Internet Draft M. Lind
<draft-ietf-v6ops-isp-scenarios-analysis-01.txt> TeliaSonera
V. Ksinant
6WIND
S. Park
Samsung Electronics
A. Baudot
France Telecom
P. Savola
CSC/Funet
Expires: August 2004 February 2004
Scenarios and Analysis 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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http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
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Abstract
This document first describes different scenarios for the
introduction of IPv6 into an ISP's existing IPv4 network without
disrupting the IPv4 service. Then, this document analyses these
scenarios and evaluates the relevance of the already defined
transition mechanisms in this context. Known challenges are also
identified.
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Table of Contents
1. Introduction................................................2
1.1 Goal and Scope of the Document...........................2
2. Brief Description of a Generic ISP Network..................3
3. Transition Scenarios........................................4
3.1 Identification of Stages and Scenarios...................4
3.2 Stages...................................................5
3.2.1 Stage 1 Scenarios: Launch..............................5
3.2.2 Stage 2a Scenarios: Backbone...........................6
3.2.3 Stage 2b Scenarios: Customer Connection................6
3.2.4 Stage 3 Scenarios: Complete............................6
3.2.5 Stages 2a and 3: Combination Scenarios.................7
3.3 Transition Scenarios.....................................7
3.4 Actions Needed When Deploying IPv6 in an ISP's network...7
4. Backbone Transition Actions.................................8
4.1 Steps in Transitioning Backbone Networks.................8
4.1.1 MPLS Backbone..........................................9
4.2 Configuration of Backbone Equipment.....................10
4.3 Routing.................................................10
4.3.1 IGP...................................................10
4.3.2 EGP...................................................11
4.3.3 Transport of Routing Protocols........................12
4.4 Multicast...............................................12
5. Customer Connection Transition Actions.....................12
5.1 Steps in Transitioning Customer Connection Networks.....12
5.2 Access Control Requirements.............................14
5.3 Configuration of Customer Equipment.....................15
5.4 Requirements for Traceability...........................16
5.5 Ingress Filtering in the Customer Connection Network....16
5.6 Multi-Homing............................................16
5.7 Quality of Service......................................16
6. Network and Service Operation Actions......................17
7. Future Stages..............................................17
8. Example Networks...........................................18
8.1 Example 1...............................................19
8.2 Example 2...............................................21
8.3 Example 3...............................................21
9. Security Considerations....................................22
10. Acknowledgements...........................................22
11. Informative References.....................................22
1. Introduction
1.1 Goal and Scope of the Document
When an ISP deploys IPv6, its goal is to provide IPv6 connectivity
to its customers. The new IPv6 service must be added to an already
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existing IPv4 service, and the introduction of IPv6 must not
interrupt this IPv4 service.
An ISP offering IPv4 service will find different ways to add IPv6 to
this service. This document discusses a small set of scenarios for
the introduction of IPv6 into an ISP's IPv4 network. It evaluates the
relevance of the existing transition mechanisms in the context of
these deployment scenarios, and points out the lack of functionality
essential to the ISP's operation of an IPv6 service.
The present document is focused on services that include both IPv6
and IPv4 and does not cover issues surrounding IPv6-only service.
It is also outside the scope of this document to describe different
types of access or network technologies.
2. Brief Description of a Generic ISP Network
A generic network topology for an ISP can be divided into two main
parts: the backbone network and the customer connection networks
connecting the customers. It includes, in addition to these, some
other building blocks such as network and service operations. The
additional building blocks used in this document are defined as
follows:
"CPE" : Customer Premises Equipment
"PE" : Provider Edge equipment
"Network and service operation"
: This is the part of the ISP's network that hosts the
services required for the correct operation of the
ISP's network. These services usually include
management, supervision, accounting, billing, and
customer management applications.
"Customer connection"
: This is the part of the network used by a customer
when connecting to an ISP's network. It includes the
CPE, the last hop link and the parts of the PE
interfacing to the last hop link.
"Backbone" : This is the rest of the ISP's network infrastructure.
It includes the parts of the PE interfacing to the
core, the core routers of the ISP, and the border
routers used to exchange routing information with
other ISPs (or other administrative entities).
"Dual-stack network":
A network that supports natively both IPv4 and
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IPv6.
It is noted that, in some cases (e.g., incumbent national or
regional operators), a given customer connection network may have
to be shared between or among different ISPs. According to the type
of customer connection network used (e.g., one involving only layer 2
devices or one involving non-IP technology), this constraint may
result in architectural considerations relevant to this document.
The basic components in the ISP's network are depicted in Figure 1.
------------ ----------
| Network and| | |
| Service |--| Backbone |
| Operation | | |\
------------ ---------- \
. / | \ \
. / | \ \_Peering( Direct and IX )
. / | \
. / | \
. / | \
---------- / ---------- \ ----------
| Customer | / | Customer | \ | Customer |
|Connection|--/ |Connection| \--|Connection|
| 1 | | 2 | | 3 |
---------- ---------- ----------
| | | ISP's Network
-------------------------------------------------------
| | | Customers' Networks
+--------+ +--------+ +--------+
| | | | | |
|Customer| |Customer| |Customer|
| | | | | |
+--------+ +--------+ +--------+
Figure 1: ISP Network Topology.
