One document matched: draft-lind-v6ops-isp-scenarios-00.txt
Internet Draft M. Lind (ed.)
<draft-lind-v6ops-isp-scenarios-00.txt> TeliaSonera
Expires: December 2003 June 2003
Scenarios for Introducing IPv6 into ISP Networks
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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Abstract
This document describes different scenarios for the introduction of
IPv6 in an IPv4 ISP network. The goal is the addition of a native
IPv6 service to the already existing IPv4 service without
interruption of the IPv4 service. During the IPv6 introduction the
network can go through 4 different stages including the initial IPv4
only stage. To move between the stages there will be some form of
transition that can be defined in different transition scenarios.
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Table of Contents
1. Introduction...................................................2
2. Scope..........................................................3
3. Brief description of a generic ISP network.....................3
4. Stages.........................................................4
4.1 Assumptions................................................4
4.2 Customer requirements and ISP offerings....................5
4.3 Stage 1 û Launch...........................................5
4.4 Stage 2a - Core............................................6
4.5 Stage 2b - Access..........................................6
4.6 Stage 3 û Complete.........................................6
4.7 Future stages..............................................7
5. Transition Scenarios...........................................7
6. Security Considerations........................................8
1. Introduction
An ISP offering an IPv4 service will find that there are different
ways to add IPv6 to this service. During the introduction of IPv6 the
network will go through different stages of IPv6 maturity. In
addition to this there has to be a transition between these stages to
make them feasible to implement. In some cases it might not be
possible to introduce IPv6 as a native part of the network, due to
hardware limitations or similar. Instead some coexistence mechanism
has to be used.
This leaves two choices; a native IPv6 transport in a part of the
network or some mechanism to transport IPv6 over the existing IPv4
network. From the customer perspective this can be seen as the ISP
offering a native IPv6 service or not depending on what is relevant
in the access network. If the ISP is not offering native IPv6
transport, then the service is limited in the sense that the customer
has to have a dual stack network, or some kind of coexistence
mechanism.
In this document different transition scenarios and situations during
the introduction of IPv6 are covered in a broader perspective and
deals only with a generic view of how an ISP network is build. This
should be seen as the starting point for further documentation of how
the introduction of IPv6 can be done in an ISP network in companion.
What also will be included in these documents are issues specific to
different network configurations and special network equipment. This
document should therefore be seen as the working frame for the
transition steps of the IPv6 introduction that will be documented in
companion documents.
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2. Scope
The scope of the document is to describe different cases for the
introduction of an IPv6 service in a generic IPv4 ISP network. This
means that the document will be limited to services that include both
IPv6 and IPv4 and will not cover issues surrounding an IPv6 only
service. The scope also includes transition scenarios between the
different stages. The different building blocks that will be
considered are a customer network, an access network, a core network
and exchange points. It is outside the scope of this document to
describe different types of access or network technologies. It is
also outside of the scope to propose different solutions. Solutions
will be covered in a separate document.
3. Brief description of a generic ISP network
A generic ISP network topology can be divided into two main parts;
core network and access network. The core network or the backbone is
the part of the network that interconnects the different access
networks and provides transport to the rest of the Internet via
exchange points or other means. The core network can be built on
different technologies but in this document the only interest is
whether it is capable of carrying IPv6 traffic natively or not. The
same applies to the access network. The access network provides
connectivity to enterprise and private customers. Other ISPs might as
well be customers and connected to the ISP's network.
__________ _________
| | | |
|Backoffice|----| CORE |
|__________| |_________|\
. / | \ \
. / | \ \_Peering( Direct & IX )
. / | \
. / | \
___.___ / ___|___ \ _______
| |____/ | | \____| |
|Access1| |Access2| |Access3|
|_______| |_______| |_______|
| | |
| | | ISP Network
----|---------------|---------------|-----------------
| | | Customer Networks
___|____ ___|____ ___|____
| | | | | |
|Customer| |Customer| |Customer|
|________| |________| |________|
Figure 1: ISP network topology
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It doesn't matter if these customer networks have a single node or a
large routed network. What is of interest is if routing information
is exchanged or not since it will affect the ISP's network. The
existence of customer placed equipment will also affect how a service
can be delivered. In addition to the ISP's actual network components
there are a lot of support and backend systems that have to be
considered.
