Behave WG B. Huang
Internet-Draft H. Deng
Obsoletes: 3338, 2767 China Mobile
(if approved) T. Savolainen
Intended status: Standards Track Nokia
Expires: October 14, 2011 April 12, 2011
Dual Stack Hosts Using "Bump-in-the-Host" (BIH)
draft-ietf-behave-v4v6-bih-04
Abstract
Bump-In-the-Host (BIH) is a host-based IPv4 to IPv6 protocol
translation mechanism that allows a class of IPv4-only applications
that work through NATs to communicate with IPv6-only peers. The host
on which applications are running may be connected to IPv6-only or
dual-stack access networks. BIH hides IPv6 and makes the IPv4-only
applications think they are talking with IPv4 peers by local
synthesis of IPv4 addresses.
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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material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 14, 2011.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
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
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to this document. Code Components extracted from this document must
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described in the Simplified BSD License.
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
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Without obtaining an adequate license from the person(s) controlling
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not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Acknowledgement of previous work . . . . . . . . . . . . . 5
2. Components of the Bump-in-the-Host . . . . . . . . . . . . . . 6
2.1. Function Mapper . . . . . . . . . . . . . . . . . . . . . 7
2.2. Protocol translator . . . . . . . . . . . . . . . . . . . 8
2.3. Extension Name Resolver . . . . . . . . . . . . . . . . . 8
2.3.1. Special exclusion sets for A and AAAA records . . . . 9
2.3.2. DNSSEC support . . . . . . . . . . . . . . . . . . . . 9
2.3.3. Reverse DNS lookup . . . . . . . . . . . . . . . . . . 10
2.4. Address Mapper . . . . . . . . . . . . . . . . . . . . . . 10
3. Behavior and network Examples . . . . . . . . . . . . . . . . 12
4. Considerations . . . . . . . . . . . . . . . . . . . . . . . . 16
4.1. Socket API Conversion . . . . . . . . . . . . . . . . . . 16
4.2. Socket bindings . . . . . . . . . . . . . . . . . . . . . 16
4.3. ICMP Message Handling . . . . . . . . . . . . . . . . . . 16
4.4. IPv4 Address Pool and Mapping Table . . . . . . . . . . . 16
4.5. Multi-interface . . . . . . . . . . . . . . . . . . . . . 17
4.6. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 18
4.7. DNS cache . . . . . . . . . . . . . . . . . . . . . . . . 18
5. Considerations due ALG requirements . . . . . . . . . . . . . 19
6. Security Considerations . . . . . . . . . . . . . . . . . . . 20
7. Changes since RFC2767 and RFC3338 . . . . . . . . . . . . . . 21
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 22
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
9.1. Normative References . . . . . . . . . . . . . . . . . . . 23
9.2. Informative References . . . . . . . . . . . . . . . . . . 23
Appendix A. Implementation option for the ENR . . . . . . . . . . 25
Appendix B. API list intercepted by BIH . . . . . . . . . . . . . 26
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 28
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1. Introduction
This document describes Bump-in-the-Host (BIH), a successor and
combination of the Bump-in-the-Stack (BIS)[RFC2767] and Bump-in-the-
API (BIA) [RFC3338] technologies, which enable IPv4-only legacy
applications to communicate with IPv6-only servers by synthesizing
IPv4 addresses from AAAA records.
The supported class of applications includes those that use DNS for
IP address resolution and that do not embed IP address literals in
protocol payloads. This essentially includes legacy client-server
applications using the DNS that are agnostic to the IP address family
used by the destination and that are able to do NAT traversal. The
synthetic IPv4 addresses shown to applications are taken from the
RFC1918 private address pool in order to ensure that possible NAT
traversal techniques will be initiated.
IETF recommends using dual-stack or tunneling based solutions for
IPv6 transition and specifically recommends against deployments
utilizing double protocol translation. Use of BIH together with a
NAT64 is NOT RECOMMENDED [I-D.arkko-ipv6-transition-guidelines].
BIH includes two major implementation options: a protocol translator
between the IPv4 and the IPv6 stacks of a host, or an API translator
between the IPv4 socket API module and the TCP/IP module.
