One document matched: draft-ietf-softwire-lw4over6-13.xml
<?xml version="1.0" encoding="US-ASCII"?>
<!DOCTYPE rfc SYSTEM "rfc2629.dtd">
<?rfc toc="yes"?>
<?rfc sortrefs="yes"?>
<?rfc compact="yes"?>
<?rfc subcompact="no"?>
<?rfc symrefs="yes"?>
<rfc category="std" docName="draft-ietf-softwire-lw4over6-13"
ipr="trust200902">
<front>
<title abbrev="Lightweight 4over6">Lightweight 4over6: An Extension to the
DS-Lite Architecture</title>
<author fullname="Yong Cui" initials="Y" surname="Cui">
<organization>Tsinghua University</organization>
<address>
<postal>
<street></street>
<city>Beijing</city>
<code>100084</code>
<country>P.R.China</country>
</postal>
<phone>+86-10-62603059</phone>
<email>yong@csnet1.cs.tsinghua.edu.cn</email>
</address>
</author>
<author fullname="Qiong Sun" initials="Q.S" surname="Sun">
<organization>China Telecom</organization>
<address>
<postal>
<street>Room 708, No.118, Xizhimennei Street</street>
<city>Beijing</city>
<code>100035</code>
<country>P.R.China</country>
</postal>
<phone>+86-10-58552936</phone>
<email>sunqiong@ctbri.com.cn</email>
</address>
</author>
<author fullname="Mohamed Boucadair" initials="M.B" surname="Boucadair">
<organization>France Telecom</organization>
<address>
<postal>
<street></street>
<city>Rennes</city>
<code>35000</code>
<region></region>
<country>France</country>
</postal>
<email>mohamed.boucadair@orange.com</email>
</address>
</author>
<author fullname="Tina Tsou" initials="T.T" surname="Tsou">
<organization>Huawei Technologies</organization>
<address>
<postal>
<street>2330 Central Expressway</street>
<city>Santa Clara</city>
<region>CA</region>
<code>95050</code>
<country>USA</country>
</postal>
<phone>+1-408-330-4424</phone>
<email>tena@huawei.com</email>
</address>
</author>
<author fullname="Yiu L. Lee" initials="Y" surname="Lee">
<organization>Comcast</organization>
<address>
<postal>
<street>One Comcast Center</street>
<city>Philadelphia</city>
<region>PA</region>
<code>19103</code>
<country>USA</country>
</postal>
<email>yiu_lee@cable.comcast.com</email>
</address>
</author>
<author fullname="Ian Farrer" initials="I.F" surname="Farrer">
<organization>Deutsche Telekom AG</organization>
<address>
<postal>
<street>CTO-ATI, Landgrabenweg 151</street>
<city>Bonn</city>
<region>NRW</region>
<code>53227</code>
<country>Germany</country>
</postal>
<email>ian.farrer@telekom.de</email>
</address>
</author>
<date year="2014" />
<workgroup>Softwire Working Group</workgroup>
<abstract>
<t>Dual-Stack Lite (RFC 6333) describes an architecture for transporting
IPv4 packets over an IPv6 network. This document specifies an extension
to DS-Lite called Lightweight 4over6 which moves the Network Address and
Port Translation (NAPT) function from the centralized DS-Lite tunnel
concentrator to the tunnel client located in the Customer Premises
Equipment (CPE). This removes the requirement for a Carrier Grade NAT
function in the tunnel concentrator and reduces the amount of
centralized state that must be held to a per-subscriber level. In order
to delegate the NAPT function and make IPv4 Address sharing possible,
port-restricted IPv4 addresses are allocated to the CPEs.</t>
</abstract>
</front>
<middle>
<section title="Introduction">
<t>Dual-Stack Lite (DS-Lite, <xref target="RFC6333"></xref>) defines a
model for providing IPv4 access over an IPv6 network using two
well-known technologies: IP in IP <xref target="RFC2473"></xref> and
Network Address Translation (NAT). The DS-Lite architecture defines two
major functional elements as follows:</t>
<t><list hangIndent="34" style="hanging">
<t hangText="Basic Bridging BroadBand element:">A B4 element is a
function implemented on a dual-stack capable node, either a directly
connected device or a CPE, that creates an IPv4-in-IPv6 tunnel to an
AFTR.</t>
<t hangText="Address Family Transition Router:">An AFTR element is
the combination of an IPv4-in-IPv6 tunnel endpoint and an IPv4-IPv4
NAT implemented on the same node.</t>
</list>As the AFTR performs the centralized NAT44 function, it
dynamically assigns public IPv4 addresses and ports to requesting host's
traffic (as described in <xref target="RFC3022"></xref>). To achieve
this, the AFTR must dynamically maintain per-flow state in the form of
active NAPT sessions. For service providers with a large number of B4