3. Transition Scenarios
3.1 Identification of Stages and Scenarios
This section describes different stages an ISP might consider when
introducing IPv6 connectivity into its existing IPv4 network and the
different scenarios that might occur in the respective stages.
The stages here are snapshots of the ISP's network with respect to
IPv6 maturity. Because the ISP's network is continually evolving, a
stage is a measure of how far along the ISP has come in terms of
implementing the functionality necessary to offer IPv6 to the
customers.
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It is possible to transition freely between different stages.
Although a network segment can only be in one stage at a time, the
ISP's network as a whole can be in different stages. Different
transition paths can be followed from the first to the final stage.
The transition between two stages does not have to be instantaneous;
it can occur gradually.
Each stage has different IPv6 properties. An ISP can, therefore,
based on its requirements, decide which set of stages it will follow
to transform its network.
This document is not aimed to cover small ISPs, hosting providers, or
data centers; only the scenarios applicable to ISPs eligible for a
/32 IPv6 prefix allocation from a RIR are covered.
3.2 Stages
The stages are derived from the generic description of an ISP's
network in Section 2. Combinations of different building blocks
that constitute an ISP's environment lead to a number of scenarios
from which the ISP can choose. The scenarios most relevant for this
document are the ones that maximize ISP's ability to offer IPv6 to
its customers in the most efficient and feasible way. The assumption
in all stages is that the ISP's goal is to offer both IPv4 and IPv6
to the customer.
The four most probable stages are:
o Stage 1 Launch
o Stage 2a Backbone
o Stage 2b Customer connection
o Stage 3 Complete
Generally, an ISP is able to upgrade a current IPv4 network to an
IPv4/IPv6 dual-stack network via Stage 2b, but the IPv6 service can
also be implemented at a small cost by adding simple tunnel
mechanisms to the existing configuration. When designing a new
network, Stage 3 might be the first and last step, because there are
no legacy concerns. Nevertheless, the absence of IPv6 capability in
the network equipment can still be a limiting factor.
Note that in every stage except Stage 1, the ISP can offer both IPv4
and IPv6 services to its customers.
3.2.1 Stage 1 Scenarios: Launch
The first stage is an IPv4-only ISP with an IPv4 customer. This is
the most common case today and the natural starting point for the
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introduction of IPv6. From this stage, the ISP can move (transition)
from Stage 1 to any other stage with the goal of offering IPv6 to its
customer.
The immediate first step consists of getting a prefix allocation
(typically a /32) from the appropriate RIR according to allocation
procedures.
3.2.2 Stage 2a Scenarios: Backbone
Stage 2a consists of an ISP with IPv4-only customer connection
networks and a backbone that supports both IPv4 and IPv6. In
particular, the ISP has the possibility of making the backbone IPv6-
capable through either software upgrades, hardware upgrades, or a
combination of both.
Since the customer connections are not yet upgraded, a tunneling
mechanism has to be used to provide IPv6 connectivity through the
IPv4 customer connection networks. The customer can terminate the
tunnel at the CPE (if it has IPv6 support) or at each individual
device. In the former case, the CPE will then provide global IPv6
connectivity to all devices in the customer's network.
3.2.3 Stage 2b Scenarios: Customer Connection
Stage 2b consists of an ISP with an IPv4 backbone network and a
customer connection network that supports both IPv4 and IPv6. Because
the service to the customer is native IPv6, the customer is not
required to support both IPv4 and IPv6. This is the biggest
difference in comparison with the previous stage. The need to
exchange IPv6 traffic still exists but might be more complicated than
in the previous case, because the backbone is not IPv6-enabled. After
completing Stage 2b, the original IPv4 backbone is unchanged. This
means that the IPv6 traffic is transported by either tunnelling over
the existing IPv4 backbone, or in an IPv6 overlay network more or
less separated from the IPv4 backbone.
Normally the ISP will continue to provide IPv4 connectivity; in
many cases private IPv4 addresses and NATs will continue to be used.
3.2.4 Stage 3 Scenarios: Complete
Stage 3 can be said to be the final step in introducing IPv6, at
least within the scope of this document. This consists of ubiquitous
IPv6 service with native support for IPv6 and IPv4 in both backbone
and customer connection networks. This stage is identical to the
previous stage from the customer's perspective, because the customer
connection network has not changed. The requirement for exchanging
IPv6 traffic is identical to Stage 2.
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3.2.5 Stages 2a and 3: Combination Scenarios
Some ISPs may use different access technologies of varying IPv6
maturity. This may result in a combination of the Stages 2a and 3:
some customer connections do not support IPv6, but others do; in both
cases the backbone is dual-stack.
This is equivalent to Stage 2a, but it requires support for native
IPv6 customer connections on some access technologies.
3.3 Transition Scenarios
Given the different stages, it is clear that an ISP has to be able
to transition from one stage to another. The initial stage, in this
document, is IPv4-only service and network. The end stage is dual
IPv4/IPv6 service and network.