4. Stages
The stages here are snapshots of an ISP's network with respect to
IPv6 maturity. Since an ISP's network is constantly evolving, a stage
is a measure of how far an ISP has come in turn of implementing
necessary functionality to offer IPv6 to the customers.
It is possible to freely transition between different stages.
However, a network segment can only be in one stage at a time but an
ISP network as a whole can be in different stages. There are
different transition paths between the first and final stage. The
transition between two stages does not have to be immediate but can
occur gradually.
Each stage has different IPv6 properties. An ISP can therefore, based
on the requirements it has, decide into which stage it will transform
its network.
4.1 Assumptions
The stages are derived from the generic description of an ISP network
in section 3. A combination of different building blocks that
constitute an ISP environment will lead to a number of scenarios,
which an ISP can choose from. The scenarios of most relevance to this
document are considered to be the ones that in the most efficient and
feasible way maximizes the ability for an ISP to offer IPv6 to its
customers.
The most predominant case today is considered to be an operator with
a core and access IPv4 network delivering IPv4 service to a customer
that is running IPv4 as well. At some point in the future, it is
expected that the customer will want to have an IPv6 service, in
addition to the already existing IPv4 service. The challenge for the
ISP is to deliver the requested IPv6 service over the existing
infrastructure and at the same time keep the IPv4 service intact. The
next step, which is not covered in this document, will be to remove
the IPv4 service when there no longer is a demand for it or deliver
the IPv4 service over an IPv6 only network.
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4.2 Customer requirements and ISP offerings
Looking at the scenarios from the end customer's perspective there
might be a demand for three different services; the customer might
demand IPv4 service, IPv6 service or both services. This can lead to
two scenarios depending on the stage the ISP's network is in.
If an ISP only offer IPv4 or IPv6 service and a customer wants to
connect a device or network that only supports one service and if
that service is not offered, it will lead to a dead-end. If the
customer or ISP instead connects a dual stack device it is possible
to circumvent the lack of the missing service in the access network
by using some kind of coexistence mechanism. This scenario will only
be considered in the perspective of the ISP offering a mechanism to
bridge the access and reach the IPv6 core.
In the case where the customer connects a single stack device to a
corresponding single stack access network, there will be no problem
from the customer's perspective. The same is valid if a single stack
device is connected to a dual stack access network. Therefore,
neither of these cases need further be explored in this document but
can be seen as a part of a full dual stack case.
After eliminating a number of cases explained above, there are four
stages that are most probable and where an ISP will find its network
in. Which stage a network is in; depend on whether or not some part
of the network previously has been upgraded to support IPv6 or if it
is easier to enable IPv6 in one part or another. For instance,
routers in the core might have IPv6 support or might be easily
upgradeable, while the hardware in the access might have to be
completely replaced in order to handle IPv6 traffic.
Note that in every stage except Stage 1, the ISP can offer both IPv4
and IPv6 services to the customer.
The four most probable stages are:
Stage 1 û Launch
Stage 2a û Core
Stage 2b û Access
Stage 3 û Complete
4.3 Stage 1 û Launch
The first stage is an IPv4 only ISP with an IPv4 customer. This is
the most common case today and has to be the starting point for the
introduction of IPv6. From this stage, an ISP can move (transition)
to any other stage with the goal to offer IPv6 to its customer.
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Customer Access Core Exchange
------ ------ ------ ------
| | | | | | | |
| IPv4 |---| IPv4 |---| IPv4 |---| IPv4 |
| | | | | | | |
------ ------ ------ ------
Figure 2. IPv4 network
4.4 Stage 2a - Core
Stage 2a is an ISP with an access network that is IPv4 only and a
core that is IPv4 and IPv6. In this stage the customer should have
support for both IPv4 and IPv6 and use a coexistence mechanism to be
able to run the IPv6 service. To offer the IPv6 service, the ISP also
has to connect to an IPv6 exchange point or somehow else exchange
IPv6 traffic with other ISPs.