clients, the size and associated costs for scaling the AFTR can quickly
become prohibitive. It can also place a large NAPT logging overhead upon
the service provider in countries where legal requirements mandate
this.</t>
<t>This document describes a mechanism called Lightweight 4 over 6
(lw4o6), which provides a solution for these problems. By relocating the
NAPT functionality from the centralized AFTR to the distributed B4s, a
number of benefits can be realised:<list style="symbols">
<t>NAPT44 functionality is already widely supported and used in
today's CPE devices. Lw4o6 uses this to provide
private<->public NAPT44, meaning that the service provider
does not need a centralized NAT44 function.</t>
<t>The amount of state that must be maintained centrally in the AFTR
can be reduced from per-flow to per-subscriber. This reduces the
amount of resources (memory and processing power) necessary in the
AFTR.</t>
<t>The reduction of maintained state results in a greatly reduced
logging overhead on the service provider.</t>
</list></t>
<t>Operator's IPv6 and IPv4 addressing architectures remain independent
of each other. Therefore, flexible IPv4/IPv6 addressing schemes can be
deployed.</t>
<t>Lightweight 4over6 is a solution designed specifically for complete
independence between IPv6 subnet prefix and IPv4 address with or without
IPv4 address sharing. This is accomplished by maintaining state for each
softwire (per-subscriber state) in the central lwAFTR and a
hub-and-spoke forwarding architecture. <xref
target="I-D.ietf-softwire-map"></xref> also offers these capabilities
or, alternatively, allows for a reduction of the amount of centralized
state using rules to express IPv4/IPv6 address mappings. This introduces
an algorithmic relationship between the IPv6 subnet and IPv4 address.
This relationship also allows the option of direct, meshed connectivity
between users.</t>
<t>The tunneling mechanism remains the same for DS-Lite and Lightweight
4over6. This document describes the changes to DS-Lite that are
necessary to implement Lightweight 4over6. These changes mainly concern
the configuration parameters and provisioning method necessary for the
functional elements.</t>
<t>Lightweight 4over6 features keeping per-subscriber state in the
service provider's network. It is categorized as Binding approach in
<xref target="I-D.ietf-softwire-unified-cpe"></xref> which defines a
unified IPv4-in-IPv6 Softwire CPE.</t>
<t>This document extends the mechanism defined in <xref
target="RFC7040"></xref> by allowing address sharing. The solution in
this document is also a variant of A+P called Binding Table Mode (see
Section 4.4 of <xref target="RFC6346"></xref>).</t>
<t>This document focuses on architectural considerations and
particularly on the expected behavior of the involved functional
elements and their interfaces. Deployment-specific issues are discussed
in a companion document. As such, discussions about redundancy and
provisioning policy are out of scope.</t>
</section>
<section anchor="conventions" title="Conventions">
<t>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 <xref
target="RFC2119"></xref>.</t>
</section>
<section title="Terminology">
<t>The document defines the following terms:<list hangIndent="30"
style="hanging">
<t hangText="Lightweight 4over6 (lw4o6):">An IPv4-over-IPv6 hub and
spoke mechanism, which extends DS-Lite by moving the IPv4
translation (NAPT44) function from the AFTR to the B4.</t>
<t hangText="Lightweight B4 (lwB4):">A B4 element (Basic Bridging
BroadBand element <xref target="RFC6333"></xref>), which supports
Lightweight 4over6 extensions. An lwB4 is a function implemented on
a dual-stack capable node, (either a directly connected device or a
CPE), that supports port-restricted IPv4 address allocation,
implements NAPT44 functionality and creates a tunnel to an
lwAFTR.</t>
<t hangText="Lightweight AFTR (lwAFTR):">An AFTR element (Address
Family Transition Router element <xref target="RFC6333"></xref>),
which supports Lightweight 4over6 extension. An lwAFTR is an
IPv4-in-IPv6 tunnel endpoint which maintains per-subscriber address
binding only and does not perform a NAPT44 function.</t>
<t hangText="Restricted Port-Set:">A non-overlapping range of
allowed external ports allocated to the lwB4 to use for NAPT44.
