Internet DRAFT - draft-shyam-real-ip-framework
draft-shyam-real-ip-framework
INTERNET DRAFT S. Bandyopadhyay
draft-shyam-real-ip-framework-61.txt January 28, 2020
Intended status: Experimental
Expires: July 28, 2020
An Architectural Framework of the Internet for the Real IP World
draft-shyam-real-ip-framework-61.txt
Abstract
This document tries to propose an architectural framework of the
internet in the real IP world. It describes how a three-tier mesh
structured hierarchy can be established in a large address space
based on fragmenting it into some regions and some sub regions inside
each of them. It shows how to make a transition from private IP to
real IP without making significant changes with the existing network.
With the useful works done through IPv6, it provides all necessary
inputs based on which a specification of IP with 64 bit address space
may be emerged.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on July 28, 2020.
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to this document.
Table of Contents
1. Introduction.....................................................2
2. Background.......................................................3
3. A Three tier mesh structured hierarchical network................4
3.1. Route propagation...........................................5
3.2. Determination of prefix lengths.............................8
3.2.1. A pseudo optimal distribution of prefixes in
a 64 bit architecture................................9
3.2.2. Whether to go for a two tier or three tier hierarchy
....................................................10
3.3. Issues related to Satellite communications.................11
4. Provider Independent addressing, name services and multihoming..12
5. Issues related to IP mobility...................................13
5.1. Changes expected with the specifications related
to IP mobility.............................................15
6. Refinements over existing IPv6 specification....................16
7. Distributed processing and Multicasting.........................19
8. Transition to real IP from private IP...........................19
9. IANA Consideration..............................................20
10. Security Consideration.........................................20
11. Acknowledgments................................................20
12. Normative References...........................................21
13. Informative References.........................................21
14. Author's Address...............................................22
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]. This document reflects changes required with the BSD 4.4
source code where ever applicable.
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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
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.
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. 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.
In IPv4 environment, there is a 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. In general, these services
are used by an organization of any size(it may be 400 or even 40000).
In the current scenario, 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.
Transitioning from private IP to real IP basically requires the
following components:
o A solution for site multihoming with provider assigned
address space
o A strategy to replace private IP to real IP
o A solution to uniquely identify a host in a real IP environment
o A solution to make individual nodes and routers/switches to work
with IPv4 and next generation IP simultaneously.
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Solution for site multihoming has been provided in a separate
document [10]. Section 9 shows how to make a transition from private
IP space to real IP space with provider assigned addresses with CIDR
based approach itself without reorganization of the existing provider
network. Section 5 provides a solution for identifying a host
uniquely with a number in a real IP environment. RFC 4213 [1] has
already described the transition mechanism from IPv4 to IPv6 for
individual nodes and routers.
Transitioning to real IP will eliminate the extra routing entries
associated with multihomed sites and thus will reduce the size of the
BGP table substantially. Assignment of addresses requires an
architectural framework. It may continue with the existing CIDR based
architecture (provided transitioning to real IP will be good enough
to handle all routing related issues for ever) or may come out with a
different approach. Mesh structured hierarchy will reduce the growth
of routing entries in a CIDR based environment as well as convenient
for distribution of network resources in a suitable manner in the
long run.
This document also tries to resolve and enhance several issues that
were carried on as part of deployment of IPv6. It shows that a 64 bit
address space is good enough for all practical purposes. With the
useful works done through IPv6, it provides all necessary inputs
based on which a specification of IP with 64 bit address space may be
emerged.
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.
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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.
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-
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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
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
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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 (in the form of a tree) 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 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/domain. 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[11]. Inside the VLSM tree, all the
physical ports of a switch have to be configured with the subnet
mask. A light weight routing protocol can be developed on top of
static routing table by setting default route inside VLSM tree.
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.
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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
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
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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 64 bit
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 16 bit user-id may become insufficient for
places like large university campus, where as 32 bit will become too
large. Hence, 24 bit 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, 16 bit equivalent space gets used within the user-id
space (i.e. one out of 256) and 8 bit equivalent nodes gets used
inside an AS (16% of 1600), for a top level node (with 16 bit
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.
Distribution of address space will be finalized based on the
consultation with IANA. Primarily, they may appear to be as follows:
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64 bit address space may be divided into two 63 bits blocks:
i. Global unicast addresses with the most significant bit set to 0.
