Network Working Group C. Bao
Internet-Draft X. Li
Intended status: Informational CERNET Center/Tsinghua University
Expires: December 17, 2009 June 15, 2009
How Host A learns the IP address of Host B
draft-bcx-behave-learn-address-00
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Abstract
This document describes how host A learns the IP address of host B in
BEHAVE's "An IPv6 network to the IPv4 Internet" scenario. In this
scenario, an IPv6-only host A must know the IPv6 address
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representation of host B.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Host A learns IP address of host B in single address family . 3
3. Convert address representation between two address families . 3
4. Host A learns IP address of host B cross address families . . 4
4.1. The user of host A gets the IP address manually . . . . . 5
4.2. The DNS resolves the IP address from a domain name . . . . 5
4.3. The application performs referrals . . . . . . . . . . . . 5
5. Using different prefixes is considered harmful . . . . . . . . 5
5.1. Case 1: LIR is used to both represent IPv4 in IPv6 and
IPv6 in IPv4 . . . . . . . . . . . . . . . . . . . . . . . 6
5.2. Case 4: WKP is used to represent IPv4 in IPv6 and LIR
is used to represent IPv6 in IPv4 . . . . . . . . . . . . 7
5.2.1. Design a protocol to download the IPv4 address
database to host A . . . . . . . . . . . . . . . . . . 7
5.2.2. Add the NAT66 function to the stateless translator
based on the IPv4 address database . . . . . . . . . . 7
5.2.3. Configure the DNS64 based on the IPv4 address
database . . . . . . . . . . . . . . . . . . . . . . . 8
6. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
9. Informative References . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
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1. Introduction
This document describes how host A learns the IP address of host B in
BEHAVE's "An IPv6 network to the IPv4 Internet" scenario
[I-D.baker-behave-v4v6-framework]. In this scenario, an IPv6-only
host A must know the IPv6 address representation of host B, where
host B could be an IPv4-only host or an IPv6-only host with IPv4
address representation [I-D.xli-behave-v4v6-prefix].
This document is intended to assist the IETF community to understand
how host A learns the IP address of host B when an IPv4/IPv6
translator is involved. This document is not expected to be
published as an RFC. This document is part of the consideration for
a prefix document.
2. Host A learns IP address of host B in single address family
The host A can use one of the following methods to learn the IP
address of host B in single address family (AF).
o The user of host A gets the IP address manually.
o The DNS resolves the IP address from a domain name.
o The application performs referrals.
Note that the "user of host A gets the IP address manually" cannot be
avoided, e.g., someone typed http://202.38.102.2 into their browser,
or was re-directed there, or HTML had a link at that URI
[I-D.wing-behave-nat64-referrals].
3. Convert address representation between two address families
In order to performance the communication between two address
families (IPv4 and IPv6), an IPv4 host must have an IPv6
representation and an IPv6 host must have an IPv4 representation, as
discussed in [I-D.xli-behave-v4v6-prefix].
There are two translation schemes named stateless translation and
stateful translation and the methods to represent IPv4 in IPv6 and to
represent IPv6 in IPv4 are somehow different
[I-D.xli-behave-v4v6-prefix].
o For the stateless translation, the address mapping algorithm is
used both to represent IPv4 in IPv6 and IPv6 in IPv4. Note that
in this case, blocks of service provider's IPv4 addresses are
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mapped into IPv6 and used by physical IPv6 hosts. The original
IPv4 form of these blocks of service provider's IPv4 addresses are
used to represent the physical IPv6 hosts in IPv4. Note that the
stateless translation supports both IPv6 initiated as well as IPv4
initiated communications.
o For the stateful translation, the address mapping algorithm is
used to represent IPv4 in IPv6, while a session initiated state
table is used to represent IPv6 in IPv4. Note that in this case,
blocks of service provider's IPv4 addresses are maintained in the
translator as the IPv4 address pools and dynamically bind to the
specific IPv6 addresses. The original IPv4 form of these blocks
of service provider's IPv4 addresses are used to represent the
physical IPv6 host in IPv4. However, due to the dynamical
binging, the stateful translation only supports the IPv6 initiated
communication.
