Internet DRAFT - draft-ietf-behave-v4v6-bih
draft-ietf-behave-v4v6-bih
Behave WG B. Huang
Internet-Draft H. Deng
Obsoletes: 3338, 2767 China Mobile
(if approved) T. Savolainen
Intended status: Standards Track Nokia
Expires: July 19, 2012 January 16, 2012
Dual Stack Hosts Using "Bump-in-the-Host" (BIH)
draft-ietf-behave-v4v6-bih-09
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. This document obsoletes RFC 2767 and
RFC 3338.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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This Internet-Draft will expire on July 19, 2012.
Copyright Notice
Copyright (c) 2012 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
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carefully, as they describe your rights and restrictions with respect
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This document may contain material from IETF Documents or IETF
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
1.2. Acknowledgement of previous work . . . . . . . . . . . . . 5
2. Components of the Bump-in-the-Host . . . . . . . . . . . . . . 6
2.1. Function Mapper . . . . . . . . . . . . . . . . . . . . . 8
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 . . . . . . . . . . . . . . . . . . . . 10
2.3.3. Reverse DNS lookup . . . . . . . . . . . . . . . . . . 10
2.3.4. DNS caches and synthetic IPv4 addresses . . . . . . . 10
2.4. Address Mapper . . . . . . . . . . . . . . . . . . . . . . 11
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
5. Application-Level Gateway requirements considerations . . . . 19
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
7. Security Considerations . . . . . . . . . . . . . . . . . . . 21
7.1. Implications on End-to-End Security . . . . . . . . . . . 21
7.2. Filtering . . . . . . . . . . . . . . . . . . . . . . . . 21
7.3. Attacks on BIH . . . . . . . . . . . . . . . . . . . . . . 21
7.4. DNS considerations . . . . . . . . . . . . . . . . . . . . 22
8. Changes since RFC2767 and RFC3338 . . . . . . . . . . . . . . 23
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 24
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 25
10.1. Normative References . . . . . . . . . . . . . . . . . . . 25
10.2. Informative References . . . . . . . . . . . . . . . . . . 25
Appendix A. API list intercepted by BIH . . . . . . . . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29
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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. Section 8 describes the reasons
for making RFC2767 and RFC3338 obsolete.
The supported class of applications includes those that use DNS for
IP address resolution and that do not embed IP address literals in
application-protocol payloads. This 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 [RFC6180].
BIH includes two major implementation alternatives: 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, former of which is the recommended implementation
alternative.
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 network layer the IPv4 packets are
intercepted and converted to IPv6 using the IP conversion mechanism
defined in Stateless IP/ICMP Translation Algorithm (SIIT) [RFC6145].
The protocol translation has the same benefits and drawbacks as SIIT.
The location of the BIH refers to the location of the protocol
translation function. The location of the IPv4 address and DNS A
record synthesis function is orthogonal to the location of the
protocol translation, and may or may not happen at the same location.
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", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119] .
This document uses terms defined in [RFC2460] and [RFC4213].
1.1. Terminology
DNS synthesis
DNS, A record, synthesis is a process where A type of DNS record
is created by Extension Name Resolver to contain synthetic IPv4
address.
Real IPv4 address
An IPv4 address of a remote node a host has learned, for example,
from DNS response to an A query.
Real IPv6 address
An IPv6 address of a remote node a host has learned, for example,
from DNS response to an AAAA query.
Synthetic IPv4 address
An IPv4 address that has meaning only inside a host and that is
used to provide IPv4 representation of remote node's real IPv6
address.
1.2. Acknowledgement of previous work
This document is a direct 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 provides IPv4-only applications on dual-stack hosts the
means to operate over IPv6. Section 8 covers the changes since those
documents.
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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 4213 [RFC4213] 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 legacy 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 the
Extension Name Resolver's placement is orthogonal to the placement of
protocol translation. For example, the Extension Name Resolver may
reside in the socket API while protocol translation takes place at
the network layer.
The choice between the socket API and the network layer architectures
varies case by case. While the socket API architecture alternative
is the recommended one, it may not always be possible to choose.
This may be the case, for example, when the used operating system
does not allow modifications to be done for API implementations, but
does allow addition of virtual network interfaces and related
software modules. On the other hand, sometimes it may not be
possible to introduce protocol translators inside the operating
system, but it may be easy to modify implementations behind the API
provided for applications. The choice of architecture also depends
on who is creating implementation of BIH. For example, an
application framework provider, an operating system provider, and a
device vendor may all choose different approaches due their different
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positions.
