wdiff rfc6908.original rfc6908.txt

Softwire
Internet Engineering Task Force (IETF) Y. Lee
Internet-Draft
Request for Comments: 6908 Comcast
Intended status:
Category: Informational R. Maglione
Expires: July 21, 2013 Telecom Italia
ISSN: 2070-1721 Cisco Systems
C. Williams
MCSR Labs
C. Jacquenet
M. Boucadair
France Telecom
January 17,
March 2013

Deployment Considerations for Dual-Stack Lite
draft-ietf-softwire-dslite-deployment-08

Abstract

This document discusses the deployment issues of and describes the requirements
for the deployment and operation of Dual-Stack Lite. Lite (DS-Lite). This
document describes the various deployment considerations and
applicability of the Dual-Stack Lite DS-Lite architecture.

Status of this This Memo

This Internet-Draft document is submitted in full conformance with the
provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents not an Internet Standards Track specification; it is
published for informational purposes.

This document is a product of the Internet Engineering Task Force
(IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list It represents the consensus of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a maximum candidate for any level of Internet
Standard; see Section 2 of RFC 5741.

Information about the current status of six months this document, any errata,
and how to provide feedback on it may be updated, replaced, or obsoleted by other documents obtained at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."

This Internet-Draft will expire on July 21, 2013.
http://www.rfc-editor.org/info/rfc6908.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.

Table of Contents

1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. AFTR Deployment Considerations . . . . . . . . . . . . . . . . 3
2.1. Interface Consideration . . . . . . . . . . . . . . . . . 3
2.2. MTU and Fragmentation Considerations . . . . . . . . . . . 4
2.3. Logging at the AFTR . . . . . . . . . . . . . . . . . . . 4
2.4. Blacklisting a Shared IPv4 Address . . . . . . . . . . . . 5
2.5. AFTR's Policies . . . . . . . . . . . . . . . . . . . . . 5
2.5.1. Outgoing Policy . . . . . . . . . . . . . . . . . . . 5
2.5.2. Incoming Policy . . . . . . . . . . . . . . . . . . . 6
2.6. AFTR Impacts on Accounting Process . . . . . . . . . . . . 6
2.7. Reliability Considerations of AFTR . . . . . . . . . . . . 7
2.8. Strategic Placement of AFTR . . . . . . . . . . . . . . . 8
2.9. AFTR Considerations for Geographically Aware Services . . 8
2.10. Impacts on QoS Policy . . . . . . . . . . . . . . . . . . 9
2.11. Port Forwarding Considerations . . . . . . . . . . . . . . 9
2.12. DS-Lite Tunnel Security . . . . . . . . . . . . . . . . . 10
2.13. IPv6-only IPv6-Only Network Considerations . . . . . . . . . . . . . 10
3. B4 Deployment Considerations . . . . . . . . . . . . . . . . . 11 10
3.1. DNS Deployment Considerations . . . . . . . . . . . . . . 11
3.2. IPv4 Service Monitoring . . . . . . . . . . . . . . . . . 11
3.2.1. B4 Remote Management . . . . . . . . . . . . . . . . . 11
3.2.2. IPv4 Connectivity Check . . . . . . . . . . . . . . . 12 11
4. Security Considerations . . . . . . . . . . . . . . . . . . . 12
5. Acknowledgement Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
7.1.
6.1. Normative References . . . . . . . . . . . . . . . . . . . 12
7.2.
6.2. Informative References . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14 12

1. Overview

Dual-stack Lite (DS-Lite)

DS-Lite [RFC6333] is a transition technique that
enable enables operators to
multiplex public IPv4 addresses while provisioning only IPv6 to
users. DS-Lite is designed to continue offering IPv4 services while
operators upgrading upgrade their network networks incrementally to IPv6. DS-Lite
combines IPv4-in-IPv6 softwire [RFC2473] and NAT44 Network Address
Translator IPv4/IPv4 (NAT44) [RFC3022] to enable more than one user
to share a public IPv4 address.