The embedded address format is used as the address mapping algorithm
[I-D.xli-behave-v4v6-prefix] as shown in Figure 1.
0 n 63 n+31 127
| | | | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| PREFIX | IPv4 addr | SUFFIX |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| | |
|<--- network part ---->|<--- host part --->|
Figure 1: Embedded Address Format
In this algorithm, the IPv4 address is embedded in IPv6 address after
the PREFIX. The PREFIX can either be LIR prefix or WKP prefix, where
the LIR is the prefix in the service provider's address block, while
the WKP is the prefix allocated by IANA and independent to the
service provider's address blocks. The advantage of LIR is that it
is part of the service provider's block and can be aggregated, while
the advantage of WKP is that it can be hard coded in the network
devices and in the end systems without manual configuration.
4. Host A learns IP address of host B cross address families
Assume host A is an IPv6 host and host B has an IPv4 address, then
host A must know the IPv6 representation of host B derived from host
B's IPv4 address.
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4.1. The user of host A gets the IP address manually
Assume host A has IPv6 address 2001:db8::1 and host B has IPv4
address 166.111.8.238, then the user of host A must convert this IPv4
address into its IPv6 representation [PREFIX:166.111.8.238:SUFFIX]
based on the address mapping algorithm [I-D.xli-behave-v4v6-prefix].
Note that the host A or the user of host A must know the PREFIX in
order to do the conversion. When the IPv4 address of host B and
PREFIX of the address mapping algorithm are known to host A, the IPv6
representation of host B can be created. In addition, if the PREFIX
is a WKP prefix, it can be hard coded in host A, while if the PREFIX
is a LIR prefix, it can be obtained by host A via the method
described in [I-D.wing-behave-learn-prefix]. For example, the user
of host A will type telnet [PREFIX:166.111.8.238:SUFFIX].
4.2. The DNS resolves the IP address from a domain name
Assume host A has IPv6 address 2001:db8::1 and host B has a domain
name www.edu.cn (there is an A record 202.205.109.203, but no AAAA
record), then the host A will ask the DNS64 for the AAAA record of
www.edu.cn. The DNS64 will get the A record 202.205.109.203 from the
global domain name system and convert to the AAAA record [PREFIX:
202.205.109.203:SUFFIX] based on the address mapping algorithm
[I-D.xli-behave-v4v6-prefix] [I-D.bagnulo-behave-dns64]. Note that
the DNS64 must know the PREFIX.
4.3. The application performs referrals
[I-D.wing-behave-nat64-referrals] discusses the referral for SIP and
BitTorrent.
In the case of SIP, "An IPv6 node SHOULD also be able to send and
receive media using IPv4 addresses, but if it cannot, it SHOULD
support STUN relay usage. Such a relay allows the IPv6 node to
indirectly send and receive media using IPv4
[I-D.ietf-sipping-v6-transition]. Thus, all IPv6 nodes running SIP
are expected to support ICE [I-D.ietf-mmusic-ice] which allows
simultaneous referral of multiple IP addresses, even from different
IP address families."
The BitTorrent uses HTTP URIs and DNS names, the examples in Sections
4.1 and 4.2 are also applied here.
5. Using different prefixes is considered harmful
The above examples are straightforward. However, for the stateless
translation in the "the user of host A gets the IP address manually"
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case and under the following condition, the situation gets very
complicated.
o As discussed in Section 3, for the stateless translation, the
address mapping algorithm is used both to represent IPv4 in IPv6
and IPv6 in IPv4. So when host A gets an arbitrary IPv4 address
of host B, it could be used by physical IPv4 host or it could be
mapped to IPv6 based on the address mapping algorithm and used by
physical IPv6 host. It is clear that host A does not have the
information to tell which case is applied.
o As discussed in Section 3, for the stateless translation, the
PREFIX can be either LIR or WKP. So the possibilities are:
1. Use LIR to represent IPv4 in IPv6 and use LIR to represent
IPv6 in IPv4.
