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Network Working Group T. Dixon Request for Comments: 1454 RARE

                                                             May 1993
           Comparison of Proposals for Next Version of IP

Status of this Memo

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


 This is a slightly edited reprint of RARE Technical Report
 The following is a brief summary of the characteristics of the three
 main proposals for replacing the current Internet Protocol. It is not
 intended to be exhaustive or definitive (a brief bibliography at the
 end points to sources of more information), but to serve as input to
 the European discussions on these proposals, to be co-ordinated by
 RARE and RIPE. It should be recognised that the proposals are
 themselves "moving targets", and in so far as this paper is accurate
 at all, it reflects the position at the 25th IETF meeting in
 Washington, DC. Comments from Ross Callon and Paul Tsuchiya on the
 original draft have been incorporated.  Note that for a time the term
 "IPv7" was use to mean the eventual next version of IP, but that the
 same term was closely associated with a particilar proposal, so the
 term "IPng" is now used to identify the eventual next generation of
 The paper begins with a "generic" discussion of the mechanisms for
 solving problems and achieving particular goals, before discussing
 the proposals invidually.


 The problem has been investigated and formulated by the ROAD group,
 but briefly reduces to the following:
  1. Exhaustion of IP Class B Address Space.
  1. Exhaustion of IP Address Space in General.
  1. Non-hierarchical nature of address allocation leading to flat

routing space.

Dixon [Page 1] RFC 1454 Comparison of Next Version IP Proposals May 1993

 Although the IESG requirements for a new Internet Protocol go further
 than simply routing and addressing issues,  it is these issues that
 make extension of the current protocol an impractical option.
 Consequently, most of the discussion and development of the various
 proposed protocols has concentrated on these specific problems.
 Near term remedies for these problems include the CIDR proposals
 (which permit the aggregation of Class C networks for routing
 purposes) and assignment policies which will allocate Class C network
 numbers in a fashion which CIDR can take advantage of. Routing
 protocols supporting CIDR are OSPF and BGP4. None of these are pre-
 requisites for the new IP (IPng), but are necessary to prolong the
 life of the current Internet long enough to work on longer-term
 solutions. Ross Callon points out that there are other options for
 prolonging the life of IP and that some ideas have been distributed
 on the TUBA list.
 Longer term proposals are being sought which ultimately allow for
 further growth of the Internet. The timescale for considering these
 proposals is as follows:
  1. Dec 15 Issue selection criteria as RFC.
  1. Feb 12 Two interoperable implementations available.
  1. Feb 26 Second draft of proposal documents available.
 The (ambitious) target is for a decision to be made at the 26th IETF
 (Columbus, Ohio in March 1993) on which proposals to pursue.
 The current likely candidates for selection are:
  1. PIP ('P' Internet Protocol - an entirely new protocol).
  1. TUBA (TCP/UDP with Big Addresses - uses ISO CLNP).
  1. SIP (Simple IP - IP with larger addresses and fewer options).
 There is a further proposal from Robert Ullman of which I don't claim
 to have much knowledge. Associated with each of the candidates are
 transition plans, but these are largely independent of the protocol
 itself and contain elements which could be adopted separately, even
 with IP v4, to further extend the life of current implementations and

Dixon [Page 2] RFC 1454 Comparison of Next Version IP Proposals May 1993


2.1 Larger Addresses

 All the proposals (of course) make provision for larger address
 fields which not only increase the number of addressable systems, but
 also permit the hierarchical allocation of addresses to facilitate
 route aggregation.

2.2 Philosophy

 The proposals also originate from a "routing implementation" view of
 the world - that is to say they focus on the internals of routing
 within the network and do not primarily look at the network service
 seen by the end-user, or by applications. This is perhaps inevitable,
 especially given the tight time constraints for producing
 interoperable implementations. However, the (few) representatives of
 real users at the 25th IETF, the people whose support is ultimately
 necessary to deploy new host implementations, were distinctly
 There is an inbuilt assumption in the proposals that IPng is
 intended to be a universal protocol: that is, that the same network-
 layer protocol will be used between hosts on the same LAN, between
 hosts and routers, between routers in the same domain, and between
 routers in different domains. There are some advantages in defining
 separate "access" and "long-haul" protocols, and this is not
 precluded by the requirements. However, despite the few opportunities
 for major change of this sort within the Internet, the need for speed
 of development and low risk have led to the proposals being
 incremental, rather than radical, changes to well-proven existing
 There is a further unstated assumption that the architecture is
 targeted at the singly-connected host. It is currently difficult to
 design IPv4 networks which permit hosts with more than one interface
 to benefit from increased bandwidth and reliability compared with
 singly-connected hosts (a consequence of the address belonging to the
 interface and not the host). It would be preferable if topological
 constraints such as these were documented. It has been asserted that
 this is not necessarily a constraint of either the PIP or TUBA
 proposals, but I believe it is an issue that has not emerged so far
 amongst the comparative criteria.