Essentially, IPv4 is translated into IPv6 at the socket API layer or
at the IP layer.
When BIH is implemented at the socket API layer, the translator
intercepts IPv4 socket API function calls and invokes corresponding
IPv6 socket API function calls to communicate with IPv6 hosts.
When BIH is implemented at the networking layer the IPv4 packets are
intercepted and converted to IPv6 using the IP conversion mechanism
defined in Stateless IP/ICMP Translation Algorithm (SIIT)
[I-D.ietf-behave-v6v4-xlate]. The protocol translation has the same
benefits and drawbacks as SIIT.
The location of the BIH refers essentially to the location of the
protocol translation function. The location of DNS synthesis is
orthogonal to the location of protocol translation, and may or may
not happen at the same level.
BIH can be used whenever an IPv4-only application needs to
communicate with an IPv6-only server, independently of the address
families supported by the access network. Hence the access network
can be IPv6-only or dual-stack capable.
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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 [RFC2119] .
This document uses terms defined in [RFC2460] , [RFC2893] , [RFC2767]
and [RFC3338].
1.1. Acknowledgement of previous work
This document is a direct update to and directly derivative from
Kazuaki TSHUCHIYA, Hidemitsu HIGUCHI, and Yoshifumi ATARASHI's Bump-
in-the-Stack [RFC2767] and from Seungyun Lee, Myung-Ki Shin, Yong-Jin
Kim, Alain Durand, and Erik Nordmark's Bump-in-the-API [RFC3338],
which similarly provide a dual stack host means to communicate with
other IPv6 hosts using existing IPv4 applications.
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2. Components of the Bump-in-the-Host
Figure 1 shows the architecture of a host in which BIH is implemented
as a socket API layer translator, i.e., as a "Bump-in-the-API".
+----------------------------------------------+
| +------------------------------------------+ |
| | | |
| | IPv4 applications | |
| | | |
| +------------------------------------------+ |
| +------------------------------------------+ |
| | Socket API (IPv4, IPv6) | |
| +------------------------------------------+ |
| +-[ API translator]------------------------+ |
| | +-----------+ +---------+ +------------+ | |
| | | Ext. Name | | Address | | Function | | |
| | | Resolver | | Mapper | | Mapper | | |
| | +-----------+ +---------+ +------------+ | |
| +------------------------------------------+ |
| +--------------------+ +-------------------+ |
| | | | | |
| | TCP(UDP)/IPv4 | | TCP(UDP)/IPv6 | |
| | | | | |
| +--------------------+ +-------------------+ |
+----------------------------------------------+
Figure 1: Architecture of a dual stack host using protocol
translation at socket layer
Figure 2 shows the architecture of a host in which BIH is implemented
as a network layer translator, i.e., a "Bump-in-the-Stack".
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+------------------------------------------------------------+
| +------------------------------------------+ |
| | IPv4 applications | |
| | Host's main DNS resolver | |
| +------------------------------------------+ |
| +------------------------------------------+ |
| | TCP/UDP | |
| +------------------------------------------+ |
| +------------------------------------------+ +---------+ |
| | IPv4 | | | |
| +------------------------------------------+ | Address | |
| +------------------+ +---------------------+ | Mapper | |
| | Protocol | | Extension Name | | | |
| | Translator | | Resolver | | | |
| +------------------+ +---------------------+ | | |
| +------------------------------------------+ | | |
| | IPv4 / IPv6 | | | |
| +------------------------------------------+ +---------+ |
+------------------------------------------------------------+
Figure 2: Architecture of a dual-stack host using protocol
translation at the network layer
Dual stack hosts defined in RFC 2893 [RFC2893] need applications,
TCP/IP modules and addresses for both IPv4 and IPv6. The proposed
hosts in this document have an API or network-layer translator to
allow existing IPv4 applications to communicate with IPv6-only peers.
The BIH architecture consists of an Extension Name Resolver, an
Address Mapper, and depending on implementation either a Function
Mapper or a Protocol Translator. It is worth noting that Extension
Name Resolver's placement is orthogonal decision to placement of
protocol translation. For example, the Extension Name Resolver may
reside in the socket API while protocol translation takes place at
the networking layer.
