An Architectural Framework of the Internet for the Real IP World
draft-shyam-real-ip-framework-18

INTERNET DRAFT                                          S. Bandyopadhyay
draft-shyam-real-ip-framework-18.txt                      April 18, 2015
Intended status: Informational
Expires: October 18, 2015

    An Architectural Framework of the Internet for the Real IP World
                  draft-shyam-real-ip-framework-18.txt

Abstract

   This document tries to propose an architectural framework of the
   internet in the real IP world. It shows how to reorganize the
   provider network with a large address space. It describes how a
   three-tier mesh structured hierarchy can be established based on
   fragmenting the entire space into some regions and some sub regions
   inside each of them. It addresses issues which could be relevant to
   this architecture in the context of IPv6.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on October 18, 2015.

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Table of Contents
   1. Introduction.....................................................2
   2. Background.......................................................2
   3. A Three tier mesh structured hierarchical network................4
      3.1. Route propagation...........................................5
      3.2. Determination of prefix lengths.............................7
           3.2.1. A pseudo optimal distribution of prefixes in
                  a 64bit architecture.................................8
           3.2.2. Whether to go for a two tier or three tier hierarchy
                  ....................................................10
      3.3. Issues related to Satellite communications.................11
   4. Issues related to PI addressing and IP mobility.................11
      4.1. IP address aliasing........................................13
      4.2. Changes expected with the specifications related
           to IP mobility.............................................15
   5. Refinements over existing IPv6 specification....................16
   6. Distributed processing and Multicasting.........................18
   7. IANA Consideration..............................................18
   8. Security Consideration..........................................18
   9. Acknowledgments.................................................18
   10. Normative References...........................................18
   11. Informative References.........................................19
   12. Authors Address................................................19

1. Introduction

   Transition from IPv4 to IPv6 is in the process. Work has been done to
   upgrade individual nodes (workstations) from IPv4 to IPv6. Also,
   there are established documents to make routers/switches to work to
   support IPv4 as well as IPv6 packets simultaneously in order to make
   the transition possible [1].  CIDR[2] based hierarchical architecture
   in the existing 32-bit system is supposed to be continued in IPv6 too
   with a large address space. There are documents/concerns over BGP
   table entries to become too large in the existing system [3]. There
   are proposals to upgrade Autonomous System number to 32-bit from
   16-bit to support the demand at the same time [4]. The challenge
   relies on how to make the transition smooth from IPv4 to a real IP
   world with least changes possible.

   The term "real IP environment" is referred to an environment where
   hosts in a customer network will possess globally unique IP addresses
   and communicate with the rest of the world without the help of
   NAT[5].

2. Background

   Existing system is in work with Autonomous System (AS) and inter-AS
   layer with the approach of CIDR. In order to meet the need within the

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   32-bit address space, Autonomous Systems of various sizes maintain
   CIDR based hierarchical architecture. With the help of NAT [5], a
   stub network can maintain an user ID space as large as a class A
   network and can meet its useful need to communicate with the rest of
   the world with very few real IP addresses. With the combination of
   CIDR and NAT applied in the entire space, most of the part of 32-bit
   address space gets effectively used as network ID. This is how,
   16-bit 'Autonomous System Number' is realized as insufficient in
   order to meet the need of growing customers. If the same gets
   continued with a larger network ID, load in the switches will become
   too high.

   With traditional CIDR based hierarchy, a node of higher prefix can be
   divided into number of nodes with lower prefixes. Each divided node
   can further be subdivided with nodes of further lower prefixes. This
   process can be continued till no further division is possible. The
   point worth noting is at each point the designer of the network has
   to preconceive the future expansion of the network with the concept
   in the mind that the resource can not be exhausted at any point of
   time. This phenomenon leads the designer to allocate resources much
   higher than whatever is needed which leads to a space of unused
   address space and the concept of H-D (host-density) ratio comes into
   play. The problem gets aggravated once resource gets exhausted by any
   chance. e.g. a node of prefix /16 can be divided with a number of
   nodes of prefixes /24. If any one of the nodes /24 gets exhausted,
   resources of other nodes of prefixes /24 can not be used even if they
   are available.

   Transition from private IP to real IP may not appear to be a simple
   task. This has happened due to the desperate attempt of the service
   providers to provide internet services with the help of NAT. e.g. a
   large educational institute meets its current requirement with 4 real
   IP addresses; one for its mail server, one for its web server, one
   for its ftp server and another one for its proxy server to provide
   web based services to all of its users.  These four types of services
   are used by any organization of any size(it may be 400 or even
   40000). In the current provider network these organizations are
   supported their need with 4 IP addresses and the CIDR based tree has
   been built using these components together. When private IP will be
   replaced with real IP, each customer network will require IP
   addresses based on its size and requirement. So, even if CIDR based
   architecture is maintained with real IP space, existing provider
   based network needs to be reorganized. The desired approach will be
   to assign address block that will be proportional to the sizes
   (bandwidth) of the ports of the switches of the provider network.