Dixon [Page 3] RFC 1454 Comparison of Next Version IP Proposals May 1993

2.3 Source Routing

 The existing IPv4 has provision for source-specified routes, though
 this is little used [would someone like to contradict me here?],
 partly because it requires knowledge of the internal structure of the
 network down to the router level. Source routes are usually required
 by users when there are policy requirements which make it preferable
 or imperative that traffic between a source and destination should
 pass through particular administrative domains. Source routes can
 also be used by routers within administrative domains to route via
 particular logical topologies. Source-specified routing requires a
 number of distinct components:
    a.  The specification by the source of the policy by which the
        route should be selected.
    b.  The selection of a route appropriate to the policy.
    c.  Marking traffic with the identified route.
    d.  Routing marked traffic accordingly.
 These steps are not wholly independent. The way in which routes are
 identified in step (c) may constrain the kinds of route which can be
 selected in previous steps. The destination, inevitably, participates
 in the specification of source routes either by advertising the
 policies it is prepared to accept or, conceivably, by a negotiation
 All of the proposals mark source routes by adding a chain of (perhaps
 partially-specified) intermediate addresses to each packet. None
 specifies the process by which a host might acquire the information
 needed to  specify these intermediate addresses [not entirely
 unreasonably at this stage, but further information is expected]. The
 negative consequences of these decisions are:
  1. Packet headers can become quite long, depending on the number of

intermediate addresses that must be specified (although there are

      mechanisms which are currently specified or which can be imagined
      to specify only the significant portions of intermediate addresses).
  1. The source route may have to be re-specified periodically if

particular intermediate addresses are no longer reachable.

 The positive consequences are:
  1. Inter-domain routers do not have to understand policies, they

simply have to mechanically follow the source route.

Dixon [Page 4] RFC 1454 Comparison of Next Version IP Proposals May 1993

  1. Routers do not have to store context identifying routes, since

the information is specified in each packet header.

  1. Route servers can be located anywhere in the network, provided

the hosts know how to find them.

2.4 Encapsulation

 Encapsulation is the ability to enclose a network-layer packet within
 another one so that the actual packet can be directed via a path it
 would not otherwise take to a router that can remove the outermost
 packet and direct the resultant packet to its destination.
 Encapsulation requires:
    a.  An indication in the packet that it contains another packet.
    b.  A function in routers which, on receiving such a packet,
        removes the encapsulation and re-enters the forwarding process.
 All the proposals support encapsulation. Note that it is possible to
 achieve the effect of source routing by suitable encapsulation by the

2.5 Multicast

 The specification of addresses to permit multicast with various
 scopes can be accomodated by all the proposals. Internet-wide
 multicast is, of course, for further study!

2.6 Fragmentation

 All the proposals support the fragmentation of packets by
 intermediate routers, though there has been some recent discussion of
 removing this mechanism from some of the proposals and requiring the
 use of an MTU-discovery process to avoid the need for fragmentation.
 Such a decision would effectively preclude the use of transport
 protocols which use message-count sequence numbering (such as OSI
 Transport) over the network, as only protocols with byte-count
 acknowledgement (such as TCP) can deal with MTU reductions during the
 lifetime of a connection. OSI Transport may not be particularly
 relevant to the IP community (though it may be of relevance to
 commercial suppliers providing multiprotocol services), however the
 consequences for the types of services which may be supported over
 IPng should be noted.