2.1. Function Mapper
The function mapper translates an IPv4 socket API function into an
IPv6 socket API function.
When detecting IPv4 socket API function calls from IPv4 applications,
the function mapper intercepts the function calls and invokes IPv6
socket API functions that correspond to the IPv4 socket API
functions.
The function mapper MUST NOT perform function mapping when the
application is initiating communications to the address range used by
local synthesis and the address mapping table does not have an entry
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mathching the address.
See Appendix B for a list of functions that MUST be intercepted by
the function mapper.
2.2. Protocol translator
The protocol translator translates IPv4 into IPv6 and vice versa
using the IP conversion mechanism defined in SIIT
[I-D.ietf-behave-v6v4-xlate]. To avoid unnecessary fragmentation,
host's IPv4 module should be configured with small enough MTU (IPv6
link MTU - 20 bytes).
Protocol translation SHOULD NOT be performend for IPv4 packets sent
to IPv4 address range used by local synthesis and for which mapping
table entry does not exist. The implementation SHOULD attempt to
route such packet via IPv4 interfaces instead.
2.3. Extension Name Resolver
The Extension Name Resolver (ENR) returns a proper answer in response
to the IPv4 application's name resolution request.
In the case of the socket API layer implementation option, when an
IPv4 application tries to do a forward lookup to resolve names via
the resolver library (e.g., gethostbyname()), BIH intercepts the
function call and instead calls the IPv6 equivalent functions (e.g.,
getnameinfo()) that will resolve both A and AAAA records. This
implementation option is name resolution protocol agnostic, and hence
supports techniques such as "hosts-file", NetBIOS, mDNS, and
essentially anything underlying operating system uses.
In the case of the network layer implementation option, the ENR
intercepts the A query and creates an additional AAAA query with
essentially the same content. The ENR will then collect replies to
both A and AAAA queries and, depending on results, either return an A
reply unmodified or synthesize a new A reply. The network layer
implementation option will only be able to catch applications' name
resolution requests that result in actual DNS queries, hence is more
limited when compared to socket API layer implementation option.
In either implementation option, if only AAAA records are available
for the queried name, the ENR asks the address mapper to assign a
local IPv4 address corresponding to each IPv6 address. In the case
of the API layer implementation option, the ENR will simply the make
API (e.g. gethostbyname) return the synthetic address. In the case
of the network-layer implementation option, the ENR synthesizes an A
record for the assigned IPv4 address, and delivers it up the stack.
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If there is a real A record available, the ENR SHOULD NOT synthesize
IPv4 addresses. By default an ENR implementation MUST NOT synthesize
IPv4 addresses when real A records exist.
If the response contains a CNAME or a DNAME record, then the CNAME or
DNAME chain is followed until the first terminating A or AAAA record
is reached.
Application | Network | ENR behavior
query | response |
------------+----------+------------------------
A | A | <return real A record>
A | AAAA | <synthesize A record>
A | A/AAAA | <return real A record>
Figure 3: ENR behavior illustration
2.3.1. Special exclusion sets for A and AAAA records
An ENR implementation MAY by default exclude certain IPv4 and IPv6
addresses seen on received A and AAAA records. The addresses to be
excluded by default SHOULD include martian addresses such as those
that should not appear in the DNS or on the wire. Additional
addresses MAY be excluded based on possibly configurable local
policies.
2.3.2. DNSSEC support
When the ENR is implemented at the network layer, the A record
synthesis can cause essentially the same issues as are described in
[I-D.ietf-behave-dns64] section 3. To avoid unwanted discarding of
synthetic A records on the host's main resolver, the host's main
resolver MUST send DNS questions with the CD "Checking Disabled" bit
cleared. The ENR can support DNSSEC as any resolver on a host.
When the ENR is implemented at the socket API level, there are no
problems with DNSSEC, as the ENR itself uses socket APIs for DNS
resolution.
DNSSEC can also be supported by configuring the (stub) resolver on a
host to trust validations done by the ENR located at network layer or
alternatively the validating resolver can implement ENR on itself.
