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Versions: (draft-touch-intarea-ipv4-unique-id) 00 01 02 03 04 05 06 07 RFC 6864

Internet Area WG                                               J. Touch
Internet Draft                                                  USC/ISI
Updates: 791,1122,2003                                 October 22, 2010
Intended status: Proposed Standard
Expires: April 2011




                Updated Specification of the IPv4 ID Field
                 draft-ietf-intarea-ipv4-id-update-01.txt


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   This Internet-Draft will expire on April 22, 2011.




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Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors. All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
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Abstract

   The IPv4 Identification (ID) field enables fragmentation and
   reassembly, and as currently specified is required to be unique
   within the maximum lifetime on all datagrams. If enforced, this
   uniqueness requirement would limit all connections to 6.4 Mbps.
   Because this is obviously not the case, it is clear that existing
   systems violate the current specification. This document updates the
   specification of the IPv4 ID field to more closely reflect current
   practice and to more closely match IPv6 so that the field is defined
   only when a datagram is actually fragmented. It also discusses the
   impact of these changes on how datagrams are used.

Table of Contents


   1. Introduction...................................................3
   2. Conventions used in this document..............................3
   3. The IPv4 ID Field..............................................3
   4. Uses of the IPv4 ID Field......................................4
   5. Background on IPv4 ID Reassembly Issues........................5
   6. Updates to the IPv4 ID Specification...........................6
      6.1. IPv4 ID Used Only for Fragmentation.......................7
      6.2. Encourage Safe IPv4 ID Use................................8
      6.3. IPv4 ID Requirements That Persist.........................9
   7. Impact on Datagram Use.........................................9
   8. Updates to Existing Standards.................................10
      8.1. Updates to RFC 791.......................................10
      8.2. Updates to RFC 1122......................................11
      8.3. Updates to RFC 2003......................................11
   9. Impact on NATs and Tunnel Ingresses...........................12
   10. Impact on Header Compression.................................13


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   11. Security Considerations......................................13
   12. IANA Considerations..........................................13
   13. References...................................................14
      13.1. Normative References....................................14
      13.2. Informative References..................................14
   14. Acknowledgments..............................................15

1. Introduction

   In IPv4, the Identification (ID) field is a 16-bit value that is
   unique for every datagram for a given source address, destination
   address, and protocol, such that it does not repeat within the
   Maximum Segment Lifetime (MSL) [RFC791][RFC1122]. As currently
   specified, all datagrams between a source and destination of a given
   protocol must have unique IPv4 ID values over a period of this MSL,
   which is typically interpreted as two minutes (120 seconds). This
   uniqueness is currently specified as for all datagrams, regardless of
   fragmentation settings.

   The uniqueness of the IPv4 ID is a known problem for high speed
   devices; if strictly enforced, it would limit the speed of a single
   protocol between two endpoints to 6.4 Mbps for typical MTUs of 1500
   bytes [RFC4963]. It is common for a single protocol to operate far in
   excess of these rates, which strongly indicates that the uniqueness
   of the IPv4 ID as specified is already moot.

   This document updates the specification of the IPv4 ID field to more
   closely reflect current practice, and to include considerations taken
   into account during the specification of the similar field in IPv6.

2. Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC-2119 [RFC2119].

   In this document, the characters ">>" proceeding an indented line(s)
   indicates a requirement using the key words listed above. This
   convention aids reviewers in quickly identifying or finding this
   document's explicit requirements.

3. The IPv4 ID Field

   IP supports datagram fragmentation, where large datagrams are split
   into smaller components to traverse links with limited maximum
   transmission units (MTUs). Fragments are indicated in different ways
   in IPv4 and IPv6:


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   o  In IPv4, fragments are indicated using four fields of the basic
      header: Identification (ID), Fragment Offset, a "Don't Fragment"
      flag (DF), and a "More Fragments" flag (MF) [RFC791]

   o  In IPv6, fragments are indicated in an extension header that
      includes an ID, Fragment Offset, and MF flag similar to their
      counterparts in IPv4 [RFC2460]

   IPv4 and IPv6 fragmentation differs in a few important ways. IPv6
   fragmentation occurs only at the source, so a DF bit is not needed to
   prevent downstream devices from initiating fragmentation (i.e., IPv6
   always acts as if DF=1). The IPv6 fragment header is present only
   when a datagram has been fragmented, so the ID field is not present
   for non-fragmented datagrams, and thus is meaningful only for
   fragments. Finally, the IPv6 ID field is 32 bits, and required unique
   per source/destination address pair for IPv6, whereas for IPv4 it is
   only 16 bits and required unique per source/destination/protocol
   triple.

