One document matched: draft-tsou-softwire-gwinit-6rd-04.xml
<?xml version="1.0" encoding="US-ASCII"?>
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<rfc category="info" submissionType="independent" docName="draft-tsou-softwire-gwinit-6rd-04" ipr="trust200902">
<!-- category values: std, bcp, info, exp, and historic
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they will automatically be output with "(if approved)" -->
<!-- ***** FRONT MATTER ***** -->
<front>
<!-- The abbreviated title is used in the page header - it is only necessary if the
full title is longer than 39 characters -->
<title>"Gateway-Initiated" 6rd</title>
<!-- add 'role="editor"' below for the editors if appropriate -->
<author fullname="Tina Tsou" initials="T." surname="Tsou">
<organization>Huawei Technologies (USA)</organization>
<address>
<postal>
<street>2330 Central Expressway</street>
<city>Santa Clara</city>
<region>CA</region>
<code>95050</code>
<country>USA</country>
</postal>
<phone></phone>
<email>Tina.Tsou.Zouting@huawei.com</email>
</address>
</author>
<author fullname="Cathy Zhou" initials="C." surname="Zhou">
<organization>Huawei Technologies</organization>
<address>
<postal>
<street>Bantian, Longgang District</street>
<city>Shenzhen</city>
<code>518129</code>
<country>P.R. China</country>
</postal>
<phone></phone>
<email>cathy.zhou@huawei.com</email>
</address>
</author>
<author fullname="Tom Taylor" initials="T." surname="Taylor">
<organization>Huawei Technologies</organization>
<address>
<postal>
<street></street>
<city>Ottawa</city>
<region>Ontario</region>
<code></code>
<country>Canada</country>
</postal>
<phone></phone>
<email>tom.taylor.stds@gmail.com</email>
</address>
</author>
<author initials="O." surname="Troan" fullname="Ole Troan">
<organization>Cisco Systems, Inc.</organization>
<address>
<postal>
<street>Telemarksvingen 20</street>
<code>N-0655</code>
<city>Oslo</city>
<region></region>
<country>Norway</country>
</postal>
<phone></phone>
<email>ot@cisco.com</email>
</address>
</author>
<author fullname="Qi Chen" initials="Q." surname="Chen">
<organization>China Telecom</organization>
<address>
<postal>
<street>109, Zhongshan Ave. West,</street>
<city>Tianhe District, Guangzhou</city>
<code>510630</code>
<country>P.R. China</country>
</postal>
<phone></phone>
<email>chenqi.0819@gmail.com</email>
</address>
</author>
<date month="December" year="2011" />
<!-- If the month and year are both specified and are the current ones,
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<area>General</area>
<workgroup>Internet Engineering Task Force</workgroup>
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which is used by the RFC Editor as a nod to the history of the IETF. -->
<abstract>
<t>This document proposes an alternative 6rd deployment model to that of
RFC 5969. The basic 6rd model allows IPv6 hosts to gain access to IPv6
networks across an IPv4 access network using 6-in-4 tunnels. 6rd requires
support by a device (the 6rd-CE) on the customer site, which must also be
assigned an IPv4 address. The alternative model described in this document
initiates the 6-in-4 tunnels from an operator-owned gateway collocated with
the operator's IPv4 network edge, rather than from customer equipment. The
advantages of this approach are that it requires no modification to customer
equipment and avoids assignment of IPv4 addresses to customer equipment.