Dixon [Page 5] RFC 1454 Comparison of Next Version IP Proposals May 1993

2.7 The End of Lifetime as We Know It

 The old IPv4 "Time to Live" field has been recast in every case as a
 simple hop count, largely on grounds of implementation convenience.
 Although the old TTL was largely implemented in this fashion anyway,
 it did serve an architectural purpose in putting an upper bound on
 the lifetime of a packet in the network. If this field is recast as a
 hop-count, there must be some other specification of the maximum
 lifetime of a packet in the network so that a source host can ensure
 that network-layer fragment ids and transport-layer sequence numbers
 are never in danger of re-use whilst there is a danger of confusion.
 There are, in fact, three separate issues here:
    1. Terminating routing loops (solved by hop count).
    2. Bounding lifetime of network-layer packets (a necessity,
       unspecified so far) to support assumptions by the transport
    3. Permitting the source to place further restrictions on packet
       lifetime (for example so that "old" real-time traffic can be
       discarded in favour of new traffic in the case of congestion
       (an optional feature, unspecified so far).


3.1 Resource Reservation

 Increasingly, applications require a certain bandwidth or transit
 delay if they are to be at all useful (for example, real-time video
 and audio transport). Such applications need procedures to indicate
 their requirements to the network and to have the required resources
 reserved.  This process is in some ways analogous to the selection of
 a source route:
    a.  The specification by the source of its requirements.
    b.  The confirmation that the requirements can be met.
    c.  Marking traffic with the requirement.
    d.  Routing marked traffic accordingly.
 Traffic which is routed according to the same set of resource
 requirements is sometimes called a "flow". The identification of
 flows requires a setup process, and it is tempting to suppose that
 the same process might also be used to set up source routes, however,
 there are a number of differences:

Dixon [Page 6] RFC 1454 Comparison of Next Version IP Proposals May 1993

  1. All the routers on a path must participate in resource

reservation and agree to it.

  1. Consequently, it is relatively straightforward to maintain

context in each router and the identification for flows can be

  1. The network can choose to reroute on failure.
 By various means, each proposal could carry flow-identification,
 though this is very much "for future study" at present. No setup
 mechansisms are defined. The process for actually reserving the
 resources is a higher-order problem. The interaction between source-
 routing and resource reservation needs further investigation:
 although the two are distinct and have different implementation
 constraints, the consequence of having two different mechanisms could
 be that it becomes difficult to select routes which meet both policy
 and performance goals.

3.2 Address-Assignment Policies

 In IPv4, addresses were bound to systems on a long-term basis and in
 many cases could be used interchangeably with DNS names. It is
 tacitly accepted that the association of an address with a particular
 system may be more volatile in IPng. Indeed, one of the proposals,
 PIP, makes a distinction between the identification of a system (a
 fixed quantity) and its address, and permits the binding to be
 altered on the fly. None of the proposals defines bounds for the
 lifetime of addresses, and the manner in which addresses are assigned
 is not necessarily bound to a particular proposal. For example,
 within the larger address space to be provided by IPng, there is a
 choice to be made of assigning the "higher order" part of the
 hierarchical address in a geographically-related fashion or by
 reference to service provider. Geographically-based addresses can be
 constant and easy to assign, but represent a renewed danger of
 degeneration to "flat" addresses within the region of assignment,
 unless certain topological restrictions are assumed.  Provider-based
 address assignment results in a change of address (if providers are
 changed) or multiple addresses (if multiple providers are used).
 Mobile hosts (depending on the underlying technology) can present
 problems in both geographic and provider-based schemes.
 Without firm proposals for address-assignment schemes and the
 consequences for likely address lifetimes, it is impossible to assume
 that the existing DNS model by which name-to-address bindings can be
 discovered remains valid.

Dixon [Page 7] RFC 1454 Comparison of Next Version IP Proposals May 1993

 Note that there is an interaction between the mechanism for
 assignment of addresses and way in which automatic configuration may
 be deployed.

3.3 Automatic Configuration

 Amongst the biggest (user) bugbears of current IP services is the
 administrative effort of maintaining basic configuration information,
 such as assigning names and addresses to hosts, ensuring these are
 refelected in the DNS, and keeping this information correct. Part of
 this results from poor implementation (or the blind belief that vi
 and awk are network management tools). However, a lot of the problems
 could be alleviated by making this process more automatic. Some of
 the possibilities (some mutually-exlusive) are:
  1. Assigning host addresses from some (relative) invariant, such

as a LAN address.

  1. Defining a protocol for dynamic assignment of addresses within a


  1. Defining "generic addresses" by which hosts can without

preconfiguration reach necessary local servers (DNS, route

      servers, etc.).
  1. Have hosts determine their name by DNS lookup.
  1. Have hosts update their name/address bindings when their

configuration changes.