While Appendix A of [RFC6333] explains how to deploy DS-Lite within
specific scenarios, the purpose of this document is to describe
problems that arise when deploying DS-Lite and what guidance should
be taken to mitigate those issues. The information is based on real
deployment experience and is compiled in one comprehensive document
so that operators aren't required to search through various RFCs
deciding which sections are applicable and impact their DS-Lite
deployment.

2. AFTR Deployment Considerations

2.1. Interface Consideration

Address Family Transition Router (AFTR) is a network element that is
deployed inside the operator's network. An AFTR can be a standalone stand-alone
device or be embedded into a router. The AFTR is the IPv4-in-IPv6
tunnel termination point and the NAT44 device. It is deployed at the IPv4-
IPv6
IPv4-IPv6 network border where the tunnel interface is IPv6 and the
external NAT44 interface is IPv4. The B4 Basic Bridging BroadBand (B4)
element [RFC6333] is a function implemented on a dual-stack capable node, either dual-stack-capable
node (either a host device or a home gateway gateway) that creates a tunnel
to an AFTR. Although an operator can configure both softwire tunnel
termination and interface for NAT44 functions on a single physical
interface (yet (yet, keep them logically separated), there are scenarios
we recommend to configure two individual interfaces (i.e. (i.e., one
dedicated for IPv4 and one dedicated for IPv6) to segregate the
functions.

o The access network between the B4 and AFTR is an IPv6-only network
network, and the network between the AFTR and IPv4 network is either an
IPv4-only network. In this deployment scenario, the AFTR
interface to the IPv6-only network and the interface to the IPv4
network should use two physical interfaces on the AFTR.

o Operators may use Operations Support System (OSS) tools (e.g.,
Multi Router Traffic Grapher) to collect interface data packet
count information. If an operator wants to separate the softwire
function and NAT44 function on different physical interfaces for
collecting a data packet count count, and the AFTR does not support
packet count for logical interfaces, they should use two physical
interfaces on the AFTR.

2.2. MTU and Fragmentation Considerations

DS-Lite is part tunneling protocol. Tunneling introduces overhead to
the packet and decreases the effective MTU size after encapsulation.
The DS-lite
DS-Lite users may experience problems with applications such as not
being able to download Internet pages or transfer large files.

Since fragmentation and reassembly is not optimal, the operator
should do everything possible to eliminate the need for it. If the
operator uses simple IPv4-in-IPv6 softwire [RFC2473], it is
recommended that the MTU size of the IPv6 network between the B4 and
the AFTR account accounts for the additional overhead (40 bytes). If the
access network MTU size is fixed and cannot be changed, the operator
should be aware that the B4 element and the AFTR must support fragmentation
as defined in [RFC6333]. The operator should also be aware that
reassembly at the Tunnel Exit-Point is resource intensive as a large
number of B4 may terminate on the same AFTR. Scalability of the AFTR
is advised in this scenario.

2.3. Logging at the AFTR

Source-Specific Log

A source-specific log is essential for back tracking backtracking specific users hosts
when a problem is identified with one of the AFTR's NAT-ed addresses.
Source-specific
The source-specific log contains the B4 IPv6 source address,
transport protocol, source port, and source IPv4 address after it has
been NAT-ed. Using the Source-specific source-specific log, operators can uniquely
identify a specific
user host when a DS-Lite user host experiences problem to access problems
accessing the IPv4 network. To maximize IPv4 shared radio, ratio, an
operator may configure a short timeout value for NAT44 entries. This
will result in a large numbers number of
log logs created by the AFTR. For
operators who desire to aggregate the logs, they can configure the
AFTR to pre-allocate preallocate a range of ports to each user. B4. This range of ports
will be used in the NAT44 function function, and the AFTR will create one log
entry for the whole port-range. port range. This aggregation can significantly
reduce the log size for Source-
specific source-specific logging.

