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rfc:rfc2101

Network Working Group B. Carpenter Request for Comments: 2101 J. Crowcroft Category: Informational Y. Rekhter

                                                                   IAB
                                                         February 1997
                    IPv4 Address Behaviour Today

Status of this Memo

 This memo provides information for the Internet community.  This memo
 does not specify an Internet standard of any kind.  Distribution of
 this memo is unlimited.

Abstract

 The main purpose of this note is to clarify the current
 interpretation of the 32-bit IP version 4 address space, whose
 significance has changed substantially since it was originally
 defined.  A short section on IPv6 addresses mentions the main points
 of similarity with, and difference from, IPv4.

Table of Contents

   1. Introduction.................................................1
   2. Terminology..................................................2
   3. Ideal properties.............................................3
   4. Overview of the current situation of IPv4 addresses..........4
     4.1. Addresses are no longer globally unique locators.........4
     4.2. Addresses are no longer all temporally unique............6
     4.3. Multicast and Anycast....................................7
     4.4. Summary..................................................8
   5. IPv6 Considerations..........................................8
   ANNEX: Current Practices for IPv4 Address Allocation & Routing..9
   Security Considerations........................................10
   Acknowledgements...............................................11
   References.....................................................11
   Authors' Addresses.............................................13

1. Introduction

 The main purpose of this note is to clarify the current
 interpretation of the 32-bit IP version 4 address space, whose
 significance has changed substantially since it was originally
 defined in 1981 [RFC 791].

Carpenter, et. al. Informational [Page 1] RFC 2101 IPv4 Address Behavior Today February 1997

 This clarification is intended to assist protocol designers, product
 implementors, Internet service providers, and user sites. It aims to
 avoid misunderstandings about IP addresses that can result from the
 substantial changes that have taken place in the last few years, as a
 result of the Internet's exponential growth.
 A short section on IPv6 addresses mentions the main points of
 similarity with, and difference from, IPv4.

2. Terminology

 It is well understood that in computer networks, the concepts of
 directories, names, network addresses, and routes are separate and
 must be analysed separately [RFC 1498].  However, it is also
 necessary to sub-divide the concept of "network address" (abbreviated
 to "address" from here on) into at least two notions, namely
 "identifier" and "locator". This was perhaps less well understood
 when RFC 791 was written.
 In this document, the term "host" refers to any system originating
 and/or terminating IPv4 packets, and "router" refers to any system
 forwarding IPv4 packets from one host or router to another.
 For the purposes of this document, an "identifier" is a bit string
 which is used throughout the lifetime of a communication session
 between two hosts, to identify one of the hosts as far as the other
 is concerned. Such an identifier is used to verify the source of
 incoming packets as being truly the other end of the communication
 concerned, e.g. in the TCP pseudo-header [RFC 793] or in an IP
 Security association [RFC 1825].  Traditionally, the source IPv4
 address in every packet is used for this.
 Note that other definitions of "identifier" are sometimes used; this
 document does not claim to discuss the general issue of the semantics
 of end-point identifiers.
 For the purposes of this document, a "locator" is a bit string which
 is used to identify where a particular packet must be delivered, i.e.
 it serves to locate the place in the Internet topology where the
 destination host is attached. Traditionally, the destination IPv4
 address in every packet is used for this. IP routing protocols
 interpret IPv4 addresses as locators and construct routing tables
 based on which routers (which have their own locators) claim to know
 a route towards the locators of particular hosts.
 Both identifiers and locators have requirements of uniqueness, but
 these requirements are different. Identifiers must be unique with
 respect to each set of inter-communicating hosts. Locators must be

Carpenter, et. al. Informational [Page 2] RFC 2101 IPv4 Address Behavior Today February 1997

