Internet DRAFT - draft-fleischhauer-ipv4-addr-saving
draft-fleischhauer-ipv4-addr-saving
Internet Engineering Task Force K. Fleischhauer, Ed.
Internet-Draft O. Bonness
Intended status: Informational Deutsche Telekom AG
Expires: August 31, 2012 February 28, 2012
draft-fleischhauer-ipv4-addr-saving-02
On demand IPv4 address provisioning in Dual-Stack PPP deployment
scenarios
Abstract
Today the Dual-Stack approach is the most straightforward and the
most common way for introducing IPv6 into existing systems and
networks. However a typical drawback of implementing Dual-Stack is
that each node will still require at least one IPv4 address. Hence,
solely deploying Dual-Stack does not provide a sufficient solution to
the IPv4 address exhaustion problem. Assuming a situation where most
of the IP communication (e.g. always-on, VoIP etc.) can be provided
via IPv6, the usage of public IPv4 addresses can significantly be
reduced and the unused public IPv4 addresses can under certain
circumstances be returned to the public IPv4 address pool of the
service provider. New Dual-Stack enabled services can be introduced
without increasing the public IPv4 address demand, when IPv6 will be
the preferred network layer protocol. This document describes such a
solution in a Dual-Stack PPP session network scenario and explains
the protocol mechanisms which are used.
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 August 31, 2012.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
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document authors. All rights reserved.
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Table of Contents
1. Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. Problem Statement and Purpose of IPv4 address efficiency . . . 4
2.1. Illustrative service provider use case . . . . . . . . . . 5
2.2. Architecture and Communication in a PPP Dual-Stack
environment . . . . . . . . . . . . . . . . . . . . . . . 6
2.3. The advantage of the dynamic IPv4 address assigning
feature . . . . . . . . . . . . . . . . . . . . . . . . . 8
3. Specification . . . . . . . . . . . . . . . . . . . . . . . . 9
3.1. Definition of the participating elements and their
functionalities . . . . . . . . . . . . . . . . . . . . . 10
3.2. Assigning IPv4 address parameter on-demand after
establishing PPP session with IPv6 connectivity . . . . . 11
3.3. Releasing unused IPv4 address parameters . . . . . . . . . 13
3.4. Timer Considerations . . . . . . . . . . . . . . . . . . . 14
4. Potential for optimization . . . . . . . . . . . . . . . . . . 14
4.1. Avoiding unnecessary load on NAS and AAA . . . . . . . . . 14
4.2. Reducing IPv4 traffic on external interfaces . . . . . . . 15
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
7. Security Considerations . . . . . . . . . . . . . . . . . . . 16
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
8.1. Normative Reference . . . . . . . . . . . . . . . . . . . 16
8.2. Informative References . . . . . . . . . . . . . . . . . . 17
Appendix A. Workplan . . . . . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18
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1. Abstract
The Dual-Stack approach as defined in [RFC4213] provides the most
straightforward and most common way for introducing IPv6 [RFC2460]
into existing systems and networks. However a typical drawback of
the Dual-Stack approach is that each network node will still require
at least one IPv4 [RFC0791] address. Assuming a situation where most
of the IP communication (e.g. always-on, VoIP etc.) can be provided
via IPv6, the usage of public IPv4 addresses can be reduced
significantly and the unused public IPv4 addresses may be returned to
the public IPv4 address pool of the provider. This document
describes how such a solution can be realised in a Dual-Stack PPP
session scenario and details the protocol mechanisms of the solution
which are also thought as contribution to [BBF-WT-242].
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]
2. Problem Statement and Purpose of IPv4 address efficiency
The Broadband Forum describes in [BBF-TR-187] a target IPv4/IPv6
Dual-Stack Architecture (assuming native implementation of IPv6).
TR-187 builds on the capabilities of existing protocols such as
Point-to-Point Protocol (PPP) [RFC1332] and Layer 2 Tunnelling
Protocol (L2TP) [RFC2661] to provide IPv6 service in addition to
today's IPv4 service. These protocols allow the parallel usage of
IPv4 and IPv6 within a single PPP respectively L2TP session. Usually
in such a scenario the service provider offers to the customer the
usage of public IPv4 and IPv6 address resources during the duration
of the PPP session. Because of the potential parallel usage of IPv4
and IPv6 within such a Dual-Stack PPP scenario a public IPv4 address
is always provisioned, also in the case where most of the
communication is running on top of IPv6. This document extends the
sketched Dual-Stack deployment scenario for PPP and L2TPv2 with a
mechanism that allows a temporary assignment and a release of an
unused IPv4 address within such a Dual-Stack capable PPP session
scenario. This approach covers also situations where the IPv4
address may only be provided on-demand later on, after initiating the
Dual-Stack PPP session with an IPv6 context only.