Some operators may require to log logging both source and destination
information for user's a host's connections. This is called Destination-
Specific Log. Destination-specific a destination-
specific log. A destination-specific log contains the B4's IPv6
address, transport protocol, source port, source IPv4 address after
it has been NAT-ed, destination port port, and destination IPv4 address. Destination-
specific
A destination-specific log is session-based, session-based; the operators should be
aware that they will not be able to aggregate log entries. When
using a destination-specific log, the operator must be careful of the
large number of log entries created by the AFTR. Some AFTR
implementations may keep the logs in their main memory. This may be
CPU and memory resource intensive. We suggest the The operators must should configure
the AFTR to periodically send logs to storage facility and then purge
them from the AFTR.

2.4. Blacklisting a Shared IPv4 Address

The AFTR is a NAT device. It enables multiple users B4s to share a single
public IPv4 address. [RFC6269] discusses some considerations when
sharing an IPv4 address. When a public IPv4 address is blacklisted
by a remote peer, this may affect multiple B4 elements sharing the
same IPv4 address. users or hosts. Operators
deploying DS-Lite should be aware that Internet hosts may rely solely on source IP address to identify an
abusive household and may not be
aware that a given single IPv4 address is actually shared by multiple households.
B4s. A content provider may might block services for a shared IPv4
address and this will would then impact all households B4s sharing this particular
IPv4 address. The operator may would be likely to receive calls of related
to service outage and will would then need to take appropriate actions. Such corrective actions include but not limited
to notifying the content provider to combine the IPv4 address with
transport (e.g., TCP) and application protocol (e.g., HTTP)
actions. [RFC6302] describes necessary information required to
identify abusive household. [RFC6302].
[I-D.ietf-intarea-nat-reveal-analysis] analyzes a user or host in shared address environment. It is also
worth mention that [NAT-REVEAL] analyses different approaches to
identify a user or host in a shared address environment.

2.5. AFTR's Policies

There are two types of AFTR policies:

o Outgoing Policies apply to packets originating from B4 to the
AFTR. These policies should be provisioned on the AFTR's IPv6
interface that is connected to the B4 elements. B4s.

o Incoming Policies apply to packets originating from IPv4 network networks
to B4s. These policies should be provisioned on the IPv4
Interface
interface connected to the IPv4 network.

2.5.1. Outgoing Policy

Outgoing policies Policies may include Access Control List (ACL) and Qualify Quality
of Service (QoS) settings. These policies control the packets from
B4 elements
B4s to the AFTR. For example, the operator may configure the AFTR
only to accept B4's B4 connections that originated from specific IPv6
prefixes configured in the AFTR. More discussion of this use case
can be found in Section 2.12. An operator may configure the AFTR to
give priority to the packets marked by certain DSCP Differentiated
Services Code Point (DSCP) values [RFC2475]. Furthermore, an AFTR
may also apply outgoing policy an Outgoing Policy to limit the rate of port
allocation for a single B4's IPv6 address.

Some operators offer different service level agreements (SLA) (SLAs) to
users to meet their requirements. Some users may require more ports
and some may require different service priority. In this deployment
scenario, the operator can implement outgoing policies Outgoing Policies specified to a
user's B4 element or a group of B4 elements B4s sharing the same policies.

2.5.2. Incoming Policy

Similar to the Outgoing Policy, an Incoming Policy may also include
ACL and QoS settings. The Outgoing Policy controls packets coming
from the IPv4 network to the B4 elements. B4s. Incoming packets are normally
treated equally, so these policies are globally applied. For
example, an operator wants to use a pre-defined predefined DSCP value to signal
the IPv6 access network to apply certain traffic policies. In this
deployment scenario, the operator can configure the AFTR to mark the
incoming packets with the pre-defined predefined DSCP value. This policy will
apply to all incoming packets from the IPv4 network.