This space is equally divided between provider assigned (PA) address
space and provider independent (PI) address space.
a) Provider assigned address space with prefix 00.
b) Provider independent (PI) address space with prefix 01. Provider
independent address space will be used for the customers who would
like to retain their number even after changing their providers. As
routing will be based on PA addresses, each PI address will be
associated to at least one PA address. Most significant part of PI
addressing is, it is independent of the architectural framework of
the provider network; even if the architectural framework changes,
same format of PI addressing can be maintained. Once implemented, PI
address of a node will be the number that will be generally used by
the common people. Section 5 describes issues related to PI
addressing in detail.
ii. Address space with the MSB set to 1 will be distributed within
the rest. Each of them will have a fixed prefix. This distribution
will be based on the requirements and the work that have already been
done in connection to IPv6:
a) Address space for multicasting with a prefix set to 1001.
b) Address space for link-local address: Link local addresses will
have a prefix 1010.
c) Router address space: Prefix 1111 will be used by routers inside
VLSM trees and 1110 will be used by backbone routers connecting them.
d) Address space for private IP: Each customer network can maintain
private address space to communicate within its users. This space
will be distributed within all the customer sites of a corporate that
can maintain VPN services. A 32 bit address space should be good
enough for private IP. Private address space will have a 32 bit
prefix with leading 4 bits are set to 1100 and the rest are set to 1.
Rest of the address space has been kept for future use.
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 26 bit (10+16) space will be available
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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
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
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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. Provider Independent addressing, name services and multihoming
Provider independent addressing can be conceived as naming a host
with a number. It can be used by customer networks who would like to
retain their number even after changing their service provider; also
it is useful to designate a host uniquely if the customer network is
multihomed. Just like in name services, as address corresponding to a
name needs to be resolved first to initiate communication, the same
is required for PI addressing. Each globally unique PI address will
be associated to at least one global unicast provider assigned
address. For a host with single interface, this number will be same
as the number of service providers the customer network is associated
with.
As either source or destination or both may be multihomed, there
could be multiple paths to communicate between two hosts. This is
required both for name services as well as for PI addressing.
A system call needs to be introduced to get the source address based
on the destination address. If application program needs to use the
destination address directly, it needs to use this system call.
int getcommaddr(int sockfd, struct in_addr *dst, struct addr_pair
*endpts);
'addr_pair' holds the addresses of communication end points as
follows:
struct addr_pair {
struct in_addr src;
struct in_addr dst;
};
'getcommaddr'[10] returns the number of source-destination pairs for
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communication; the field 'endpt' will hold the array of these
addresses. The array will be in sorted manner based on the best
possible route. 'sockfd' is used to get the 'type of service'
assigned. So, an application program needs to set its type of service
before using this call.
'getcommaddr needs to call a routine 'getmappedaddr' to resolve the
mapped provider assigned addresses of a provider independent address.
int getmappedaddr(struct in_addr *piaddr, struct in_addr *mpiaddr);
'getmappedaddr' will return number of mapped addresses and 'mpiaddr'
will hold their values.
"Host Identification with Provider Independent Address"[12] resolves
provider assigned addresses corresponding to a provider independent
address.
Users may use name instead of IP address to reach the destination. A
new system call needs to be introduced 'gethostbynamewithsrcaddr',
which is an extension to 'gethostbyname' as follows:
struct hostent *gethostbynamewithsrcaddr(int sockfd,const char *name,
int *nroutes, struct addr_pair *endpts);
'gethostbynamewithsrcaddr'[10] takes 'name' and 'sockfd' as input
parameters and finds out the best possible route to reach the
destination. It returns the pointer to the 'hostent' structure as
returned by 'gethostbyname' system call. The parameter 'nroutes'
gets the number of possible routes to be used and the corresponding
source and destination addresses gets assigned to 'endpts' in sorted
manner. 'sockfd' is used to get the 'type of service' assigned. So,
an application program needs to set its type of service before using
this call.
An application program needs to use these source addresses from the
top (i.e. the 0th) to establish connection with the destination. It
needs to bind source address 'src' and then connect with the
destination address 'dst'.
5. Issues related to IP mobility
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 private
addresses). For a mobile node that has been moved to a customer
network which gets service from a service provider and maintains
private IP addresses, will have at least three IP addresses; provider
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assigned unicast address, private address and its permanent "Home
Address". The "Home Address" will be aliased with the provider
assigned address (i.e. the co-located care-of address). So the
interface structure needs to have an additional field to hold the
value of care-of address. The PCB structure will have an additional
field 'inp_lcladdr'. So 'inp_lcladdr' will have the current provider
assigned address that a foreign node needs to use for communication.
The field 'inp_laddr' that is used to hold the value of local address
will hold the value of "Home Address" of a mobile node. Similarly,
PCB needs to introduce another field 'inp_fcladdr' to support the
destination address to be mobile. The existing field 'inp_faddr'
which is used to address a foreign address will hold the value of
"Home Address" of the mobile node. Customers with PI address who
would like to have mobility support, the mapped address will be
considered as the "Home Address" of the mobile node.
An outgoing packet from a mobile node in a foreign site needs to be
stacked with the associated care-of address. While initiating
communication, 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 value of
'inp_lcladdr' of PCB accordingly.