The transition starts with an IPv4 ISP and then moves in one of
three directions. This choice corresponds to the different
transition scenarios. Stage 2a consists of upgrading the backbone
first. Stage 2b consists of upgrading the customer connection
network. Finally, Stage 3 consists of introducing IPv6 in both the
backbone and customer connections as needed.
Because most of ISPs continually evolve their backbone IPv4 networks
(firmware replacements in routers, new routers, etc.), they will be
able to get them ready for IPv6 without additional investment
(except staff training). This may be a slower but still useful
transition path, because it allows for IPv6 introduction without any
actual customer demand. This may be superior to doing everything
at the last minute, which may entail a higher investment. However, it
is important to start considering (and requesting from the vendors)
IPv6 features in all new equipment from the start. Otherwise, the
time and effort to remove non-IPv6-capable hardware from the network
will be significant.
3.4 Actions Needed When Deploying IPv6 in an ISP's network
Examination of the transitions described above reveals that it
is possible to split the work required for each transition into a
small set of actions. Each action is largely independent from the
others, and some actions may be common to multiple transitions.
Analysis of the possible transitions leads to a small list of
actions:
* Actions required for backbone transition:
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- Connect dual-stack customer connection networks to other
IPv6 networks through an IPv4 backbone.
- Transform an IPv4 backbone into a dual-stack one. This
action can be performed directly or through intermediate
steps.
* Actions required for customer connection transition:
- Connect IPv6 customers to an IPv6 backbone through an IPv4
network.
- Transform an IPv4 customer connection network into a dual-
stack one.
* Actions required for network and service operation transition:
- Configure IPv6 functions into network components.
- Upgrade regular network management and monitoring
applications to take IPv6 into account.
- Extend customer management (e.g., RADIUS) mechanisms
to be able to supply IPv6 prefixes and other information
to customers.
- Enhance accounting, billing, etc. to work with IPv6
as needed. (Note: if dual-stack service is offered, this
may not be necessary.)
- Implement security for network and service operation.
Sections 4, 5, and 6 contain detailed descriptions of each action.
4. Backbone Transition Actions
4.1 Steps in Transitioning Backbone Networks
In terms of physical equipment, backbone networks consist mainly of
high-speed core and edge routers. Border routers provide peering
with other providers. Filtering, routing policy, and policing
functions are generally managed on border routers.
The initial step is an IPv4-only backbone, and the final step is a
completely dual-stack backbone. In between, intermediate steps may be
identified:
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Tunnels Tunnels
IPv4-only ----> or ---> or + DS -----> Full DS
dedicated IPv6 dedicated IPv6 routers
links links
Figure 2: Migration Path.
The first step involves tunnels or dedicated links but leaves
existing routers unchanged. Only a small set of routers then have
IPv6 capabilities. Using configured tunnels is adequate during
this step.
In the second step, some dual stack routers are added, progressively,
to this network.
The final step is reached when all or almost all routers are dual-
stack.
For many reasons (technical, financial, etc.), the ISP may progress
step by step or jump directly the final one. One of the important
criteria in planning this evolution is the number of IPv6
customers the ISP expects during its initial deployments. If few
customers connect to the original IPv6 infrastructure, then the ISP
is likely to remain in the initial steps for a long time.
In short, each intermediate step is possible, but none is mandatory.
4.1.1 MPLS Backbone
If MPLS is already deployed in the backbone, it may be desirable
to provide IPv6-over-MPLS connectivity. However, setting up an IPv6
Label Switched Path (LSP) requires signaling through the MPLS
network; both LDP and RSVP-TE can set up IPv6 LSPs, but this would
require a software upgrade in the MPLS core network. An alternative
approach is to use BGP for signaling or to perform, for example,
IPv6-over-IPv4/MPLS or IPv6-over-IPv4-over-IPv4/MPLS encapsulation,
as described in [BGPTUNNEL]. Some of the multiple possibilities are
preferable to others depending on the specific environment under
consideration. More analysis is needed, case by case, to determine
the best approach or approaches:
1) Require that MPLS networks deploy native IPv6 support or
use configured tunneling for IPv6.
2) Require that MPLS networks support setting up IPv6 LSPs,
and set up IPv6 connectivity by using either these or
configured tunneling.
3) Use only configured tunneling over IPv4 LSPs; this seems
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practical with small-scale deployments having few tunnels.
4) Use [BGPTUNNEL] or something comparable to perform IPv6-over-
IPv4/MPLS encapsulation for IPv6 connectivity.
Approaches 1 and 2 are the most attractive if the ISP is willing to
perform an upgrade to the MPLS network. Approach 3 does not require
any upgrades but may lack scalability. Approach 4 may be economically
attractive for an operator who does not wish to upgrade the MPLS
network and has a large-scale deployment.
MPLS networks have typically been deployed to facilitate services
such as Provider-Provisioned VPNs. Software upgrades are commonplace
in MPLS networks. No particular reason exists to avoid adding IPv6
functionality, except if the vendor is unable to provide sufficient
IPv6 forwarding capability (e.g., line-speed) in the existing
hardware (independent of the capabilities for handling MPLS frames).