2.6. AFTR Impacts on Accounting Process

This section discusses IPv4 and IPv6 traffic accounting in DS-Lite the DS-
Lite environment. In a typical broadband access scenario (e.g. (e.g., DSL
or Cable), the B4 element is embedded in the a Residential Gateway and the Gateway. The edge
router (e.g., Broadband Network Gateway or Cable Modem
Termination System) is for the B4s in the provider's network is an IPv6 edge router.
The edge router is usually responsible for IPv6 accounting and the
user management functions such as authentication, authorization authorization, and
accounting (AAA). However, given the fact that IPv4 traffic is
encapsulated in an IPv6 packet at the B4 and only decapsulated at the ATFR,
AFTR, the edge router will require additional function functionality to
associate IPv4 accounting information to the B4 IPv6 address. If DS-lite DS-
Lite is the only application using the IPv4-in-IPv6 protocol in the
IPv6 access network, the operator can configure the edge router to
check the IPv6 Next Header field in the IPv6 header and header, identify the
protocol type (i.e.
0x04) (i.e., 0x04), and collect IPv4 accounting information.

Alternatively, the AFTR may perform accounting for IPv4 traffic.
However, operators must be aware that this will introduce some
challenges
challenges, especially in DSL deployment. In DSL deployment, the AAA
transaction normally happens between the edge router (i.e., Broadband
Network Gateway) router, i.e., (BNG),
and AAA server. [RFC6333] does not require the AFTR to interact with
the AAA server or edge router. Thus, the AFTR may not have the AAA
parameters (e.g., Account Session ID) associated to
users with B4s to generate
an IPv4 accounting record. IPv4 traffic accounting at the AFTR is
not recommended when the AAA parameters necessary to generate
complete IPv4 accounting records are not available. The accounting
process at the AFTR is only necessary if the operator requires
separating per
user per-B4 accounting records for IPv4 and IPv6 traffic. If
the per user per-B4 IPv6 accounting records, collected by the edge router, are
sufficient, and then the additional complexity of enabling IPv4
accounting at the ATFR AFTR is not required. It is important to notice
that, since the IPv4 traffic is encapsulated in IPv6 packets, the
data collected by the edge router for IPv6 traffic already contain contains
the total amount of traffic (i.e. (i.e., IPv4 and IPv6).

Even if detailed accounting records collection for IPv4 traffic may
not be required, it would be useful for an operator operator, in some scenarios
scenarios, to have information that the edge router generates that for the
IPv6
traffic and traffic. This information can be used to identify the AFTR who
is handling the IPv4 traffic for that user. B4. This can be achieved by
adding additional information to the IPv6 accounting records. For example:
example, operators can use RADIUS attribute information specified in
[RFC6519] or a new attribute to be specified in Internet Protocol
Detailed Record (IPDR).

2.7. Reliability Considerations of AFTR

For robustness, reliability reliability, and load distribution purposes,
operators may deploy multiple AFTRs. In such case, cases, the same IPv6
prefixes and algorithm to build the tunneling mechanisms will be configured
on
those AFTRs. each of these AFTRs will be the same. In [RFC6333] [RFC6333], Appendix A.3
mentions that High Availability (HA) is the operator's
responsibility. Since DS-lite DS-Lite is a stateful mechanism, all
requirements for load-balancing and failover mechanism mechanisms apply. There
are many ways to implement HA in a stateful mechanism, mechanism; the most
common are Cold Standby mode and Hot Standby mode. More discussion
on deploying of these two modes for NAT can be found in
[I-D.xu-behave-stateful-nat-standby] [NAT-STANDBY].
In Cold Standby mode mode, the AFTR states are not replicated from the
Primary AFTR to the Backup AFTR. When the Primary AFTR fails, all
the existing established sessions will be flushed out. The internal
hosts are required to re-establish reestablish sessions with the external hosts.
In Hot Standby mode mode, the user's session's states are replicated on-the-fly
from the Primary AFTR to the Backup AFTR. When the Primary AFTR
fails, the Backup AFTR will take over all the existing established
sessions. In this mode mode, the internal hosts are not required to re-establish
reestablish sessions with the external hosts.