 Whilst a number of the proposals make mention of some of these
 possibilities, the choice of appropriate solutions depends to some
 extent on address-assignment policies. Also, dynamic configuration
 results in some difficult philosopical and practical issues (what
 exactly is the role of an address?, In what sense is a host "the same
 host" when its address changes?, How do you handle dynamic changes to
 DNS mappings and how do you authenticate them?).
 The groups involved in the proposals would, I think, see most of
 these questions outside their scope. It would seem to be a failure in
 the process of defining and selecting candidates for IPng that
 "systemness" issues like these will probably not be much discussed.
 This is recognised by the participants, and it is likely that, even
 when a decision is made, some of these ideas will be revisited by a
 wider audience.
 It is, however, unlikely that IP will make an impact on proprietary
 networking systems for the non-technical environment (e.g., Netware,

Dixon [Page 8] RFC 1454 Comparison of Next Version IP Proposals May 1993

 Appletalk), without automatic configuration being taken seriously
 either in the architecture, or by suppliers. I believe that there are
 ideas on people's heads of how to address these issues - they simply
 have not made it onto paper yet.

3.4 Application Interface/Application Protocol Changes

 A number of common application protocols (FTP, RPC, etc.) have been
 identified which specifically transfer 32-bit IPv4 addresses, and
 there are doubtless others, both standard and proprietary. There are
 also many applications which treat IPv4 addresses as simple 32-bit
 integers. Even applications which use BSD sockets and try to handle
 addresses opaquely will not understand how to parse or print longer
 addresses (even if the socket structure is big enough to accommodate
 Each proposal, therefore, needs to specify mechanisms to permit
 existing applications and interfaces to operate in the new
 environment whilst conversion takes place. It would be useful also,
 to have (one) specification of a reference programming interface for
 (TCP and) IPng (which would also operate on IPv4), to allow
 developers to begin changing applications now. All the proposals
 specify transition mechansisms from which existing application-
 compatibility can be inferred. There is no sign yet of a new
 interface specification independent of chosen protocol.

3.5 DNS Changes

 It is obvious that there has to be a name to address mapping service
 which supports the new, longer, addresses. All the proposals assume
 that this service will be provided by DNS, with some suitably-defined
 new resource record. There is some discussion ongoing about the
 appropriateness of returning this information along with "A" record
 information in response to certain enquiries, and which information
 should be requested first. There is a potential tradeoff between the
 number of queries needed to establish the correct address to use and
 the potential for breaking existing implementations by returning
 information that they do not expect.
 There has been heat, but not light, generated by discussion of  the
 use of DNS for auto-configuration and the scaling (or otherwise) of
 reverse translations for certain addressing schemes.

Dixon [Page 9] RFC 1454 Comparison of Next Version IP Proposals May 1993


4.1 Congestion Avoidance

 IPv4 offers "Source Quench" control messages which may be used by
 routers to indicate to a source that it is congested and has or may
 shortly drop packets. TUBA/PIP have a "congestion encountered" bit
 which provides similar information to the destination. None of these
 specifications offers detailed instructions on how to use these
 facilities. However, there has been a substantial body of analysis
 over recent years that suggests that such facilities can be used (by
 providing information to the transport protocol) not only to signal
 congestion, but also to minimise delay through the network layer.
 Each proposal can offer some form of congestion  signalling, but none
 specifies a mechanism for its use (or an analysis of whether the
 mechanism is in fact useful).
 As a user of a network service which currently has a discard rate of
 around 30% and a round-trip-time of up to 2 seconds for a distance of
 only 500 miles I would be most interested in some proposals for a
 more graceful degradation of the network service under excess load.

4.2 Mobile Hosts

 A characteristic of mobile hosts is that they (relatively) rapidly
 move their physical location and point of attachment to the network
 topology.  This obviously has signficance for addressing (whether
 geographical or topological) and routing. There seems to be an
 understanding of the problem, but so far no detailed specification of
 a solution.

4.3 Accounting

 The IESG selection criteria require only that proposals do not have
 the effect of preventing the collection of information that may be of
 interest for audit or billing purposes. Consequently, none of the
 proposals  consider potential accounting mechanisms.