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3. A Three-tier mesh structured hierarchical network

   As Autonomous Systems of various sizes are supported, Autonomous
   Systems and the nodes inside the Autonomous Systems can be viewed as
   graphically lying on the same plane within the address apace. If
   network can be viewed as lying on different planes, routing issues
   can be made simpler. If network is designed with a fixed length of
   prefix for the Autonomous System everywhere, routing information for
   the rest will get confined with the other part of the network prefix.
   Which means the maximum size of AS gets assigned to all irrespective
   of their actual sizes. This can be made possible with the advantage
   of using a large address space and dividing it into number of regions
   of fixed sizes inside it. Thus entire network can be viewed as a
   network of inter-AS layer nodes. Each node in the inter-AS layer can
   act either only as a router in the inter-AS layer or as a router in
   the inter-AS layer with an Autonomous System attached to it with a
   single point of attachment or as an Autonomous System with multiple
   Autonomous System border routers (ASBR) appearing like a mesh. Thus
   two tier mesh structured hierarchy gets established between AS layer
   and inter-AS layer with each AS having a fixed length of prefix.

   Based on the definition of Autonomous System, it is a small area
   within the entire network that maintains its own independent identity
   that communicates with the rest of the world through some specific
   border routers. In the similar manner, if a larger area (say region
   or state) can be considered as network of Autonomous Systems, that
   can maintain its own identity by communicating with the rest of the
   world through some border routers (say, state border router), mesh
   structured hierarchy can be established within the inter-AS layer.
   The inter-AS layer will be split into inter-AS-top and inter-AS-
   bottom. To maintain this hierarchy, each node of inter-AS-top needs
   to have multiple regional or state border routers (say, SBR) through
   which each one will communicate with the rest of the world in the
   similar manner an Autonomous System maintains ASBR. Thus, entire
   network will appear as a network of nodes of inter-AS-top layer. To
   maintain hierarchy, each node of the inter-AS-top needs to have a
   fixed length of prefix. i.e. each node of the inter-AS top will be
   assigned a maximum (fixed) number of nodes of Autonomous Systems.

   Thus, with three-tier mesh structured hierarchy in the network layer,
   network ID can be viewed as A.B.C. If pA, pB and pC be the prefix
   lengths of inter-AS-top, inter-AS-bottom and AS layers respectively,
   there will be 2^pA nodes at the topmost layer, 2^pB at the inter-AS-
   bottom layer and 2^pC nodes at the AS layer. Thus the entire space
   gets divided into a fixed number of regions and each region gets
   divided into fixed number of sub regions. This division is supposed
   to be made based on geography, population density and their demands
   and related factors.

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   Let nMaxInterASTopNodes be the possible maximum number of nodes
   assigned at the top most layer and nMaxInterASBottomNodes be that at
   the inter-AS-bottom layer and nMaxASNodes at the AS layer. Where
   nMaxInterASTopNodes <= 2^pA and nMaxInterASBottomNodes <= 2^pB and
   nMaxASNodes <= 2^pC.

3.1. Route propagation

   With hierarchy established, routing information that gets established
   inside a node of inter-AS-top, does not need to be propagated to
   another node of inter-AS-top. Entire routing information of inter-AS-
   top layer needs to be propagated to inter-AS-bottom layer. So, each
   router of inter-AS layer will have two tables of information, one for
   the inter-AS-top and another for the inter-AS-bottom of the inter-AS-
   top node that it belongs to. BGP (with little modification) will work
   very well with a trick applied at the SBRs. Each SBR will not
   propagate the routing information of inter-AS-bottom layer of its
   domain to another SBR of neighboring domain. i.e. SBR of one top
   layer node will propagate routing information only of inter-AS-top
   layer to SBR of another top layer node. Inside a node of inter-AS-
   top, routing information of inter-AS-top and inter-AS-bottom need to
   be propagated from one ASBR to another neighboring ASBR. Inside a top
   layer node A, routing information of another top layer node B will
   have two parts; one for the list of SBRs through which a packet will
   traverse from top layer node A to B and another for the list of ASBRs
   through which the packet will traverse from one AS to another inside
   A. In terms of BGP, AS_PATH attribute will be split into two parts;
   one for the information of the top layer and another for the bottom
   layer. Within the same node A routing information of one AS to
   another AS will not have any top layer information. i.e. the top
   layer information will be set to as NULL.

   Similarly, each node of the AS layer will have three tables of
   routing entries. One for the inter-AS-top, one for the inter-AS-
   bottom and another for the routing information inside the Autonomous
   System itself.

   Introduction of hierarchy at the inter-AS layer reduces the size of
   the routing table substantially. With the availability of hardware
   resources if flat address space is maintained at each layer, problems
   related to CIDR can be avoided. With flat address space, no
   hierarchical relationship needs to be established between any two
   nodes in the same layer. So, all the nodes inside each layer can be
   used till they get exhausted. With flat address space (i.e.  without
   prefix reduction), BGP tables will have maximum nMaxInterASTopNodes +
   nMaxInterASBottomNodes entries.