The latter point means less pressure on IPv4 addresses in a high-growth
environment.</t>
</abstract>
</front>
<middle>
<section title="Introduction">
<t> 6rd ([RFC5969]) provides a transition tool for connecting IPv6
devices across an IPv4 network to an IPv6 network, at which point the
packets can be routed natively. The network topology is shown in
<xref target="fig_topol"/>.</t>
<figure anchor="fig_topol" title="6rd Deployment Topology">
<artwork>
+--------------+ +-----------------+ +---------+
| | | | | |
+-----+ +-----+ | Provider +--------+ | |
|IPv6 | | 6rd |__| IPv4 | Border |__| IPv6 |
|Host | | CE | | network | Router | | network |
+-----+ +-----+ | +--------+ | |
| Customer LAN | | | | |
+--------------+ +-----------------+ +---------+
</artwork>
</figure>
<t>In <xref target="fig_topol"/>, the CE is the customer edge router. It
is provisioned with a delegated IPv6 prefix, but also with an IPv4 address
so that it is reachable through the IPv4 network. If a public IPv4 address
is provisioned to every customer, it will aggravate the pressure due to
IPv4 address shortage for operators faced with a high rate of growth in
the number of broadband subscribers to their network. It is out of scope
of this document if private IPv4 address is provisioned. </t>
<section title="Requirements Language">
<t>This document uses no requirements language.</t>
</section>
</section>
<section anchor="probStat" title="Problem Statement">
<t>Consider an operator facing a high subscriber growth rate. As a result
of this growth rate, the operator faces pressure on its stock of available
public IPv4 addresses. For this reason, the operator is motivated to offer
IPv6 access as quickly as possible. </t>
<t>The backbone network will be the first part of the operator's network
to support IPv6. The metro network is not so easily upgraded to support
IPv6 since many devices need to be modified and there may be some impact
to existing services. Thus any means of providing IPv6 access has to
minimize the changes required to devices in the metro network.</t>
<t>In contrast to the situation described for basic 6rd
<xref target="RFC5569"/>, the operator is assumed to be unable to manage
IP devices on the customer premises. As a result, the operator cannot
assume that any of these devices are capable of supporting 6rd.</t>
<t>If the customer equipment is in bridged mode and IPv6 is deployed to
sites via a Service Provider's (SP's) IPv4 network, the IPv6-only host
needs a IPv6 address to visit the IPv6 service. In this scenario, 6to4
or 6rd can be used. However, each IPv6-only host may need one
corresponding IPv4 address when using public IPv4 address in 6to4 or 6rd,
which puts great address pressure on the operators.</t>
<t>If the customer equipment is operating in routing mode, the operator has
an opportunity to avoid assigning IPv4 addresses to sites running IPv6 only.
Some other means is available for routing IPv6 traffic through the IPv4
network to that site. The Gateway in the existing IPv4 access network
should be updated to support IPv6. But the metro network does not need
to be updated.</t>
<t>In the 6rd scenario, reachability between CEs in 6rd should go to the BR.
But in this gateway-initiated 6rd case, it does not need to go to the BR
which only needs gateway to gateway traffic. How the interaction between
gateway and gateway works is for further elaboration.</t>
</section><!-- probStat -->
<section anchor="propSol" title="Proposed Solution">
<t>For basic 6rd, the 6rd-CE described in [RFC5969] initiates the
6-in-4 tunnel to the Border Router to carry its IPv6 traffic. To
avoid the requirement for customer premises equipment to fulfill this
role, it is necessary to move the tunneling function to a network
device. This document identifies a functional element termed the 6rd
provider edge (6rd PE) to perform this task. The functions of 6rd
PE are:
<list style="symbols">
<t>to generate and allocate gateway initiated 6rd delegated prefixes
for IPv6-capable customer devices, as described in
<xref target="prefix"/>.</t>
<t>to forward outgoing IPv6 packets through a tunnel to a Border Relay,
which extracts and forwards them to an IPv6 network as for 6rd;</t>
<t>to extract incoming IPv6 packets tunneled from the 6rd Border Relay
and forward them to the correct user device.</t>
</list>
</t>
<t>In the proposed solution, there is only one tunnel initiated from
each Gateway to the Border Router, which greatly reduces the number of
tunnels the Border Router has to handle. The deployment scenario
consistent with the problem statement in <xref target="probStat"/>
collocates the Gateway with the IP edge of the access network. This
is shown in <xref target="fig_gwInit"/>, and is the typical placement
of the Broadband Network Gateway (BNG) in a fixed broadband network.