Source ports of IPv4 packets sent by the B4 must belong to the
assigned port-set. The port set is used for all port aware IP
protocols (TCP, UDP, SCTP etc.).</t>
<t hangText="Port-restricted IPv4 Address:">A public IPv4 address
with a restricted port-set. In Lightweight 4over6, multiple B4s may
share the same IPv4 address, however, their port-sets must be
non-overlapping.</t>
</list></t>
<t>Throughout the remainder of this document, the terms B4/AFTR should
be understood to refer specifically to a DS-Lite implementation. The
terms lwB4/lwAFTR refer to a Lightweight 4over6 implementation.</t>
<t></t>
</section>
<section title="Lightweight 4over6 Architecture">
<t>The Lightweight 4over6 architecture is functionally similar to
DS-Lite. lwB4s and an lwAFTR are connected through an IPv6-enabled
network. Both approaches use an IPv4-in-IPv6 encapsulation scheme to
deliver IPv4 connectivity. The following figure shows the data plane
with the main functional change between DS-Lite and lw4o6:</t>
<figure>
<artwork><![CDATA[
+--------+ +---------+ IPv4-in-IPv6 +---------+ +-------------+
|IPv4 LAN|---| B4 |================|AFTR/NAPT|----|IPv4 Internet|
+--------+ +---------+ +---------+ +-------------+
DS-Lite NAPT model: all state in the AFTR
+--------+ +---------+ IPv4-in-IPv6 +------+ +-------------+
|IPv4 LAN|---|lwB4/NAPT|================|lwAFTR|----|IPv4 Internet|
+--------+ +---------+ +------+ +-------------+
LW4over6 NAPT model:
subscriber state in the lwAFTR, NAPT state in lwB4
]]></artwork>
<postamble>Figure 1 Comparison of DS-Lite and Lightweight 4over6 Data
Plane</postamble>
</figure>
<t>There are three main components in the Lightweight 4over6
architecture:</t>
<t><list style="symbols">
<t>The lwB4, which performs the NAPT function and
encapsulation/de-capsulation IPv4/IPv6.</t>
<t>The lwAFTR, which performs the encapsulation/de-capsulation
IPv4/IPv6.</t>
<t>The provisioning system, which tells the lwB4 which IPv4 address
and port set to use.</t>
</list></t>
<t>The lwB4 differs from a regular B4 in that it now performs the NAPT
functionality. This means that it needs to be provisioned with the
public IPv4 address and port set it is allowed to use. This information
is provided though a provisioning mechanism such as DHCP, Port Control
Protocol (PCP, <xref target="RFC6887"></xref>) or TR-69.</t>
<t>The lwAFTR needs to know the binding between the IPv6 address of each
subscriber and the IPv4 address and port set allocated to that
subscriber. This information is used to perform ingress filtering
upstream and encapsulation downstream. Note that this is per-subscriber
state as opposed to per-flow state in the regular AFTR case.</t>
<t>The consequence of this architecture is that the information
maintained by the provisioning mechanism and the one maintained by the
lwAFTR MUST be synchronized (See figure 2). The precise mechanism
whereby this synchronization occurs is out of scope for this
document.</t>
<t>The solution specified in this document allows the assignment of
either a full or a shared IPv4 address to requesting CPEs. <xref
target="RFC7040"></xref> provides a mechanism for assigning a full IPv4
address only.</t>
<figure>
<artwork><![CDATA[
+------------+
/-------|Provisioning|<-----\
| +------------+ |
| |
V V
+--------+ +---------+ IPv4/IPv6 +------+ +-------------+
|IPv4 LAN|---|lwB4/NAPT|==================|lwAFTR|----|IPv4 Internet|
+--------+ +---------+ +------+ +-------------+
]]></artwork>
<postamble>Figure 2 Lightweight 4over6 Provisioning
Synchronization</postamble>
</figure>
</section>
<section title="Lightweight B4 Behavior">
<section anchor="lwb4pro"
title="Lightweight B4 Provisioning with DHCPv6">
<t>With DS-Lite, the B4 element only needs to be configured with a
single DS-Lite specific parameter so that it can set up the softwire
(the IPv6 address of the AFTR). Its IPv4 address can be taken from the
well-known range 192.0.0.0/29.</t>
<t>In lw4o6, a number of lw4o6 specific configuration parameters must
be provisioned to the lwB4. These are:</t>
<t><list style="symbols">
<t>IPv6 Address for the lwAFTR</t>
<t>IPv4 External (Public) Address for NAPT44</t>
<t>Restricted port-set to use for NAPT44</t>
<t>IPv6 Binding Prefix</t>
</list></t>
<t>The lwB4 MUST implement DHCPv6 based configuration using
OPTION_S46_CONT_LW as described in section 5.3 of <xref
target="I-D.ietf-softwire-map-dhcp"></xref>. This means that the
lifetime of the softwire and the derived configuration information
(e.g. IPv4 shared address, IPv4 address) is bound to the lifetime of
the DHCPv6 lease. If stateful IPv4 configuration or additional IPv4
configuration information is required, DHCP 4o6 <xref
target="RFC7341"></xref> MUST be used.</t>
<t>Although it would be possible to extend lw4o6 to have more than one
active lw4o6 tunnel configured simultaneously, this document is only
concerned with the use of a single tunnel.</t>
<t>The IPv6 binding prefix field is provisioned so that the CE can