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 MUST intercept the function calls and invoke 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
mathching the address.
See Appendix A for an informational list of functions that would be
appropriate to intercept 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 [RFC6145]. To
avoid unnecessary fragmentation, the host's IPv4 module SHOULD be
configured with a small enough MTU (MTU of the IPv6 enabled link - 20
bytes).
Protocol translation cannot be performed for IPv4 packets sent to the
IPv4 address range used by local synthesis and for which a mapping
table entry does not exist. The implementation SHOULD attempt to
route such packets via IPv4 interfaces instead.
2.3. Extension Name Resolver
The Extension Name Resolver (ENR) returns an answer in response to
the IPv4 application's name resolution request.
In the case of the socket API layer implementation alternative, 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.,
getaddrinfo()) that will resolve both A and AAAA records. This
implementation alternative is name resolution protocol agnostic, and
hence supports techniques such as "hosts-file", NetBIOS, mDNS, and
anything else the underlying operating system uses.
In the case of the network layer implementation alternative, the ENR
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intercepts the A query and creates an additional AAAA query with
similar 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. If no reply for A query is
received after ENR implementation specific timeout, after reception
of positive AAAA response, the ENR MAY choose to proceed as if there
were only AAAA record available for the destination.
The network layer implementation alternative will only be able to
catch applications' name resolution requests that result in actual
DNS queries, hence is more limited when compared to the socket API
layer implementation alternative. Hence the socket API layer
alternative is RECOMMENDED.
In either implementation alternative, if DNS A record reply contains
non-excluded real IPv4 addresses the ENR MUST NOT synthesize IPv4
addresses.
The ENR asks the address mapper to assign a synthetic IPv4 address
corresponding to each received IPv6 address if the A record query
resulted in negative response, all received real IPv4 addresses were
excluded, or the A query timed out. The timeout value is
implementation specific and may be short in order to provide good
user experience.
In the case of the API layer implementation alternative, the ENR will
simply make the API (e.g. gethostbyname) return the synthetic IPv4
address. In the case of the network-layer implementation
alternative, the ENR synthesizes an A record for the assigned
synthetic IPv4 address, and delivers it up the stack. 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 |
---------------+-----------------------+----------------------------
IPv4 address(es) | IPv4 address(es) | return real IPv4 address(es)
IPv4 address(es) | IPv6 address(es) | synthesize IPv4 address(es)
IPv4 address(es) | IPv4/IPv6 address(es) | return real IPv4 address(es)
Figure 3: ENR behavior illustration
2.3.1. Special exclusion sets for A and AAAA records
An ENR implementation SHOULD by default exclude certain real IPv4 and
IPv6 addresses seen on received A and AAAA records. The addresses to
be excluded by default MAY include addresses such as those that
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should not appear in the DNS or on the wire (see [RFC6147] section
5.1.4 and [RFC5735]). 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 similar issues as are described in [RFC6147]
section 3. While running BIH, the main resolver of the host SHOULD
NOT perform validation of A records as synthetic A records created by
ENR would fail in validation. While not running BIH, host's resolver
can use DNSSEC in the same way that any other resolver can. The ENR
MAY support DNSSEC, in which case the (stub) resolver on a host can
be configured to trust validations done by the ENR located at the
network layer. In some cases the host's validating stub resolver can
implement the ENR by itself.
When the ENR is implemented at the socket API level, there are no
issues with DNSSEC use, as the ENR itself uses socket APIs for DNS
resolution. This approach is RECOMMENDED.
2.3.3. Reverse DNS lookup
When an application requests a reverse lookup (PTR query) for an IPv4
address, the ENR MUST check whether the queried IPv4 address can be
found in the Address Mapper's mapping table and is a synthetic IPv4
address. If an entry is found and the queried IPv4 address is
synthetic, the ENR MUST initiate a corresponding reverse lookup for
the real IPv6 address. In the case where the application requested a
reverse lookup for an address not part of the synthetic IPv4 address
pool, e.g., a global address, the request MUST be passed on
unmodified.
For example, when an application requests a reverse lookup for a
synthetic IPv4 address, the ENR needs to intercept that query. The
ENR asks the address mapper for the real IPv6 address that
corresponds to the synthetic 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.
2.3.4. DNS caches and synthetic IPv4 addresses
When BIH shuts down or address mapping table entries are cleared for
any reason, DNS cache entries for synthetic IPv4 addresses MUST be
flushed. There may be a DNS cache in the network-layer ENR itself,
but also at the host's stub resolver.