By assumption, the metro network beyond the BNG is IPv4. Transport
between the customer site and the Gateway is over layer 2.</t>
<figure anchor="fig_gwInit" title="Gateway-Initiated 6rd At the IP Edge">
<artwork>
+-------+ +-------------------+ +---------+
+-----+ | | | | | |
|IPv6 | | | +---------+ IPv4 +--------+ | IPv6 |
|Cust |_|Access |_| Gateway | Metro | Border |_| core |
|site | |network| |(IP edge)| network | Router | | network |
+-----+ | | +---------+ +--------+ | |
| | | | | |
+-------+ +-------------------+ +---------+
</artwork>
</figure>
<t>The elements of the proposed solution are these:
<list style="symbols">
<t>The IPv6 prefix assigned to the customer site contains the
compressed IPv4 address of the network-facing side of the Gateway,
plus a manually provisioned or Gateway-generated customer site
identifier. This is illustrated in <xref target="fig_addrFmt"/>
below.</t>
<t>The Border Router is able to route incoming IPv6 packets to the
correct Gateway by extracting the compressed Gateway address from
the IPv6 destination address of the incoming packet, expanding it
to a full 32-bit IPv4 address, and setting it as the destination
address of the encapsulated packet.</t>
<t>The Gateway can route incoming packets to the correct link after
decapsulation using a mapping from either the full IPv6 prefix or
the customer site identifier extracted from that prefix to the
appropriate link.</t>
</list>
</t>
<section anchor="prefix" title="Prefix Delegation">
<t>Referring back to <xref target="fig_gwInit"/>, prefix assignment to
the customer equipment occurs in the normal fashion through the Gateway/IP
edge, using either DHCPv6 or SLAAC. <xref target="fig_addrFmt"/>
illustrates the structure of the assigned prefix, and how the components
are derived, within the context of a complete address.</t>
<figure anchor="fig_addrFmt" title="Gateway-Initiated 6rd Address Format for a Customer Site">
<artwork>
+--------------------+-----------+
| 32 bit Gateway IPv4 address |
+--------------------+-----------+
|<---IPv4MaskLen --->| o bits | Gateway or manually
/ / generated value, unique
Configured / / / for the gateway
| / / |
| / / V
| V p bits | o bits | n bits |m bits | 64 bits |
+----------------+------------+---------+-------+----------------+
| | Gateway |Customer | | |
| Common prefix | identifier | site |subnet | interface ID |
| | | index | ID | |
+----------------+------------+---------+-------+----------------+
|<------ GI 6rd delegated prefix ------>|
</artwork>
</figure>
<t>The common prefix, i.e., the first p bits of the GI 6rd delegated
prefix, is configured in the Gateway. This part of the prefix is
common across multiple customers and multiple Gateways. Multiple
common prefix values may be used in a network either for service
separation or for scalability.</t>
<t>The Gateway Identifier is equal to the o low-order bits of the Gateway
IPv4 address on the virtual link to the Border Router. The number of bits
o is equal to 32 - IPv4MaskLen, where the latter is the length of the IPv4
prefix from which the Gateway IPv4 addresses are derived. The value of
IPv4MaskLen is configured in both the Gateways and the Border Routers.</t>
<t>The Customer Site Index is effectively a sequence number assigned to an
individual customer site served by the Gateway. The value of the index for
a given customer site must be unique across the Gateway. The length n of
the Customer Site Index is provisioned in the Gateway, and must be large
enough to accommodate the number of customer sites that the Gateway is
expected to serve.</t>
<t>To give a numerical example, consider a 6rd domain containing ten million
IPv6-capable customer devices (a rather high number given that 6rd is meant
for the early stages of IPv6 deployment). The estimated number of 6rd
Gateways needed to serve this domain would be in the order of 3,300, each
serving 30,000 customer devices. Assuming best-case compression for the
Gateway addresses, the Gateway Identifier field has length o = 12 bits.
If IPv6-in-IPv4 tunneling is being used, this best case is more likely
to be achievable than it would be if the IPv4 addresses belonged to the
customer devices. More controllably, the customer device index has length
n = 15 bits.</t>
<t>Overall, these figures suggest that the length p of the common prefix
can be 29 bits for a /56 delegated prefix, or 21 bits if /48 delegated
prefixes need to be allocated.</t>
</section><!-- prefix -->
<section anchor="diffs" title="Relevant Differences From Basic 6rd">
<t>A number of the points in <xref target="RFC5969"/> apply with the
simple substitution of the Gateway for the 6rd CE. When it comes to
configuration, the definition of IPv4MaskLen changes, and there are
other differences as indicated in the previous section. Since special
configuration of customer equipment is not required, the 6rd DHCPv6
option is inapplicable.</t>
<t>Since the link for the customer site to the network now extends only
as far as the Gateway, Neighbour Unreachability Detection on the part of
customer devices is similarly limited in scope.</t>
</section><!-- diffs -->
</section><!-- propSol -->
<section anchor="IANA" title="IANA Considerations">
<t>This memo includes no request to IANA.</t>
</section>
<section anchor="Security" title="Security Considerations">
<t>No change from <xref target="RFC5969"/>.</t>
</section>
</middle>
<!-- *****BACK MATTER ***** -->
<back>
<!-- References split into informative and normative -->
<references title="Normative References">
&RFC5969;
</references>
<references title="Informative References">
&RFC5569;
</references>
</back>
</rfc>| PAFTECH AB 2003-2026 | 2026-04-24 04:09:16 |