Basically the here described mechanism is also applicable in cable
and mobile networks. The corresponding DOCSIS and 3GPP standards may
be adapted as a follow-on work to this draft later on.
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2.1. Illustrative service provider use case
In order to illustrate the applicability and usefulness of the
proposed "On demand IPv4 address provisioning" mechanism an
illustrative network provider use case should be sketched here. Lets
assume a network access and service provider which is offering Dual-
Stack services via a single PPP connection to its customers.
Independently of the concrete subscribed customer service (Single,
Play, Double Play etc.) all customers should be produced and
provisioned in the same way in order to keep the network operation
costs and the network complexity as low as possible. Lets assume
furthermore that the above mentioned network access and service
provider has already migrated its VoIP service to IPv6, so that all
Single play (VoIP) customers do only need IPv6 connectivity and have
no need for an IPv4 context within their Dual-Stack PPP session.
However, the standard Dual-Stack PPP connection set-up today
initiates an IPCP and as well as an IPCPv6 negotiation independently
of the concrete need for IPv4 and/or IPv6 connectivity, so that after
a successful Dual-Stack PPP connection establishment the PPP client
site is provisioned with a complete set of IPv6 and IPv4 connection
parameters. As a consequence in our example, the whole Single Play
customer base of the network access and service provider has also
been provisioned with public IPv4 addresses, although these customers
will never need IPv4 Internet connectivity during the whole lifetime
of their PPP session. Hence a huge amount of unneeded and
potentially unused IPv4 addresses has been wasted, that should be
better kept in the provider address pool and delegated to other
customers that really need IPv4 connectivity. In order to allow a
more dynamic and on-demand provisioning of IPv4 parameters within
Dual-Stack PPP sessions, a new mechanism is needed, that requests and
also releases IPv4 addresses on-demand when they are really needed
during the PPP session lifetime. Such a mechanism is proposed and
described within this document.
(An additional advantage of such an on-demand IPv4 address releasing
and provisioning mechanism consists in the fact that a very easy to
operate and dynamic change customer profiles (e.g. upgrade of Single
Play customers to Double Play services and vice versa) becomes
possible with only minor changes to the customer service profile in
the AAA platform of the service provider - no changes in he CPE or
NAS port configuration are needed. Besides that, this dynamic on-
demand IPv4 address provisioning and releasing approach allows it to
share one public IPv4 address timely sequential between a bunch of
customers.)
The following sections will describe the basic network architecture
and the "On demand IPv4 address provisioning" mechanisms in more
detail.
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2.2. Architecture and Communication in a PPP Dual-Stack environment
Assuming a Dual-Stack network access via PPP, end devices can in
general communicate via IPv4 and/or IPv6 transport, depending on
their own and their IP communication partners capabilities. The
actual usage of IPv4 or IPv6 or both protocols depends on the
capabilities of
o the IP communication endpoints (e.g. protocol stack, applications,
configuration of the preferences etc.),
o the network deployment itself and also on
o the used communication services (like e.g. VoIP).
The last two points are mainly in responsibility of the network and
service provider. The approach, sketched in this document, is based
on the assumption that the customer starts a Dual-Stack PPP session
in "IPv6-only" mode and "adds" IPv4 later on only in the case that
applications or services explicitly request IPv4 connectivity. When
IPv4 connectivity is not needed during the whole time of PPP network
connectivity than a continuous provisioning of a global IPv4 address
to the customer device (e.g. end system, CPE etc.) is not necessary.
Therefore mechanisms are needed to provision and release public IPv4
addresses for Dual-Stack PPP sessions dynamically and on-demand.
The goal of the solution sketched in this document, is to limit and
decrease the public IPv4 address pool size of the PPP network access
provider. Assuming that always-on services are reachable via IPv6, a
Dual-Stack capable PPP connected device should per default request
IPv4 address parameters only on demand, when the need for
establishing IPv4 connectivity has explicitly been detected and IPv4
traffic towards the PPP WAN interface (e.g. of a CPE) is intended.