2. Use WKP to represent IPv4 in IPv6 and use WKP to represent
IPv6 in IPv4.
3. Use LIR to represent IPv4 in IPv6 and use WKP to represent
IPv6 in IPv4.
4. Use WKP to represent IPv4 in IPv6 and use LIR to represent
IPv6 in IPv4.
[I-D.xli-behave-v4v6-prefix] discussed why WKP cannot be used to
represent IPv6 in IPv4, which means that case (2) and case (3) should
not be used. This document shows that case (1) should be used and
case (4) is considered harmful.
For the stateful translator, this problem does not exist, since the
PREFIX is only used to present IPv4 in IPv6.
5.1. Case 1: LIR is used to both represent IPv4 in IPv6 and IPv6 in
IPv4
Assume host B has IPv4 address 202.38.108.2, if the LIR is used to
both represent IPv4 in IPv6 and IPv6 in IPv4, the "more specific win"
routing principle will forward the packets to the right destination
[I-D.xli-behave-v4v6-prefix], no matter whether it is used by IPv4
host or by IPv6 host.
o If 202.38.108.2 is used by physical IPv4 host, the routing entry
covers the IPv4 address 202.38.108.2 will be [LIR::]/M, where M is
the LIR prefix length, which is corresponding to the IPv4 default
route. The IPv6 packets containing [PREFIX:202.38.108.2:SUFFIX]
as the destination address will be forwarded to the IPv4/IPv6
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translator and translated into the IPv4 packets and will be
forwarded to the host B 202.38.108.2.
o If 202.38.108.2 is mapped to IPv6 and used by physical IPv6 host,
the routing entry covers the IPv4 address 202.38.108.2 will be
[LIR:202.38.108.0:SUFFIX]/(M+k), where M is the LIR prefix length
and k is the prefix length of the service provider's IPv4 block
which is mapped to IPv6. The IPv6 packets containing [PREFIX:
202.38.108.2:SUFFIX] as the destination address will be forwarded
to the host B [PREFIX:202.38.108.2:SUFFIX] directly.
5.2. Case 4: WKP is used to represent IPv4 in IPv6 and LIR is used to
represent IPv6 in IPv4
In this case, depending on whether the IPv4 address is used by
physical IPv4 host or the physical IPv6 host, the WKP or LIR should
be correctly determined, since the former means representing IPv4 in
IPv6 and the latter means representing IPv6 in IPv4.
o If the IPv4 address 202.38.108.2 is used by IPv4 host, the routing
entry covers the address will be [WKP::]/M, where M is the WKP
prefix length. Then user of host A must type in telnet [WKP:
202.38.108.2:SUFFIX] to access host B.
o If the IPv4 address 202.38.108.2 is mapped to IPv6 and used by
IPv6 host, the routing entry covers the address will be [LIR:
202.38.108.0:SUFFIX]/(N+k), where N is the LIR prefix length and k
is the prefix length of the service provider's IPv4 block which is
mapped to IPv6, then the user of host A must type in telnet [LIR:
202.38.108.2:SUFFIX] to access host B.
Therefore, host A must know which prefix to use. There are several
methods to use, but they all have drawbacks.
5.2.1. Design a protocol to download the IPv4 address database to host
A
It is possible to design a protocol to download the database of all
the IPv4 blocks which are mapped to IPv6 and used by physical IPv6
hosts (in the service provider's administrative domain) to host A.
However, this is not a good solution due to the complicity.