Therefore, recommending mechanisms like [BGPTUNNEL] as the final
solution might not be such a good idea.
4.2 Configuration of Backbone Equipment
In the backbone, the number of devices is small and IPv6
configuration mainly deals with routing protocol parameters,
interface addresses, loop-back addresses, ACLs, etc.
These IPv6 parameters are not supposed to be configured
automatically.
4.3 Routing
ISPs need routing protocols to advertise reachability and to
find the shortest working paths, both internally and externally.
OSPFv2 and IS-IS are typically used as an IPv4 IGP. RIPv2 is not
typically used in operator networks. BGP is the only IPv4 EGP.
Static routes also are used in both cases.
Note that it is possible to configure a given network so that it
results in having an IPv6 topology different from its IPv4 topology.
For example, some links or interfaces may be dedicated to IPv4-only
or IPv6-only traffic, or some routers may be dual-stack whereas
others may be IPv4 or IPv6 only. In this case, routing protocols must
be able to understand and cope with multiple topologies.
4.3.1 IGP
Once the IPv6 topology has been determined, the choice of IPv6 IGP
must be made: either OSPFv3 or IS-IS for IPv6. RIPng is less
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appropriate in many contexts and is not discussed here. The IGP
typically includes the routers' point-to-point and loop-back
addresses.
The most important decision is whether one wishes to have separate
routing protocol processes for IPv4 and IPv6. Separating them
requires more memory and CPU for route calculations, e.g., when the
links flap. On the other hand, separation provides a certain measure
of assurance that if problems arise with IPv6 routing, they will not
affect IPv4 the routing protocol at all. In the initial phases, if
it is uncertain whether joint IPv4-IPv6 networking is working as
intended, running separate processes may be desirable and easier to
manage.
Thus the possible combinations are:
- with separate processes:
o OSPFv2 for IPv4, IS-IS for IPv6 (only)
o OSPFv2 for IPv4, OSPFv3 for IPv6, or
o IS-IS for IPv4, OSPFv3 for IPv6
- with the same process:
o IS-IS for both IPv4 and IPv6
Note that if IS-IS is used for both IPv4 and IPv6, the IPv4/IPv6
topologies must be "convex," unless the Multiple-topology IS-IS
extensions [MTISIS] have been implemented. In simpler networks or
with careful planning of IS-IS link costs, it is possible to keep
even incongruent IPv4/IPv6 topologies "convex."
Therefore, the use of same process is recommended especially for
large ISPs intending to deploy, in the short-term, a fully dual-
stack backbone infrastructure. If the topologies will not be similar
in the short term, two processes (or Multi-topology IS-IS
extensions) are recommended.
The IGP is not typically used to carry customer prefixes or external
routes. Internal BGP (iBGP), as described in the next section, is
most often deployed in all routers to distribute such other routing
information.
Because some of the simplest devices, e.g., CPE routers, may not
implement routing protocols other than RIPng, in some cases it may
also be necessary to run RIPng in addition to one of the above IGPs,
at least in a limited fashion, and somehow to redistribute routing
information between the routing protocols.
4.3.2 EGP
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BGP is used for both internal and external BGP sessions.
BGP with Multi-protocol extensions [RFC 2858] can be used for IPv6
[RFC 2545]. These extensions enable exchanging both IPv6 routing
information and establishing BGP sessions using TCP over IPv6.
It is possible to use a single BGP session to advertise both IPv4
and IPv6 prefixes between two peers. However, typically, separate
BGP sessions are used.
4.3.3 Transport of Routing Protocols
IPv4 routing information should be carried by IPv4 transport and
similarly IPv6 routing information by IPv6 for several reasons:
* IPv6 connectivity may work when IPv4 connectivity is down
(or vice-versa).
* The best route for IPv4 is not always the best one for IPv6.
* The IPv4 logical topology and the IPv6 one may be different,
because the administrator may want to assign different metrics
to a physical link for load balancing or tunnels may be used.
4.4 Multicast
Currently, IPv6 multicast is not a major concern for most ISPs.
However, some of them are considering deploying it. Multicast is
achieved using the PIM-SM and PIM-SSM protocols. These also work with
IPv6.
Information about multicast sources is exchanged using MSDP in IPv4,
but MSDP is intentionally not defined for IPv6. Instead, one should
use only PIM-SSM or an alternative mechanism for conveying the
information [EMBEDRP].
5. Customer Connection Transition Actions
5.1 Steps in Transitioning Customer Connection Networks
Customer connection networks are generally composed of a small set of
PEs connected to a large set of CPEs. Transitioning this
infrastructure to IPv6 can be accomplished in several steps, but some
ISPs, depending on their perception of the risks, may avoid some of
the steps.
Connecting IPv6 customers to an IPv6 backbone through an IPv4
network can be considered as a first careful step taken by an ISP to
provide IPv6 services to its IPv4 customers. In addition, some
ISPs may also provide IPv6 services to customers who get their IPv4
services from another ISP.