   This document focuses on the IPv4 ID field issues, because in IPv6
   the field is larger and present only in fragments.

4. Uses of the IPv4 ID Field

   The IPv4 ID field was originally intended for fragmentation and
   reassembly [RFC791]. Within a given source address, destination
   address, and protocol, fragments of an original datagram are matched
   based on their IPv4 ID. This requires that IDs are unique within the
   address/protocol triple when fragmentation is possible (e.g., DF=0)
   or when it has already occurred (e.g., frag_offset>0 or MF=1).

   The IPv4 ID field can be useful for other purposes. The field has
   been suggested as a way to detect and remove duplicate datagrams,
   e.g., at congested routers, although this has been noted and no
   current deployments are known (see Sec. 3.2.1.5 of [RFC1122]). It can
   similarly be used at end hosts to reduce the impact of duplication on
   higher-layer protocols (e.g., additional processing in TCP, or the
   need for application-layer duplicate suppression in UDP).

   The IPv4 ID field can also be used to validate payloads of ICMP
   responses as matching the originally transmitted datagram at a host
   [RFC4963]. In this case, the ICMP payload - an IP datagram prefix -
   is matched against a cache of recently transmitted IP headers to
   check that the received ICMP reflects a transmitted datagram. At a
   tunnel ingress, the IPv4 ID enables returning ICMP messages to be
   matched to a cache of recently transmitted datagrams, to support ICMP
   relaying, with similar challenges [RFC2003].


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   Uses of the IPv4 ID field beyond fragmentation and reassembly require
   that the IPv4 ID be unique across all datagrams, not only when
   fragmentation is enabled. This document deprecates all such non-
   fragmentation uses.

5. Background on IPv4 ID Reassembly Issues

   The following is a summary of issues with IPv4 fragment reassembly in
   high speed environments raised previously [RFC4963]. Readers are
   encouraged to consult RFC 4963 for a more detailed discussion of
   these issues.

   With the maximum IPv4 datagram size of 64KB, a 16-bit ID field that
   does not repeat within 120 seconds means that the aggregate of all
   TCP connections of a given protocol between two endpoints is limited
   to roughly 286 Mbps; at a more typical MTU of 1500 bytes, this speed
   drops to 6.4 Mbps [RFC4963]. This limit currently applies for all
   IPv4 datagrams within a single protocol (i.e., the IPv4 protocol
   field) between two IP addresses, regardless of whether fragmentation
   is enabled or inhibited, and whether a datagram is fragmented or not.

   IPv6, even at typical MTUs, is capable of 18.7 Tbps with
   fragmentation between two endpoints as an aggregate across all
   protocols, due to the larger 32-bit ID field (and the fact that the
   IPv6 next-header field, the equivalent of the IPv4 protocol field, is
   not considered in differentiating fragments). When fragmentation is
   not used the field is absent, and in that case IPv6 speeds are not
   limited by the ID field uniqueness.

   Note also that 120 seconds is only an estimate on the maximum
   datagram lifetime. It is loosely based on half maximum value of the
   IP TTL field (255), measured in seconds, because the TTL is
   decremented not only for each hop, but also for each second a
   datagram is held at a router (as implied in [RFC791]). Network delays
   are incurred in other ways, e.g., satellite links, which can add
   seconds of delay even though the TTL is often not decremented by a
   corresponding amount. There is thus no enforcement mechanism to
   ensure that datagrams older than 120 seconds are discarded.

   Wireless Internet devices are frequently connected at speeds over 54
   Mbps, and wired links of 1 Gbps have been the default for several
   years. Although many end-to-end transport paths are congestion
   limited, these devices easily achieve 100+ Mbps application-layer
   throughput over LANs (e.g., disk-to-disk file transfer rates), and
   numerous throughput demonstrations have been performed with COTS
   systems over wide-area paths at these speeds for over a decade. This



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   strongly suggests that IPv4 ID uniqueness has been moot for a long
   time.