4.4 Security

 "Network Layer Security Issues are For Further Study". Or secret.
 However, it would be useful to have it demonstrated that each
 candidate could be extended to provide a level of security, for
 example against address-spoofing. This will be particularly
 important if resource-allocation features will permit certain hosts
 to claim large chunks of available bandwidth for specialised

Dixon [Page 10] RFC 1454 Comparison of Next Version IP Proposals May 1993

 Note that providing some level of security implies manual
 configuration of security information within the network and must be
 considered in relationship to auto-configuration goals.


 Each proposal is about as different to the others as it is to IPv4 -
 that is the differences are small in principle, but may have
 significant effects (extending the size of addresses is only a small
 difference in principle!). The main distinct characteristics are:
    PIP has an innovative header format that facilitates hierarchical,
    policy and virtual-circuit routing. It also has "opaque" fields in
    the header whose semantics can be defined differently in different
    administrative domains and whose use and translation can be
    negotiated across domain boundaries. No control protocol is yet
    SIP offers a "minimalist" approach - removing all little-used
    fields from the IPv4 header and extending the size of addresses to
    (only) 64 bits. The control protocol is based on modifications to
    ICMP. This proposal has the advantages of processing efficiency
    and familiarity.
    TUBA is based on CLNP (ISO 8473) and the ES-IS (ISO 9542) control
    protocol. TUBA provides for the operation of TCP transport and UDP
    over a CLNP network. The main arguments in favour of TUBA are that
    routers already exist which can handle the network-layer protocol,
    that the extensible addresses offer a wide margin of "future-
    proofing" and that there is an opportunity for convergence of
    standards and products.

5.1 PIP

 PIP packet headers contain a set of instructions to the router's
 forwarding processor to perform certain actions on the packet. In
 traditional protocols, the contents of certain fields imply certain
 actions; PIP gives the source the flexibility to write small
 "programs" which direct the routing of packets through the network.
 PIP addresses have an effectively unlimited length: each level in the
 topological hierarchy of the network contributes part of the address

Dixon [Page 11] RFC 1454 Comparison of Next Version IP Proposals May 1993

 and addresses change as the network topology changes. In a completely
 hierarchical network topology, the amount of routing information
 required at each level could be very small. However, in practice,
 levels of hierarchy will be determined more by commercial and
 practical factors than by the constraints of any particular routing
 protocol. A greater advantage is that higher-order parts of the
 address may be omitted in local exchanges and that lower-order parts
 may be omitted in source routes, reducing the amount of topological
 information that host systems are required to know.
 There is an assumption that PIP addresses are liable to change, so a
 further quantity, the PIP ID, is assigned to systems for the purposes
 of identification. It isn't clear that this quantity has any purpose
 which could not equally be served by a DNS name [it is more compact,
 but equally it does not need to be carried in every packet and
 requires an additional lookup]. However, the problem does arise of
 how two potentially-communicating host systems find the correct
 addresses to use.
 The most complex part of PIP is that the meaning of some of the
 header fields is determined by mutual agreement within a particular
 domain. The semantics of specific processing facilities (for example,
 queuing priority) are registered globally, but the actual use and
 encoding of requests for these facilities in the packet header can be
 different in different domains. Border routers between two domains
 which use different encodings must map  from one encoding to another.
 Since routers may not only be adjacent physically to other domains,
 but also via "tunnels", the number of different encoding rules a
 router may need to understand is potentially quite large. Although
 there is a saving in header space by using such a scheme as opposed
 to the more familiar "options", the cost in the complexity of
 negotiating the use and encoding of these facilities, together with
 re-coding the packets at each domain border, is a subject of some
 concern. Although it may be possible for hosts to "precompile" the
 encoding rules for their local domain, there are many potential
 implementaion difficulties.
 Although PIP offers the most flexibility of the three proposals, more
 work needs to be done on "likely use" scenarios which make the
 potential advantages and disadvantages more concrete.

5.2 SIP

 SIP is simply IP with larger addresses and fewer options. Its main
 advantage is that it is even simpler that IPv4 to process. Its main
 disadvantages are:

Dixon [Page 12] RFC 1454 Comparison of Next Version IP Proposals May 1993

  1. It is far from clear that, if 32 bits of address are

insufficient, 64 will be enough for the forseeable future;

  1. although there are a few "reserved" bits in the header, the

extension of SIP to support new features is not obvious.

 There's really very little else to say!

