFC 1812 [RFC1812].

4.6.3.  Threats

   No security issues are known for this option, other than the general
   security implications of IP options discussed in Section 3.

4.6.4.  Operational and Interoperability Impact if Blocked

   None.





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4.6.5.  Advice

   Routers, security gateways, and firewalls SHOULD drop IP packets
   containing a Stream Identifier option.

4.7.  Internet Timestamp (Type = 68)

4.7.1.  Uses

   This option provides a means for recording the time at which each
   system processed this datagram.

4.7.2.  Option Specification

   Specified by RFC 791 [RFC0791].

4.7.3.  Threats

   The timestamp option has a number of security implications.  Among
   them are:

   o  It allows an attacker to obtain the current time of the systems
      that process the packet, which the attacker may find useful in a
      number of scenarios.

   o  It may be used to map the network topology, in a similar way to
      the IP Record Route option.

   o  It may be used to fingerprint the operating system in use by a
      system processing the datagram.

   o  It may be used to fingerprint physical devices, by analyzing the
      clock skew.

   [Kohno2005] describes a technique for fingerprinting devices by
   measuring the clock skew.  It exploits, among other things, the
   timestamps that can be obtained by means of the ICMP timestamp
   request messages [RFC0791].  However, the same fingerprinting method
   could be implemented with the aid of the Internet Timestamp option.

4.7.4.  Operational and Interoperability Impact if Blocked

   No security issues are known for this option, other than the general
   security implications of IP options discussed in Section 3.







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4.7.5.  Advice

   Routers, security gateways, and firewalls SHOULD drop IP packets
   containing an Internet Timestamp option.

4.8.  Router Alert (Type = 148)

4.8.1.  Uses

   The Router Alert option has the semantic "routers should examine this
   packet more closely, if they participate in the functionality denoted
   by the Value of the option".

4.8.2.  Option Specification

   The Router Alert option is defined in RFC 2113 [RFC2113] and later
   updates to it have been clarified by RFC 5350 [RFC5350].  It contains
   a 16-bit Value governed by an IANA registry (see [RFC5350]).

4.8.3.  Threats

   The security implications of the Router Alert option have been
   discussed in detail in [RFC6398].  Basically, the Router Alert option
   might be exploited to perform a Denial of Service (DoS) attack by
   exhausting CPU resources at the processing routers.

4.8.4.  Operational and Interoperability Impact if Blocked

   Applications that employ the Router Alert option (such as RSVP
   [RFC2205]) would break.

4.8.5.  Advice

   This option SHOULD be allowed only in controlled environments, where
   the option can be used safely.  [RFC6398] identifies some such
   environments.  In unsafe environments, packets containing this option
   SHOULD be dropped.

   A given router, security gateway, or firewall system has no way of
   knowing a priori whether this option is valid in its operational
   environment.  Therefore, routers, security gateways, and firewalls
   SHOULD, by default, ignore the Router Alert option.  Additionally,
   Routers, security gateways, and firewalls SHOULD have a configuration
   setting that indicates whether they should react act on the Router
   Alert option as indicated in the corresponding specification or
   ignore the option, or whether packets containing this option should
   be dropped (with the default configuration being to ignore the Router
   Alert option).



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4.9.  Probe MTU (Type = 11) (obsolete)

4.9.1.  Uses

   This option originally provided a mechanism to discover the Path-MTU.
   It has been declared obsolete.

4.9.2.  Option Specification

   This option was originally defined in RFC 1063 [RFC1063], and was
   obsoleted with RFC 1191 [RFC1191].  This option is now obsolete, as
   RFC 1191 obsoletes RFC 1063 without using IP options.

4.9.3.  Threats

   No security issues are known for this option, other than the general
   security implications of IP options discussed in Section 3.

4.9.4.  Operational and Interoperability Impact if Blocked

   None

4.9.5.  Advice

   Routers, security gateways, and firewalls SHOULD drop IP packets that
   contain a Probe MTU option.

4.10.  Reply MTU (Type = 12) (obsolete)

4.10.1.  Uses

   This option and originally provided a mechanism to discover the Path-
   MTU.  It is now obsolete.