6. Updates to the IPv4 ID Specification

   This document updates the specification of the IPv4 ID field in three
   distinct ways, as discussed in subsequent subsections:

   o  Use the IPv4 ID field only for fragmentation

   o  Avoiding a performance impact when the IPv4 ID field is used

   o  Encourage safe operation when the IPv4 ID field is used

   There are two kinds of datagrams used in the following discussion,
   named as follows:

   o  Atomic datagrams: datagrams not yet having been fragmented  (MF=0
      and fragment offset=0) and for which further fragmentation has
      been inhibited (DF=1), i.e., as a C-code expression:

         (DF==1)&&(MF==0)&&(frag_offset==0)

   o  Non-atomic datagrams: datagrams which have either already been
      fragmented, i.e.:

         (MF=1)||(frag_offset>0)

      or for which fragmentation remains possible:

         (DF=0)

      I.e., non-atomic datagrams can be expressed in two equivalent
      tests:

         (DF==0)||(MF==1)||(frag_offset>0)

      which can also be expressed as follows, using DeMorgan's Law and
      other identities:

         ~((DF==1)&&(MF==0)&&(frag_offset==0))

      Note that this final expression is the same as "not(atomic)".






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6.1. IPv4 ID Used Only for Fragmentation

   Although RFC1122 suggests the IPv4 ID field has other uses, this
   document asserts that this field is defined only for fragmentation
   and reassembly.

   o  >> IPv4 ID field MUST NOT be used for purposes other than
      fragmentation and reassembly.

   This has a few implications. In atomic datagrams, the IPv4 ID field
   has no meaning, and thus can be set to an arbitrary value, i.e., the
   requirement for non-repeating IDs within the address/protocol triple
   is no longer required for atomic datagrams:

   o  >> Originating sources MAY set the IPv4 ID field of atomic
      datagrams to any value.

   Second, all network nodes, whether at intermediate routers,
   destination hosts, or other devices (e.g., NATs, firewalls, tunnel
   egresses), cannot rely on the field:

   o  >> All devices that examine IPv4 headers MUST ignore the IPv4 ID
      field of atomic datagrams.

   The IPv4 ID field is thus meaningful only for non-atomic datagrams -
   datagrams that have either already been fragmented, or those for
   which fragmentation remains permitted. Atomic datagrams are detected
   by their DF, MF, and fragmentation offset fields as explained in
   Section 6, because such a test is completely backward compatible;
   this document thus does not reserve any IPv4 ID values, including 0,
   as distinguished.

   Deprecating the use of the IPv4 ID field for non-reassembly uses
   should have little - if any - impact. IPv4 IDs are already frequently
   repeated, e.g., over even moderately fast connections. Duplicate
   suppression was only suggested [RFC1122], and no impacts of IPv4 ID
   reuse have been noted. Routers are not required to issue ICMPs on any
   particular timescale, and so IPv4 ID repetition should not have been
   used for validation, and again repetition occurs and probably could
   have been noticed [RFC1812]. ICMP relaying at tunnel ingresses is
   specified to use soft state rather than a datagram cache, and should
   have been noted if the latter for similar reasons [RFC2003].







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6.2. Encourage Safe IPv4 ID Use

   This document makes further changes to the specification of the IPv4
   ID field and its use to encourage its safe use as corollary
   requirements changes as follows.

   RFC 1122 discusses that TCP retransmits a segment it may be possible
   to reuse the IPv4 ID (see Section 8.2). This can make it difficult
   for a source to avoid IPv4 ID repetition for received fragments. RFC
   1122 concludes that this behavior "is not useful"; this document
   formalizes that conclusion as follows:

   o  >> The IPv4 ID of non-atomic datagrams MUST NOT be reused when
      sending a copy of an earlier non-atomic datagram.

   RFC 1122 also suggests that fragments can overlap [RFC1122]. Such
   overlap can occur if successive retransmissions are fragmented in
   different ways but the same reassembly IPv4 ID.

   This overlap is noted as the result of reusing IPv4 IDs when
   retransmitting datagrams, which this document deprecates. Overlapping
   fragments are themselves a hazard [RFC4963]. As a result:

   o  >> Overlapping datagrams MUST be silently ignored during
      reassembly.

   The IPv4 ID of non-atomic datagrams also needs to remain stable, to
   ensure that existing fragments are not reassembled incorrectly, as
   well as to ensure that the uniqueness of the IDs as generated by the
   source is not undermined.