identify the correct prefix to use as the tunnel source. On receipt of
the necessary configuration parameters listed above, the lwB4 performs
a longest prefix match between the IPv6 binding prefix and its currently
active IPv6 prefixes. The result forms the subnet to be used for sourcing
the lw4o6 tunnel. The full /128 address is then constructed in the
same manner as <xref target="I-D.ietf-softwire-map"></xref>.</t>
<figure>
<artwork><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Operator Assigned Prefix |
. (64-bits) .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Zero Padding | IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Addr cont. | PSID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
<postamble>Figure 3 Construction of the lw4o6 /128
Prefix</postamble>
</figure>
<t><list hangIndent="14" style="hanging">
<t hangText="Operator Assigned Prefix:">IPv6 prefix allocated to
the client. If the prefix length is less than 64, right padded
with zeros to 64-bits.</t>
<t hangText="Padding:">Padding (all zeros)</t>
<t hangText="IPv4 Address:">Public IPv4 address allocated to the
client</t>
<t hangText="PSID:">Port Set ID allocated to the client, left
padded with zeros to 16-bits. If no PSID is provisioned, all
zeros.</t>
</list></t>
<t>In the event that the lwB4's IPv6 encapsulation source address is
changed for any reason (such as the DHCPv6 lease expiring), the lwB4's
dynamic provisioning process MUST be re-initiated. When the lwB4's
public IPv4 address or port set ID is changed for any reason, the lwB4
MUST flush its NAPT table.</t>
<t>An lwB4 MUST support dynamic port-restricted IPv4 address
provisioning. The port set algorithm for provisioning this is
described in Section 5.1 of <xref
target="I-D.ietf-softwire-map"></xref>. For lw4o6, the number of
a-bits SHOULD be 0, thus allocating a single contiguous port set to
each lwB4.</t>
<t>Provisioning of the lwB4 using DHCPv6 as described here allocates a
single PSID to the client. In the event that the client is
concurrently using all of the provisioned L4 ports it may be unable to
initiate any additional outbound connections. DHCPv6 based
provisioning does not provide a mechanism for the client to request
more L4 port numbers. Other provisioning mechanisms (e.g. PCP based
provisioning <xref target="I-D.ietf-pcp-port-set"></xref>) provide
this function. Issues relevant to IP address sharing are discussed in
more detail in <xref target="RFC6269"></xref>.</t>
<t>Unless an lwB4 is being allocated a full IPv4 address, it is
RECOMMENDED that PSIDs containing the system ports (0-1023) are not
allocated to lwB4s. The reserved ports are more likely to be reserved
by middleware, and therefore we recommend that they not be issued to
clients other than as a deliberate assignment. Section 5.2.2 of <xref
target="RFC6269"></xref> provides analysis of allocating system ports
to clients with IPv4 address sharing.</t>
<t>In the event that the lwB4 receives an ICMPv6 error message (type
1, code 5) originating from the lwAFTR, the lwB4 interprets this to
mean that no matching entry in the lwAFTR's binding table has been
found, so the IPv4 payload is not being forwarded by the lwAFTR. The
lwB4 MAY then re-initiate the dynamic port-restricted provisioning
process. The lwB4's re-initiation policy SHOULD be configurable.</t>
<t>On receipt of such an ICMP error message, the lwB4 MUST validate
the source address to be the same as the lwAFTR address that is
configured. In the event that these addresses do not match, the lwAFTR
MUST discard the ICMP error message.</t>
<t>In order to prevent forged ICMP messages (using the spoofed lwAFTR
address as the source) from being sent to lwB4s, the operator can
implement network ingress filtering as described in <xref
target="RFC2827"></xref>.</t>
<t>The DNS considerations described in Section 5.5 and Section 6.4 of
<xref target="RFC6333"></xref> apply to Lightweight 4over6; lw4o6
implementations MUST comply with all requirements stated there.</t>
</section>
<section title="Lightweight B4 Data Plane Behavior">
<t>Several sections of <xref target="RFC6333"></xref> provide
background information on the B4's data plane functionality and MUST
be implemented by the lwB4 as they are common to both solutions. The
relevant sections are:</t>
<t><list hangIndent="34" style="hanging">
<t hangText="5.2 Encapsulation">Covering encapsulation and
de-capsulation of tunneled traffic</t>
<t hangText="5.3 Fragmentation and Reassembly">Covering MTU and
fragmentation considerations (referencing <xref
target="RFC2473"></xref>).</t>
<t hangText="7.1 Tunneling">Covering tunneling and traffic class
mapping between IPv4 and IPv6 (referencing <xref
target="RFC2473"></xref> and <xref target="RFC2983"></xref>)</t>
</list></t>
<t>The lwB4 element performs IPv4 address translation (NAPT44) as well
as encapsulation and de-capsulation. It runs standard NAPT44 <xref