4.10.2.  Option Specification

   This option was originally defined in RFC 1063 [RFC1063], and was
   obsoleted with RFC 1191 [RFC1191].  This option is now obsolete, as
   RFC 1191 obsoletes RFC 1063 without using IP options.

4.10.3.  Threats

   No security issues are known for this option, other than the general
   security implications of IP options discussed in Section 3.







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4.10.4.  Operational and Interoperability Impact if Blocked

   None

4.10.5.  Advice

   Routers, security gateways, and firewalls SHOULD drop IP packets that
   contain a Reply MTU option.

4.11.  Traceroute (Type = 82)

4.11.1.  Uses

   This option originally provided a mechanism to trace the path to a
   host.

4.11.2.  Option Specification

   This option was originally specified by RFC 1393 [RFC1393].  The
   Traceroute option is defined as "experimental" and it was never
   widely deployed on the public Internet.

4.11.3.  Threats

   No security issues are known for this option, other than the general
   security implications of IP options discussed in Section 3.

4.11.4.  Operational and Interoperability Impact if Blocked

   None

4.11.5.  Advice

   Routers, security gateways, and firewalls SHOULD drop IP packets that
   contain a Traceroute option.

4.12.  DoD Basic Security Option (Type = 130)

4.12.1.  Uses

   This option is used by Multi-Level-Secure (MLS) end-systems and
   intermediate systems in specific environments to [RFC1108]:

   o  Transmit from source to destination in a network standard
      representation the common security labels required by computer
      security models [Landwehr81],





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   o  Validate the datagram as appropriate for transmission from the
      source and delivery to the destination, and,

   o  Ensure that the route taken by the datagram is protected to the
      level required by all protection authorities indicated on the
      datagram.

   The DoD Basic Security Option (BSO) is currently implemented in a
   number of operating systems (e.g., [IRIX2008], [SELinux2008],
   [Solaris2008], and [Cisco-IPSO]), and deployed in a number of high-
   security networks.  These networks are typically either in physically
   secure locations, protected by military/governmental communications
   security equipment, or both.  Such networks are typically built using
   commercial off-the-shelf (COTS) IP routers and Ethernet switches, but
   are not normally interconnected with the global public Internet.
   This option probably has more deployment now than when the IESG
   removed this option from the IETF standards-track.  [RFC5570]
   describes a similar option recently defined for IPv6 and has much
   more detailed explanations of how sensitivity label options are used
   in real-world deployments.

4.12.2.  Option Specification

   It is specified by RFC 1108 [RFC1108]], which obsoleted RFC 1038
   [RFC1038] (which in turn obsoleted the Security Option defined in RFC
   791 [RFC0791]).

      RFC 791 [RFC0791] defined the "Security Option" (Type = 130),
      which used the same option type as the DoD Basic Security option
      discussed in this section.  Later, RFC 1038 [RFC1038] revised the
      IP security options, and in turn was obsoleted by RFC 1108
      [RFC1108].  The "Security Option" specified in RFC 791 is
      considered obsolete by Section 3.2.1.8 of RFC 1122 [RFC1122] and
      Section 4.2.2.1 of RFC 1812 [RFC1812], and therefore the
      discussion in this section is focused on the DoD Basic Security
      option specified by RFC 1108 [RFC1108].

   Section 4.2.2.1 of RFC 1812 states that routers "SHOULD implement
   this option".

      Many Cisco routers that run Cisco IOS include support dropping
      packets that contain this option with per-interface granularity.
      This capability has been present in many Cisco routers since the
      early 1990s [Cisco-IPSO-Cmds].  Some governmental products
      reportedly support BSO, notably CANEWARE [RFC4949].  Support for
      BSO is included in the "IPsec Configuration Policy Information
      Model" [RFC3585] and in the "IPsec Security Policy Database
      Configuration MIB" [RFC4807].



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4.12.3.  Threats

   Presence of this option in a packet does not by itself create any
   specific new threat (other than the usual generic issues that might
   be created if packets with options are forwarded via the "slow
   path").  Packets with this option ought not normally be seen on the
   global public Internet.