   IGP like OSPF has got provision to divide AS into smaller areas. OSPF

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   hides the topology of an area from the rest of the Autonomous System.
   This information hiding enables a significant reduction in routing
   traffic. With the support of subnetting, OSPF attaches an IP address
   mask to indicate a range of IP addresses being described by that
   particular route. With this approach it reduces the size of the
   routing traffic instead of describing all the nodes inside it, but
   introduces another level of hierarchy. If subnetting concept can be
   avoided from the AS layer(with the additional overhead of computation
   inside the SPF tree), each area can be configured from a free pool of
   addresses based on its requirement dynamically. So, an AS can be
   divided into number of areas of heterogeneous sizes with the nodes
   from a free pool of address space.

   Similarly, the concept of area can be introduced in the inter-AS-
   bottom layer the way it works in OSPF. The area border routers in the
   inter-AS-bottom layer have to behave exactly in the similar manner
   the way an ABR behaves in OSPF.  i.e. an area border router will hide
   the topology inside an area to the rest of the world and will
   distribute the collected information inside the area to the rest. It
   will distribute the collected routing information from outside to the
   nodes inside as well. In order to implement this, protocol running in
   the inter-AS layer (say BGP) will have to introduce a 'cost' factor.
   This cost factor can be interpreted as the cost of propagation of a
   packet from one AS to another. The protocols running inside AS layer
   (RIP/OSPF, etc) will have to the supply the cost information for a
   packet to travel from one ASBR to another. All the protocols must
   behave in unison for supplying this information. The cost factor is
   needed for a remote node while sending a packet to a node inside an
   area while more than one area border routers are equidistant from
   that remote node. Thus inter-AS-bottom layer (i.e. one inter-AS-top
   level node) can be divided into number of areas of heterogeneous
   sizes with nodes of AS from a free pool of address space. BGP adopts
   a technique called route aggregation. Along with route aggregation it
   reduces routing information within a message. In the similar manner,
   introduction of area inside inter-AS-bottom layer will not only
   reduce the complexity of the protocol, but will reduce the size of a
   BGP packet substantially.

   With this architecture, each node(router) inside an AS is represented
   as A.B.C.  Each node may or may not be attached with a network which
   acts as a leaf node (i.e. a network will not act as a transit). In
   order to make use of user-id space properly and to support customer
   networks of heterogeneous sizes, the user-ID space needs to be
   divided as subnet-ID and user-ID. Profoundly, a VLSM (variable length
   subnet mask) type of approach has to be adopted at each node of an
   AS. So, each node of the AS layer will act as the root of a tree
   whose leaves are independent small customer networks which will act
   as stub. As the routing information of inter-AS layer as well as AS

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   layer need not be passed inside any node of the VLSM tree, each
   router inside the tree should maintain default route for any address
   outside of its network. With this approach, load on each router of
   the service providers will become negligible. Protocols that supports
   VLSM with MPLS/VPN has to be implemented inside the tree (inside the
   VLSM tree, all the physical ports of a switch have to be configured
   with the subnet mask. So, mere MPLS on top of static routing table
   should do the rest).

   The fundamental assumptions based on which this architecture lies can
   be summarized as follows:

   i) Entire network can be viewed as a network of regions or states
   where each region or state can have its own identity by communicating
   with the rest of the world through some state border routers. Each
   region or state is a network of Autonomous Systems. Each region as
   well as each Autonomous System inside them will have a fixed
   (maximum) length of prefix.

   ii) Availability of hardware resources is such that flat address
   space can be maintained at the inter-AS layer.

   Introduction of mesh-structured hierarchy will have several
   advantages:

      o  Load at each router will get reduced substantially.
      o  Concept of CIDR style approach and complexity related to
           prefix reduction can be easily avoided.
      o  Mesh structured hierarchy will make traffic evenly distributed.
      o  Physical cable connection can be optimized.
      o  Administrative issues will become easier.

3.2. Determination of prefix lengths

   With this architecture, IP address can be described as A.B.C.D where
   the D part represents the user id. Each router in the inter-AS layer
   will have two tables of information, one for the inter-AS-top and
   another for the inter-AS-bottom of the inter-AS-top node that it
   belongs to. Whereas, each node of the AS layer will have three tables
   of routing entries; one for the inter-AS-top, one for the inter-AS-
   bottom and another for the routing information inside the Autonomous
   System itself. In the worst case. a node inside an AS needs to
   maintain nMaxInterASTopNodes + nMaxInterASBottomNodes + nMaxASNodes
   entries in its routing table.

   The dynamic nature of allocating an area from a free pool of address
   space is more frequent at the AS layer than at the inter-AS-bottom
   layer. As OSPF supports all the features needed, it can be considered

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   as default choice in the AS layer.  Existing implementation of OSPF
   (Version 2) supports subnetting, by which an entire area can be
   represented as a combination of network address and subnet mask. With
   this approach, entire routing table gets reduced substantially.  With
   the removal of subnetting, all the nodes inside an area will have an
   entry inside the routing table (OSPF Version 1). So the deterministic
   factor is what is the maximum number of nodes inside an AS OSPF can
   support once subnetting support gets removed. So the prefix length of
   AS layer will be determined by this factor of OSPF.