In order to properly support DNSSEC, the ENR SHOULD be implemented at
the socket API level. If the socket API level implementation is not
possible, DNSSEC support SHOULD be provided by other means.
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2.3.3. Reverse DNS lookup
When an application initiates a reverse DNS query for a PTR record,
to find a name for an IP address, the ENR MUST check whether the
queried IP address can be found in the Address Mapper's mapping table
and is a local IP address. If an entry is found and the queried
address is locally generated, the ENR MUST initiate a corresponding
reverse DNS query for the real IPv6 address. In the case application
requested reverse lookup for an address not part of the local IPv4
address pool, e.g., a global address, the request MUST be forwarded
unmodified to the network.
For example, when an application initiates a reverse DNS query for a
synthesized locally valid IPv4 address, the ENR needs to intercept
that query. The ENR asks the address mapper for the IPv6 address
that corresponds to the IPv4 address. The ENR shall perform a
reverse lookup procedure for the destination's IPv6 address and
return the name received as a response to the application that
initiated the IPv4 query.
2.4. Address Mapper
The address mapper maintains a local IPv4 address pool. The pool
consists of private IPv4 addresses as per section 4.3. Also, the
address mapper maintains a table consisting of pairs of locally
selected IPv4 addresses and destinations' IPv6 addresses.
When the extension name resolver, translator, or the function mapper
requests the address mapper to assign an IPv4 address corresponding
to an IPv6 address, the address mapper selects and returns an IPv4
address out of the local pool, and registers a new entry into the
table. The registration occurs in the following 3 cases:
(1) When the extension name resolver gets only AAAA records for the
target host name in the dual stack or IPv6-only network and there is
no existing mapping entry for the IPv6 addresses. One or more local
IPv4 addresses will be returned to application and mappings for local
IPv4 addresses to real IPv6 addresses are created.
(2) When the extension name resolver gets both A records and AAAA
records, but the A records contain only excluded IPv4 addresses.
Behavior will follow the case (1).
(3) When the function mapper gets a socket API function call
triggered by a received IPv6 packet and there is no existing mapping
entry for the IPv6 source address (for example, client sent UDP
request to anycast address but response was received from unicast
address).
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Other possible combinations are outside of BIH and BIH is not
involved in those.
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3. Behavior and network Examples
Figure 4 illustrates a very basic network scenario. An IPv4-only
application is running on a host attached to the IPv6-only Internet
and is talking to an IPv6-only server. Communication is made
possible by Bump-In-the-Host.
+----+ +-------------+
| H1 |----------- IPv6 Internet -------- | IPv6 server |
+----+ +-------------+
v4 only
application
Figure 4: Network Scenario #1
Figure 5 illustrates a possible network scenario where an IPv4-only
application is running on a host attached to a dual-stack network,
but the destination server is running on a private site that is
numbered with public IPv6 addresses and private IPv4 addresses
without port forwarding setup on the NAT44. The only means to
contact the server is to use IPv6.
+----------------------+ +------------------------------+
| Dual Stack Internet | | IPv4 Private site (Net 10) |
| | | |
| | | +----------+ |
| | | | | |
| +----+ +---------+ | | |
| | H1 |-------- | NAT44 |-------------| Server | |
| +----+ +---------+ | | |
| v4 only | | +----------+ |
| application | | Dual Stack |
| | | 10.1.1.1 |
| | | AAAA:2009::1 |
| | | |
+----------------------+ +------------------------------+
Figure 5: Network Scenario #2
Illustrations of host behavior in both implementation options are
given here. Figure 6 illustrates the setup where BIH is implemented
as a bump in the API, and figure 7 illustrates the setup where BIH is
implemented as a bump in the stack.