4.12.4.  Operational and Interoperability Impact if Blocked

   If packets with this option are blocked or if the option is stripped
   from the packet during transmission from source to destination, then
   the packet itself is likely to be dropped by the receiver because it
   isn't properly labelled.  In some cases, the receiver might receive
   the packet but associate an incorrect sensitivity label with the
   received data from the packet whose BSO 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.

4.12.5.  Advice

   Routers, security gateways, and firewalls SHOULD NOT by default
   modify or remove this option from IP packets and SHOULD NOT by
   default drop packets containing this option.  For auditing reasons,
   Routers, security gateways, and firewalls SHOULD be capable of
   logging the numbers of packets containing the BSO on a per-interface
   basis.  Also, Routers, security gateways, and firewalls SHOULD be
   capable of dropping packets based on the BSO presence as well as the
   BSO values.

4.13.  DoD Extended Security Option (Type = 133)

4.13.1.  Uses

   This option permits additional security labeling information, beyond
   that present in the Basic Security Option (Section 4.12), to be
   supplied in an IP datagram to meet the needs of registered
   authorities.

4.13.2.  Option Specification

   The DoD Extended Security Option (ESO) is specified by RFC 1108
   [RFC1108].





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      Many Cisco routers that run Cisco IOS include support for dropping
      packets that contain this option with a per-interface granularity.
      This capability has been present in many Cisco routers since the
      early 1990s [Cisco-IPSO-Cmds].  Some governmental products
      reportedly support ESO, notably CANEWARE [RFC4949].  Support for
      ESO is included in the "IPsec Configuration Policy Information
      Model" [RFC3585] and in the "IPsec Security Policy Database
      Configuration MIB" [RFC4807].

4.13.3.  Threats

   Presence of this option in a packet does not by itself create any
   specific new threat (other than the usual generic issues that might
   be created if packets with options are forwarded via the "slow
   path").  Packets with this option ought not normally be seen on the
   global public Internet

4.13.4.  Operational and Interoperability Impact if Blocked

   If packets with this option are blocked or if the option is stripped
   from the packet during transmission from source to destination, then
   the packet itself is likely to be dropped by the receiver because it
   isn't properly labelled.  In some cases, the receiver might receive
   the packet but associate an incorrect sensitivity label with the
   received data from the packet whose ESO 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.

4.13.5.  Advice

   Routers, security gateways, and firewalls SHOULD NOT by default
   modify or remove this option from IP packets and SHOULD NOT by
   default drop packets containing this option.  For auditing reasons,
   Routers, security gateways, and firewalls SHOULD be capable of
   logging the numbers of packets containing the ESO on a per-interface
   basis.  Also, Routers, security gateways, and firewalls SHOULD be
   capable of dropping packets based on the ESO presence as well as the
   ESO values.

4.14.  Commercial IP Security Option (CIPSO) (Type = 134)

4.14.1.  Uses

   This option was proposed by the Trusted Systems Interoperability
   Group (TSIG), with the intent of meeting trusted networking



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   requirements for the commercial trusted systems market place.

   It is currently implemented in a number of operating systems (e.g.,
   IRIX [IRIX2008], Security-Enhanced Linux [SELinux2008], and Solaris
   [Solaris2008]), and deployed in a number of high-security networks.

4.14.2.  Option Specification

   This option is specified in [CIPSO1992] and [FIPS1994].  There are
   zero known IP router implementations of CIPSO.  Several MLS operating
   systems support CIPSO, generally the same MLS operating systems that
   support IPSO.

      The TSIG proposal was taken to the Commercial Internet Security
      Option (CIPSO) Working Group of the IETF [CIPSOWG1994], and an
      Internet-Draft was produced [CIPSO1992].  The Internet-Draft was
      never published as an RFC, but the proposal was later standardized
      by the U.S. National Institute of Standards and Technology (NIST)
      as "Federal Information Processing Standard Publication 188"
      [FIPS1994].