   With the introduction of hierarchy in the inter-AS layer, number of
   entries in the BGP routing table will get reduced substantially. Even
   if pA and pB both are selected as 16, number of routing entries come
   within the admissible range of existing BGP protocol. But, it is the
   responsibility of IANA to come out with a scheme how
   nMaxInterASTopNodes and nMaxInterASBottomNodes are to be selected.
   Each top level node will have nMaxInterASBottomNodes nodes. It will
   be a waste of address space if each country gets assigned a top level
   nodes (e.g. china has got a population of 1,306,313,800 people where
   as Vatican City has got only 920 according to a census of 2006). So a
   moderate value of nMaxInterASBottomNodes is desirable, with which
   larger countries will have a number of top level nodes. e.g. each
   state of USA can be assigned a top level node. With the introduction
   of area in the inter-AS-bottom layer, each top level node can be
   divided into number of areas of heterogeneous sizes. So, a group of
   neighboring countries with less population can share the address
   space of a top level node. Similarly, user-id space has to be decided
   based on the largest area VLSM tree should be spanned through. All
   these issues are completely geo political and have to be decided by
   IANA.

3.2.1. A pseudo optimal distribution of prefixes in a 64bit architecture

   In order to have optimal use of cable connections, length of the VLSM
   tree is expected to be as short as possible. Also any single
   organization may prefer to have its user id space to be under the
   same network id. So, a 16bit user-id may become insufficient for
   places like large university campus, where as 32bit will become too
   large. Hence, 24bit user-id will be a moderate one which is the class
   A address space in IPv4 (also used as the space for private IP). As
   published in 1998 [6], OSPF can support an area with 1600 routers and
   30K external LSAs. So, 11 bits are needed to support this space. With
   the assumption that OSPF can support much more address space with the
   advancement of hardware technology as well as to keep the space open
   for future expansions, 12 bits are assigned for the AS layer. 16 bits
   are assigned for the inter-AS-bottom layer. So, if on the average,
   16bit equivalent space gets used within the user-id space (i.e. one
   out of 256) and 8bit equivalent nodes gets used inside an AS (16% of

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   1600), for a top level node (with 16bit equivalent AS nodes), it will
   generate 2^40 IP addresses, which will give 8629 IP addresses per
   person in Japan (with a population of 127417200; Japan is at the 10th
   position from the top in the population list of the world). So, even
   if all the countries with population less than or equal to Japan are
   assigned a top level node and all the provinces/states of countries
   with larger population are assigned a top level node each, total
   number of nodes will come well under 1024. If a number of neighboring
   countries with lesser population shares a top level node, total
   number of top level nodes will come down further.  This suggests that
   62 bit equivalent (10(pA)+16(pB)+12(pC)+24(user-id)) space will be
   good enough for unicast addresses. This distribution expects OSPF to
   support 65K (64K+1K) external LSAs.

   64bit address space may be divided into two 63bit blocks as follows:

   i. Global unicast addresses with the most significant bit set to 0.
   In order to separate out router address space from the host computers
   of customer networks, routers may be assigned a prefix 01 whereas the
   host computers will have prefix 00. With three-tier hierarchy,
   network ID is represented as A.B.C.  Any router inside the VLSM tree
   including the root will have an address 01A.B.C.router-id.  Where as
   a host interface inside a customer network will be represented as
   00A.B.C.uid.

   As the number of nodes representing routers in the provider network
   will be way too less than the user-id space for the customer
   networks, in order to keep more space for unicast addresses of
   customer networks as well as to keep the option open for future
   expansion, entire 63 bit address space with the MSB set to 0 has been
   assigned to customer networks for unicast addresses. So, the
   distribution will look like 10(pA)+17(pB)+12(pC)+24(user-id). Router
   address space will be assigned from the address space with the MSB
   set to 1.

   One can think of a larger size for the VLSM tree. It has to be
   compensated with a smaller size for the inter-AS space. Say the
   distribution may look like 10(pA)+15(pB)+12(pC)+26(user-id). As the
   size of the user-id space (or the VLSM tree) is fixed, larger the
   size of the tree, larger will be the waste. This factor can be
   decided based on the data supplied (or suggested) by the service
   providers.

   ii. Address space with the MSB set to 1 will be distributed within
   the rest. Each of them will have a fixed prefix which will be
   determined with the consultation with IANA.  This distribution will
   be based on the requirements and the work that have already been done
   in connection to IPv6 along with the following requirements:

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   a) Router address space: Any node in the router address space will be
   designated with a prefix followed by A.B.C.router-id.

   b) Address space for multicasting:

   c) Address space for private IP: A 32 bit address space should be
   good enough for private IP.

   d) Provider independent address space: This space will be used for
   the customers who would like to retain their number even after
   changing their providers. With this architecture, addressing is based
   on the routing topology i.e.  all unicast addresses will be based on
   the provider assigned address space.  So, each of these provider
   independent addresses has to be mapped with an address from the
   global unicast address space. Section 4 describes issues related to
   PI addressing and IP mobility in detail.