As already described above it is sufficient, when initially only IPv6
address parameters are provisioned to the PPP customer endpoint (e.g.
end systems, Home Gateway, CPE).
This means as a consequence that a customer device does not initially
start a complete Dual-Stack PPP session but an "IPv6 only" PPP
session. The IPv4 part of the complete Dual-Stack is initiated later
on only in the case that IPv4 connectivity is explicitly requested.
The figure below illustrates the network architecture of a PPP Dual-
Stack environment for providing Internet access to residential
customers.
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| +------------+ |
| | external | |
| | Address | |
| | Pool | |
| | Management | |
| +------------+ |
| service | provider |
| AAA | area |
+-------+ +--------------|--------------+
|Private|__ |
| Host |_ \IPv4 |
| 1 | \ \ +-------------+ |
+-------+ \ \ | CPE | IPv4 |
\ \ | App | over |
IPv6\ \_+------+------+ PPP +---------+ IPv4 +--------+
\__| CPE | CPE |--------| NAS |--------| Public |
__|Router| PPP | | (PPP | | Host |
/ _| | Peer |--------| Peer) |--------| n |
IPv6/ / +------+------+ IPv6 +---------+ IPv6 +--------+
/ / over
+-------+ / / PPP
|Private|_/ /
| Host |__/IPv4
| n |
+-------+
\_______________________/\__________________________________________/
Private Internet Public Internet
Figure 1: PPP Dual-Stack architecture
This abstract network topology consists of 3 major components:
1. Private Internet (aka. Customer LAN)
2. Public Internet
3. Service Provider AAA area
The Private Internet as defined in [RFC1918] is the local area
network on customer site wherein IPv4 and IPv6 communication are
used. From this document point of view the Private Internet is an
optional part of the PPP Dual-Stack architecture. Within this
Private Internet (Customer LAN) exist one or more private hosts which
are connected to the local area network interfaces of the Customer
Premise Equipment. These hosts can have IPv4-only, IPv6-only or
Dual-Stack communication capabilities. For an IPv6 communication
inside the Customer LAN Link-local, Unique Local or/and public IPv6
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addresses may be used. For an IPv6 communication to the public
Internet public IPv6 addresses have to be used. For an IPv4
communication within the Customer LAN and to the public Internet it
is assumed that private IPv4 addresses are used by the private hosts.
In order to ensure an IPv4 communication between the private hosts of
the Customer LAN and the public Internet the CPE must hence provide
IPv4 Network Address Translation (NAT44) functionality and has to map
the private IPv4 addresses of the private hosts to a public IPv4
address of the WAN interface of CPE NAT device and vice versa. The
NAT functionality on the CPE is the border element between the
private IPv4 Internet (aka. Customer LAN) and the public IPv4
Internet. In the case of using public IPv6 addresses for the
communication between Customer LAN hosts and the Internet the CPE and
its interfaces are an integral part of the IPv6 End-to-End public
Internet architecture.
To the public Internet belong the Access Network of the service
provider and all other networks outside the customer LAN that are
addressed with global IPv4 and / or IPv6 addresses and can be
accessed from the private Internet as well as from other systems
within the public Internet.
The focus of this draft is mainly directed to the access network of
the service provider where in our scenario PPP is used between the
CPE and the provider Network Access Server (NAS) in order to provide
public Internet access to the customer.
The Service Provider AAA area is a network which consists of several
systems to control the Network Access Server (NAS) and to provide AAA
functionalities in order to reduce the load on the NAS. Such Service
Provider AAA functionalities include also management of the public
IPv4 and public IPv6 address pools inside the NAS and can hence also
be integrated directly into the NAS.
2.3. The advantage of the dynamic IPv4 address assigning feature
The dynamic IPv4 address assigning approach, sketched in this
document, is based on the assumption that the customer CPE initiates
a PPP session based on IPv6 and adds IPv4 later on only if certain
IPv4 applications or services require explicit IPv4 connectivity. A
particular public IPv4 address can therefore be assigned sequentially
to different customers for the lifetime of their IPv4 PPP connection
and has not to be bound to a single customer for the whole lifetime
of the Dual-Stack PPP session. This sequential assignment of public
IPv4 addresses enables a smoother IPv4-to-IPv6 migration in
comparison to other IPv4-to-IPv6 migration approaches that are based
on Carrier Grade NATs in service provider network or shared IPv4
addresses. The customer will be provisioned with a public IPv4
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address only in the case when global IPv4 connectivity is really
needed and will not be provisioned with an IPv4 address per default
when the Dual-Stack PPP session is initiated. Furthermore, a
provisioned IPv4 address can be released (e.g. after a certain time
interval) in the case that the CPE detects that there is no need any
more for global IPv4 connectivity. In other words, when global IPv4
connectivity is not needed during the whole time of the Dual-Stack
PPP session then a (continuous) provisioning of a public IPv4 address
to the CPE is not necessary and the provisioning of a public IPv4
address can be done on-demand and dynamically.