For operators, the decision to use Cold Standby mode or Hot Standby
mode depends on the trade-off between capital cost and operational
cost. Cold Standby mode does not require a Backup Standby AFTR to
synchronize user session states. This simplifies the operational model.
When the Primary AFTR went goes down, any AFTR with extra capacity could can
take over. Hot Standby mode provides a smoother failover experience
to users, users; the cost for the operators is more careful failover
planning. For most deployment scenarios, we believe that Cold
Standby mode should be sufficient enough and is thus recommended.

2.8. Strategic Placement of AFTR

In the DS-Lite environment, the AFTR is the logical next-hop router
of the B4
elements B4s to access the IPv4 network, so the placement of the AFTR
will affect the traffic flows in the access network and overall
network design. In general, there are two placement models to deploy
an AFTR. Model One is to deploy deploys the AFTR in at the edge of the network to
cover a small region. Model Two is to deploy deploys the AFTR in at the core of the
network to cover a large region.

When an operator considers where to deploy the AFTR, it the operator
must make trade-offs. The AFTR in Model One serves fewer B4 elements, B4s; thus,
it requires a less powerful AFTR. Moreover, the traffic flows are
more evenly distributed to the AFTRs. However, it requires deploying
more AFTRs to cover the entire network. Often Often, the operation cost
increases proportionally with to the number amount of network equipment.

The AFTR in Model Two covers a larger area, area; thus, it serves more B4
elements. B4s.
The operator could deploy only a few AFTRs to support the entire user
base. However, this model requires a more powerful AFTR to sustain
the load at peak hours. Since the AFTR would support B4 elements B4s from
different regions, the AFTR would be deployed closer to the core
network.

DS-Lite framework can be incrementally deployed. An operator may
consider to start starting with Model Two. When the demand increases, the
operator could can push the AFTR closer to the edge, which would
effectively become Model One.

2.9. AFTR Considerations for Geographically Aware Services

By centralizing public IPv4 addresses in the AFTR, remote services
can no longer rely on an IPv4 address and IPv4 routing information to
derive a user's host's geographical information. For example, the IPv6
access network and the AFTR may be in two different cities. If the
remote services rely on the IPv4 address to locate a user, host, they may
have thought the user host was in a different city. [RFC6269] Section 7
describe
describes the problem in more details. detail. Applications could explicitly
ask users to enter location information information, such as postal code or
telephone number number, before offering geographical service. In contrast,
applications could use HELD HTTP-Enabled Location Delivery (HELD)
[RFC5985] to get the location information from the Location
Information Server and give this information to the remote peer.
[RFC6280] describes an architecture to enable location-
based location-based
services. However However, to mitigate the impact, we recommend that
operators to deploy the AFTR as close to users B4s as possible.

2.10. Impacts on QoS Policy

This section describes the application of [RFC2983] to the DS-Lite
deployment model. Operators must ensure that the QoS policy that is
in place operates properly within the DS-Lite deployment. In this
regard, operators commonly use DSCP [RFC2475] to classify and
prioritize different types of traffic in their networks. DS-Lite
tunnel can be seen as a particular case of uniform conceptual tunnel
model
model, as described in section Section 3.1 of [RFC2983]. The uniform model
views an IP tunnel only as just a necessary mechanism to forward traffic
to its
destination, but destination: the tunnel has no significant impact on traffic
conditioning. In this model, any packet has exactly one DSCP Field field
that is used for traffic conditioning at any point point, and it is the
field in the outermost IP header. In the DS-Lite model model, this is the
Traffic Class field in the IPv6 header. According to [RFC2983] [RFC2983],
implementations of this model copy the DSCP value to the outer IP
header at encapsulation and copy the outer header's DSCP value to the
inner IP header at decapsulation.