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"dual stack" "host6"
IPv4 Socket | [ API Translator ] | TCP(UDP)/IP Name
appli- API | ENR Address Function| (v6/v4) Server
cation | Mapper Mapper |
| | | | | | | |
<<Resolve an IPv4 address for "host6".>> | | |
| | | | | | | |
|------->|------->| Query of IPv4 address for host6. | |
| | | | | | | |
| | |------------------------------------------------->|
| | | Query of 'A' records and 'AAAA' for host6 |
| | | | | | | |
| | |<-------------------------------------------------|
| | | Reply with the 'AAAA' record. | |
| | | | | | |
| | |<<The 'AAAA' record is resolved.>> |
| | | | | | |
| | |+++++++>| Request one IPv4 address |
| | | | corresponding to the IPv6 address.
| | | | | | |
| | | |<<Assign one IPv4 address.>> |
| | | | | | |
| | |<+++++++| Reply with the IPv4 address. |
| | | | | | |
|<-------|<-------| Reply with the IPv4 address |
| | | | | | |
| | | | | | |
<<Call IPv4 Socket API function >> | | |
| | | | | | |
|=======>|=========================>|An IPv4 Socket API function call
| | | | | | |
| | | |<+++++++| Request IPv6 addresses|
| | | | | corresponding to the |
| | | | | IPv4 addresses. |
| | | | | | |
| | | |+++++++>| Reply with the IPv6 addresses.
| | | | | | |
| | | | |<<Translate IPv4 into IPv6.>>
| | | | | | |
| An IPv6 Socket API function call.|=======================>|
| | | | | | |
| | | | |<<IPv6 data received |
| | | | | from network.>> |
| | | | | | |
| An IPv6 Socket API function call.|<=======================|
| | | | | | |
| | | | |<<Translate IPv6 into IPv4.>>
| | | | | | |
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| | | |<+++++++| Request IPv4 addresses|
| | | | | corresponding to the |
| | | | | IPv6 addresses. |
| | | | | | |
| | | |+++++++>| Reply with the IPv4 addresses.
| | | | | | |
|<=======|<=========================| An IPv4 Socket function call.
| | | | | | |
Figure 6: Example of BIH as API addition
"dual stack" "host6"
IPv4 stub TCP/ ENR address translator IPv6
app res. IPv4 mapper
| | | | | | | |
<<Resolve an IPv4 address for "host6".>> | |
|-->| | | | | | |
| |----------->| Query of 'A' records for "host6". | Name
| | | | | | | | Server
| | | |------------------------------------------->|
| | | | Query of 'A' records and 'AAAA' for "host6"
| | | | | | | | |
| | | |<-------------------------------------------|
| | | | Reply only with 'AAAA' record. |
| | | | | | | |
| | | |<<Only 'AAAA' record is resolved.>> |
| | | | | | | |
| | | |-------->| Request one IPv4 address |
| | | | | corresponding to each IPv6 address.
| | | | | | | |
| | | | |<<Assign IPv4 addresses.>> |
| | | | | | | |
| | | |<--------| Reply with the IPv4 address.
| | | | | | | |
| | | |<<Create 'A' record for the IPv4 address.>>
| | | | | | | |
| |<-----------| Reply with the 'A' record. | |
| | | | | | | |
|<--|<<Reply with the IPv4 address | | |
| | | | | | | |
<<Send an IPv4 packet to "host6".>>| | |
| | | | | | | |
|=======>|========================>| An IPv4 packet. |
| | | | | | | |
| | | | |<------| Request IPv6 addresses
| | | | | | corresponding to the IPv4
| | | | | | addresses. |
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| | | | | | | |
| | | | |------>| Reply with the IPv6|
| | | | | | addresses. |
| | | | | | | |
| | | | | |<<Translate IPv4 into IPv6.>>
| | | | | | | |
| | | |An IPv6 packet. |==========>|========>|
| | | | | | | |
| | | | | <<Reply with an IPv6 packet to.>>
| | | | | | | |
| | | |An IPv6 packet. |<==========|<========|
| | | | | | | |
| | | | | |<<Translate IPv6 into IPv4.>>
| | | | | | | |
|<=======|=========================| An IPv4 packet. |
| | | | | | | |
Figure 7: Example of BIH at the network layer
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4. Considerations
4.1. Socket API Conversion
IPv4 socket API functions are translated into IPv6 socket API
functions that are semantically as identical as possible and vice
versa. See Appendix B for the API list intercepted by BIH. However,
IPv4 socket API functions are not fully compatible with IPv6 since
IPv4 supports features that are not present in IPv6, such as
SO_BROADCAST.