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2.4. Address Mapper
The address mapper maintains an IPv4 address pool that can be used
for IPv4 address synthesis. The pool consists of [RFC1918] IPv4
addresses as per section 4.4. Also, the address mapper maintains a
table consisting of pairs of synthetic IPv4 addresses and
destinations' real IPv6 addresses.
When the extension name resolver, translator, or the function mapper
requests the address mapper to assign a synthetic 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 three
cases:
(1) When the extension name resolver gets only IPv6 addresses for the
target host name and there is no existing mapping entry for the IPv6
addresses. One or more synthetic IPv4 addresses will be returned to
the application and mappings for synthetic IPv4 addresses to real
IPv6 addresses are created.
(2) When the extension name resolver gets both real IPv4 and IPv6
addresses, but the real IPv4 addresses contain only excluded IPv4
addresses (e.g., 127.0.0.1). The behavior will follow case (1).
(3) When the function mapper is triggered by a received IPv6 packet
and there is no existing mapping entry for the IPv6 source address
(for example, the client sent a UDP request to an anycast address but
a response was received from a unicast address).
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 not globally reachable IPv4
addresses, such as [RFC1918] addresses, without port forwarding set
up on the NAT44. The only means to contact the server is to use
IPv6.
+----------------------+ +------------------------------+
| Dual Stack Internet | | IPv4 Private site (Net 10) |
| | | IPv6 routed site |
| +---------+ +----------+ |
| +-| NAT44 |-------------+ | |
| +----+ | +---------+ | | |
| | H1 |---------+ | | | Server | |
| +----+ | +-----------+ | | |
| v4 only +-|IPv6 Router|-----------+ | |
| application +-----------+ +----------+ |
| | | Dual Stack |
| | | 10.1.1.1 |
| | | 2001:DB8::1 |
+----------------------+ +------------------------------+
Figure 5: Network Scenario #2
Illustrations of host behavior in both implementation alternatives
are given here. Figure 6 illustrates a setup where BIH (including
the ENR) is implemented at the sockets API layer, and Figure 7
illustrates a setup where BIH (including the ENR) is implemented at
the network layer.
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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 IPv4 addresses for "host6".>> | | |
| | | | | | | |
|------->|------->| Query IPv4 addresses for host6. | |
| | | | | | | |
| | |------------------------------------------------->|
| | | Query 'A' and 'AAAA' records for host6 |
| | | | | | | |
| | |<-------------------------------------------------|
| | | Reply with the 'AAAA' record. | |
| | | | | | |
| | |<<The 'AAAA' record is resolved.>> |
| | | | | | |
| | |+++++++>| Request synthetic IPv4 address |
| | | | corresponding to the IPv6 address.
| | | | | | |
| | | |<<Assign one synthetic IPv4 address.>>
| | | | | | |
| | |<+++++++| Reply with the synthetic IPv4 address.
| | | | | | |
|<-------|<-------| Reply with the IPv4 address |
| | | | | | |
| | | | | | |
<<Call IPv4 Socket API function >> | | |
| | | | | | |
|=======>|=========================>|An IPv4 Socket API action
| | | | | | |
| | | |<+++++++| Request IPv6 addresses|
| | | | | corresponding to the |
| | | | | synthetic IPv4 addresses.
| | | | | | |
| | | |+++++++>| Reply with the IPv6 addresses.
| | | | | | |
| | | | |<<Translate IPv4 into IPv6.>>
| | | | | | |
| An IPv6 Socket API action |=======================>|
| | | | | | |
| | | | |<<IPv6 data received |
| | | | | from network.>> |
| | | | | | |
| An IPv6 Socket API action |<=======================|
| | | | | | |
| | | | |<<Translate IPv6 into IPv4.>>
| | | | | | |
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| | | |<+++++++| Request synthetic IPv4 addresses
| | | | | corresponding to the |
| | | | | IPv6 addresses. |
| | | | | | |
| | | |+++++++>| Reply with the IPv4 addresses.
| | | | | | |
|<=======|<=========================| An IPv4 Socket API action
| | | | | | |
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 'A' records for "host6". | Name
| | | | | | | | Server
| | | |------------------------------------------->|
| | | | Query 'A' and 'AAAA' records for "host6"
| | | | | | | | |
| | | |<-------------------------------------------|
| | | | Reply only with 'AAAA' record. |
| | | | | | | |
| | | |<<Only 'AAAA' record is resolved.>> |
| | | | | | | |
| | | |-------->| Request synthetic IPv4 address
| | | | | corresponding to each IPv6 address.
| | | | | | | |
| | | | |<<Assign synthetic IPv4 addresses.>>
| | | | | | | |
| | | |<--------| Reply with the synthetic 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
| | | | | | synthetic IPv4 addresses.