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This IPv6 service can be provided by using tunneling techniques. The
tunnel may terminate at the CPE corresponding to the IPv4 service or
in some other part of the customer's infrastructure (for instance,
on IPv6-specific CPE or even on a host).
Several tunneling techniques have already been defined: configured
tunnels with tunnel broker, 6to4, Teredo, etc.
The selection of one candidate depends largely on the presence or
absence of NATs between the two tunnel end-points and whether the
user's IPv4 tunnel end-point address is static or dynamic. In most
cases, 6to4 and ISATAP are incompatible with NATs, and UDP
encapsulation for configured tunnels has not been specified.
However, NAT traversal can be avoided if the NAT supports
forwarding protocol-41 [PROTO41].
Firewalls in the path can also break these types of tunnels. The
administrator of the firewall needs to create a hole for the
tunnel. This is usually manageable, as long as the firewall is
controlled by either the customer or the ISP, which is almost always
the case.
When the CPE is performing NAT or firewall functions, terminating the
tunnels directly at the CPE typically simplifies the scenario
considerably, avoiding the NAT and firewall traversal. If such an
approach is adopted, the CPE has to support the tunneling mechanism
used, or be upgraded to do so.
In practice, an ISP has two kinds of customers in its customer
connection networks: small end users (mostly unmanaged networks--
home and SOHO users) and others. The former category typically uses
a dynamic IPv4 address, which is often non-routable; a reasonably
static address is also possible. The latter category typically has
static IPv4 addresses, and at least some of them are public; however,
NAT traversal or configuration may be required to reach an internal
IPv6 access router.
Tunneling consideration for small end sites are discussed in
[UNMANCON] and [UNMANEVA]. These identify solutions relevant to the
first category of unmanaged networks.
The connectivity mechanisms can be categorized as "managed" or
"opportunistic." The former consist of native service or a
configured tunnel (with or without a tunnel broker); the latter
include 6to4 and, e.g., Teredo; they provide "short-cuts" between
nodes using the same mechanisms and are available without contracts
with the ISP.
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The ISP may offer opportunistic services, mainly a 6to4 relay,
especially as a test when no "real" service is offered yet. At the
later phases, ISPs might also deploy 6to4 relays or Teredo servers
(or similar) to optimize their customers' connectivity to 6to4 or
Teredo nodes.
Most interesting are the managed services. When dual-stack is not an
option, a form of tunneling must be used. When configured tunneling
is not an option (e.g., due to dynamic IPv4 addressing), some form of
automation has to be used. The options are basically either to deploy
an L2TP architecture (whereby the customers would run L2TP clients
and PPP over it to initiate IPv6 sessions) or to deploy a tunnel
configuration service. The prime candidates for tunnel configuration
are STEP [STEP] and TSP [TSP], which are not analyzed further in this
document.
For connecting larger customers:
* Dual-stack access service is often a realistic possibility since
the customer network is managed.
* Configured tunnels, as-is, are a good solution when a NAT is not in
the way and the IPv4 end-point addresses are static. In this
scenario, NAT traversal is not typically required. If fine-grained
access control is needed, an authentication protocol needs to be
used.
* A tunnel brokering solution, to help facilitate the set-up of a
bi-directional tunnel, has been proposed: the Tunnel Set-up
Protocol. Whether this is the right approach needs to be
determined.
* Automatic tunneling mechanisms such as 6to4 or Teredo are not
suggested in this scenario.
Other ISPs may take a more direct approach and avoid the use of
tunnels as much as possible.
Note that when customers use dynamic IPv4 addresses, the
tunneling techniques may be more difficult to deploy at the ISP's
end, especially if a protocol including authentication (like PPP for
IPv6) is not used. This may need to be considered in more detail
with tunneling mechanisms.
5.2 Access Control Requirements
Access control is usually required in ISP networks, because the ISPs
need to control to whom they are granting access. For instance, it is
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important to check whether the user who tries to connect is really a
valid customer. In some cases, it is also important for billing.
However, IPv6-specific access control is not always required.
This is the case, for instance, when a customer of the IPv4 service
has automatically access to IPv6 service. Then, the IPv4 access
control also provides access to the IPv6 services.
When a provider does not wish to give its IPv4 customers
automatic access to IPv6 services, specific IPv6 access control must
be performed in parallel with the IPv4 access control. This does not
imply that different user authentication must be performed for IPv6,
but merely that the authentication process may lead to different
results for IPv4 and IPv6 access.
Access control traffic may use IPv4 or IPv6 transport. For instance,
Radius traffic related to IPv6 service can be transported over
IPv4.
5.3 Configuration of Customer Equipment
The customer connection networks are composed of PE and CPE(s).
Usually, each PE connects multiple CPE components to the backbone
network infrastructure. This number may reach tens of thousands or
more. The configuration of CPE is, in general, a difficult task for
the ISP, and even more so in this case, because configuration must be
done remotely. In this context, the use of auto-configuration
mechanisms is beneficial, even if manual configuration is still an
option.
The parameters that usually need to be provided to customers
automatically are:
- The network prefix delegated by the ISP,
- The address of the Domain Name System server (DNS),
- Possibly other parameters, e.g., the address of a NTP server.