 unique with respect to each set of inter-communicating routers (which
 we will call a routing "realm"). While locators must be unique within
 a given routing realm, this uniqueness (but not routability) could
 extend to more than one realm.  Thus we can further distinguish
 between a set of realms with unique locators versus a set of realms
 with non-unique (overlapping) locators.
 Both identifiers and locators have requirements of lifetime, but
 these requirements are different. Identifiers must be valid for at
 least the maximum lifetime of a communication between two hosts.
 Locators must be valid only as long as the routing mechanisms so
 require (which could be shorter or longer than the lifetime of a
 communication).
 It will be noted that it is a contingent fact of history that the
 same address space and the same fields in the IP header (source and
 destination addresses) are used by RFC 791 and RFC 793 for both
 identifiers and locators, and that in the traditional Internet a
 host's identifier is identical to its locator, as well as being
 spatially unique (unambiguous) and temporally unique (constant).
 These uniqueness conditions had a number of consequences for design
 assumptions of routing (the infrastructure that IPv4 locators enable)
 and transport protocols (that which depends on the IP connectivity).
 Spatial uniqueness of an address meant that it served as both an
 interface identifier and a host identifier, as well as the key to the
 routing table.  Temporal uniqueness of an address meant that there
 was no need for TCP implementations to maintain state regarding
 identity of the far end, other than the IP address. Thus IP addresses
 could be used both for end-to-end IP security and for binding upper
 layer sessions.
 Generally speaking, the use of IPv4 addresses as locators has been
 considered more important than their use as identifiers, and whenever
 there has been a conflict between the two uses, the use as a locator
 has prevailed. That is, it has been considered more useful to deliver
 the packet, then worry about how to identify the end points, than to
 provide identity in a packet that cannot be delivered. In other
 words, there has been intensive work on routing protocols and little
 concrete work on other aspects of address usage.

3. Ideal properties.

 Whatever the constraints mentioned above, it is easy to see the ideal
 properties of identifiers and locators. Identifiers should be
 assigned at birth, never change, and never be re-used. Locators
 should describe the host's position in the network's topology, and
 should change whenever the topology changes.

Carpenter, et. al. Informational [Page 3] RFC 2101 IPv4 Address Behavior Today February 1997

 Unfortunately neither of the these ideals are met by IPv4 addresses.
 The remainder of this document is intended as a snapshot of the
 current real situation.

4. Overview of the current situation of IPv4 addresses.

 It is a fact that IPv4 addresses are no longer all globally unique
 and no longer all have indefinite lifetimes.
 4.1 Addresses are no longer globally unique locators
    [RFC 1918] shows how corporate networks, a.k.a. Intranets, may if
    necessary legitimately re-use a subset of the IPv4 address space,
    forming multiple routing realms. At the boundary between two (or
    more) routing realms, we may find a spectrum of devices that
    enables communication between the realms.
    At one end of the spectrum is a pure Application Layer Gateway
    (ALG). Such a device acts as a termination point for the
    application layer data stream, and is visible to an end-user.  For
    example, when an end-user Ua in routing realm A wants to
    communicate with an end-user Ub in routing realm B, Ua has first
    to explicitly establish communication with the ALG that
    interconnects A and B, and only via that can Ua establish
    communication with Ub. We term such a gateway a "non-transparent"
    ALG.
    Another form of ALG makes communication through the ALG
    transparent to an end user. Using the previous example, with a
    "transparent" ALG, Ua would not be required to establish explicit
    connectivity to the ALG first, before starting to communicate with
    Ub. Such connectivity will be established transparently to Ua, so
    that Ua would only see connectivity to Ub.
    For completeness, note that it is not necessarily the case that
    communicating via an ALG involves changes to the network header.
    An ALG could be used only at the beginning of a session for the
    purpose of authentication, after which the ALG goes away and
    communication continues natively.
    Both non-transparent and transparent ALGs are required (by
    definition) to understand the syntax and semantics of the
    application data stream.  ALGs are very simple from the viewpoint
    of network layer architecture, since they appear as Internet hosts
    in each realm, i.e. they act as origination and termination points
    for communication.

Carpenter, et. al. Informational [Page 4] RFC 2101 IPv4 Address Behavior Today February 1997