4.2. Socket bindings
BIH SHOULD select a source address for a socket from the recommended
source address pool if a socket used for communications has not been
explicitly bound to any IPv4 address.
Binding of explicitly bound socket MUST NOT be changed by the BIH.
4.3. ICMP Message Handling
When an application needs ICMP messages values (e.g., Type, Code,
etc.) sent from the network layer, ICMPv4 message values MAY be
translated into ICMPv6 message values based on SIIT
[I-D.ietf-behave-v6v4-xlate], and vice versa.
4.4. IPv4 Address Pool and Mapping Table
The address pool consists of the private IPv4 addresses as per
[RFC1918]. This pool can be implemented at different granularities
in the node, e.g., a single pool per node, or at some finer
granularity such as per-user or per-process. In the case of a large
number of IPv4 applications communicating with a large number of IPv6
servers, the available address space may be exhausted if the
granularity is not fine enough. This should be a rare event and
chances will decrease as IPv6 support increases. The applications
may use IPv4 addresses they learn for much longer period than DNS
time-to-live indicates. Therefore, the mapping table entries should
be kept active for a long period of time. For example, a web browser
may initiate one DNS query and then create multiple TCP sessions over
time to the address it learns. When address mapping table clean-up
is required the BIH may utilize techniques used by network address
translators, such as described in [RFC2663], [RFC5382], and
[RFC5508].
The RFC1918 address space was chosen because generally legacy
applications understand it as a private address space. A new
dedicated address space would run a risk of not being understood by
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applications as private. 127/8 and 169.254/16 are rejected due to
possible assumptions applications may make when seeing those.
The RFC1918 addresses used by the BIH have a risk of conflicting with
addresses used in host's possible IPv4 interfaces and corresponding
local networks. The conflicts can be mitigated, but not fully
avoided, by using less commonly used portions of the RFC1918 address
space. Addresses from 172.16/12 are thought to be less likely to be
in conflict than addresses from 10/8 or 192.168/16 spaces. A source
address can usually be selected in non-conflicting manner, but small
possibility exist for synthesized destination addresses being in
conflict with real addresses used in local IPv4 networks.
The RECOMMENDED IPv4 addresses are following:
Primary source addresses: 172.21.112.0/30. Source addresses have to
be allocated because applications use getsockname() calls and in the
network layer mode an IP address of the IPv4 interface has to be
shown (e.g., by 'ifconfig'). More than one address is allocated to
allow implementation flexibility, e.g., for cases where a host has
multiple IPv6 interfaces. The source addresses are from different
subnets than destination addresses to that ensure applications would
not make on-link assumptions and would instead enable NAT traversal
functions.
Secondary source addresses: 10.170.224.0/20. These addresses are
recommended a if host has conflict with primary source addresses.
Primary destination addresses: 10.170.160.0/20. The address mapper
will select destination addresses primarily out of this pool.
Secondary destination addresses: 172.21.80.0/20. The address mapper
will select destination addresses out of this pool if the node has a
dual-stack connection conflicting with primary destination addresses.
4.5. Multi-interface
In the case of dual-stack destinations BIH MUST NOT do protocol
translation from IPv4 to IPv6 when the host has any IPv4 interfaces,
native or tunneled, available for use.
It is possible that an IPv4 interface is activated during BIH
operation, for example if a node moves to a coverage area of an IPv4-
enabled network. In such an event, BIH MUST stop initiating protocol
translation sessions for new connections and BIH MAY disconnect
active sessions. The choice of disconnection is left for
implementations and it may depend on whether IPv4 address conflict
occurs between addresses used by BIH and addresses used by the new
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IPv4 interface.
4.6. Multicast
Protocol translation for multicast is not supported.
4.7. DNS cache
When BIH shuts down, e.g., due to an IPv4 interface becoming
available, BIH MUST flush the node's DNS cache of possible locally
generated entries. This cache may be in the ENR itself, but also
possibly host's caching stub resolver.