When user identification is required on the ISP's network, DHCPv6 may
be used to provide configurations otherwise either DHCPv6 or a
stateless mechanism can be used. This is discussed in more detail in
[DUAL ACCESS].
Note that when the customer connection network is shared between the
users or the ISPs, and not just a point-to-point link, authenticating
the configuration of the parameters (esp. prefix delegation) requires
further study.
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As long as IPv4 service is available alongside of IPv6, no critical
need exists to be able to autoconfigure IPv6 parameters (except for
the prefix) in the CPE-- IPv4 settings work as well.
5.4 Requirements for Traceability
Most ISPs have some kind of mechanism to trace the origin of traffic
in their networks. This also has to be available for IPv6 traffic,
which means that a specific IPv6 address or prefix has to be tied to
a certain customer, or that records of which customer had which
address or prefix must be maintained. This also applies to the
customers with tunneled connectivity.
This can be done, for example, by mapping a DHCP response to a
physical connection and storing this in a database. It can also be
done by assigning a static address or prefix to the customer.
5.5 Ingress Filtering in the Customer Connection Network
Ingress filtering must be deployed towards the customers, everywhere,
to ensure traceability, to prevent DoS attacks using spoofed
addresses, to prevent illegitimate access to the management
infrastructure, etc.
Ingress filtering can be done, for example, by using access lists or
Unicast Reverse Path Forwarding (uRPF). Mechanisms for these are
described in [BCP38UPD].
5.6 Multi-Homing
Customers may desire multi-homing or multi-connecting for a number of
reasons [RFC3582].
Multi-homing to more than one ISP is a subject still under debate.
Deploying multiple addresses from each ISP and using the addresses
of the ISP when sending traffic to that ISP is at least one working
model; in addition, tunnels may be used for robustness [RFC3178].
Currently, there are no provider-independent addresses for end-
sites.
Multi-connecting more than once to just one ISP is a simple
practice, and this can be done, e.g., by using BGP with public or
private AS numbers and a prefix assigned to the customer.
5.7 Quality of Service
In most networks, quality of service in one form or another is
important.
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Naturally, the introduction of IPv6 should not impair existing
Service Level Agreements (SLAs) or similar quality reassurances.
Depending on the deployment of the IPv6 service, the service could
be best-effort, at least initially, even if the IPv4 service had a
SLA.
Both IntServ and DiffServ are equally applicable in IPv6 as well as
in IPv4 and work in a similar fashion. Of these, typically only
DiffServ has been implemented.
6. Network and Service Operation Actions
The network and service operation actions fall into different
categories as listed below:
- IPv6 network device configuration: for initial configuration
and updates
- IPv6 network management
- IPv6 monitoring
- IPv6 customer management
- IPv6 network and service operation security
Some of these items will require an IPv6 native transport layer to
be available, whereas others will not.
As a first step, network device configuration and regular network
management operations can be performed over an IPv4 transport,
because IPv6 MIBs are also available over IPv4 transport.
Nevertheless, some monitoring functions require the availability of
IPv6 transport. This is the case, for instance, when ICMPv6 messages
are used by the monitoring applications.
The current inability to get IPv4 and IPv6 traffic statistics for
management purposes by using SNMP separately from dual-stack
interfaces is an issue.
As a second step, IPv6 transport can be provided for any of these
network and service operation facilities.
7. Future Stages
At some point, an ISP might want to transition to a service that is
IPv6 only, at least in certain parts of its network. This
transition creates a lot of new cases into which it must factor how
to maintain the IPv4 service. Providing an IPv6-only service is not
much different from the dual IPv4/IPv6 service described in stage 3
except for the need to phase out the IPv4 service. The delivery of
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IPv4 services over an IPv6 network and the phase out of IPv4 are left
for a subsequent document.
8. Example Networks
In this section, a number of different network examples are
presented. These are only example networks and will not necessarily
match any existing networks. Nevertheless, the examples are intended
be useful even in cases in which they do not match specific target
networks. The purpose of the example networks is to exemplify
the applicability of the transition mechanisms described in this
document to a number of different situations with different
prerequisites.
The sample network layout will be the same in all network examples.
The network examples should be viewed as specific representations of
a generic network with a limited number of network devices. A small
number of routers have been used in the network examples. However,
because the network examples follow the implementation strategies
recommended for the generic network scenario, it should be possible
to scale the examples to fit a network with an arbitrary number, e.g.
several hundreds or thousands, of routers.
The routers in the sample network layout are interconnected with each
other as well as with another ISP. The connection to another ISP can
be either direct or through an exchange point. In addition to these
connections, a number of customer connection networks are also
connected to the routers. Customer connection networks can be, for
example, xDSL or cable network equipment.