Operators should use this model by provisioning the network such that
the AFTR copies the DSCP value in the IPv4 header to the Traffic
Class field in the IPv6 header header, after the encapsulation for the
downstream traffic. Similarly Similarly, the B4 copies the DSCP value in the
IPv4 header to the Traffic Class field to the IPv6 header header, after the
encapsulation for the upstream traffic. Traffic identification and
classification can be done by examining the outer IPv6 header in the
IPv6 access network.

2.11. Port Forwarding Considerations

Some applications behind the B4 element require the B4 element to accept incoming
requests. If the remote application wants to communicate to the
application behind the B4 element, B4, the remote application must know both the
NAT-ed IPv4 address used by the B4
element and the IPv4 destination port.
Some applications use Universal Plug and Play (UPnP) (e.g., popular
gaming consoles) or ICE Interactive Community Establishment (ICE)
[RFC5245] to request incoming ports. Some applications rely on
Application Level Gateway (ALG) or manual port configuration to
reserve a port in the NAT. For the DS-Lite deployment scenario
whereby the B4 does not own a dedicated public full IPv4 address or all
the available ports, address, the operator will
manage port-forwarding in the serving AFTR. Operators may use Port
Control Protocol (PCP)
[I-D.ietf-pcp-base] [RFC6887] as guidance to provide port-forwarding port
forwarding service. Operators will deploy PCP client in the B4 elements. B4s.
PCP permits the PCP server to be deployed in a standalone stand-alone server.
However, we recommend
the that operators to consider deploying the PCP
server in the AFTR. This will ease the overhead to design a global
configuration for the PCP server for many AFTRs because each PCP
server will be dedicated to the collocated AFTR.

When sharing an IPv4 address, not all of the ports are available to a
user.
B4. Some restricted ports (i.e., 0-1023) are well-known well known such as TCP
port 25 and 80. Many users may want to be provisioned with the
restricted ports. For fairness, we recommend that operators to
configure the AFTR and not to allocate the restricted ports to regular
DS-Lite
users. B4s. This operation model ensures that DS-lite users DS-Lite B4s will have
uniform configuration, which can simplify provisioning and operation.
For users who want to use the restricted ports, operators can
consider to provision provisioning a full IPv4 address to those users. users' B4s. If an
operator still want wants to provision restricted ports to specific users, B4s,
it may require to implement implementing a static user's B4's configuration in the AFTR
to match the B4's IPv6 address to the NAT rules. Alternatively, the
B4 element may dynamically allocate the ports ports, and the AFTR authenticates the user's
session's request using PCP [I-D.ietf-pcp-base]. [RFC6887].

2.12. DS-Lite Tunnel Security

[RFC6333]

[RFC6333], Section 11 describes security issues associated to with the
DS-Lite mechanism. To restrict the service offered by the AFTR only
to registered users, B4s, an operator can implement the Outgoing Policy on
the AFTR's tunnel interface to accept only the IPv6 prefixes defined
in the policy. For static provisioning, the operator will need to
know in advance the IPv6 prefixes provisioned to the users B4s for the
softwire in order to configure the policy. To simplify operation,
operators should configure the AFTRs in the same region with the same
IPv6 prefixes prefixes' Outgoing Policy. The AFTRs will accept both regular
connections and failover connections from the B4 elements B4s in the same service
region.

2.13. IPv6-only IPv6-Only Network Considerations

In environments where the operator wants to deploy the AFTR in the IPv6-
only an
IPv6-only network, the AFTR nodes may not have direct IPv4
connectivity. In this scenario scenario, the operator extends the IPv6-only
boundary to the border of the network and only the border routers
have IPv4 connectivity. For both scalability and performance
purposes, the AFTR is located in the IPv6-only network closer to B4 elements. B4s.
In this
scenario scenario, the AFTR has only IPv6 connectivity and must be
able to send and receive IPv4 packets. Enhancements to the DS-Lite
AFTR are required to achieve this. [I-D.boucadair-softwire-dslite-v6only] [DS-LITE] describes such issues
and enhancements to DS-Lite in IPv6-only deployments.