Hence, one of the main achievement of this mechanism is to limit and
decrease the pool size for public IPv4 addresses at the service
provider site.
A similar effect in limiting and decreasing the IPv4 address demand
could also be reached by using separate PPP sessions for IPv4 and
IPv6. But in that case the following problems occur:
o For each additional PPP session additional AAA parameters have to
be created and handled which leads to an extension of AAA domains
and more complex processes.
o Each additional PPP session will require additional resources on
the PPP endpoints (e.g. for handling additional customer
credentials) also in devices that act as PPP intermediate agents.
o Accounting and controlling of traffic classes on an access line or
customer base will be impeded or at least complicated.
Because of these reasons the introduction of an additional PPP
session for IPv6 as additional network layer protocol on a access
line with an additional PPP session is not recommended.
3. Specification
As defined in RFC 2661 [RFC2661] PPP and L2TP provide the following
main functionalities:
1. A method for encapsulating datagrams over serial links.
2. A Link Control Protocol (LCP) for establishing, configuring, and
testing the data-link connection.
3. (Optional) Authentication Protocol for one or both peers.
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4. A family of Network Control Protocols (NCPs) for establishing and
configuring different network-layer protocols.
For provisioning of IPv4 or IPv6 communication parameters (e.g.
addresses, DNS resolver) as network-layer protocols only the NCPs
Internet Protocol (Version 4) Control Protocol (IPCP) RFC 1332
[RFC1332] and Internet Protocol (Version 6) Control Protocol (IPV6CP)
RFC 2472 [RFC2472] are used. Whereas IPCP is responsible for
configuring, enabling, and disabling the IPv4 protocol modules on
both ends of the point-to-point link, IPV6CP is responsible for
configuring, enabling, and disabling the IPv6 protocol modules on
both ends of the point-to-point link. Once one of both network-layer
protocols has been configured, datagrams belonging to this network-
layer protocol can be sent over the PPP link. Both NCP protocol
mechanisms act independent of each other (see also requirement WLL-3
in [RFC6204]) and can be used to establish and pull-down IPv4 and
IPv6 connection contexts within a Dual-Stack PPP session
independently.
As an example an implementation that wishes to close a dedicated NCP
connection (e.g. IPCP or IPv6CP) SHOULD transmit a Terminate-Request
to the peer. Upon reception of a Terminate-Request, a Terminate-Ack
MUST be transmitted to the sender of the Terminate-Request. The PPP
session itself and the other NCP connection inside the PPP session
will remain existent. Only in the case that both NCP connections are
closed, the Dual-Stack PPP session will be terminated.
3.1. Definition of the participating elements and their functionalities
This chapter identifies the network elements that are involved in the
message flows to enable the on-demand IPv4 address provisioning
functionality and describes their functionalities related to this
mechanism.
o Customer Edge Router (CER aka. CPE)/End System
Within the context of this document the CER/End System is any device
implementing a Dual-Stack PPP stack and acting as a PPP client to the
PPP server in the service provider network in order to achieve
connectivity to the service provider network. In the case of a
Customer Edge Router (CER) this is a node (e.g. intended for home or
small office usage) which forwards IPv4 and IPv6 packets those are
not explicitly addressed to itself between the Local Area Network and
WAN interface. The CER itself is separated into three devices or
functional blocks, one that carries the PPP session (e.g. a
standalone DSL modem), one that is operating simply as a local router
which includes the NAPT44 function and any IPV6 PD/ND, DHCPv6 and
DHCP for both stacks and one which includes the local CPE
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functionalities (e.g. DNS forwarder/cache, VoIP Clients). The PPP
interface of this device is also called WAN (Wide Area Network)
interface [RFC6204]. In the case of IPv4 an additional Network
Address Translation (NAT) functionality is implemented on the router
part. So within the Local Area Network private IPv4 addresses can be
used as defined in [RFC1918]. Therefore the demand for global IPv4
connectivity of such a Customer Edge Router will be triggered either
by own applications or by receiving IPv4 packets on its customer
network facing interfaces that are addressed to the public Internet.