    At the other end of the spectrum is a Network Address Translator
    (NAT) [RFC 1631]. In the context of this document we define a NAT
    as a device that just modifies the network and the transport layer
    headers, but does not understand the syntax/semantics of the
    application layer data stream (using our terminology what is
    described in RFC1631 is a device that has both the NAT and ALG
    functionality).
    In the standard case of a NAT placed between a corporate network
    using private addresses [RFC 1918] and the public Internet, that
    NAT changes the source IPv4 address in packets going towards the
    Internet, and changes the destination IPv4 address in packets
    coming from the Internet.  When a NAT is used to interconnect
    routing realms with overlapping addresses, such as a direct
    connection between two intranets, the NAT may modify both
    addresses in the IP header.  Since the NAT modifies address(es) in
    the IP header, the NAT also has to modify the transport (e.g.,
    TCP, UDP) pseudo-header checksum.  Upon some introspection one
    could observe  that  when interconnecting routing realms with
    overlapping addresses, the set of operations on the network and
    transport header performed by a NAT forms a (proper) subset of the
    set of operations on the network and transport layer performed by
    a transparent ALG.
    By definition a NAT does not understand syntax and semantics of an
    application data stream. Therefore, a NAT cannot support
    applications that carry IP addresses at the application layer
    (e.g., FTP with PORT or PASV command [RFC 959]). On the other
    hand, a NAT can support any application, as long as such an
    application does not carry IP addresses at the application layer.
    This is in contrast with an ALG that can support only the
    applications coded into the ALG.
    One can conclude that both NATs and ALGs have their own
    limitations, which could constrain their usefulness. Combining NAT
    and ALG functionality in a single device could be used to overcome
    some, but not all, of these limitations.  Such a device would use
    the NAT functionality for the applications that do not carry IP
    addresses, and would resort to the ALG functionality when dealing
    with the applications that carry IP addresses. For example, such a
    device would use the NAT functionality to deal with the FTP data
    connection, but would use the ALG functionality to deal with the
    FTP control connection.  However, such a device will fail
    completely handling an application that carries IP addresses, when
    the device does not support the application via the ALG
    functionality, but rather handles it via the NAT functionality.

Carpenter, et. al. Informational [Page 5] RFC 2101 IPv4 Address Behavior Today February 1997

    Communicating through either ALGs or NATs involves changes to the
    network header (and specifically source and destination
    addresses), and to the transport header. Since IP Security
    authentication headers assume that the addresses in the network
    header are preserved end-to-end, it is not clear how one could
    support IP Security-based authentication between a pair of hosts
    communicating through either an ALG or a NAT. Since IP Security,
    when used for confidentiality, encrypts the entire transport layer
    end-to-end, it is not clear how an ALG or NAT could modify
    encrypted packets as they require to.  In other words, both ALGs
    and NATs are likely to force a boundary between two distinct IP
    Security domains, both for authentication and for confidentiality,
    unless specific enhancements to IP Security are designed for this
    purpose.
    Interconnecting routing realms via either ALGs or NATs relies on
    the DNS [RFC 1035].  Specifically, for a given set of
    (interconnected) routing realms, even if network layer addresses
    are no longer unique across the set, fully qualified domain names
    would need to be unique across the set. However, a site that is
    running a NAT or ALG probably needs to run two DNS servers, one
    inside and one outside the NAT or ALG, giving different answers to
    identical queries. This is discussed further in [kre].  DNS
    security [RFC 2065] and some dynamic DNS updates [dns2] will
    presumably not be valid across a NAT/ALG boundary, so we must
    assume that the external DNS server acquires at least part of its
    tables by some other mechanism.
    To summarize, since RFC 1918, we have not really changed the
    spatial uniqueness of an address, so much as recognized that there
    are multiple spaces. i.e.  each space is still a routing realm
    such as an intranet, possibly connected to other intranets, or the
    Internet, by NATs or ALGs (see above discussion). The temporal
    uniqueness of an address is unchanged by RFC 1918.
 4.2. Addresses are no longer all temporally unique
    Note that as soon as address significance changes anywhere in the
    address space, it has in some sense changed everywhere. This has
    in fact already happened.
    IPv4 address blocks were for many years assigned chronologically,
    i.e.  effectively at random with respect to network topology.
    This led to constantly growing routing tables; this does not
    scale. Today, hierarchical routing (CIDR [RFC 1518], [RFC 1519])
    is used as a mechanism to improve scaling of routing within a
    routing realm, and especially within the Internet (The Annex goes
    into more details on CIDR).