When TCP receives a SYN for connection establishment, it allocates a
PCB and assigns the values for 'inp_laddr', and related fields.
During this phase, TCP also needs to check whether the local address
is aliased or not (based on the fields of interface structure; which
is applicable for a mobile node at foreign site) and needs to fill
the values of 'inp_lcladdr' accordingly. Similarly if destination
address is found to be aliased, based on the stacking type, it needs
to fill up the field 'inp_fcladdr'.
IP address stacking can be performed with the approach introduced in
section 6.4 of RFC6275[7]. 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 'inp_lcladdr', use 'inp_lcladdr' as
the source address and 'inp_laddr' will appear in the stack. If the
socket contains a valid 'inp_fcladdr' use 'inp_fcladdr' as the
destination address and 'inp_faddr' will appear in the stack. If only
'inp_fcladdr' contains a valid address where as 'inp_lcladdr' is
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NULL, use type 0 stacking. If only 'inp_lcladdr' contains a valid
address where as 'inp_fcladdr' is set as NULL, use type 1 stacking.
If both 'inp_lcladdr' and 'inp_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
stack as the source address; for type 2 stacking use both source
address and destination address from the stack.
5.1. 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 'inp_lcladdr' in the stack while sending SYN+ACK. TCP client
which initiates communication through 'connect' needs to set
'inp_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 RFC2003. 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
'inp_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
'inp_hagentaddr' to the PCB along with 'inp_lcladdr' 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 IP header will contain
Source Address: Home address of the mobile node
(i.e. 'inp_laddr')
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Destination address: Address of the correspondent node
(i.e. 'inp_faddr')
The outer IP header will contain
Source Address: co-located care of address of the mobile node
(i.e. 'inp_lcladdr')
Destination Address: Address of the home agent of the mobile node
(i.e. 'inp_hagentaddr')
Protocol field: IP in IP
6. 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 64 bit 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 4 bit type of service field
along with a 24 bit flow label field. These two were modified to a 8
bit type of service field and a 20 bit 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 4 bit 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 8 bit value in the existing spec. The
role of this field needs to be discussed properly with a large
address space.
RFC4862[8] introduces the concept of "Stateless auto configuration"
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
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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 subnet of a customer network will consume a 64 bit equivalent
addresses. 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 auto
configuration 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, auto
configuration 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[10], prefix information needs to
include the fields 'default router' and 'next hop address' to reach
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the default router for each of the prefixes.
In a 64 bit 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 4 bit link-local prefix followed by a 60 bit
link-layer address. IPv6 supports Modified EUI-64 format for hardware
that supports 48 bit addressing by inserting a padding of 16 bit (FF
FE) in between company_id and manufacturer selected extension
identifier. In order to make things work, this padding has to be
reduced to 12 bit. For hardware that support E.164 format, uses a 15
digits number in BCD format followed by a padding of four bits set to
1111. Thus in this case, link local address can be formed with the
link-local prefix followed by the most significant 60 bit of E.164
format.
Section 3.1 of RFC 7421[9] states "It is sometimes suggested that
assigning a prefix such as /48 or /56 to every user site (including
the smallest) as recommended by [RFC6177] is wasteful. In fact, the
currently released unicast address space, 2000::/3, contains 35
trillion /48 prefixes ((2**45 = 35,184,372,088,832), of which only a
small fraction have been allocated. Allowing for a conservative
estimate of allocation efficiency, i.e., an HD-ratio of 0.94
[RFC4692], approximately 5 trillion /48 prefixes can be allocated.
Even with a relaxed HD-ratio of 0.89, approximately one trillion /48
prefixes can be allocated. Furthermore, with only 2000::/3 currently
committed for unicast addressing, we still have approximately 85% of
the address space in reserve. Thus, there is no objective risk of
prefix depletion by assigning /48 or /56 prefixes even to the
smallest sites."
So, each customer network can be assigned a /48 prefix, i.e 80 bits
address space.
In IPv4, class A(24 bits), class B(16 bits) and class C(8 bits)
networks were classified with the thoughts in mind that there will be
very few large networks (class A), a large number of mid sized
networks (class B) and a very large number of small sized networks
(class C). If we go back to the assignment of address space in IPv4,
before the emergence of CIDR, class B address space were getting
exhausted very fast. Moreover, it was realized that 16 bits class B
address space is way too large compared to the requirement of most of
the mid sized networks [2]. So, if we look at the actual need of
customer networks, on the average, it needs less than 16 bits (say, m
bits) address space.
So, if 80 bits address space is used for each customer network in
IPv6, more than 64 bits will remain unused on the average. In effect,
out of 128 bits, less than 64 bits will be of actual use. i.e. if RFC
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7421 justifies 128 bits address space as good enough for the need of
this world, 64 bits address space will satisfy the need of this world
when customer networks are assigned address space based on their
sizes.