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ISP1 | ISP2
+------+ | +------+
| | | | |
|Router|--|--|Router|
| | | | |
+------+ | +------+
/ \ +-----------------------
/ \
/ \
+------+ +------+
| | | |
|Router|----|Router|
| | | |
+------+ +------+\
| | \ | Exchange point
+------+ +------+ \ +------+ | +------+
| | | | \_| | | | |--
|Router|----|Router|----\|Router|--|--|Switch|--
| | | | | | | | |--
+------+ /+------+ +------+ | +------+
| / | |
+-------+/ +-------+ |
| | | |
|Access1| |Access2|
| | | |
+-------+ +-------+
||||| ||||| ISP Network
----|-----------|----------------------
| | Customer Networks
+--------+ +--------+
| | | |
|Customer| |Customer|
| | | |
+--------+ +--------+
Figure 3: ISP Sample Network Layout.
8.1 Example 1
Example 1 presents a network built according to the sample network
layout with a native IPv4 backbone. The backbone is running IS-IS and
IBGP as routing protocols for internal and external routes,
respectively. MBGP is used to exchange routes over the connections to
ISP2 and the exchange point. Multicast using PIM-SM routing is
present. QoS using DiffServ is deployed.
Access 1 is xDSL connected to the backbone through an access
router. The xDSL equipment, except for the access router, is
considered to be layer 2 only, e.g., Ethernet or ATM. IPv4 addresses
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are dynamically assigned to the customer using DHCP. No routing
information is exchanged with the customer. Access control and
traceability are preformed in the access router. Customers are
separated into VLANs or separate ATM PVCs up to the access router.
Access 2 is Fiber to the building or home (FTTB/H) connected directly
to the backbone router. This is considered to be layer-3-aware,
because it is using layer 3 switches and it performs access control
and traceability through its layer 3 awareness by using DHCP
snooping. IPv4 addresses are dynamically assigned to the customers
using DHCP. No routing information is exchanged with the customer.
The actual IPv6 deployment might start by enabling IPv6 on a couple
of backbone routers, configuring tunnels between them (if not
adjacent), and connecting to a few peers or upstream providers
(either through tunnels or at an internet exchange).
After a trial period, the rest of the backbone is upgraded to dual-
stack, and IS-IS without multi-topology extensions (the upgrade order
is considered with care) is used as an IPv6 and IPv4 IGP. When
upgrading, it's important to note that until IPv6 customers are
connected behind a backbone router, the convexity requirement is not
critical: the routers just will not be able to be reached using IPv6.
That is, a software supporting IPv6 could be installed even though
the routers would not be used for (customer) IPv6 traffic yet. That
way, IPv6 could be enabled in the backbone on a need-to-enable basis
when needed.
Separate IPv6 BGP sessions are built, similar to IPv4. Multicast
(through SSM and Embedded-RP) and DiffServ are offered at a later
phase of the network, e.g., after a year of stable IPv6 unicast
operations.
Customers (with some exceptions) are not connected using a tunnel
broker, because offering native service faster is considered more
important -- and then there will not be unnecessary parallel
infrastructures to tear down later on. However, a 6to4 relay is
provided in the meantime for optimized 6to4 connectivity. xDSL
equipment, operating as bridges at Layer 2 only, do not require
changes in CPE: IPv6 connectivity can be offered to the customers by
upgrading the PE router to IPv6. In the initial phase, only Router
Advertisements are used; DHCPv6 Prefix Delegation can be added as the
next step if no other mechanisms are available.
The FTTB/H access has to be upgraded to support access control and
traceability in the switches, probably by using DHCP snooping or a
similar IPv6 capability, but it also has to be compatible with prefix
delegation and not just address assignment. This could, however, lead
to the need to use DHCPv6 for address assignment.
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8.2 Example 2
In example 2 the backbone is running IPv4 with MPLS and is using OSPF
and IBGP are for internal and external routes respectively. The
connection to ISP2 and the exchange point run BGP to exchange routes.
Multicast and QoS are not deployed.
Access 1 is a fixed line, e.g., fiber, connected directly to the
backbone. Routing information is in some cases exchanged with CPE at
the customer's site; otherwise static routing is used. Access 1 can
also be connected to BGP/MPLS-VPN running in the backbone.
Access 2 is xDSL connected directly to the backbone router. The xDSL
is layer 2 only, and access control and traceability are achieved
through PPPoE/PPPoA. PPP also provides address assignment. No routing
information is exchanged with the customer.
IPv6 deployment might start with an upgrade of a couple of PE routers
to support [BGPTUNNEL], because this will allow large-scale IPv6
support without hardware or software upgrades in the core. In a later
phase, perhaps years later, IPv6 traffic would run natively in the
whole network. In that case IS-IS or OSPF could be used for the
internal routing, and a separate IPv6 BGP session would be run.
For the fixed-line customers the CPE has to be upgraded and prefix
delegation using DHCPv6 or static assignment would be used. An IPv6
MBGP session would be used when routing information has to be
exchanged. In the xDSL case the same conditions for IP-tunneling as
in Example 1 apply. In addition to IP-tunneling an additional PPP
session can be used to offer IPv6 access to a limited number of
customers. Later, when clients and servers have been updated, the
IPv6 PPP session can be replaced with a combined PPP session for both
IPv4 and IPv6. PPP has to be used for address and prefix assignment.
8.3 Example 3
A transit provider offers IP connectivity to other providers, but
not to end users or enterprises. IS-IS and IBGP are used internally
and BGP externally. Its accesses connect Tier-2 provider cores. No
multicast or QoS is used.