Carpenter, et. al. Informational [Page 6] RFC 2101 IPv4 Address Behavior Today February 1997

    Scaling capabilities of CIDR are based on the assumption that
    address allocation reflects network topology as much as possible,
    and boundaries for aggregation of addressing information are not
    required to be fully contained within a single organization - they
    may span multiple organizations (e.g., provider with its
    subscribers).  Thus if a subscriber changes its provider, then to
    avoid injecting additional overhead in the Internet routing
    system, the subscriber may need to renumber.
    Changing providers is just one possible reason for renumbering.
    The informational document [RFC 1900] shows why renumbering is an
    increasingly frequent event.  Both DHCP [RFC 1541] and PPP [RFC
    1661] promote the use of dynamic address allocation.
    To summarize, since the development and deployment of DHCP and
    PPP, and since it is expected that renumbering is likely to become
    a common event, IP address significance has indeed been changed.
    Spatial uniqueness should be the same, so addresses are still
    effective locators. Temporal uniqueness is no longer assured. It
    may be quite short, possibly shorter than a TCP connection time.
    In such cases an IP address is no longer a good identifier. This
    has some impact on end-to-end security, and breaks TCP in its
    current form.
 4.3. Multicast and Anycast
    Since we deployed multicast [RFC 1112], we must separate the
    debate over meaning of IP addresses into meaning of source and
    destination addresses.  A destination multicast address (i.e. a
    locator for a topologically spread group of hosts) can traverse a
    NAT, and is not necessarily restricted to an intranet (or to the
    public Internet).  Its lifetime can be short too.
    The concept of an anycast address is of an address that
    semantically locates any of a group of systems performing
    equivalent functions. There is no way such an address can be
    anything but a locator; it can never serve as an identifier as
    defined in this document, since it does not uniquely identify
    host.  In this case, the effective temporal uniqueness, or useful
    lifetime, of an IP address can be less than the time taken to
    establish a TCP connection.
    Here we have used TCP simply to illustrate the idea of an
    association - many UDP based applications (or other systems
    layered on IP) allocate state after receiving or sending a first
    packet, based on the source and/or destination. All are affected
    by absence of temporal uniqueness whereas only the routing
    infrastructure is affected by spatial uniqueness changes.

Carpenter, et. al. Informational [Page 7] RFC 2101 IPv4 Address Behavior Today February 1997

 4.4. Summary
    Due to dynamic address allocation and increasingly frequent
    network renumbering, temporal uniqueness of IPv4 addresses is no
    longer globally guaranteed, which puts their use as identifiers
    into severe question.  Due to the proliferation of Intranets,
    spatial uniqueness is also no longer guaranteed across routing
    realms; interconnecting routing realms could be accomplished via
    either ALGs or NATs. In principle such interconnection will have
    less functionality than if those Intranets were directly
    connected. In practice the difference in functionality may or may
    not matter, depending on individual circumstances.

5. IPv6 Considerations

 As far as temporal uniqueness (identifier-like behaviour) is
 concerned, the IPv6 model [RFC 1884] is very similar to the current
 state of the IPv4 model, only more so.  IPv6 will provide mechanisms
 to autoconfigure IPv6 addresses on IPv6 hosts. Prefix changes,
 requiring the global IPv6 addresses of all hosts under a given prefix
 to change, are to be expected. Thus, IPv6 will amplify the existing
 problem of finding stable identifiers to be used for end-to-end
 security and for session bindings such as TCP state.
 The IAB feels that this is unfortunate, and that the transition to
 IPv6 would be an ideal occasion to provide upper layer end-to-end
 protocols with temporally unique identifiers. The exact nature of
 these identifiers requires further study.
 As far as spatial uniqueness (locator-like behaviour) is concerned,
 the IPv6 address space is so big that a shortage of addresses,
 requiring an RFC 1918-like approach and address translation, is
 hardly conceivable.  Although there is no shortage of IPv6 addresses,
 there is also a well-defined mechanism for obtaining link-local and
 site-local addresses in IPv6 [RFC 1884, section 2.4.8].  These
 properties of IPv6 do not prevent separate routing realms for IPv6,
 if so desired (resulting in multiple security domains as well).
 While at the present moment we cannot identify a case in which
 multiple IPv6 routing realms would be required, it is also hard to
 give a definitive answer to whether there will be only one, or more
 than one IPv6 routing realms.  If one hypothesises that there will be
 more than one IPv6 routing realm, then such realms could be
 interconnected together via ALGs and NATs. Considerations for such
 ALGs and NATs appear to be identical to those for IPv4.