target="RFC3022"></xref> using the allocated port-restricted address
as its external IPv4 address and port numbers.</t>
<t>The working flow of the lwB4 is illustrated in figure 4.</t>
<figure>
<artwork><![CDATA[
+-------------+
| lwB4 |
+--------+ IPv4 |------+------| IPv4-in-IPv6 +----------+
|IPv4 LAN|------->| |Encap.|-------------->|Configured|
| |<-------| NAPT | or |<--------------| lwAFTR |
+--------+ | |Decap.| +----------+
+------+------+
]]></artwork>
<postamble>Figure 4 Working Flow of the lwB4</postamble>
</figure>
<t>Hosts connected to the customer's network behind the lwB4 source
IPv4 packets with an <xref target="RFC1918"></xref> address. When the
lwB4 receives such an IPv4 packet, it performs a NAPT44 function on
the source address and port by using the public IPv4 address and a
port number from the allocated port-set. Then, it encapsulates the
packet with an IPv6 header. The destination IPv6 address is the
lwAFTR's IPv6 address and the source IPv6 address is the lwB4's IPv6
tunnel endpoint address. Finally, the lwB4 forwards the encapsulated
packet to the configured lwAFTR.</t>
<t>When the lwB4 receives an IPv4-in-IPv6 packet from the lwAFTR, it
de-capsulates the IPv4 packet from the IPv6 packet. Then, it performs
NAPT44 translation on the destination address and port, based on the
available information in its local NAPT44 table.</t>
<t>If the IPv6 source address does not match the configured lwAFTR
address, then the packet MUST be discarded. If the decapsulated IPv4
packet does not match the lwB4's configuration (i.e. invalid
destination IPv4 address or port) then the packet MUST be dropped. An
ICMPv4 error message (type 13 - Communication Administratively
Prohibited) message MAY be sent back to the lwAFTR. The ICMP policy
SHOULD be configurable.</t>
<t>The lwB4 is responsible for performing ALG functions (e.g., SIP,
FTP), and other NAPT traversal mechanisms (e.g., UPnP, NAPT-PMP,
manual binding configuration, PCP) for the internal hosts, if
necessary. This requirement is typical for NAPT44 gateways available
today.</t>
<t>It is possible that a lwB4 is co-located in a host. In this case,
the functions of NAPT44 and encapsulation/de-capsulation are
implemented inside the host.</t>
<section title="Fragmentation Behaviour">
<t>For TCP and UDP traffic the NAPT44 implemented in the lwB4 MUST
conform with the behaviour and best current practices documented in
<xref target="RFC4787"></xref>, <xref target="RFC5508"></xref>, and
<xref target="RFC5382"></xref>. If the lwB4 supports DCCP, then the
requirements in <xref target="RFC5597"></xref> MUST be
implemented.</t>
<t>The NAPT44 in the lwB4 MUST implement ICMP message handling
behaviour conforming to the best current practice documented in
<xref target="RFC5508"></xref>. If the lwB4 receives an ICMP error
(for errors detected inside the IPv6 tunnel), the node relays the
ICMP error message to the original source (the lwAFTR). This
behaviour SHOULD be implemented conforming to the section 8 of <xref
target="RFC2473"></xref>.</t>
<t>If IPv4 hosts behind different lwB4s sharing the same
IPv4 address send fragments to the same IPv4 destination host
outside the Lightweight 4over6 domain, those hosts may use
the same IPv4 fragmentation identifier, resulting in incorrect
reassembly of the fragments at the destination host. Given
that the IPv4 fragmentation identifier is a 16-bit field,
it could be used similarly to port ranges: A lwB4 could rewrite
the IPv4 fragmentation identifier to be within its allocated
port-set, if the resulting fragment identifier space is large
enough related to the rate fragments are sent. However,
splitting the identifier space in this fashion would increase
the probability of reassembly collision for all connections
through the lwB4. See also Section 5.3.1 of <xref
target="RFC6864"/>.</t>
</section>
</section>
</section>
<section title="Lightweight AFTR Behavior">
<section title="Binding Table Maintenance">
<t>The lwAFTR maintains an address binding table containing the
binding between the lwB4's IPv6 address, the allocated IPv4 address
and restricted port-set. Unlike the DS-Lite extended binding table
defined in section 6.6 of <xref target="RFC6333"></xref> which is a
5-tuple NAPT table, each entry in the Lightweight 4over6 binding table
contains the following 3-tuples:</t>
<t><list style="symbols">
<t>IPv6 Address for a single lwB4</t>
<t>Public IPv4 Address</t>
<t>Restricted port-set</t>
</list>The entry has two functions: the IPv6 encapsulation of
inbound IPv4 packets destined to the lwB4 and the validation of
outbound IPv4-in-IPv6 packets received from the lwB4 for
de-capsulation.</t>
<t>The lwAFTR does not perform NAPT and so does not need session
entries.</t>
<t>The lwAFTR MUST synchronize the binding information with the
port-restricted address provisioning process. If the lwAFTR does not
participate in the port-restricted address provisioning process, the
binding MUST be synchronized through other methods (e.g. out-of-band