4.14.3.  Threats

   Presence of this option in a packet does not by itself create any
   specific new threat (other than the usual generic issues that might
   be created if packets with options are forwarded via the "slow
   path").  Packets with this option ought not normally be seen on the
   global public Internet.

4.14.4.  Operational and Interoperability Impact if Blocked

   If packets with this option are blocked or if the option is stripped
   from the packet during transmission from source to destination, then
   the packet itself is likely to be dropped by the receiver because it
   isn't properly labelled.  In some cases, the receiver might receive
   the packet but associate an incorrect sensitivity label with the
   received data from the packet whose CIPSO 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.

4.14.5.  Advice

   Because of the design of this option, with variable syntax and
   variable length, it is not practical to support specialized filtering
   using the CIPSO information.  No routers or firewalls are known to



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   support this option.  However, Routers, security gateways, and
   firewalls SHOULD NOT by default modify or remove this option from IP
   packets and SHOULD NOT by default drop packets containing this
   option.

4.15.  VISA (Type = 142)

4.15.1.  Uses

   This options was part of an experiment at USC and was never widely
   deployed.

4.15.2.  Option Specification

   Not publicly available.

4.15.3.  Threats

   Not possible to determine (other the general security implications of
   IP options discussed in Section 3), since the corresponding
   specification is not publicly available.

4.15.4.  Operational and Interoperability Impact if Blocked

   None.

4.15.5.  Advice

   Routers, security gateways, and firewalls SHOULD drop IP packets that
   contain this option.

4.16.  Extended Internet Protocol (Type = 145)

4.16.1.  Uses

   The EIP option was introduced by one of the proposals submitted
   during the IPng efforts to address the problem of IPv4 address
   exhaustion.

4.16.2.  Option Specification

   Specified in [RFC1385].  This option is in the process of being
   formally obsoleted by [I-D.gp-intarea-obsolete-ipv4-options-iana].

4.16.3.  Threats

   There are no know threats arising from this option, other than the
   general security implications of IP options discussed in Section 3.



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4.16.4.  Operational and Interoperability Impact if Blocked

   None.

4.16.5.  Advice

   Routers, security gateways, and firewalls SHOULD drop packets that
   contain this option.

4.17.  Address Extension (Type = 147)

4.17.1.  Uses

   The Address Extension option was introduced by one of the proposals
   submitted during the IPng efforts to address the problem of IPv4
   address exhaustion.

4.17.2.  Option Specification

   Specified in [RFC1475].  This option is in the process of being
   formally obsoleted by [I-D.gp-intarea-obsolete-ipv4-options-iana].

4.17.3.  Threats

   There are no know threats arising from this option, other than the
   general security implications of IP options discussed in Section 3.

4.17.4.  Operational and Interoperability Impact if Blocked

   None.

4.17.5.  Advice

   Routers, security gateways, and firewalls SHOULD drop packets that
   contain this option.

4.18.  Sender Directed Multi-Destination Delivery (Type = 149)

4.18.1.  Uses

   This option originally provided unreliable UDP delivery to a set of
   addresses included in the option.

4.18.2.  Option Specification

   This option is defined in RFC 1770 [RFC1770].





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4.18.3.  Threats

   This option could have been exploited for bandwidth-amplification in
   Denial of Service (DoS) attacks.

4.18.4.  Operational and Interoperability Impact if Blocked

   None.

4.18.5.  Advice

   Routers, security gateways, and firewalls SHOULD drop IP packets that
   contain a Sender Directed Multi-Destination Delivery option.

4.19.  Dynamic Packet State (Type = 151)

4.19.1.  Uses

   The Dynamic Packet State option was used to specify specified Dynamic
   Packet State (DPS) in the context of the differentiated service
   architecture.

4.19.2.  Option Specification

   The Dynamic Packet State option was specified in
   [I-D.stoica-diffserv-dps].  The aforementioned document was meant to
   be published as "Experimental", but never made it into an RFC.  This
   option is in the process of being formally obsoleted by
   [I-D.gp-intarea-obsolete-ipv4-options-iana].

4.19.3.  Threats

   Possible threats include theft of service and Denial of Service.
   However, we note that is option has never been widely implemented or
   deployed.