Carpenter, et. al. Informational [Page 8] RFC 2101 IPv4 Address Behavior Today February 1997

ANNEX: Current Practices for IPv4 Address Allocation & Routing

 Initially IP address structure and IP routing were designed around
 the notion of network number classes (Class A/B/C networks) [RFC
 790].  In the earlier 90s growth of the Internet demanded significant
 improvements in both the scalability of the Internet routing system,
 as well as in the IP address space utilization.  Classful structure
 of IP address space and associated with it classful routing turned
 out to be inadequate to meet the demands, so during 1992 - 1993
 period the Internet adopted Classless Inter-Domain Routing (CIDR)
 [RFC 1380], [RFC 1518], [RFC 1519].  CIDR  encompasses a new address
 allocation architecture, new routing protocols,  and a new structure
 of IP addresses.
 CIDR improves scalability of the Internet routing system by extending
 the notion of hierarchical routing beyond the level of individual
 subnets and networks, to allow routing information aggregation not
 only at the level of individual subnets and networks, but at the
 level of individual sites, as well as at the level of Internet
 Service Providers.  Thus an organization (site) could act as an
 aggregator for all the destinations within the organization.
 Likewise, a provider could act as an aggregator for all the
 destinations within its subscribers (organizations directly connected
 to the provider).
 Extending the notion of hierarchical routing to the level of
 individual sites and providers, and allowing sites and providers to
 act as aggregators of routing information, required changes both to
 the address allocation procedures, and to the routing protocols.
 While in pre-CIDR days address allocation to sites was done without
 taking into consideration the need to aggregate the addressing
 information above the level of an individual network numbers, CIDR-
 based  allocation recommends that address allocation be done in such
 a way as to enable sites and providers to act as aggregators of
 addressing information - such allocation is called "aggregator
 based". To benefit from the "aggregator based" address allocation,
 CIDR introduces an inter-domain routing protocol (BGP-4) [RFC 1771,
 RFC 1772] that provides capabilities for routing information
 aggregation at the level of individual sites and providers.
 CIDR improves address space utilization by eliminating the notion of
 network classes,  and replacing it with the notion of contiguous
 variable size (power of 2) address blocks. This allows a better match
 between the amount of address space requested and the amount of
 address space allocated [RFC 1466]. It also facilitates "aggregator
 based" address allocation. Eliminating the notion of network classes
 requires new capabilities in the routing protocols (both intra and
 inter-domain), and IP forwarding. Specifically, the CIDR-capable

Carpenter, et. al. Informational [Page 9] RFC 2101 IPv4 Address Behavior Today February 1997

 protocols are required to handle reachability (addressing)
 information expressed in terms of variable length address prefixes,
 and forwarding  is required to implement the "longest match"
 algorithm.  CIDR implications on routing protocols are described in
 [RFC 1817].
 The scaling capabilities of CIDR are based on the assumption that
 address allocation reflects network topology as much as possible,
 especially at the level of sites, and their interconnection with
 providers, to enable sites and providers to act as aggregators. If a
 site changes its provider, then to avoid injecting additional
 overhead in the Internet routing system, the site may need to
 renumber. While CIDR does not require every site that changes its
 providers to renumber, it is important to stress that if none of the
 sites that change their providers will renumber, the Internet routing
 system might collapse due to the excessive amount of routing
 information it would need to handle.
 Maintaining "aggregator based" address allocation (to promote
 scalable routing), and the need to support the ability of sites to
 change their providers (to promote competition) demands practical
 solutions for renumbering sites.  The need to contain the  overhead
 in a rapidly growing Internet routing system is likely to make
 renumbering  more and more common [RFC 1900].
 The need to scale the Internet routing system, and the use of CIDR as
 the primary mechanism for scaling, results in the evolution of
 address allocation and management policies for the Internet. This
 evolution results in adding the "address lending" policy as an
 alternative to the "address ownership" policy [RFC 2008].
 IP addressing and routing have been in constant evolution since IP
 was first specified [RFC 791]. Some of the addressing and routing
 principles have been deprecated, some of the principles have been
 preserved, while new principles have been introduced. Current
 Internet routing and addresses (based on CIDR) is an evolutionary
 step that extends the use of hierarchy to maintain a routable global
 Internet.

Security Considerations

 The impact of the IP addressing model on security is discussed in
 sections 4.1 and 5 of this document.