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5. Considerations due ALG requirements
No ALG functionality is specified herein as ALG design is generally
not encouraged for host-based translation and as BIH is intended for
applications that do not include IP addresses in protocol payloads.
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6. Security Considerations
The security considerations of BIH mostly relies on that of
[I-D.ietf-behave-v6v4-xlate-stateful].
In the socket-layer implementation approach, the differences are due
to the address translation occurring at the API and not in the
network layer. That is, since the mechanism uses the API translator
at the socket API layer, hosts can utilize the security of the
network layer (e.g., IPsec) when they communicate with IPv6 hosts
using IPv4 applications via the mechanism. As such, there is no need
for DNS ALG as in NAT-PT, so there is no interference with DNSSEC
either.
In the network-layer implementation approach, IPv4-using IKE will not
work. This means IPv4-based IPsec/IKE using VPN solutions cannot
work through BIH. However, transport and application layer solutions
such as TLS or SSL-VPN do work through BIH.
The use of address pooling may open a denial-of-service attack
vulnerability. So BIH should employ the same sort of protection
techniques as NAT64 [I-D.ietf-behave-v6v4-xlate-stateful] does.
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7. Changes since RFC2767 and RFC3338
This document combines and obsoletes both [RFC2767] and [RFC3338].
The changes in this document mainly reflect the following components:
1. Supporting IPv6-only network connections
2. The IPv4 address pool uses private address instead of reserved
IPv4 addresses (0.0.0.1 - 0.0.0.255)
3. Extending ENR and address mapper to operate differently
4. Adding an alternative way to implement the ENR
5. Standards track instead of experimental/informational
6. Supporting reverse (PTR) queries
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8. Acknowledgments
The author thanks the discussion from Gang Chen, Dapeng Liu, Bo Zhou,
Hong Liu, Tao Sun, Zhen Cao, Feng Cao et al. in the development of
this document.
The efforts of Mohamed Boucadair, Dean Cheng, Lorenzo Colitti, Paco
Cortes, Marnix Goossens, Ala Hamarsheh, Ed Jankiewizh, Suresh
Krishnan, Julien Laganier, Yiu L. Lee, Jan M. Melen, Qibo Niu,
Pierrick Seite, Christian Vogt, Magnus Westerlund, Dan Wing, and
James Woodyatt in reviewing this document are gratefully
acknowledged.
Special acknowledgements go to Dave Thaler for his extensive review
and support.
The authors of RFC2767 acknowledged WIDE Project, Kazuhiko YAMAMOTO,
Jun MURAI, Munechika SUMIKAWA, Ken WATANABE, and Takahisa MIYAMOTO.
The authors of RFC3338 acknowledged implementation contributions by
Wanjik Lee (wjlee@arang.miryang.ac.kr) and i2soft Corporation
(www.i2soft.net).
The authors of Bump-in-the-Wire (BIW) (draft-ietf-biw-00.txt, October
2006), P. Moster, L. Chin, and D. Green, are acknowledged. Some
ideas and clarifications from BIW have been adapted to this document.
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9. References
9.1. Normative References
[I-D.ietf-behave-dns64]
Bagnulo, M., Sullivan, A., Matthews, P., and I. Beijnum,
"DNS64: DNS extensions for Network Address Translation
from IPv6 Clients to IPv4 Servers",
draft-ietf-behave-dns64-11 (work in progress),
October 2010.
[I-D.ietf-behave-v6v4-xlate]
Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
Algorithm", draft-ietf-behave-v6v4-xlate-23 (work in
progress), September 2010.
[I-D.ietf-behave-v6v4-xlate-stateful]
Bagnulo, M., Matthews, P., and I. Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers",
draft-ietf-behave-v6v4-xlate-stateful-12 (work in
progress), July 2010.
[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.
[RFC2767] Tsuchiya, K., HIGUCHI, H., and Y. Atarashi, "Dual Stack
Hosts using the "Bump-In-the-Stack" Technique (BIS)",
RFC 2767, February 2000.