   For atomic datagrams, because the IPv4 ID field is ignored on
   receipt, it can be possible to rewrite the field. Rewriting can be
   useful to prevent use of the field as a covert channel, or to enable
   more efficient header compression. However, the IPv4 ID field needs
   to remain immutable when it is validated by higher layer protocols,
   such as IPsec. As a result:

   o  >> The IPv4 ID field of non-atomic datagrams, or protected atomic
      datagrams MUST NOT change in transit; the IPv4 ID field of
      unprotected atomic datagrams MAY be changed in transit.

   Protected datagrams are defined as those whose header fields are
   covered by integrity validation, such as IPsec AH [RFC4302].





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6.3. IPv4 ID Requirements That Persist

   This document does not relax the IPv4 ID field uniqueness
   requirements of [RFC791] for non-atomic datagrams, i.e.:

   o  >> Sources emitting non-atomic datagrams MUST NOT repeat IPv4 ID
      values within one MSL for a given source address/destination
      address/protocol triple.

   Such sources include originating hosts, tunnel ingresses, and NATs
   (see Section 9).

   This document does not relax the requirement that all network devices
   honor the DF bit, i.e.:

   o  >> IPv4 datagrams whose DF=1 MUST NOT be fragmented.

   o  >> IPv4 datagram transit devices MUST NOT clear the DF bit.

   In specific, DF=1 prevents fragmenting datagrams that are integral.
   DF=1 also prevents further fragmenting received fragments.
   Fragmentation, either of an unfragmented datagram or of fragments, is
   current permitted only where DF=0 in the original emitted datagram,
   and this document does not change that requirement.

7. Impact on Datagram Use

   The following is a summary of the recommendations that are the result
   of the previous changes to the IPv4 ID field specification.

   Because atomic datagrams can use arbitrary IPv4 ID values, the ID
   field no longer imposes a performance impact in those cases. However,
   the performance impact remains for non-atomic datagrams. As a result:

   o  >> Sources of non-atomic IPv4 datagrams MUST rate-limit their
      output to comply with the ID uniqueness requirements.

   Such sources include, in particular, DNS over UDP [RFC2671].

   Because there is no strict definition of the MSL, reassembly hazards
   exist regardless of the IPv4 ID reuse interval or the reassembly
   timeout. As a result:

   o  >> Higher layer protocols SHOULD verify the integrity of IPv4
      datagrams, e.g., using a checksum or hash that can detect
      reassembly errors (the UDP checksum is weak in this regard, but
      better than nothing), as in SEAL [RFC5320].


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   Additional integrity checks can be employed using tunnels, as in
   SEAL, IPsec, or SCTP [RFC4301][RFC4960][RFC5320]. Such checks can
   avoid the reassembly hazards that can occur when using UDP and TCP
   checksums [RFC4963], or when using partial checksums as in UDP-Lite
   [RFC3828]. Because such integrity checks can avoid the impact of
   reassembly errors:

   o  >> Sources of non-atomic IPv4 datagrams using strong integrity
      checks MAY reuse the ID within MSL values smaller than is typical.

   Note, however, that such more frequent reuse can still result in
   corrupted reassembly and poor throughput, although it would not
   propagate reassembly errors to higher layer protocols.

8. Updates to Existing Standards

   The following sections address the specific changes to existing
   protocols indicated by this document.

8.1. Updates to RFC 791

   RFC 791 states that:

      The originating protocol module of an internet datagram sets the
      identification field to a value that must be unique for that
      source-destination pair and protocol for the time the datagram
      will be active in the internet system.

   And later that:

      Thus, the sender must choose the Identifier to be unique for this
      source, destination pair and protocol for the time the datagram
      (or any fragment of it) could be alive in the internet.

      It seems then that a sending protocol module needs to keep a table
      of Identifiers, one entry for each destination it has communicated
      with in the last maximum datagram lifetime for the internet.

      However, since the Identifier field allows 65,536 different
      values, some host may be able to simply use unique identifiers
      independent of destination.

      It is appropriate for some higher level protocols to choose the
      identifier. For example, TCP protocol modules may retransmit an
      identical TCP segment, and the probability for correct reception
      would be enhanced if the retransmission carried the same



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      identifier as the original transmission since fragments of either
      datagram could be used to construct a correct TCP segment.