4.19.4.  Operational and Interoperability Impact if Blocked

   None.

4.19.5.  Advice

   Routers, security gateways, and firewalls SHOULD drop packets that
   contain this option.







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4.20.  Upstream Multicast Pkt. (Type = 152)

4.20.1.  Uses

   This option was meant to solve the problem of doing upstream
   forwarding of multicast packets on a multi-access LAN.

4.20.2.  Option Specification

   This option was originally specified in [draft-farinacci-bidir-pim].
   Its use was obsoleted by [RFC5015], which employs a control plane
   mechanism to solve the problem of doing upstream forwarding of
   multicast packets on a multi-access LAN.  This option is in the
   process of being formally obsoleted by
   [I-D.gp-intarea-obsolete-ipv4-options-iana].

4.20.3.  Threats

   TBD.

4.20.4.  Operational and Interoperability Impact if Blocked

   None.

4.20.5.  Advice

   Routers, security gateways, and firewalls SHOULD drop packets that
   contain this option.

4.21.  Quick-Start (Type = 25)

4.21.1.  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].

4.21.2.  Option Specification

   Specified in RFC 4782 [RFC4782], on the "Experimental" track.

4.21.3.  Threats

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




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   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

4.21.4.  Operational and Interoperability Impact if Blocked

   The Quick-Start functionality would be disabled, and additional
   delays in e.g.  TCP's connection establishment could be introduced
   (please see Section 4.7.2 of [RFC4782].  We note, however, that
   Quick-Start has been proposed as 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].

4.21.5.  Advice

   A given router, security gateway, or firewall system has no way of
   knowing a priori whether this option is valid in its operational
   environment.  Therefore, routers, security gateways, and firewalls
   SHOULD, by default, ignore the Quick Start option.  Additionally,
   routers, security gateways, and firewalls SHOULD have a configuration
   setting that indicates whether they should react act on the Quick
   Start option as indicated in the corresponding specification or
   ignore the option, or whether packets containing this option should
   be dropped (with the default configuration being to ignore the Quick
   Start option).

      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 3) would apply.

4.22.  RFC3692-style Experiment (Types = 30, 94, 158, and 222)

   Section 2.5 of RFC 4727 [RFC4727] allocates an option number with all
   defined values of the "copy" and "class" fields for RFC3692-style
   experiments.  This results in four distinct option type codes: 30,
   94, 158, and 222.

4.22.1.  Uses

   It is only appropriate to use these values in explicitly-configured
   experiments; they MUST NOT be shipped as defaults in implementations.







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4.22.2.  Option Specification

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

4.22.3.  Threats

   No security issues are known for this option, other than the general
   security implications of IP options discussed in Section 3.

4.22.4.  Operational and Interoperability Impact if Blocked

   None.

4.22.5.  Advice

   Routers, security gateways, and firewalls SHOULD drop IP packets that
   contain RFC3692-style Experiment options.

4.23.  Other IP Options

   Unrecognized IP Options are to be ignored.  Section 3.2.1.8 of RFC
   1122 [RFC1122] and Section 4.2.2.6 of RFC 1812 [RFC1812] specify this
   behavior as follows:

   RFC 1122:  "The IP and transport layer MUST each interpret those IP
            options that they understand and silently ignore the
            others."

   RFC 1812:  "A router MUST ignore IP options which it does not
            recognize."

   This document adds that unrecognized IP Options MAY also be logged.

   A number of additional options are specified in the "IP OPTIONS
   NUMBERS" IANA registry [IANA-IP].  Specifically:

   Copy Class Number Value Name                               Reference
   ---- ----- ------ ----- ------------------------------- ------------
      0     0     10    10 ZSU    - Experimental Measurement      [ZSu]
      1     2     13   205 FINN   - Experimental Flow Control    [Finn]
      0     0     15    15 ENCODE - ???                      [VerSteeg]
      1     0     16   144 IMITD  - IMI Traffic Descriptor        [Lee]
      1     0     22   150        - Unassigned (Released 18 Oct. 2005)







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5.  IANA Considerations

   The "IP OPTION NUMBERS" registry [IANA-IP] contains the list of the
   currently assigned IP option numbers.  This registry also denotes an
   obsoleted IP Option Number by marking it with a single asterisk
   ("*").  The Stream Identifier Option (Type = 136) is obsolete (see
   Section 4.6 and should therefore be marked as such.