In the case of an End System, this system is a node that intends to
send IPv4 and/or IPv6 packets. On an End System the IPv4
connectivity demand can only be triggered by own applications.
However, in both cases (CER or End system) the IPv4_idle_timer
resides on the WAN interface in order to detect IPv4 packets passing
the WAN interface (incoming/ outgoing) and to measure the related
IPv4 idle time when no IPv4 packet has been sent or received.
o Network Access Server (NAS)/Layer 2 Network Server (LNS)
The Network Access Server (NAS) is a device providing local Dual-
Stack PPP connectivity to the Service Provider network and acting as
a PPP server to the PPP client on the Customer Edge Router or
customer end system. Within a RFC 2661 architecture the PPP server
within the service provider network is the L2TP Network Server (LNS).
The address pool management can be provided locally on the NAS/LNS or
remotely. In the case of a local address pool management no
information exchange to an external address pool management system is
needed in order to assign or release IPv4 addresses. In the case of
an external address pool management an information exchange between
the NAS/LNS and the address pool management system is required.
o External Address Pool Management
External Address Pool Management is used in the case when no local
Address Pool Management system is implemented in the NAS/LNS. In
this case it is necessary that the NAS/LNS communicates with an
External Address Pool Management System for signalling assignment or
release of IPv4 addresses. RADIUS as specified in [RFC2865] or
DIAMETER as specified in [RFC3588] can be used as protocol between
NAS/LNS and the External Address Pool Management System.
3.2. Assigning IPv4 address parameter on-demand after establishing PPP
session with IPv6 connectivity
A PPP client implementation wishing to open a connection MUST
transmit a NCP Configure-Request to the PPP server. If every
Configuration Option received in a NCP Configure-Request is
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recognizable and all values are acceptable, then the PPP server
implementation MUST transmit a NCP Configure-Ack to the initiator of
the NCP Configure-Request.
Applied to the above sketched Dual-Stack PPP session use case the
configuration and enabling of the IPv6 protocol module will be done
immediately after a successful LCP data link configuration (and maybe
successful authentication) of the PPP session. Assuming that this
IPCPv6 configuration exchange finished successfully the PPP session
is now established and operational containing an IPv6-only network
layer connection.
Separately from that, the IPv4 protocol module can (later on and
dynamically on-demand) be configured and enabled using IPCP. However
this SHALL only be done in the case that an IPv4 connectivity demand
has been detected on the PPP customer end system or CPE (PPP client).
Therefore the NAS MUST not initiate the negotiation of IPCP.
The following diagram illustrates the appropriate IPCP (and
accounting) message exchange that is needed to configure the IPv4
protocol modules of an existing (Dual-Stack) PPP session on-demand.
CPE/End System NAS ext. Address
(PPP Peer) (PPP Peer) Pool management
(if necessary)
| | |
1. ->| | |
2. |-IPCP-Configure-Request->| |
3. | |----Access-Request--->|
4. | |<---Access-Accept-----|
5. |<-IPCP-Configure-Request-| |
6. |---IPCP-Configure-Ack--->| |
7. |<--IPCP-Configure-Nack---| |
8. |-IPCP-Configure-Request->| |
9. |<---IPCP-Configure-Ack---| |
10. | |--Accounting-Request->|
11. | |<---Accounting-Resp.--|
Figure 2: Message flow for assigning IPv4 address parameter
In the diagram above, the CPE/End System is triggered (1) to set up
IPv4 connectivity via an already existing PPP session. The CPE/End
System detects that there is no public IPv4 address for its WAN
interface available and starts the negotiation of the needed IPv4
address parameter by sending an IPCP Configure-Request to the NAS
(2). The NAS will request the corresponding IPv4 connectivity
parameters (e.g. IPv4 address, DNS resolver address) from a local
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(e.g. within the NAS) or remote database representing the Address
Pool Management System(e.g. via RADIUS/DIAMETER) (3, 4). After this
the PPP peers use the standard IPCP procedures to finalize the IPv4
address parameter negotiation (5, 6, 7, 8, 9). After the successful
provisioning of the IPv4 address parameter the CPE/End system has
full global IPv4 connectivity and can proceed with the IPv4
communication (in parallel to IPv6). In case of an external Address
Pool Management, the NAS will send an Accounting-Request message (10)
to the external Address Pool Management System in order to signal the
successful negotiation of the IPv4 address parameter. The external
Address Pool Management System will answer with an Accounting-
Response (11) message.