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| | | | | | | |
| | | | |++++++>| Reply with the IPv6|
| | | | | | addresses. |
| | | | | | | |
| | | | | |<<Translate IPv4 into IPv6.>>
| | | | | | | |
| | | |An IPv6 packet. |==========>|========>|
| | | | | | | |
| | | | | <<Reply with an IPv6 packet.>>
| | | | | | | |
| | | |An IPv6 packet. |<==========|<========|
| | | | | | | |
| | | | | |<<Translate IPv6 into IPv4.>>
| | | | | | | |
| | | | |<++++++| Request synthetic IPv4
| | | | | | addresses corresponding
| | | | | | to the IPv6 addresses.
| | | | | | | |
| | | | |++++++>| Reply with the IPv4 addresses.
| | | | | | | |
|<=======|=========================| 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,
some 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.
The binding of an explicitly bound socket MUST NOT be changed by the
BIH.
4.3. ICMP Message Handling
ICMPv4 and ICMPv6 messages MUST be translated as defined by SIIT
[RFC6145]. In the network layer implementation alternative, protocol
translator MUST translate ICMPv6 packets to ICMPv4 and vice versa,
and in the socket API implementation alternative, the socket API MUST
handle conversions in similar fashion.
4.4. IPv4 Address Pool and Mapping Table
The address pool consists of the [RFC1918] private IPv4 addresses.
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 a 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
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dedicated address space would run a risk of not being understood by
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 the 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 a non-
conflicting manner, but a small possibility exists for synthesized
destination addresses being in conflict with real addresses used in
attached IPv4 networks.
The RECOMMENDED IPv4 addresses are following:
Primary source addresses: 172.21.112.0/20. 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 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 if a host has a 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
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implementations and it may depend on whether IPv4 address conflict
occurs between addresses used by BIH and addresses used by the new
IPv4 interface.
4.6. Multicast
Protocol translation for multicast is not supported.
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5. Application-Level Gateway requirements considerations
No Application-Level Gateway (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. IANA Considerations
There are no actions for IANA.
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7. Security Considerations
The security considerations of BIH follows closely, but not
completely, those of NAT64 [RFC6146] and DNS64 [RFC6147]. The
following sections are copied from RFC6146 and RFC6147 and modified
for BIH scenario.
7.1. Implications on End-to-End Security
Any protocols that protect IP header information are essentially
incompatible with BIH. This implies that end-to-end IPsec
verification will fail when the Authentication Header (AH) is used
(both transport and tunnel mode) and when ESP is used in transport
mode. This is inherent in any network-layer translation mechanism.
End-to-end IPsec protection can be restored, using UDP encapsulation
as described in [RFC3948]. The actual extensions to support IPsec
are out of the scope of this document.
7.2. Filtering
BIH creates binding state using packets flowing from the IPv4 side to
the IPv6 side. In accordance with the procedures defined in this
document following the guidelines defined in [RFC4787], a BIH
implementation MUST offer "Endpoint-Independent Mapping".
Implementations MAY also provide support for "Address-Dependent
Mapping" following the guidelines defined in [RFC4787].
The security properties, however, are determined by which packets the
BIH allows in and which it does not. The security properties are
determined by the filtering behavior and by the possible filtering
configuration in the filtering portions of the BIH, not by the
address mapping behavior.
7.3. Attacks on BIH
The BIH implementation itself is a potential victim of different
types of attacks. In particular, the BIH can be a victim of DoS
attacks. The BIH implementation has a limited number of resources
that can be consumed by attackers creating a DoS attack. The BIH has
a limited number of IPv4 addresses that it uses to create the
bindings. Even though the BIH performs address translation, it is
possible for an attacker to consume the synthetic IPv4 address pool
by triggering a host to issue DNS queries for names that cause ENR to
synthesise A records. DoS attacks can also affect other limited
resources available in the host running BIH such as memory or link
capacity. For instance, it is possible for an attacker to launch a
DoS attack on the memory of the BIH running device by sending
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fragments that the BIH will store for a given period. If the number
of fragments is large enough, the memory of the host could be
exhausted. BIH implementations MUST implement proper protection
against such attacks, for instance, allocating a limited amount of
memory for fragmented packet storage.