static update).</t>
<t>If the lwAFTR participates in the port-restricted provisioning
process, then its binding table MUST be created as part of this
process.</t>
<t>For all provisioning processes, the lifetime of binding table
entries MUST be synchronized with the lifetime of address
allocations.</t>
<t><vspace blankLines="1" /></t>
</section>
<section title="lwAFTR Data Plane Behavior">
<t>Several sections of <xref target="RFC6333"></xref> provide
background information on the AFTR's data plane functionality and MUST
be implemented by the lwAFTR as they are common to both solutions. The
relevant sections are:</t>
<t><list hangIndent="34" style="hanging">
<t hangText="6.2 Encapsulation">Covering encapsulation and
de-capsulation of tunneled traffic</t>
<t hangText="6.3 Fragmentation and Reassembly">Fragmentation and
re-assembly considerations (referencing <xref
target="RFC2473"></xref>)</t>
<t hangText="7.1 Tunneling">Covering tunneling and traffic class
mapping between IPv4 and IPv6 (referencing <xref
target="RFC2473"></xref> and <xref target="RFC2983"></xref>)</t>
</list></t>
<t>When the lwAFTR receives an IPv4-in-IPv6 packet from an lwB4, it
de-capsulates the IPv6 header and verifies the source addresses and
port in the binding table. If both the source IPv4 and IPv6 addresses
match a single entry in the binding table and the source port is in
the allowed port-set for that entry, the lwAFTR forwards the packet to
the IPv4 destination.</t>
<t>If no match is found (e.g., no matching IPv4 address entry, port
out of range, etc.), the lwAFTR MUST discard or implement a policy
(such as redirection) on the packet. An ICMPv6 type 1, code 5 (source
address failed ingress/egress policy) error message MAY be sent back
to the requesting lwB4. The ICMP policy SHOULD be configurable.</t>
<t>When the lwAFTR receives an inbound IPv4 packet, it uses the IPv4
destination address and port to lookup the destination lwB4's IPv6
address in its binding table. If a match is found, the lwAFTR
encapsulates the IPv4 packet. The source is the lwAFTR's IPv6 address
and the destination is the lwB4's IPv6 address from the matched entry.
Then, the lwAFTR forwards the packet to the lwB4 natively over the
IPv6 network.</t>
<t>If no match is found, the lwAFTR MUST discard the packet. An ICMPv4
type 3, code 1 (Destination unreachable, host unreachable) error
message MAY be sent back. The ICMP policy SHOULD be configurable.</t>
<t>The lwAFTR MUST support hairpinning of traffic between two lwB4s,
by performing de-capsulation and re-encapsulation of packets from one
lwB4 that need to be sent to another lwB4 associated with the same
AFTR. The hairpinning policy MUST be configurable.</t>
</section>
</section>
<section title="Additional IPv4 address and Port Set Provisioning Mechanisms">
<t>In addition to the DHCPv6 based mechanism described in section 5.1,
several other IPv4 provisioning protocols have been suggested. These
protocols MAY be implemented. These alternatives include:</t>
<t><list style="symbols">
<t>DHCPv4 over DHCPv6: <xref target="RFC7341"></xref> describes
implementing DHCPv4 messages over an IPv6 only service providers
network. This enables leasing of IPv4 addresses and makes DHCPv4
options available to the DHCPv4-over-DHCPv6 client. An lwB4 MAY
implement <xref target="RFC7341"/> and
<xref target="I-D.ietf-dhc-dynamic-shared-v4allocation"/> to
retrieve a shared IPv4 address with a set of ports.</t>
<t>PCP<xref target="RFC6887"></xref>: an lwB4 MAY use <xref
target="I-D.ietf-pcp-port-set"></xref> to retrieve a restricted IPv4
address and a set of ports.</t>
</list></t>
<t>In a Lightweight 4over6 domain, the binding information MUST be
synchronized across the lwB4s, the lwAFTRs and the provisioning
server.</t>
<t>To prevent interworking complexity, it is RECOMMENDED that an
operator uses a single provisioning mechanism / protocol for their
implementation. In the event that more than one provisioning mechanism /
protocol needs to be used (for example during a migration to a new
provisioning mechanism), the operator SHOULD ensure that each
provisioning mechanism has a discrete set of resources (e.g. IPv4
address/PSID pools and lwAFTR tunnel addresses and binding tables).</t>
</section>
<section title="ICMP Processing">
<t>For both the lwAFTR and the lwB4, ICMPv6 MUST be handled as described
in <xref target="RFC2473"></xref>.</t>
<t>ICMPv4 does not work in an address sharing environment without
special handling <xref target="RFC6269"></xref>. Due to the port-set
style address sharing, Lightweight 4over6 requires specific ICMP message
handling not required by DS-Lite.</t>
<section title="ICMPv4 Processing by the lwAFTR">
<t>For inbound ICMP messages The following behavior SHOULD be
implemented by the lwAFTR to provide ICMP error handling and basic
remote IPv4 service diagnostics for a port restricted CPE:</t>
<t><list style="numbers">
<t>Check the ICMP Type field.</t>