3.3. Releasing unused IPv4 address parameters
An implementation wishing to close a dedicated NCP connection (e.g.
IPCP or IPv6CP) SHOULD transmit a Terminate-Request to the peer.
Upon reception of a NCP Terminate-Request, a Terminate-Ack MUST be
transmitted to the sender of the Terminate-Request.
In the PPP Dual-Stack session scenario discussed here, the generation
of the Terminate-Request message for the IPCP part of the PPP Dual-
Stack session MUST be triggered by an IPv4 traffic idle timer within
the PPP client (e.g. end system, CPE). As long as there is still an
ongoing IPv6 connection within the PPP session, the PPP session MUST
be kept open. Equivalently, when no IPv6 connectivity is detected
the IPV6CP session can be terminated again by sending an IPv6CP
Terminate-Request and accepting this by a Terminate-Ack. Afterwards
the link layer connectivity and hence the whole PPP connection can be
terminated by exchanging the LCP Terminate-Request and Terminate-Ack
messages.
CPE/End System NAS ext. Address
(PPP Peer) (PPP Peer) Pool Management
| | |
1. ->| | |
2. |--IPCP-Termin.-Request-->| |
3. |<----IPCP-Termin.-Ack.---| |
4. | |-Interim-Acc.-Requ.-->|
5. | |<---Accounting-Resp.--|
Figure 3: Message flow for releasing IPv4 address parameter
The termination of an IPCP connection within a Dual-Stack PPP session
is illustrated in figure 3 above.
For this exemplary message flow it is assumed that there is still an
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IPV6CP connection active inside the Dual-Stack PPP session. After
the expiration of the IPv4 traffic idle timer (1) the CPE/End system
sends an IPCP terminate request to the peer (2). The request will be
answered with an Terminate-Ack message (3). The IPv4 address can be
returned to the local address pool (e.g. within the NAS) or to the
remote IPv4 address pool by sending Interim-Accounting messages (4,
5) (e.g. via RADIUS/DIAMETER).
3.4. Timer Considerations
IPv4_Idle_Timer
The sending of the Terminate-Request message MUST be triggered by an
IPv4 traffic idle timer within the PPP client (e.g. end system, CPE).
The timer value MUST be configurable to adopt the mechanism due to
the needs of the applications which are using IPv4 and with respect
to an optimization of the IPv4 address saving potential.
4. Potential for optimization
The efficiency of the "On demand IPv4 address provisioning" mechanism
can be measured in the ratio of IPCP/RADIUS/DIAMETER signalling
traffic to the amount of the saved global IPv4 addresses. Hence
different options to optimize the efficiency of the proposed solution
are possible, by supressing unnecessary signalling load and blocking
forbidden IPv4 connectivity requests.
4.1. Avoiding unnecessary load on NAS and AAA
Unnecessary signalling load between PPP peers as well as between NAS
and external Address Pool Management can for instance occur when a
IPv6-only customer requests IPv4 address parameter. This can be
prevented by restricting the usage of a Dual-Stack CPE/CER for IPv6-
only customers to IPv6 only and/or by administratively refusing the
IPCP configure requests of such an IPv6-only customer inside the NAS.
The former case is more or less a business and customer relationship
related issue which needs no engineering concepts.
The latter case can be solved by answering an IPCP Configure Request
message from a IPv6-only customer with a LCP reject message as
described in chapter 5.7 of [RFC1661]. The field Rejected-Protocol
of the LCP reject message contains the value 0x8021 for IPCP and the
Rejected-Information field contains a copy of the IPCP packet which
is being rejected. Due to [RFC1661] upon reception of a Protocol-
Reject, the implementation of the IPv4 capable CER/CPE of the IPv6-
only customer MUST immediately stop sending packets of the indicated
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protocol at the earliest opportunity. So the transmission of
unnecessary IPCP and RADIUS messages during the running PPP session
should be prevented.
Another opportunity to reduce IPCP signalling load and the
corresponding signalling overhead between NAS and external Address
Pool Management is the definition of default IPv4 traffic idle timer
values for always-on applications that are sending periodic messages
(see chapter 3.3). The value of this IPv4 traffic idle timer should
be chosen a bit larger than the interval between periodic messages of
always-on applications. Such an approach avoids problems for these
applications when IPv4 is used and optimize IPv4 address release and
address assign message exchange. Very short and periodic IPv4
address renewal cycles can be avoided by such an approach.