Even though the RIR policies on getting IPv6 prefixes require the
assignment of at least 200 /48 prefixes to the customers, this type
of transit provider obtains an allocation nonetheless, as the number
of customers their customers serve is significant. The whole backbone
can be upgraded to dual-stack in a reasonably rapid pace after
trialing it with a couple of routers. IPv6 routing is performed
using the same IS-IS and separate IPv6 BGP sessions.
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The ISP provides IPv6 transit to its customers for free, as a
competitive advantage. It also provides, at the first phase only, a
configured tunnel service with BGP peering to the significant sites
and customers (those with an AS number) which are the customers of
its customers whenever its own customer networks are not offering
IPv6. This is done both to introduce them to IPv6 and to create a
beneficial side-effect: a bit of extra revenue is generated from its
direct customers as the total amount of transited traffic grows.
9. Security Considerations
This document analyses scenarios and identifies some transition
mechanisms that could be used for the scenarios. It does not
introduce any new security issues. Security considerations of each
mechanism are described in the respective documents.
However, a few generic observations are in order.
o introducing IPv6 adds new classes of security threats or
requires adopting new protocols or operational models
than with IPv6; typically these are generic issues, and
to be further discussed in other documents, for example,
[V6SEC].
o the more complex the transition mechanisms employed become,
the more difficult it will be to manage or analyze their
impact on security; consequently, simple mechanisms are to
be preferred.
o this document has identified a number of requirements for
analysis or further work which should be explicitly considered
when adopting IPv6: how to perform access control over
shared media or shared ISP customer connection media,
how to manage the configuration management security on such
environments (e.g., DHCPv6 authentication keying), and
how to manage customer traceability if stateless address
autoconfiguration is used.
10. Acknowledgements
This draft has greatly benefited from inputs by Marc Blanchet, Jordi
Palet, Francois Le Faucheur and Cleve Mickles. Special thanks to
Richard Graveman for proofreading the document.
11. Informative References
[EMBEDRP] Savola, P., Haberman, B., "Embedding the Address of
RP in IPv6 Multicast Address" -
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Work in progress
[MTISIS] Przygienda, T., Naiming Shen, Nischal Sheth, "M-
ISIS: Multi Topology (MT) Routing in IS-IS"
Work in progress
[RFC 2858] T. Bates, Y. Rekhter, R. Chandra, D. Katz,
"Multiprotocol Extensions for BGP-4"
RFC 2858
[RFC 2545] P. Marques, F. Dupont, "Use of BGP-4 Multiprotocol
Extensions for IPv6 Inter-Domain Routing"
RFC 2545
[BCP38UPD] F. Baker, P. Savola "Ingress Filtering for
Multihomed Networks"
Work in progress
[RFC3582] J. Abley, B. Black, V. Gill, "Goals for IPv6 Site-
Multihoming Architectures"
RFC 3582
[RFC3178] J. Hagino, H. Snyder, "IPv6 Multihoming Support at
Site Exit Routers"
RFC 3178
[BGPTUNNEL] J. De Clercq, G. Gastaud, D. Ooms, S. Prevost,
F. Le Faucheur "Connecting IPv6 Islands across IPv4
Clouds with BGP"
draft-ooms-v6ops-bgp-tunnel-00.txt
[DUAL ACCESS] Y. Shirasaki, S. Miyakawa, T. Yamasaki, A. Takenouchi
"A Model of IPv6/IPv4 Dual Stack Internet Access
Service"
Work in progress
[UNMANCON] T.Chown, R. van der Pol, P. Savola, "Considerations
for IPv6 Tunneling Solutions in Small End Sites"
Work in progress
[UNMANEVA] C. Huitema, R. Austein, S. Satapati, R. van der Pol,
"Evaluation of Transition Mechanisms for Unmanaged
Networks"
Work in progress
[PROTO41] J. Palet, C. Olvera, D. Fernandez, "Forwarding
Protocol 41 in NAT Boxes"
Work in progress
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[V6SEC] P. Savola, "IPv6 Transition/Co-existence Security
Considerations"
Work in progress
Authors' Addresses
Mikael Lind
TeliaSonera
Vitsandsgatan 9B
SE-12386 Farsta, Sweden
Email: mikael.lind@teliasonera.com
Vladimir Ksinant
6WIND S.A.
Immeuble Central Gare - Bat.C
1, place Charles de Gaulle
78180, Montigny-Le-Bretonneux - France
Phone: +33 1 39 30 92 36
Email: vladimir.ksinant@6wind.com
Soohong Daniel Park
Mobile Platform Laboratory, SAMSUNG Electronics.
416, Maetan-3dong, Paldal-Gu,
Suwon, Gyeonggi-do, Korea
Email: soohong.park@samsung.com
Alain Baudot
France Telecom R&D
42, rue des coutures
14066 Caen - FRANCE
Email: alain.baudot@rd.francetelecom.com
Pekka Savola
CSC/FUNET
Espoo, Finland
EMail: psavola@funet.fi
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