   This document changes RFC 791 as follows:

   o  IPv4 ID uniqueness applies to only non-atomic datagrams.

   o  Non-atomic IPv4 datagrams retransmitted by higher level protocols
      are no longer permitted to reuse the ID value.

8.2. Updates to RFC 1122

   RFC 1122 states that:

        3.2.1.5  Identification: RFC-791 Section 3.2

            When sending an identical copy of an earlier datagram, a
            host MAY optionally retain the same Identification field in
            the copy.

            DISCUSSION:

            Some Internet protocol experts have maintained that when a
            host sends an identical copy of an earlier datagram, the new
            copy should contain the same Identification value as the
            original.  There are two suggested advantages:  (1) if the
            datagrams are fragmented and some of the fragments are lost,
            the receiver may be able to reconstruct a complete datagram
            from fragments of the original and the copies; (2) a
            congested gateway might use the IP Identification field (and
            Fragment Offset) to discard duplicate datagrams from the
            queue.

   This document changes RFC 1122 as follows:

   o  The IPv4 ID field is no longer permitted for duplicate detection.

   o  The IPv4 ID field is no longer repeatable for higher level
      protocol retransmission.

   o  IPv4 datagram fragments no longer are permitted to overlap.

8.3. Updates to RFC 2003

   This document updates how IPv4-in-IPv4 tunnels create IPv4 ID values
   for the IPv4 outer header [RFC2003], but only in the same way as for
   any other IPv4 datagram source.


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9. Impact on NATs and Tunnel Ingresses

   Network address translators (NATs) and address/port translators
   (NAPTs) rewrite IP fields, and tunnel ingresses (using IPv4
   encapsulation) copy and modify some IPv4 fields, so all are
   considered sources, as do any devices that rewrite any portion of the
   source address, destination address, protocol, and ID tuple for non-
   atomic datagrams [RFC3022]. As a result, they are subject to all the
   requirements of any source, as has been noted.

   NATs present a particularly challenging situation for fragmentation.
   Because NATs overwrite portions of the reassembly tuple in both
   directions, they can destroy tuple uniqueness and result in a
   reassembly hazard. Whenever IPv4 source address, destination address,
   or protocol fields are modified, a NAT needs to ensure that the ID
   field is generated appropriately, rather than simply copied from the
   incoming datagram. In specific:

   o  >> NATs MUST ensure that the IPv4 ID field of datagrams whose
      address or protocol are translated comply with requirements as if
      the datagram were sourced by the NAT.

   This compliance means that the IPv4 ID field of non-atomic datagrams
   translated at a NAT need to obey the uniqueness requirements of any
   IPv4 datagram source. Unfortunately, fragments already violate that
   requirement, as they repeat an IPv4 ID within the MSL for a given
   source address, destination address, and protocol triple.

   Such problems with transmitting fragments through NATs are already
   known; translation is based on the transport port number, which is
   present in only the first fragment anyway [RFC3022]. This document
   underscores the point that not only is reassembly (and possibly
   subsequent fragmentation) required for translation, it can be used to
   avoid issues with IPv4 ID uniqueness.

   Note that NATs/NAPTs already need to exercise special care when
   emitting datagrams on their public side, because merging datagrams
   from many sources onto a single outgoing source address can result in
   IPv4 ID collisions. This situation precedes this document, and is not
   affected by it. It is exacerbated in large-scale, so-called "carrier
   grade" NATs [Ni09].

   Tunnel ingresses act as sources for the outermost header, but tunnels
   act as routers for the inner headers (i.e., the datagram as arriving
   at the tunnel ingress). Ingresses can fragment as originating sources
   of the outer header, because they control the uniqueness of that IPv4
   ID field. They need to avoid fragmenting the datagram at the inner


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   header, for the same reasons as any intermediate device, as noted
   elsewhere in this document.

10. Impact on Header Compression

   Header compression algorithms already accommodate various ways in
   which the IPv4 ID changes between sequential datagrams. Such
   algorithms currently need to preserve the IPv4 ID.

   When compression can assume a nonchanging IPv4 ID, efficiency can be
   increased. However, when compression assumes a changing ID as a
   default, having a non-changing ID can make compression less efficient
   (see footnote 21 of [RFC1144], which is optimized for non-atomic
   datagrams). This document thus does not recommend whether atomic IPv4
   datagrams should use nonchanging or changing IDs, but rather allows
   those IDs to be modified in transit (as per Sec. 6.2), which can be
   used to accommodate more efficient compression as desired.