5.3 TUBA

 The characteristics of ISO CLNS are reasonably well known: the
 protocol bears a strong cultural resemblance to IPv4, though with
 20-byte network-layer addressing. Apart from a spurious "Not Invented
 Here" prejudice, the main argument againt TUBA is that it is rather
 too like IPv4, offering nothing other than larger, more flexible,
 addresses.  There is proof-by-example that routers are capable of
 handling the (very) long addresses efficiently, rather less that the
 longer headers do not adversely impact network bandwidth.
 There are a number of objections to the proposed control protocol
 (ISO 9542):
  1. My early experience is that the process by which routers

discover hosts is inefficient and resource consuming for

      routers - and requires quite fine timer resolution on hosts -
      if large LANs are to be accomodated reasonably. Proponents of
      TUBA suggest that recent experience suggests that ARP is no
      better, but I think this issue needs examination.
  1. The "redirect" mechanism is based on (effectively) LAN

addresses and not network addresses, meaning that local routers

      can only "hand-off" complex routing decisions to other routers
      on the same LAN.  Equally, redirection schemes (such as that of
      IPv4) which redirect to network addresses can result in
      unnecessary extra hops.  Analysis of which solution is better
      is rather dependent on the scenarios which are constructed.
 To be fair, however, the part of the protocol which provides for
 router-discovery provides a mechanism, absent from other proposals,
 by which hosts can locate nearby gateways and potentially
 automatically configure their addresses.

6. Transition Plans

 It should be obvious that a transition which permits "old" hosts to
 talk to "new" hosts requires:

Dixon [Page 13] RFC 1454 Comparison of Next Version IP Proposals May 1993

    (a) That IPng hosts can also use IPv4 or
    (b) There is translation by an intermediate system
 and either:
    (c) The infrastructure between systems is capable of carrying both
        IPng and IPv4 or (d) Tunneling or translation is used to carry
        one protocol within another in parts of the network
 The transition plans espoused by the various proposals are simply
 different combinations of the above. Experience would tend to show
 that all these things will in fact happen, regardless of which
 protocol is chosen.
 One problem of the tunneling/translation process is that there is
 additional information (the extra address parts) which must be
 carried across IPv4 tunnels in the network. This can either be
 carried by adding an extra "header" to the data before encapsulation
 in the IPv4 packet, or by encoding the information as new IPv4 option
 types. In the former case, it may be difficult to map error messages
 correctly, since the original packet is truncated before return; in
 the latter case there is a danger of the packet being discarded (IPv4
 options are not self-describing and new ones may not pass through
 IPv4 routers). There is thus the possibility of having to introduce a
 "new" version of IPv4 in order to support IPng tunneling.
 The alternative (in which IPng hosts have two stacks and the
 infrastructure may or may not support IPng or IPv4) of course
 requires a mechanism for resolving which protocols to try.

7. Random Comments

 This is the first fundamental change in the Internet protocols that
 has occurred since the Internet was manageable as an entity and its
 development was tied to US government contracts. It was perhaps
 inevitable that the IETF/IESG/IAB structure would not have evolved to
 manage a change of this magnitude and it is to be hoped that the new
 structures that are proposed will be more successful in promoting a
 (useful) consensus. It is interesting to see that many of the
 perceived problems of the OSI process (slow progress, factional
 infighting over trivia, convergence on the lowest-common denominator
 solution, lack of consideration for the end-user) are in danger of
 attaching themselves to IPng and it will be interesting to see to
 what extent these difficulties are an inevitable consequence of wide
 representation and participation in network design.

Dixon [Page 14] RFC 1454 Comparison of Next Version IP Proposals May 1993

 It could be regarded either as a sign of success or failure of the
 competitive process for the selection of IPng that the three main
 proposals  have few really significant differences. In this respect,
 the result of the selection process is not of particular
 significance, but the process itself is perhaps necessary to repair
 the social and technical cohesion of the Internet Engineering

8. Further Information

 The main discussion lists for the proposals listed are:
      (Requests to: <list name>-request@<host>)
 Internet-Drafts and RFCs for the various proposals can be found in
 the usual places.

Security Considerations

 Security issues are not discussed in this memo.

Author's Address

 Tim Dixon
 RARE Secretariat
 Singel 466-468
 NL-1017AW Amsterdam
 Phone: +31 20 639 1131 or + 44 91 232 0936
 EMail: or

Dixon [Page 15]

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