5.2.2. Add the NAT66 function to the stateless translator based on the
IPv4 address database
If the IPv4/IPv6 translator can perform the NAT66 translation
function, i.e. swap the prefixes between LIR and WKP, then it is
possible for host A to use WKP to reach host B no matter which
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address family it locates. However, in this case, the routing is not
optimal. For example, host A can convert the host B's IPv4 address
202.38.108.2 to [WKP:202.38.108.2:SUFFIX]. The network will forward
the packets containing [WKP:202.38.108.2:SUFFIX] as the destination
address to the translator. Then the translator will check the
database of all the IPv4 blocks which are mapped to IPv6 and used by
physical IPv6 hosts.
o If the destination address in the packets does not match the entry
in the database, the translator will translate the IPv6 packets to
IPv4 and forward the packets to host B 202.38.108.2.
o If the destination address in the packets matches the entry in the
database, the NAT66 function will swap the WKP to LIR and re-route
the packets back to the IPv6 network to the host B [LIR:
202.38.108.2:SUFFIX].
However, this is not a good solution due to the nature of non-optimal
routing.
5.2.3. Configure the DNS64 based on the IPv4 address database
If the DNS64 is configured with database of all the IPv4 blocks which
are mapped to IPv6 and used by physical IPv6 hosts, the DNS64 can
return the AAAA record with the correct PREFIX.
However, this is not a good solution due to the lack of support for
"The user of host A gets the IP address manually" case.
6. Conclusions
In the unicast communication scheme, when host A needs to communicate
with host B, host A must know the IP address of host B. This document
describe how host A learn the IPv6 address representation of host B
in BEHAVE's "An IPv6 network to the IPv4 Internet" scenario.
It clear that for the stateless translation case, the PREFIX used to
represent IPv4 in IPv6 and to represent IPv6 in IPv4 must be the same
and LIR must be used.
7. Security Considerations
There is no security considerations.
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8. IANA Considerations
This memo adds no new IANA considerations.
9. Informative References
[I-D.bagnulo-behave-dns64]
Bagnulo, M., Sullivan, A., Matthews, P., Beijnum, I., and
M. Endo, "DNS64: DNS extensions for Network Address
Translation from IPv6 Clients to IPv4 Servers",
draft-bagnulo-behave-dns64-02 (work in progress),
March 2009.
[I-D.baker-behave-v4v6-framework]
Baker, F., Li, X., and C. Bao, "Framework for IPv4/IPv6
Translation", draft-baker-behave-v4v6-framework-02 (work
in progress), February 2009.
[I-D.baker-behave-v4v6-translation]
Baker, F., "IP/ICMP Translation Algorithm",
draft-baker-behave-v4v6-translation-02 (work in progress),
February 2009.
[I-D.ietf-behave-turn-ipv6]
Camarillo, G. and O. Novo, "Traversal Using Relays around
NAT (TURN) Extension for IPv6",
draft-ietf-behave-turn-ipv6-06 (work in progress),
March 2009.
[I-D.ietf-mmusic-ice]
Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols",
draft-ietf-mmusic-ice-19 (work in progress), October 2007.
[I-D.ietf-sipping-v6-transition]
Camarillo, G., "IPv6 Transition in the Session Initiation
Protocol (SIP)", draft-ietf-sipping-v6-transition-07 (work
in progress), August 2007.
[I-D.wing-behave-learn-prefix]
Wing, D., Wang, X., and X. Xu, "Learning the IPv6 Prefix
of an IPv6/IPv4 Translator",
draft-wing-behave-learn-prefix-02 (work in progress),
May 2009.
[I-D.wing-behave-nat64-referrals]
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Wing, D., "Referrals Across a NAT64",
draft-wing-behave-nat64-referrals-00 (work in progress),
March 2009.
[I-D.xli-behave-v4v6-prefix]
Bao, C., Baker, F., and X. Li, "IPv4/IPv6 Translation
Prefix Recommendation", draft-xli-behave-v4v6-prefix-00
(work in progress), April 2009.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006.
Authors' Addresses
Congxiao Bao
CERNET Center/Tsinghua University
Room 225, Main Building, Tsinghua University
Beijing 100084
CN
Phone: +86 62785983
Email: congxiao@cernet.edu.cn
Xing Li
CERNET Center/Tsinghua University
Room 225, Main Building, Tsinghua University
Beijing 100084
CN
Phone: +86 62785983
Email: xing@cernet.edu.cn
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