3. B4 Deployment Considerations

In order to configure the IPv4-in-IPv6 tunnel, the B4 element needs the IPv6
address of the AFTR element. AFTR. This IPv6 address can be configured using a
variety of methods, methods ranging from an out-of-band mechanism, manual
configuration, and DHCPv6 option to RADIUS. If an operator uses
DHCPv6 to provision the B4, the B4 element must implement the DHCPv6 option
defined in [RFC6334]. If an operator uses RADIUS to provision the
B4, the B4 element must implement [RFC6519].

3.1. DNS Deployment Considerations

[RFC6333] recommends that the B4 element should send DNS queries to an external
recursive resolver over IPv6. The B4 element should implement a proxy
resolver that will proxy a DNS query from IPv4 transport to the DNS
server in the IPv6 network. [RFC6333] does not describe the DNS
proxy behavior. In deployment, the operator must ensure that the DNS
proxy implementation must follow [RFC5625]. This is important
especially for operators who have deployed deployed, or will consider
to deploy
deploying, DNSSEC [RFC4035].

Some operators may want to give clients hosts behind the B4's element B4 an IPv4 address
of an external DNS recursive resolver. The B4 element will treat the DNS
packets as normal IP packets and forward them over the softwire.
Note that there is no effective way to provision an IPv4 DNS address
to the B4 over IPv6, IPv6; operators who use this DNS deployment model must
be aware that it is undefined how to provision an IPv4 DNS address over an IPv6 network,
network is undefined, so it will introduce additional complexity in
B4 provisioning. Moreover, this will increase the load to the AFTR
by creating entries in the NAT table for DNS sessions. Operators may
deploy a local DNS caching resolver in the AFTR to reduce the load in
the NAT table. Nonetheless, this DNS model is not covered in
[RFC6333] and is not recommended.

3.2. IPv4 Service Monitoring

3.2.1. B4 Remote Management

B4 is connected to the IPv6 access network to offer IPv4 services.
When users experience IPv4 connectivity issue, issues, operators must be
able to remotely access (e.g. (e.g., TR-069) the B4 element to verify its B4's
configuration and status. Operators should access B4 elements B4s using native
IPv6. Operators should not access B4 over the softwire.

3.2.2. IPv4 Connectivity Check

The DS-Lite framework provides IPv4 services over the IPv6 access
network. Operators and users must be able to check the IPv4
connectivity from the B4 element to its AFTR using PING ping and IPv4 Traceroute. traceroute.
The AFTR should be configured with an IPv4 address to enable a PING
test and a Traceroute test. Operators should assign the same IPv4
address
(i.e., 192.0.0.2/32) (e.g., 192.0.0.2/32 [RFC6333]) to all AFTRs. IANA allocates has
allocated the 192.0.0.0/29
[RFC6333] Section 5.7 that can be used network prefix to provide IPv4 addresses
for this purpose. purpose [RFC6333].

4. Security Considerations

This document does not present any new security issues. [RFC6333]
discusses DS-Lite related security issues.

5. Acknowledgement Acknowledgements

Thanks to Mr. Nejc Skoberne and Dr. Maoke Chen for their thorough
review and helpful comments. We also want to thank Mr. Hu Jie for
sharing his DS-Lite deployment experience to with us. He gave us
recommendations of what his company learned while testing DS-Lite in
the production network.

6. IANA Considerations

This memo includes no request to IANA.

7. References

7.1.

6.1. Normative References

[RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
Stack
"Dual-Stack Lite Broadband Deployments Following IPv4
Exhaustion", RFC 6333, August 2011.

[RFC6334] Hankins, D. and T. Mrugalski, "Dynamic Host
Configuration Protocol for IPv6 (DHCPv6) Option for
Dual-Stack Lite", RFC 6334, August 2011.

[RFC6519] Maglione, R. and A. Durand, "RADIUS Extensions for Dual-
Stack
Dual-Stack Lite", RFC 6519, February 2012.