   [[ IANA is requested to mark it as such, please remove this note upon
   publication. ]] [[ IANA is also requested to fix the "Expermental"
   typo. ]]


6.  Security Considerations

   This document provides advice on the filtering of IP packets that
   contain IP options.  Dropping such packets can help to mitigate the
   security issues that arise from use of different IP options.


7.  Acknowledgements

   The authors would like to thank Panos Kampanakis and Donald Smith for
   providing valuable comments on earlier versions of this document.

   Part of this document is based on the document "Security Assessment
   of the Internet Protocol" [CPNI2008] that is the result of a project
   carried out by Fernando Gont on behalf of UK CPNI (formerly NISCC).

   Fernando Gont would like to thank UK CPNI (formerly NISCC) for their
   continued support.


8.  References

8.1.  Normative References

   [RFC0791]  Postel, J., "Internet Protocol", STD 5, RFC 791,
              September 1981.

   [RFC1108]  Kent, S., "U.S", RFC 1108, November 1991.

   [RFC1122]  Braden, R., "Requirements for Internet Hosts -
              Communication Layers", STD 3, RFC 1122, October 1989.

   [RFC1191]  Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
              November 1990.




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   [RFC1770]  Graff, C., "IPv4 Option for Sender Directed Multi-
              Destination Delivery", RFC 1770, March 1995.

   [RFC1812]  Baker, F., "Requirements for IP Version 4 Routers",
              RFC 1812, June 1995.

   [RFC2113]  Katz, D., "IP Router Alert Option", RFC 2113,
              February 1997.

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

   [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.

   [RFC5015]  Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano,
              "Bidirectional Protocol Independent Multicast (BIDIR-
              PIM)", RFC 5015, October 2007.

8.2.  Informative References

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

   [CIPSO1992]
              CIPSO, "COMMERCIAL IP SECURITY OPTION (CIPSO 2.2)",
              draft-ietf-cipso-ipsecurity-01 (work in progress), 1992.

   [CIPSOWG1994]
              CIPSOWG, "Commercial Internet Protocol Security Option
              (CIPSO) Working Group", 1994, <http://www.ietf.org/
              proceedings/94jul/charters/cipso-charter.html>.

   [CPNI2008]
              Gont, F., "Security Assessment of the Internet Protocol",
               <http://www.cpni.gov.uk/Docs/InternetProtocol.pdf>, 2008.

   [Cisco-IPSO]
              Cisco Systems, Inc., "Cisco IOS Security Configuration
              Guide, Release 12.2 - Configuring IP Security Options",  <
              http://www.cisco.com/en/US/docs/ios/12_2/security/
              configuration/guide/scfipso.html>, 2006.




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   [Cisco-IPSO-Cmds]
              Cisco Systems, Inc., "Cisco IOS Security Command
              Reference, Release 12.2 - IP Security Options Commands",
              <http://www.cisco.com/en/US/docs/ios/12_2/security/
              command/reference/srfipso.html>.

   [FIPS1994]
              FIPS, "Standard Security Label for Information Transfer",
              Federal Information Processing Standards Publication. FIP
              PUBS 188,  <http://csrc.nist.gov/publications/fips/
              fips188/fips188.pdf>, 1994.

   [I-D.gp-intarea-obsolete-ipv4-options-iana]
              Pignataro, C. and F. Gont, "Formally Obsoleting some
              Historic IPv4 Options",
              draft-gp-intarea-obsolete-ipv4-options-iana-00 (work in
              progress), February 2012.

   [I-D.stoica-diffserv-dps]
              Stoica, I., Zhang, H., Baker, F., and Y. Bernet, "Per Hop
              Behaviors Based on Dynamic Packet State",
              draft-stoica-diffserv-dps-02 (work in progress),
              October 2002.