   In order to provide support of IP mobility as well as provider
   independent addressing, each customer network has to be assigned some
   extra space along with their usual need. The actual amount of space
   to be reserved has to be determined by IANA.

3.2.2. Whether to go for a two-tier or three-tier hierarchy

   Establishment of hierarchy in the inter-AS layer reduces the size of
   BGP entries to a great extent, but leads to an improper use of
   address space due to geo-political reason. If hierarchy in the inter-
   AS space gets removed, entire 26bit (10+16) space will be available
   for a single layer and use of inter-AS space will be true to its
   sense, but will increase external LSA (and/or number of entries in
   the BGP table) dramatically. So, it depends on to what extent OSPF
   can support external LSAs. BGP expects the packet length to be
   limited to 4096 bytes. BGP manages to make it work with this
   limitation with the concept of prefix reduction in the CIDR based
   environment.  As the number of inter-AS nodes increases, BGP has to
   change this limit in order to make it work in flat address space. The
   alternate will be to divide the inter-AS space into number of areas
   as defined in section 2.1. The area border routers will advertise the
   aggregated information to the rest of the world. BGP may have to
   incorporate both the options at the same time.  As the number of
   nodes in the inter-AS layer increases, in order to reduce the number
   of entries in the routing table, inter-AS space has to be split into
   two separate planes.  So, two-tier hierarchy can be considered as an
   interim state to go for three-tier hierarchy.  If it so happen that
   current available data is good enough to support the present need, it
   will be worth to look for to what extent it can support in the
   future. Assignment of inter-AS nodes in two-tier hierarchy should be
   based on the geographical distribution as if it is part of three-tier

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   hierarchy.  Otherwise, introduction of three-tier hierarchy in the
   future will become another difficult task to go through. Based on the
   report of year 2011, BGP supports ~400,000 entries in the routing
   table. With this growing trend, BGP may have to change the limit of
   packet length even in a CIDR based environment. With the introduction
   of two-tier hierarchy, number of entries in the routing table will
   come down drastically and with the three-tier approach, it will come
   down further.

3.3. Issues related to Satellite communications

   Establishment of hierarchy in the inter-AS layer expects the only way
   any two autonomous systems in two different top level nodes
   communicate is through their SBRs. If two autonomous systems inside
   the same top level node communicate through satellite, it will be
   considered as a direct link between them. Whenever autonomous system
   'ASa' of top level node 'A' communicates with autonomous system 'ASb'
   of top level node 'B' through satellite, they have to go through
   their state border routers. i.e.  satellite port inside 'A' that
   communicates with a satellite port inside 'B' will be considered as
   state border router. If multiple such ports exists inside node 'A',
   all of them will be equidistant from any port inside 'B'.  Which
   expects any satellite port inside 'B' to have prior knowledge of list
   of autonomous systems that will be under the purview of any port
   inside 'A'. So, all the satellite ports of 'A' have to exchange such
   group of information with all the satellite ports of 'B' and vice
   versa.  These group of autonomous systems can be considered as a
   cluster of autonomous systems inside an area of a top level node. If
   number of such ports is small, some heuristics can be applied while
   assigning AS numbers in order to reduce the processing time during
   the circuit establishment phase.  It will become difficult to
   maintain such heuristics once the number of such ports becomes large.
   So, in case of satellite communication, the advantage of establishing
   hierarchy inside inter-AS layer diminishes as the number of satellite
   ports increases. If any private corporate maintains its own satellite
   channel to communicate between its offices at distant locations, all
   of these offices are going to be considered as under the user-id
   space of its network. Service providers that provide satellite
   services to the end-site customers, can operate in the usual manner
   as they will provide connection to customer networks which will act
   as stub.

4. Issues related to PI addressing and IP mobility

   As far as implementation is concerned, provider independent
   addressing will be a costly affair. First of all in order to resolve
   the currently mapped location, there has to be a mechanism which is
   to some extent similar to the DNS entry resolution. Inside a customer

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   network which is based on the provider assigned address space,
   routing of IP packets will be based on the provider assigned
   addresses. So, for every IP packet that is destined to a PI address
   will have a stack of addresses; the mapped address (or the care-of
   address) and the PI address. While initiating communication with a PI
   address, the mapped address has to be resolved first and then both
   the PI address as well as the mapped address has to be passed down to
   the transport layer. Transport layer needs to form a stack of
   addresses while filling up the IP packet. The above complexities can
   be avoided if the entire customer network is assigned a contiguous
   set of PI addresses. So, for the entire system, provider independent
   addressing has to be supported either based on the individual
   customer basis or on the entire customer network basis but not both.
   Customers who would like to have mobility support, the mapped address
   can be considered as the "Home Address" of the mobile node as defined
   in the specification of "IP Mobility Support"[7]. Once a node with PI
   address moves to a co-located care-of address[7], system needs to
   make decision based on PI address, its mapped address as well as the
   co-located care-of address.  So, provider independent address with
   mobility support will be the costliest operation.