Customer Access Core Exchange
------ ------ ------ ------
| | | | | | | IPv4 |
| Dual |---| IPv4 |---| Dual |---| + |
| | | | | | | IPv6 |
------ ------ ------ ------
Figure 3. Upgraded core
4.5 Stage 2b - Access
Stage 2b is an ISP with a core network that is IPv4 and an access
that is IPv4 and IPv6. Since the service to the customer is native
IPv6 there is no requirement for the customer to support both IPv4
and IPv6. This is the biggest difference in comparison to the
previous stage. The need to exchange IPv6 traffic or similar still
exists but might be more complicated than in the previous case since
the core isn't IPv6 enabled.
Customer Access Core Exchange
------ ------ ------ ------
| | | | | | | IPv4 |
| Dual |---| Dual |---| IPv4 |---| + |
| | | | | | | IPv6 |
------ ------ ------ ------
Figure 4. Upgraded access
4.6 Stage 3 û Complete
Stage 3 can be said to be the final step in introducing IPv6, at
least in the scope of this document. This is an all over IPv6 service
with native support for IPv6 and IPv4 in both core and access
networks. This stage is identical to the previous stage in the
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customer's perspective since the access network hasn't changed. The
connection to the IPv6 exchange point is identical to stage 2.
Customer Access Core Exchange
------ ------ ------ ------
| | | | | | | IPv4 |
| Dual |---| Dual |---| Dual |---| + |
| | | | | | | IPv6 |
------ ------ ------ ------
Figure 5. Completely upgraded network
4.7 Future stages
After a while the ISP might want to transition to a service that is
IPv6 only, at least in certain parts of the network. This transition
creates a lot of new cases in which to factor in how to maintain the
IPv4 service. Providing an IPv6 only service is not much different
than the dual IPv4/IPv6 service described in stage 3 except from the
need to phase out the IPv4 service. The delivery of IPv4 services
over an IPv6 network and the phase out will be left for a future
document.
5. Transition Scenarios
Given the different stages it is clear that the ISP has to be able to
transition from one stage to another. The initial stage, in this
document, is the IPv4 only service and network. The end stage is the
dual IPv4/IPv6 service and network. As mentioned in the scope, this
document does not cover the IPv6 only service and network and its
implications on IPv4 customers. This has nothing to do with the
usability of an IPv6 only service.
The transition starts out with the IPv4 ISP and then moves to one of
three choices. These choices are the different transition scenarios.
One way would be to upgrade the core first which leads to stage 2a.
Another way to go could be to upgrade the access network which leads
to stage 2b. The final possibility is to introduce IPv6 in the whole
network at once which would lead to stage 3.
The choice is dependent on many different issues. For example it
might not be possible to upgrade the core or the access network
without large investments in new equipment which could lead to any of
the two first choices. In another case it might be easier to take the
direct step to a complete IPv6/IPv4 network due to routing protocol
issues or similar.
If a partially upgraded network (stage 2a or 2b) was chosen as the
first step, a second step remains before the network is all over
native IPv6/IPv4. This is the transition to an all over dual stack
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network. This step is perhaps not necessary for stage 2b with an
already native IPv6 service to the customer but might still occur
when the timing is right. For stage 2a it is more obvious that a
transition to a dual stack network is necessary since it has to be
done to offer a native IPv6 service.
6. Security Considerations
This document describes different cases for the introduction of IPv6
in an IPv4 ISP network. Solutions are described in other documents
hence this document has no security considerations.
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Acknowledgements
This draft has benefited from input by Jordi Palet, Suresh Satapati,
Myung-Ki Shin, Vladmir Ksinant, Alain Baudot, Soohong Daniel Park,
Cleve Mickles, Pekka Savola and Margaret Wasserman.
Authors' Addresses
Mikael Lind
TeliaSonera
Vitsandsgatan 9B
SE-12386 Farsta
Email: mikael.lind@teliasonera.com
Jasminko Mulahusic
TeliaSonera
Vitsandsgatan 9B
SE-12386 Farsta
Email: jasminko.mulahusic@teliasonera.com
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