11. Security Considerations

   This document attempts to address the security considerations
   associated with fragmentation in IPv4 [RFC4459].

   When the IPv4 ID is ignored on receipt (e.g., for atomic datagrams),
   its value becomes unconstrained; that field then can more easily be
   used as a covert channel. For some atomic datagrams - notably those
   not protected by IPsec Authentication Header (AH) [RFC4302] - it is
   now possible, and may be desirable, to rewrite the IPv4 ID field to
   avoid its use as such a channel.

   The IPv4 ID also now adds much less entropy of the header of a
   datagram. The IPv4 ID had previously been unique (for a given
   source/address pair, and protocol field) within one MSL, although
   this requirement was not enforced and clearly is typically ignored.
   IDs of non-atomic datagrams are now required unique only within the
   expected reordering of fragments, which could substantially reduce
   the amount of entropy in that field. The IPv4 ID of atomic datagrams
   is not required unique, and so contributes no entropy to the header.

   The deprecation of the IPv4 ID field's uniqueness for atomic
   datagrams can defeat the ability to count devices behind a NAT
   [Be02]. This is not intended as a security feature, however.

12. IANA Considerations

   There are no IANA considerations in this document.



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   The RFC Editor should remove this section prior to publication

13. References

13.1. Normative References

   [RFC791]  Postel, J., "Internet Protocol", RFC 791 / STD 5, September
             1981.

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

   [RFC1812] Baker, F. (Ed.), "Requirements for IP Version 4 Routers",
             RFC 1812 / STD 4, Jun. 1995.

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

   [RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003,
             October 1996.

13.2. Informative References

   [Be02]    Bellovin, S., "A Technique for Counting NATted Hosts",
             Internet Measurement Conference, Proceedings of the 2nd ACM
             SIGCOMM Workshop on Internet Measurement, November 2002.

   [Ni09]    Nishitani, T., I. Yamagata, S. Miyakawa, A. Nakagawa, H.
             Ashida, "Common Functions of Large Scale NAT (LSN) ", (work
             in progress), draft-nishitani-cgn-05, July 2010.

   [RFC1144] Jacobson, V., "Compressing TCP/IP Headers", RFC 1144, Feb.
             1990.

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

   [RFC2671] Vixie,P., "Extension Mechanisms for DNS (EDNS0)", RFC 2671,
             August 1999.

   [RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network
             Address Translator (Traditional NAT)", RFC 3022, January
             2001.

   [RFC3828] Larzon, L-A., M. Degermark, S. Pink, L-E. Jonsson, Ed., G.
             Fairhurst, Ed., "The Lightweight User Datagram Protocol
             (UDP-Lite)", RFC 3828, July 2004.


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Internet-Draft    Updated Spec. of the IPv4 ID Field       October 2010


   [RFC4301] Kent, S., K. Seo, "Security Architecture for the Internet
             Protocol", RFC 4301, Dec. 2005.

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

   [RFC4459] Savola, P., "MTU and Fragmentation Issues with In-the-
             Network Tunneling", RFC 4459, April 2006.

   [RFC4960] Stewart, R. (Ed.), "Stream Control Transmission Protocol",
             RFC 4960, Sep. 2007.

   [RFC4963] Heffner, J., M. Mathis, B. Chandler, "IPv4 Reassembly
             Errors at High Data Rates," RFC 4963, July 2007.

   [RFC5320] Templin, F., Ed., "The Subnetwork Encapsulation and
             Adaptation Layer (SEAL)", RFC 5320, Feb. 2010.

14. Acknowledgments

   This document was inspired by of numerous discussions among the
   authors, Jari Arkko, Lars Eggert, Dino Farinacci, and Fred Templin,
   as well as members participating in the Internet Area Working Group.
   Detailed feedback was provided by Carlos Pignataro and Gorry
   Fairhurst. This document originated as an Independent Stream draft
   co-authored by Matt Mathis, PSC, and his contributions are greatly
   appreciated.

   This document was prepared using 2-Word-v2.0.template.dot.

Author's Address

   Joe Touch
   USC/ISI
   4676 Admiralty Way
   Marina del Rey, CA 90292-6695
   U.S.A.

   Phone: +1 (310) 448-9151
   Email: touch@isi.edu










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