[RFC2893] Gilligan, R. and E. Nordmark, "Transition Mechanisms for
IPv6 Hosts and Routers", RFC 2893, August 2000.
[RFC3338] Lee, S., Shin, M-K., Kim, Y-J., Nordmark, E., and A.
Durand, "Dual Stack Hosts Using "Bump-in-the-API" (BIA)",
RFC 3338, October 2002.
9.2. Informative References
[I-D.arkko-ipv6-transition-guidelines]
Arkko, J. and F. Baker, "Guidelines for Using IPv6
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Transition Mechanisms during IPv6 Deployment",
draft-arkko-ipv6-transition-guidelines-14 (work in
progress), December 2010.
[RFC2663] Srisuresh, P. and M. Holdrege, "IP Network Address
Translator (NAT) Terminology and Considerations",
RFC 2663, August 1999.
[RFC3493] Gilligan, R., Thomson, S., Bound, J., McCann, J., and W.
Stevens, "Basic Socket Interface Extensions for IPv6",
RFC 3493, February 2003.
[RFC5382] Guha, S., Biswas, K., Ford, B., Sivakumar, S., and P.
Srisuresh, "NAT Behavioral Requirements for TCP", BCP 142,
RFC 5382, October 2008.
[RFC5508] Srisuresh, P., Ford, B., Sivakumar, S., and S. Guha, "NAT
Behavioral Requirements for ICMP", BCP 148, RFC 5508,
April 2009.
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Appendix A. Implementation option for the ENR
It is not necessary to implement the ENR at the kernel level, but it
can be implemented instead at the user space by setting the host's
default DNS server to point to 127.0.0.1. DNS queries would then
always be sent to the ENR, which furthermore ensures that both A and
AAAA queries are sent to the actual DNS server and A queries are
always answered and required mappings created.
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Appendix B. API list intercepted by BIH
The following functions are the API list which SHOULD be intercepted
by BIH module when implemented at socket layer. Please note that
this list may not be fully exhaustive.
The functions that the application uses to pass addresses into the
system are:
bind()
connect()
sendmsg()
sendto()
gethostbyaddr()
getnameinfo()
The functions that return an address from the system to an
application are:
accept()
recvfrom()
recvmsg()
getpeername()
getsockname()
gethostbyname()
getaddrinfo()
The functions that are related to socket options are:
getsocketopt()
setsocketopt()
As well, raw sockets for IPv4 and IPv6 MAY be intercepted.
Most of the socket functions require a pointer to the socket address
structure as an argument. Each IPv4 argument is mapped into
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corresponding an IPv6 argument, and vice versa.
According to [RFC3493], the following new IPv6 basic APIs and
structures are required.
IPv4 new IPv6
------------------------------------------------
AF_INET AF_INET6
sockaddr_in sockaddr_in6
gethostbyname() getaddrinfo()
gethostbyaddr() getnameinfo()
inet_ntoa()/inet_addr() inet_pton()/inet_ntop()
INADDR_ANY in6addr_any
Figure 8
BIH MAY intercept inet_ntoa() and inet_addr() and use the address
mapper for those. Doing that enables BIH to support literal IP
addresses. However, IPv4 address literals can only be used after a
mapping entry between the IPv4 address and corresponding IPv6 address
has been created.
The gethostbyname() and getaddrinfo() calls return a list of
addresses. When the name resolver function invokes getaddrinfo() and
getaddrinfo() returns multiple IP addresses, whether IPv4 or IPv6,
they SHOULD all be represented in the addresses returned by
gethostbyname(). Thus if getaddrinfo() returns multiple IPv6
addresses, this implies that multiple address mappings will be
created; one for each IPv6 address.
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Authors' Addresses
Bill Huang
China Mobile
53A,Xibianmennei Ave.,
Xuanwu District,
Beijing 100053
China
Email: bill.huang@chinamobile.com
Hui Deng
China Mobile
53A,Xibianmennei Ave.,
Xuanwu District,
Beijing 100053
China
Email: denghui02@gmail.com
Teemu Savolainen
Nokia
Hermiankatu 12 D
FI-33720 TAMPERE
Finland
Email: teemu.savolainen@nokia.com
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