Carpenter, et. al. Informational [Page 10] RFC 2101 IPv4 Address Behavior Today February 1997

Acknowledgements

 This document was developed in the IAB. Constructive comments were
 received from Ran Atkinson, Jim Bound, Matt Crawford, Tony Li,
 Michael A. Patton, Jeff Schiller. Earlier private communications from
 Noel Chiappa helped to clarify the concepts of locators and
 identifiers.

References

 [RFC 791] Postel, J., "Internet Protocol", STD 5, RFC 791, September
 1981.
 [RFC 790] Postel, J., "Assigned Numbers", September 1981.
 [RFC 959] Postel, J., and J. Reynolds, "File Transfer Protocol", STD
 9, RFC 959, October 1985.
 [RFC 1035] Mockapetris, P., "Domain Names - Implementation and
 Specification", STD 13, RFC 1035, November 1987.
 [RFC 1112] Deering, S., "Host Extensions for IP Multicasting", STD 5,
 RFC 1112, September 1989.
 [RFC 1380] Gross, P., and P. Almquist, "IESG Deliberations on Routing
 and Addressing", RFC 1380, November 1992.
 [RFC 1466] Gerich, E., "Guidelines for Management of IP Address
 Space", RFC 1466, May 1993.
 [RFC 1498] Saltzer, J., "On the Naming and Binding of Network
 Destinations", RFC 1498, August 1993 (originally published 1982).
 [RFC 1518] Rekhter, Y., and T. Li, "An Architecture for IP Address
 Allocation with CIDR", RFC 1518, September 1993.
 [RFC 1519] Fuller, V., Li, T., Yu, J., and K. Varadhan, "Classless
 Inter-Domain Routing (CIDR): an Address Assignment and Aggregation
 Strategy", RFC 1519, September 1993.
 [RFC 1541] Droms, R., "Dynamic Host Configuration Protocol", RFC
 1541, October 1993.
 [RFC 1661] Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51,
 RFC 1661, July 1994.
 [RFC 1771] Rekhter, Y., and T. Li, "A Border Gateway Protocol 4
 (BGP-4)", RFC 1771, March 1995.

Carpenter, et. al. Informational [Page 11] RFC 2101 IPv4 Address Behavior Today February 1997

 [RFC 1772] Rekhter, Y., and P. Gross, "Application of the Border
 Gateway Protocol in the Internet", RFC 1772, March 1995.
 [RFC 1817] Rekhter, Y., "CIDR and Classful Routing", RFC 1817,
 September 1995.
 [RFC 1825] Atkinson, R., "Security Architecture for the Internet
 Protocol", RFC 1825, September 1995.
 [RFC 1900] Carpenter, B., and Y. Rekhter, "Renumbering Needs Work",
 RFC 1900, February 1996.
 [RFC 1918] Rekhter, Y.,  Moskowitz, B., Karrenberg, D., de Groot, G.
 J., and E. Lear, "Address Allocation for Private Internets", RFC
 1918, February 1996.
 [RFC 1933] Gilligan, R., and E. Nordmark, "Transition Mechanisms for
 IPv6 Hosts and Routers", RFC 1933, April 1996.
 [RFC 2008] Rekhter, Y., and T. Li, "Implications of  Various Address
 Allocation Policies for Internet Routing", RFC 2008, October 1996.
 [kre] Elz, R., et. al., "Selection and Operation of Secondary DNS
 Servers", Work in Progress.
 [RFC 2065] Eastlake, E., and C. Kaufman, "Domain Name System Security
 Extensions", RFC 2065, January 1997.
 [dns2] Vixie, P., et. al., "Dynamic Updates in the Domain Name System
 (DNS UPDATE)", Work in Progress.

Carpenter, et. al. Informational [Page 12] RFC 2101 IPv4 Address Behavior Today February 1997

Authors' Addresses

 Brian E. Carpenter
 Computing and Networks Division
 CERN
 European Laboratory for Particle Physics
 1211 Geneva 23, Switzerland
 EMail: brian@dxcoms.cern.ch
 Jon Crowcroft
 Dept. of Computer Science
 University College London
 London WC1E 6BT, UK
 EMail: j.crowcroft@cs.ucl.ac.uk
 Yakov Rekhter
 Cisco systems
 170 West Tasman Drive
 San Jose, CA, USA
 Phone: +1 914 528 0090
 Fax: +1 408 526-4952
 EMail: yakov@cisco.com

Carpenter, et. al. Informational [Page 13]

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