<t>If the ICMP type is set to 0 or 8 (echo reply or request), then
the lwAFTR MUST take the value of the ICMP identifier field as the
source port, and use this value to lookup the binding table for an
encapsulation destination. If a match is found, the lwAFTR
forwards the ICMP packet to the IPv6 address stored in the entry;
otherwise it MUST discard the packet.</t>
<t>If the ICMP type field is set to any other value, then the
lwAFTR MUST use the method described in REQ-3 of <xref
target="RFC5508"></xref> to locate the source port within the
transport layer header in ICMP packet's data field. The
destination IPv4 address and source port extracted from the ICMP
packet are then used to make a lookup in the binding table. If a
match is found, it MUST forward the ICMP reply packet to the IPv6
address stored in the entry; otherwise it MUST discard the
packet.</t>
</list></t>
<t>Otherwise the lwAFTR MUST discard all inbound ICMPv4 messages.</t>
<t>The ICMP policy SHOULD be configurable.</t>
</section>
<section title="ICMPv4 Processing by the lwB4">
<t>The lwB4 MUST implement the requirements defined in <xref
target="RFC5508"></xref> for ICMP forwarding. For ICMP echo request
packets originating from the private IPv4 network, the lwB4 SHOULD
implement the method described in <xref target="RFC6346"></xref> and
use an available port from its port-set as the ICMP Identifier.</t>
</section>
</section>
<section title="Security Considerations">
<t>As the port space for a subscriber shrinks due to address sharing,
the randomness for the port numbers of the subscriber is decreased
significantly. This means it is much easier for an attacker to guess the
port number used, which could result in attacks ranging from throughput
reduction to broken connections or data corruption.</t>
<t>The port-set for a subscriber can be a set of contiguous ports or
non-contiguous ports. Contiguous port-sets do not reduce this threat.
However, with non-contiguous port-set (which may be generated in a
pseudo-random way <xref target="RFC6431"></xref>), the randomness of the
port number is improved, provided that the attacker is outside the
Lightweight 4over6 domain and hence does not know the port-set
generation algorithm.</t>
<t>The lwAFTR MUST rate limit ICMPv6 error messages (see <xref
target="lwb4pro"></xref>) to defend against DoS attacks generated by an
abuse user.</t>
<t>More considerations about IP address sharing are discussed in Section
13 of <xref target="RFC6269"></xref>, which is applicable to this
solution.</t>
<t>This document describes a number of different protocols which may be
used for the provisioning of lw4o6. In each case, the security
considerations relevant to the provisioning protocol are also relevant
to the provisioning of lw4o6 using that protocol. Lw4o6 does not add any
additional provisioning protocol specific security considerations.</t>
</section>
<section title="IANA Considerations">
<t>This document does not include an IANA request.</t>
</section>
<section title="Author List">
<t>The following are extended authors who contributed to the effort:</t>
<t><list>
<t>Jianping Wu <vspace blankLines="1" /> Tsinghua University <vspace
blankLines="1" /> Department of Computer Science, Tsinghua
University <vspace blankLines="1" /> Beijing 100084 <vspace
blankLines="1" /> P.R.China</t>
<t>Phone: +86-10-62785983 <vspace blankLines="1" /> Email:
jianping@cernet.edu.cn</t>
<t></t>
<t>Peng Wu <vspace blankLines="1" /> Tsinghua University <vspace
blankLines="1" /> Department of Computer Science, Tsinghua
University <vspace blankLines="1" /> Beijing 100084 <vspace
blankLines="1" /> P.R.China</t>
<t>Phone: +86-10-62785822 <vspace blankLines="1" /> Email:
pengwu.thu@gmail.com</t>
<t></t>
<t>Qi Sun <vspace blankLines="1" /> Tsinghua University <vspace
blankLines="1" /> Beijing 100084 <vspace blankLines="1" />
P.R.China</t>
<t>Phone: +86-10-62785822 <vspace blankLines="1" /> Email:
sunqi@csnet1.cs.tsinghua.edu.cn</t>
<t></t>
<t>Chongfeng Xie <vspace blankLines="1" /> China Telecom <vspace
blankLines="1" /> Room 708, No.118, Xizhimennei Street <vspace
blankLines="1" /> Beijing 100035 <vspace blankLines="1" />
P.R.China</t>
<t>Phone: +86-10-58552116 <vspace blankLines="1" /> Email:
xiechf@ctbri.com.cn</t>
<t></t>
<t>Xiaohong Deng <vspace blankLines="1" /> France Telecom</t>
<t>Email: xiaohong.deng@orange.com</t>
<t></t>
<t>Cathy Zhou <vspace blankLines="1" /> Huawei Technologies <vspace
blankLines="1" /> Section B, Huawei Industrial Base, Bantian
Longgang <vspace blankLines="1" /> Shenzhen 518129 <vspace
blankLines="1" /> P.R.China</t>
<t>Email: cathyzhou@huawei.com</t>
<t></t>
<t>Alain Durand <vspace blankLines="1" /> Juniper Networks <vspace
blankLines="1" /> 1194 North Mathilda Avenue <vspace
blankLines="1" /> Sunnyvale, CA 94089-1206 <vspace blankLines="1" />
USA</t>
<t>Email: adurand@juniper.net</t>
<t></t>
<t>Reinaldo Penno <vspace blankLines="1" /> Cisco Systems, Inc.