Another consideration related to BIH resource depletion refers to the
preservation of binding state. Attackers may try to keep a binding
state alive forever by sending periodic packets that refresh the
state. In order to allow the BIH to defend against such attacks, the
BIH implementation MAY choose not to extend the session entry
lifetime for a specific entry upon the reception of packets for that
entry through the external interface. However, such an action would
not allow one-way communication sessions to stay alive.
7.4. DNS considerations
BIH operates in combination with the DNS, and is therefore subject to
whatever security considerations are appropriate to the DNS mode in
which the BIH is operating (i.e. recursive or stub-resolver mode).
BIH has the potential to interfere with the functioning of DNSSEC,
because BIH modifies DNS answers, and DNSSEC is designed to detect
such modifications and to treat modified answers as bogus.
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8. Changes since RFC2767 and RFC3338
This document combines and obsoletes both [RFC2767] and [RFC3338].
The changes in this document mainly reflect the following:
1. RFC1918 addresses used used for synthesis
The RFC3338 used unassigned IPv4 addresses (e.g., 0.0.0.1 -
0.0.0.255) for synthetic IPv4 addresses. Those addresses should
not have been used and that may cause problems with applications.
It is preferable to use RFC1918 defined addresses instead, as
described in Section 4.4.
2. Support for reverse (PTR) DNS queries
Neither RFC2767 or RFC3338 included support for reverse (PTR) DNS
queries. This document adds the support at Section 2.3.3.
3. DNSSEC support
RFC2767 did not include DNSSEC considerations, which are now
included in Section 2.3.2
4. Architectural recommendation
This document recommends socket API layer implementation option
over network layer translation, i.e. recommends approach
introduced in RFC2767 over the approach of RFC3338.
5. Standards track document
RFC2767 is classified as Informational RFC and RFC3338 as
Experimental RFC. It was discussed and decided in the IETF that
this technology should be on the standards track.
6. Set of other extensions and improvements
Set of lesser extensions, improvements, and clarifications have
been introduced. These include but are not limited to: IPv4 and
IPv6 address exclusion sets at Section 2.3.1, host's DNS cache
considerations, ENR behaviour updates, updated security
considerations, example updates, and deployment scenario updates.
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9. Acknowledgments
The authors thank 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, Ralph Droms, Stephen Farrell, Fernando Gont, Marnix Goossens,
Wassim Haddad, Ala Hamarsheh, Dave Harrington, 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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10. References
10.1. Normative References
[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.
[RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms
for IPv6 Hosts and Routers", RFC 4213, October 2005.
[RFC4787] Audet, F. and C. Jennings, "Network Address Translation
(NAT) Behavioral Requirements for Unicast UDP", BCP 127,
RFC 4787, January 2007.
[RFC6145] Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
Algorithm", RFC 6145, April 2011.
[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, April 2011.
[RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van
Beijnum, "DNS64: DNS Extensions for Network Address
Translation from IPv6 Clients to IPv4 Servers", RFC 6147,
April 2011.
10.2. Informative References
[RFC2663] Srisuresh, P. and M. Holdrege, "IP Network Address
Translator (NAT) Terminology and Considerations",
RFC 2663, August 1999.
[RFC2767] Tsuchiya, K., HIGUCHI, H., and Y. Atarashi, "Dual Stack
Hosts using the "Bump-In-the-Stack" Technique (BIS)",
RFC 2767, February 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.
[RFC3493] Gilligan, R., Thomson, S., Bound, J., McCann, J., and W.
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Stevens, "Basic Socket Interface Extensions for IPv6",
RFC 3493, February 2003.
[RFC3948] Huttunen, A., Swander, B., Volpe, V., DiBurro, L., and M.
Stenberg, "UDP Encapsulation of IPsec ESP Packets",
RFC 3948, January 2005.
[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.
[RFC5735] Cotton, M. and L. Vegoda, "Special Use IPv4 Addresses",
BCP 153, RFC 5735, January 2010.
[RFC6180] Arkko, J. and F. Baker, "Guidelines for Using IPv6
Transition Mechanisms during IPv6 Deployment", RFC 6180,
May 2011.
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Appendix A. API list intercepted by BIH
The following informational list includes some of the API functions
that would be appropriate to intercept by BIH module when implemented
at the socket API layer. Please note that this list is not fully
exhaustive, as the function names and services that are available on
different APIs vary significantly.
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.
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Most of the socket functions require a pointer to the socket address
structure as an argument. Each IPv4 argument is mapped into
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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