   [IANA-IP]  Internet Assigned Numbers Authority, "IP OPTION NUMBERS",
              April 2011,
              <http://www.iana.org/assignments/ip-parameters>.

   [IRIX2008]
              IRIX, "IRIX 6.5 trusted_networking(7) manual page",  <http
              ://techpubs.sgi.com/library/tpl/cgi-bin/
              getdoc.cgi?coll=0650&db=man&fname=/usr/share/catman/a_man/
              cat7/trusted_networking.z>, 2008.

   [Kohno2005]
              Kohno, T., Broido, A., and kc. Claffy, "Remote Physical
              Device Fingerprinting", IEEE Transactions on Dependable
              and Secure Computing Vol. 2, No. 2, 2005.

   [Landwehr81]
              Landwehr, C., "Formal Models for Computer Security", ACM
              Computing Surveys Vol 13, No 3, September 1981, Assoc for
              Computing Machinery, New York, NY, USA, 1981.

   [MEDINA]   Medina, A., Allman, M., and S. Floyd, "Measuring
              Interactions Between Transport Protocols and Middleboxes",
              Proc. 4th ACM SIGCOMM/USENIX Conference on
              Internet Measurement, October 2004.



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   [Microsoft1999]
              Microsoft, "Microsoft Security Program: Microsoft Security
              Bulletin (MS99-038). Patch Available for "Spoofed Route
              Pointer" Vulnerability", 1999, <http://www.microsoft.com/
              technet/security/bulletin/ms99-038.mspx>.

   [OpenBSD1998]
              OpenBSD, "OpenBSD Security Advisory: IP Source Routing
              Problem", 1998,
              <http://www.openbsd.org/advisories/sourceroute.txt>.

   [RFC1038]  St. Johns, M., "Draft revised IP security option",
              RFC 1038, January 1988.

   [RFC1063]  Mogul, J., Kent, C., Partridge, C., and K. McCloghrie, "IP
              MTU discovery options", RFC 1063, July 1988.

   [RFC1385]  Wang, Z., "EIP: The Extended Internet Protocol", RFC 1385,
              November 1992.

   [RFC1393]  Malkin, G., "Traceroute Using an IP Option", RFC 1393,
              January 1993.

   [RFC1475]  Ullmann, R., "TP/IX: The Next Internet", RFC 1475,
              June 1993.

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

   [RFC3585]  Jason, J., Rafalow, L., and E. Vyncke, "IPsec
              Configuration Policy Information Model", RFC 3585,
              August 2003.

   [RFC4807]  Baer, M., Charlet, R., Hardaker, W., Story, R., and C.
              Wang, "IPsec Security Policy Database Configuration MIB",
              RFC 4807, March 2007.

   [RFC4949]  Shirey, R., "Internet Security Glossary, Version 2",
              RFC 4949, August 2007.

   [RFC5350]  Manner, J. and A. McDonald, "IANA Considerations for the
              IPv4 and IPv6 Router Alert Options", RFC 5350,
              September 2008.

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



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   [RFC6192]  Dugal, D., Pignataro, C., and R. Dunn, "Protecting the
              Router Control Plane", RFC 6192, March 2011.

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

   [SELinux2008]
              Security Enhanced Linux, "http://www.nsa.gov/selinux/".

   [Solaris2008]
              Solaris Trusted Extensions - Labeled Security for Absolute
              Protection, "http://www.sun.com/software/solaris/ds/
              trusted_extensions.jsp#3", 2008.

   [draft-farinacci-bidir-pim]
              Estrin, D. and D. Farinacci, "Bi-Directional Shared Trees
              in PIM-SM",  IETF Internet Draft,
              draft-farinacci-bidir-pim, work in progress, May 1999.


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


   RJ Atkinson
   Consultant
   McLean, VA  22103
   USA

   Email: rja.lists@gmail.com












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   Carlos Pignataro
   Cisco Systems, Inc.
   7200-12 Kit Creek Road
   Research Triangle Park, NC  27709
   US

   Email: cpignata@cisco.com












































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