   If PI addresses are assigned on individual customer basis, protocol
   control block structure associated with socket needs to introduce
   another field 'fmpiaddr' to store the mapped destination address. It
   needs to have another field 'fcladdr', the destination node care-of
   address to support IP mobility. If foreign address is stationary and
   provider independent, both 'fmpiaddr' and 'fcladdr' will have the
   same value. The existing field 'faddr' which is used to address a
   foreign address will hold the value of PI address for a node with PI
   address. Similarly it will hold the value of "Home Address" of the
   mobile node if it is not provider independent. Protocol output
   routines like 'tcp_output' and 'udp_output' need these information to
   fill the IP packet. A new system call 'regrmtcladdr' needs to be
   introduced to store both PI address and the mapped address with the
   PCB.

   int regrmtcladdr(int sockfd, const struct sockaddr *mpiaddr,
                    socklen_t mpiaddrlen, const struct sockaddr *claddr,
                    socklen_t claddrlen);

   A client program needs to call 'regrmtcladdr' before it calls
   'connect' to establish connection with its peer. 'regrmtcladdr'(or
   its system level routine) can be used by a correspondent node while a
   remote mobile node registers its care-of address with the
   correspondent node[7].

   There could be several approaches to resolve the mapped address for a
   PI address. This issue needs to be discussed in a separate document.

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   A function call needs to be introduced to get the mapped address.

   struct in_addr getmappedaddr(struct in_addr *piaddr);

   It is worthwhile to introduce a function call 'connrmtaddr' that will
   connect a remote address of any type. 'connrmtaddr' will check
   whether the address is provider independent and connect the remote
   site accordingly.

   int connrmtaddr(int sockfd, const struct sockaddr *dst,
                   socklen_t addrlen);

   Assignment of contiguous block of PI address space to an entire
   customer network apparently do not make much sense. This is just
   equivalent to assigning PA address space to a customer network. So,
   assignment of PI address space to an entire customer network has to
   be avoided unless there is a real need that can not be solved (or
   avoided) by using PA address space. PI address assignment always have
   to be burdened with the look up procedure to resolve the mapped
   address even if an entire customer network gets assigned PI
   addresses.

   Assignment of PI addresses has to be restricted to a limited number
   of users.  This limit has to be decided by IANA. As the number of
   users with PI addresses increases, complexities within the entire
   system increases proportionately.

4.1 IP address aliasing

   An interface of a customer network may have several IP addresses
   (e.g. for a multihomed customer site, each interface will have
   multiple global unicast addresses also it may have a private
   address). This phenomenon is commonly known as IP address aliasing.

   A second type of aliasing is required to support IP mobility and
   provider independent addressing. For a mobile node that has been
   moved to a customer network which get services from two service
   providers and maintains private IP addresses, will have at least four
   IP addresses; provider one assigned unicast address, provider two
   assigned unicast address, private address and its permanent "Home
   Address". The "Home Address" will be aliased with one of the provider
   assigned addresses (i.e. the co-located care-of address). Similarly
   for a node with provider independent address will have four IP
   addresses. The interface address holding the PI address will be
   aliased with one of the provider assign addresses as its mapped
   address. If the node with PI address moved to a foreign site, will
   have a care-of address. The mapped address will be treated as the
   "Home Address".  So the interface structure needs to have two

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   additional fields to hold the values of care-of address and mapped
   address. The PCB structure will have two additional fields 'lmpiaddr'
   and 'lcladdr' to hold these information.  In case a PI node that has
   not been moved, both 'lcladdr' and 'lmpiaddr' will have the same
   value. So 'lcladdr' will have the current provider assigned address
   that a foreign node needs to use for communication. The field 'laddr'
   that is used to hold the vale of local address will hold the value of
   PI address for a node with PI address; it will hold the value of
   "Home Address" of a mobile node in case it does not have a PI
   address.

   In order to support multihoming, an outgoing IP packet needs to be
   forwarded based on its source address [8]. In order to support this,
   an outgoing packet from a mobile node or a node with PI address needs
   to be stacked with the associated care-of address. A client
   application program needs to call 'getsrcaddr'[8] to get the source
   address based on the destination address. The client program needs to
   to bind this address before communicating with its peer. The 'bind'
   system call needs to go through the interface list and fetch the
   associated structure to check whether the source address is aliased
   or not and needs to fill the values of 'lcladdr' and 'lmpiaddr' of
   PCB accordingly.  Protocol output routines like 'tcp_output' and
   'udp_output' need this information while filling up the IP packet.

   IP address stacking can be performed with the approach introduced in
   section 6.4 of RFC6275[9]. RFC6275 talks about the stacking of IP
   addresses for a destination address (Let us call it as type 0
   stacking). Two more types of stacking need to be introduced; type 1
   stacking where only source address will appear in the stack and type
   2 stacking where both source address and destination address will
   appear in the stack with a particular type of ordering.

   Protocol output routine like 'tcp_output' or 'udp_output' needs to
   fill the IP packet in the following manner.