<vspace blankLines="1" /> 170 West Tasman Drive<vspace
blankLines="1" /> San Jose, California 95134<vspace
blankLines="1" /> USA</t>
<t>Email: repenno@cisco.com</t>
<t></t>
<t>Axel Clauberg <vspace blankLines="1" /> Deutsche Telekom AG
<vspace blankLines="1" /> CTO-ATI <vspace blankLines="1" />
Landgrabenweg 151 <vspace blankLines="1" /> Bonn, 53227 <vspace
blankLines="1" /> Germany</t>
<t>Email: axel.clauberg@telekom.de</t>
<t></t>
<t>Lionel Hoffmann <vspace blankLines="1" /> Bouygues Telecom
<vspace blankLines="1" /> TECHNOPOLE <vspace blankLines="1" /> 13/15
Avenue du Marechal Juin <vspace blankLines="1" /> Meudon 92360
<vspace blankLines="1" /> France</t>
<t>Email: lhoffman@bouyguestelecom.fr</t>
<t></t>
<t>Maoke Chen <vspace blankLines="1" /> FreeBit Co., Ltd. <vspace
blankLines="1" />13F E-space Tower, Maruyama-cho 3-6<vspace
blankLines="1" />Shibuya-ku, Tokyo 150-0044<vspace
blankLines="1" />Japan</t>
<t>Email: fibrib@gmail.com</t>
</list></t>
</section>
<section title="Acknowledgement">
<t>The authors would like to thank Ole Troan, Ralph Droms and Suresh
Krishnan for their comments and feedback.</t>
<t>This document is a merge of three documents: <xref
target="I-D.cui-softwire-b4-translated-ds-lite"></xref>, <xref
target="I-D.zhou-softwire-b4-nat"></xref> and <xref
target="I-D.penno-softwire-sdnat"></xref>.</t>
</section>
</middle>
<back>
<references title="Normative References">
<?rfc include="reference.RFC.1918"?>
<?rfc include="reference.RFC.2119" ?>
<?rfc include="reference.RFC.2473"?>
<?rfc include="reference.RFC.4787"?>
<?rfc include="reference.RFC.5382"?>
<?rfc include="reference.RFC.5508"?>
<?rfc include="reference.RFC.5597"?>
<?rfc include="reference.RFC.6333"?>
<?rfc include="reference.I-D.ietf-softwire-map-dhcp"?>
</references>
<references title="Informative References">
<?rfc include="reference.RFC.2983"?>
<?rfc include="reference.RFC.3022"?>
<?rfc include="reference.RFC.6269"?>
<?rfc include="reference.RFC.6346"?>
<?rfc include="reference.RFC.6431"?>
<?rfc include="reference.RFC.6887"?>
<?rfc include="reference.RFC.6864"?>
<?rfc include="reference.RFC.7040"?>
<?rfc include="reference.I-D.ietf-softwire-map"?>
<?rfc include="reference.I-D.cui-softwire-b4-translated-ds-lite"?>
<?rfc include="reference.I-D.zhou-softwire-b4-nat"?>
<?rfc include="reference.I-D.penno-softwire-sdnat"?>
<?rfc include="reference.I-D.ietf-dhc-dynamic-shared-v4allocation"?>
<?rfc include="reference.I-D.ietf-pcp-port-set"?>
<?rfc include="reference.I-D.ietf-softwire-unified-cpe"?>
<?rfc include="reference.RFC.7341"?>
<?rfc include="reference.RFC.2827"?>
</references>
</back>
</rfc>
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