4.2. Reducing IPv4 traffic on external interfaces
The easiest way to reduce IPv4 traffic demand (and hence the need for
public IPv4 addresses) is to shift applications from usage of IPv4 to
IPv6. In using the Dual-Stack approach which is a prerequisite of
the here described mechanism no differences regarding the service
level of both protocols are expected. Each service can be provided
with the same quality level independently of the chosen version of
the Internet Protocol.
But regarding applications on end systems the Internet access
provider has only very limited influence. However for applications
and services running on the CER/CPE itself (e.g. VoIP User Agent)
the internet access provider should be able to define and require
their IPv6 readiness.
An additional point is the preferred usage of IPv6 on all external
(WAN) interfaces in the case when the CPE/CER acts as a relay and
caches on behalf of certain protocols (e.g. DNS). When on a LAN
interface a request message for such a protocol is received via IPv4
and a relaying to the external WAN interface is needed IPv6 should be
the preferred network protocol. Such a requirement has already been
defined for relaying/caching devices in [BBF-TR-124-i2] (section
LAN.DNSv6, item 6).
5. Acknowledgements
The author and contributors also wish to acknowledge the assistance
and feedback of the following individuals or groups.
Tina Tsou
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Alain Durand
Sven Schmidtke
Dan Wing
Vernon Schryer
Mark Townsley
Wesley George
Joel M. Halpern
6. IANA Considerations
This memo includes no request to IANA.
TBD.
All drafts are required to have an IANA considerations section (see
Guidelines for Writing an IANA Considerations Section in RFCs
[RFC5226] for a guide). If the draft does not require IANA to do
anything, the section contains an explicit statement that this is the
case (as above). If there are no requirements for IANA, the section
will be removed during conversion into an RFC by the RFC Editor.
7. Security Considerations
TBD.
All drafts are required to have a security considerations section.
See RFC 3552 [RFC3552] for a guide.
8. References
8.1. Normative Reference
[BBF-TR-124-i2]
Broadbandforum, "Functional Requirements for Broadband
Residential Gateway Devices (Issue 2)", May 2010.
[BBF-TR-187]
Broadbandforum, "Technical Report TR187 IPv6 over PPP
Broadband Access (Issue 1)", May 2010.
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[BBF-WT-242]
Broadbandforum, "Draft WT-242 IPv6 Transition Mechanisms
for Broadband Networks".
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
September 1981.
[RFC1332] McGregor, G., "The PPP Internet Protocol Control Protocol
(IPCP)", RFC 1332, May 1992.
[RFC1661] Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51,
RFC 1661, July 1994.
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, February 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC2472] Haskin, D. and E. Allen, "IP Version 6 over PPP",
RFC 2472, December 1998.
[RFC2661] Townsley, W., Valencia, A., Rubens, A., Pall, G., Zorn,
G., and B. Palter, "Layer Two Tunneling Protocol "L2TP"",
RFC 2661, August 1999.
[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)",
RFC 2865, June 2000.
[RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J.
Arkko, "Diameter Base Protocol", RFC 3588, September 2003.
[RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms
for IPv6 Hosts and Routers", RFC 4213, October 2005.
[RFC6204] Singh, H., Beebee, W., Donley, C., Stark, B., and O.
Troan, "Basic Requirements for IPv6 Customer Edge
Routers", RFC 6204, April 2011.
8.2. Informative References
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552,
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July 2003.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
Appendix A. Workplan
v00 2011-03-07 KF/OB initial version
v01 2011-09-06 adding figures + explanation + Feedback IETF80 &mail
discussion
v02 before IETF 82 review + feedback mail discussion
Authors' Addresses
Karsten Fleischhauer (editor)
Deutsche Telekom AG
Heinrich-Hertz-Strasse 3-7
64295 Darmstadt
DE
Phone: +49 6151 58 12831
Email: k.fleischhauer@telekom.de
Olaf Bonness
Deutsche Telekom AG
Winterfeldtstr. 21-27
10781 Berlin
DE
Phone: +49 30 835358826
Email: olaf.bonness@telekom.de
Fleischhauer & Bonness Expires August 31, 2012 [Page 18]