7.2.

6.2. Informative References

[I-D.boucadair-softwire-dslite-v6only]

[DS-LITE] Boucadair, M., Jacquenet, C., Grimault, J., Kassi-Lahlou, Kassi-
Lahlou, M., Levis, P., Cheng, D., and Y. Lee,
"Deploying Dual-
Stack Dual-Stack Lite in IPv6 Network",
draft-boucadair-softwire-dslite-v6only-01 (work Work
in
progress), Progress, April 2011.

[I-D.ietf-intarea-nat-reveal-analysis]

[NAT-REVEAL] Boucadair, M., Touch, J., Levis, P., and R. Penno,
"Analysis of Solution Candidates to Reveal a Host
Identifier (HOST_ID) in Shared Address Deployments",
draft-ietf-intarea-nat-reveal-analysis-04 (work in
progress), August 2012.

[I-D.ietf-pcp-base]
Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
Selkirk, "Port Control Protocol (PCP)",
draft-ietf-pcp-base-29 (work
Work in progress), November 2012.

[I-D.xu-behave-stateful-nat-standby] Progress, February 2013.

[NAT-STANDBY] Xu, X., Boucadair, M., Lee, Y., and G. Chen,
"Redundancy Requirements and Framework for Stateful
Network Address Translators (NAT)",
draft-xu-behave-stateful-nat-standby-06 (work Work in
progress), Progress,
October 2010.

[RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in
IPv6 Specification", RFC 2473, December 1998.

[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang,
Z., and W. Weiss, "An Architecture for Differentiated
Services", RFC 2475, December 1998.

[RFC2983] Black, D., "Differentiated Services and Tunnels",
RFC 2983, October 2000.

[RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network
Address Translator (Traditional NAT)", RFC 3022,
January 2001.

[RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and
S. Rose, "Protocol Modifications for the DNS Security
Extensions", RFC 4035, March 2005.

[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols", RFC 5245,
April 2010.

[RFC5625] Bellis, R., "DNS Proxy Implementation Guidelines",
BCP 152, RFC 5625, August 2009.

[RFC5985] Barnes, M., "HTTP-Enabled Location Delivery (HELD)",
RFC 5985, September 2010.

[RFC6269] Ford, M., Boucadair, M., Durand, A., Levis, P., and P.
Roberts, "Issues with IP Address Sharing", RFC 6269,
June 2011.

[RFC6280] Barnes, R., Lepinski, M., Cooper, A., Morris, J.,
Tschofenig, H., and H. Schulzrinne, "An Architecture
for Location and Location Privacy in Internet
Applications", BCP 160, RFC 6280, July 2011.

[RFC6302] Durand, A., Gashinsky, I., Lee, D., and S. Sheppard,
"Logging Recommendations for Internet-Facing Servers",
BCP 162, RFC 6302, June 2011.

[RFC6887] Wing, D., Ed., Cheshire, S., Boucadair, M., Penno, R.,
and P. Selkirk, "Port Control Protocol (PCP)",
RFC 6887, March 2013.

Authors' Addresses

Yiu L. Lee
Comcast
One Comcast Center
Philadelphia, PA 19103
U.S.A.

Email:

EMail: yiu_lee@cable.comcast.com
URI: http://www.comcast.com

Roberta Maglione
Telecom Italia
Via Reiss Romoli 274
Torino 10148
Italy

Email: roberta.maglione@telecomitalia.it
URI:
Cisco Systems
181 Bay Street
Toronto, ON M5J 2T3
Canada

EMail: robmgl@cisco.com

Carl Williams
MCSR Labs
U.S.A.

Email:

EMail: carlw@mcsr-labs.org

Christian Jacquenet
France Telecom
Rennes
France

Email:

EMail: christian.jacquenet@orange.com

Mohamed Boucadair
France Telecom
Rennes
France

Email:

EMail: mohamed.boucadair@orange.com