Where ever one network gets satisfied with 80 bits address space
based on RFC 7421, 2^(16-m) networks get satisfied with 16 bits
address space if customer networks are assigned address space based
on their sizes. If total M networks with /48 prefixes can be
satisfied with 128 bits address space based on RFC 7421, total
M*2^(16-m) networks will be satisfied with 64 bits address space once
networks are assigned address space based on their sizes.
7. 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.
8. Transition to real IP from private IP
Both CIDR and mesh structured hierarchy expects a VLSM tree at the
bottom. In VLSM, in real IP space with provider assigned (PA)
addresses, assignment of network resources has to be associated with
the address space to be used with the type of service. Within a
typical switch supporting multiple types of ports, a line card of
strength OC48 can be replaced with 4 line cards of strength OC12. An
OC12 card may also be replaced with 4 OC3 cards. An OC12 card may be
attached to another switch with DS3 ports and so on. When it reaches
to the customer network port density of a switch has to be directly
proportional to the address block that a customer network will be
assigned to. i.e. each customer network has to be assigned a block of
address space (say, 128, 256, 512, 1K, 2K etc). Within the switch
these ports have to be assigned net address/net mask the way VLSM
works.
In IPv4 environment, providers have provided services in terms of
bandwidth of the ports say, 2 Mbps/4 Mbps/1 Gbps line etc. If these
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ports were assigned addresses based on the number of users of the
customer network, transition from private IP to real IP is simple.
Consider a switch that has supplied 2 Mbps line to a set of customers
with number of users within 1K to 2k, each of them will be assigned a
block of 2K each. But if number of users are not proportional to the
bandwidth used, say same 2 Mbps line were used to customers of sizes
1K, 2K 4K and 16K respectively reorganization will be needed if
possible. This rearrangement may be possible within the switch itself
or by connecting ports of appropriate sizes from different switch,
otherwise each of them has to be assigned an address block of 16K
each or with the way VLSM works whatever is suitable. So, address
block assignment in the VLSM tree has to grow in a bottom up
approach.
Thus, transition of existing provider network without (or very
little) rearrangement to a real IP space with CIDR based approach is
apparently not a difficult job. In a CIDR based approach, sizes of
the VLSM trees are heterogeneous that leads to number of routing
entries to be very high. Mesh structured hierarchy is convenient to
reduce the routing overhead as well as for distribution of network
resources in a suitable manner in the long run. To covert CIDR based
approach to mesh structured hierarchy requires reorganization mainly
in the routing domain and by splitting trees of very large sizes (>24
bit address space) at the top.
Mesh structured hierarchy makes use of a large address space and
distributes the entire space into some regions and sub regions inside
each region by maintaining flat address space in each layer for the
convenience of routing and distribution. It shows that 64 bit address
space is good enough for all practical purposes. If address space
gets assigned based on the actual need of the customer networks,
there will be lots of unused address space within 64 bit address
space. If CIDR based hierarchy is maintained, unused address space
will be much higher.
9. IANA Consideration
This document does not include any IANA related issues.
10. Security Consideration
This document does not include any security related issues.
11. Acknowledgments
The author would like to thank to Professor Amitava Datta of
University of Western Australia for his review and constructive
comments.
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12. 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
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, Ed., D. Johnson, J. Arkko, "Mobility Support in
IPv6" RFC 6275, July 2011.
[8] S. Thomson, T. Narten, T. Jinmei, "IPv6 Stateless Address
Autoconfiguration", RFC 4862, September 2007.
[9] B. Carpenter, Ed., T. Chown, F. Gont, S. Jiang, A. Petrescu,
A. Yourtchenko, "Analysis of the 64-bit Boundary in IPv6
Addressing", RFC 7421, January 2015.
[10] S. Bandyopadhyay, "Solution for Site Multihoming in a Real IP
Environment", <draft-shyam-site-multi-43>, work in progress.
[11] S. Bandyopadhyay, "VLSM Tree Routing Protocol",
<draft-shyam-vlsmtrp-00.txt>, work in progress.
[12] S. Bandyopadhyay, "Host Identification with Provider Independent
Address" <draft-shyam-hipi-00.txt>, work in progress.
13. Informative References
[13] Postel, J., "Internet Protocol", STD 5, RFC 791,
September 1981.
[14] Rekhter, Y., and T., Li, "A Border Gateway Protocol 4 (BGP-
4)",RFC 1771, March 1995.
[15] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
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Specification, RFC 1883, December 1995.
[16] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
Specification", RFC 2460, December 1998.
[17] Rosen, E., Viswanathan, A. and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031, January 2001.
14. 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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