   If the socket contains a valid 'lcladdr', use 'lcladdr' as the source
   address and 'laddr' will appear in the stack. If the socket contains
   a valid 'fcladdr' use 'fcladdr' as the destination address and
   'faddr' will appear in the stack. If only 'fcladdr' contains a valid
   address where as 'lcladdr' is NULL, use type 0 stacking. If only
   'lcladdr' contains a valid address where as 'fcladdr' is set as NULL,
   use type 1 stacking. If both 'lcladdr' and 'fcladdr' contains valid
   addresses, use type 2 stacking.

   Protocol input routine like 'tcp_input' or 'udp_input' needs to
   process the packet in the reverse order based on the type of
   stacking.  For type 0 stacking, use the address in the stack as the
   destination address; for type 1 stacking, use the address in the

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   stack as the source address; for type 2 stacking use both source
   address and destination address from the stack.

   When TCP receives a SYN for connection establishment, it allocates a
   PCB and assigns the values for 'laddr', and related fields.  During
   this phase, TCP also needs to check whether the local address is
   aliased or not and needs to fill the values of 'lcladdr' and
   'lmpiaddr' accordingly. Similarly if destination address is found to
   be aliased, based on the stacking type, it needs to fill up the field
   'fcladdr'.

4.2. Changes expected with the specifications related to IP mobility

   RFC6275 demands correspondent node binding from mobile nodes for
   route optimization. This binding is required when a connection gets
   established as well as when the mobile node changes it address space.
   There are application like HTTP which opens up multiple connections
   on the run time which are very short lived. If mobile nodes need to
   send binding messages for all the connections, network will be
   unnecessarily congested. This congestion can be avoided with the
   establishment of binding at the time of connection establishment
   itself.  So, if TCP server happens to be mobile, it will set the
   value of 'lcladdr' in the stack while sending SYN+ACK. TCP client
   which initiates communication through 'connect' needs to set
   'fcladdr' field on receiving TCP+ACK. With this approach
   correspondent node binding messages need to be sent only when a
   mobile node changes its position from one address space to another.

   Route optimization is not applicable to applications which are of
   multicast type.  In these cases packets need to be forwarded with the
   mechanism of reverse tunneling with the approach of "IP Encapsulation
   within IP" as defined in RFC 2003.  In order to support packet
   delivery with route optimization method as well as with
   "Encapsulating Delivery Style" based on the application type the
   protocol control block needs to introduce another field 'hagentaddr'
   to hold the address of the home agent of the mobile node. The
   interface structure also needs to have same field. The 'bind' system
   call needs to go through the interface list to fetch 'hagentaddr' to
   the PCB along with 'lcladdr' and 'lmpiaddr' as described earlier. So,
   protocol output routines like 'tcp_output', 'udp_output' need to fill
   up the packets based on the application type. In "Encapsulating
   Delivery Style" packets need to be formed in the following manner.

   The inner header will contain
     Source Address: Home address of the mobile node
     Destination address: Address of the correspondent node

   The outer IP header will contain

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     Source Address: co-located care of address of the mobile node
     Destination Address: Address of the home agent of the mobile node
     Protocol field: IP in IP

5. Refinements over existing IPv6 specification

   As IPv6 was envisioned long before some of the newer technologies
   e.g. MPLS came into picture, some refinements can be made over the
   existing specification. These considerations are related to bandwidth
   usages and performance inside switches. Experimental results show
   that smaller packet size gives better result for the processing of RT
   packets.  So, it is desirable to have IP packet header to be as small
   as possible.

   As described earlier, evaluation of the parameters
   nMaxInterASTopNodes, nMaxInterASBottomNodes and nMaxASNodes is geo-
   political and have to be decided by IANA. Once these parameters are
   determined with mutual agreements, values of pA, pB, pC and prefix
   length of user id can be determined. With 64bit address space, IP
   header will be reduced by 16 bytes.

   The 'flow label' field of IPv6 packet header may not be of any use
   with MPLS is in use. ATM used to have 4 priority classes. The first
   specification of IPv6 RFC-1883 used a 4bit type of service field
   along with a 24bits flow label field. These two were modified to a
   8bit type of service field and a 20bit flow label field in the
   current spec RFC-2460.  Too many priority classes may increase
   complexities to process inside switches. If type of service field of
   IPv6 header may be reduced to be of 4bit length as it was stated in
   RFC-1883 and 'flow label' field gets removed, another three bytes may
   be reduced from the IPv6 header.

   The field 'Hop Limit' has got a 8bit value in the existing spec. The
   role of this field needs to be discussed properly with a large
   address space.

   RFC4862[10] introduces the concept of "Stateless autoconfiguration"
   with the goal in mind that no manual configuration is required by
   individual machines before connecting them to the network. It
   generates a link local address with a link-local prefix and the link
   address (e.g. Ethernet/E.164 for ISDN) first. This link local address
   is used to configure global unicast address and any other
   configurable parameters based on router advertisement.  Global
   unicast addresses are generated by the prefix supplied by the router
   advertisement and the link specific interface identifier. This
   identifier can be as large as 64 bit length. So irrespective of the
   size of the network (it may be 10000 or 100 or even less than that)
   every customer network will consume a 64bit equivalent addresses.

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   This seems to be a huge blunder. What is expected is the length of
   the interface identifier is equivalent to support the number of nodes
   supported by that subnet. In order to achieve this the router itself
   or a server in that subnet needs to maintain a storage which will
   generate the interface identifier based on the request from
   individual hosts.  It may be desirable that interface identifiers are
   generated from DHCP servers. With the option of generating interface
   identifier through DHCP, changes in the autoconfiguration process can
   be looked at as follows:

   From the point of view of a host, it can be considered as a two step
   process. Host needs to send Router Solicitations message to find out
   the presence of a router. Router Advertisement message should include
   an option field which will inform whether prefix information should
   be configured through Router Advertisement or through DHCP.  Host
   needs to send a request message to get the interface identifier.  If
   both the information needs to be obtained from a DHCP server they can
   be obtained through a single message.

   From the server's point of view, it needs to maintain a database for
   a mapping of the link-layer address and subnet specific interface
   identifier. Lifetime of an interface identifier has to be processed
   in the usual manner the way existing DHCP implementation treats IP
   addresses.

   There seem to be another possible danger to obtain prefix information
   through Router Advertisement. As the Router Advertisement comes in
   the form of ICMP messages, once it is received by the ICMP layer, it
   looses information from which interface the message has been received
   (This problem arises for hosts that are having multiple interfaces
   and not all of them are attached to the same subnet).  So,
   autoconfiguration of a host has to be performed one interface at a
   time by making all other interfaces disabled. Once configuration of
   all the interfaces are done, all of them have to be enabled.

   If it is expected that hosts should reconfigure their addresses
   dynamically based on Router Advertisement message, Router
   Advertisement needs to generate a special message for a certain
   amount of time that needs to include old prefix and the corresponding
   new prefix in the message.

   In order to support multihoming[8], prefix information needs to
   include the fields 'default router' and 'next hop address' to reach
   the default router for each of the prefixes.

   In a 64bit architecture, link-local address can be formed with a
   link-local prefix and link-layer address in a suitable manner; say it
   can be formed with a 16bit link-local prefix followed by a 48bit

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   link-layer address. For hardware that supports more than 48bit
   addressing (say E.164), the least significant 48bits may be
   considered to generate link-local addresses.

6. Distributed processing and Multicasting

   With the inherent hierarchy involved in this architecture,
   distributed applications can also be structured in a suitable manner.
   Say, for a commonly used web based application a master level server
   will be there at every top level node. Any change that might happen
   in the application, has to be synchronized within these master level
   servers first. There might be servers at the middle layer (inside
   each inter-AS-bottom) inside each top level node. Once the changes
   get reflected at the master node, all the servers at the middle layer
   needs to update themselves with their master level node. This will
   reduce network traffic substantially. Inherent hierarchy in the
   architecture will also help establishing multicast tree in the
   similar manner. Work on these issues can be progressed only after
   this architecture gets approved.

7. IANA Consideration

   This is a first level draft for proposed standard. Hence, IANA
   actions should come into play at a later stage, if needed.

8. Security Consideration

   This document does not include any security related issues.

9. Acknowledgments

   The author would like to thank to Professor Amitava Datta of
   University of Western Australia for his review and constructive
   comments.

10. Normative References

   [1]  Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms for
        IPv6 Hosts and Routers", RFC 4213, October 2005.

   [2]  Fuller V., Li. T., "Classless Inter-Domain Routing (CIDR): The
        Internet Address Assignment and Aggregation Plan", RFC 4632,
        August 2006.

   [3]  Huston, G., "Commentary on Inter-Domain Routing in the
        Internet", RFC 3221, December 2001.

   [4]  Q. Vohra, E. Chen., "BGP Support for Four-octet AS Number

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        Space", RFC 4893, May 2007.

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

   [6]  J. Moy., OSPF Standardization Report, RFC 2329, April 1998

   [7]  C. Perkins, "IP Mobility Support for IPv4, Revised", RFC5944,
        November 2010.

   [8]  S. Bandyopadhyay, "Solution for Site Multihoming in a Real IP
        Environment", <draft-shyam-site-multi-13> work in progress.

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

   [10] S. Thomson, T. Narten, T. Jinmei, "IPv6 Stateless Address
        Autoconfiguration", RFC 4862, September 2007.

11. Informative References

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

   [12] Rekhter, Y., and T., Li, "A Border Gateway Protocol 4 (BGP-
        4)",RFC 1771, March 1995.

   [13] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
        Specification, RFC 1883, December 1995.

   [14] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.

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

   [16] Rosen, E., Viswanathan, A. and R. Callon, "Multiprotocol
        Label Switching Architecture", RFC 3031, January 2001.

12. Author's Address

   Shyamaprasad Bandyopadhyay
   HL No 205/157/7, Kharagpur 721305, India
   Phone: +91 3222 225137
   e-mail: shyamb66@gmail.com

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