HIP Working Group M. Komu
Internet-Draft HIIT
Intended status: Experimental T. Henderson
Expires: May 4, 2009 The Boeing Company
P. Matthews
(Unaffiliated)
H. Tschofenig
Nokia Siemens Networks
A. Keranen, Ed.
Ericsson Research Nomadiclab
October 31, 2008
Basic HIP Extensions for Traversal of Network Address Translators
draft-ietf-hip-nat-traversal-05.txt
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Abstract
This document specifies extensions to the Host Identity Protocol
(HIP) to facilitate Network Address Translator (NAT) traversal. The
extensions are based on the use of the Interactive Connectivity
Establishment (ICE) methodology to discover a working path between
two end-hosts, and on standard techniques for encapsulating
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Encapsulating Security Payload (ESP) packets within the User Datagram
Protocol (UDP). This document also defines elements of procedure for
NAT traversal, including the optional use of a HIP relay server.
With these extensions HIP is able to work in environments that have
NATs and provides a generic NAT traversal solution to higher-layer
networking applications.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Overview of Operation . . . . . . . . . . . . . . . . . . . . 7
4. Protocol Description . . . . . . . . . . . . . . . . . . . . . 8
4.1. Relay Registration . . . . . . . . . . . . . . . . . . . . 8
4.2. ICE Candidate Gathering . . . . . . . . . . . . . . . . . 10
4.3. NAT Traversal Mode Negotiation . . . . . . . . . . . . . . 10
4.4. Connectivity Check Pacing Negotiation . . . . . . . . . . 12
4.5. Base Exchange via HIP Relay Server . . . . . . . . . . . . 12
4.6. ICE Connectivity Checks . . . . . . . . . . . . . . . . . 14
4.7. NAT Keepalives . . . . . . . . . . . . . . . . . . . . . . 15
4.8. Base Exchange without ICE Connectivity Checks . . . . . . 16
4.9. Simultaneous Base Exchange with and without UDP
Encapsulation . . . . . . . . . . . . . . . . . . . . . . 16
4.10. Sending Control Messages after the Base Exchange . . . . . 17
5. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . . 17
5.1. HIP Control Packets . . . . . . . . . . . . . . . . . . . 18
5.2. Connectivity Checks . . . . . . . . . . . . . . . . . . . 18
5.3. Keepalives . . . . . . . . . . . . . . . . . . . . . . . . 19
5.4. NAT Traversal Mode Parameter . . . . . . . . . . . . . . . 20
5.5. Connectivity Check Transaction Pacing Parameter . . . . . 20
5.6. Relay and Registration Parameters . . . . . . . . . . . . 21
5.7. LOCATOR Parameter . . . . . . . . . . . . . . . . . . . . 22
5.8. RELAY_HMAC Parameter . . . . . . . . . . . . . . . . . . . 23
5.9. Registration Types . . . . . . . . . . . . . . . . . . . . 23
5.10. ESP Data Packets . . . . . . . . . . . . . . . . . . . . . 24
6. Security Considerations . . . . . . . . . . . . . . . . . . . 24
6.1. Privacy Considerations . . . . . . . . . . . . . . . . . . 24
6.2. Opportunistic Mode . . . . . . . . . . . . . . . . . . . . 25
6.3. Base Exchange Replay Protection for HIP Relay Server . . . 25
6.4. Demuxing Different HIP Associations . . . . . . . . . . . 25
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 26
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 26
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26
10.1. Normative References . . . . . . . . . . . . . . . . . . . 26
10.2. Informative References . . . . . . . . . . . . . . . . . . 27
Appendix A. Selecting a Value for Check Pacing . . . . . . . . . 28
Appendix B. IPv4-IPv6 Interoperability . . . . . . . . . . . . . 29
Appendix C. Base Exchange through a Rendezvous Server . . . . . . 29
Appendix D. Document Revision History . . . . . . . . . . . . . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 30
Intellectual Property and Copyright Statements . . . . . . . . . . 32
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1. Introduction
HIP [RFC5201] is defined as a protocol that runs directly over IPv4
or IPv6, and HIP coordinates the setup of ESP security associations
[RFC5202] that are also specified to run over IPv4 or IPv6. This
approach is known to have problems traversing NATs and other
middleboxes [RFC5207]. This document defines HIP extensions for the
traversal of both Network Address Translator (NAT) and Network
Address and Port Translator (NAPT) middleboxes. The document
generally uses the term NAT to refer to these types of middleboxes.
Currently deployed NAT devices do not operate consistently even
though a recommended behavior is described in [RFC4787]. The HIP
protocol extensions in this document make as few assumptions as
possible about the behavior of the NAT devices so that NAT traversal
will work even with legacy NAT devices. The purpose of these
extensions is to allow two HIP-enabled hosts to communicate with each
other even if one or both of the communicating hosts are in a network
that is behind one or more NATs.
Using the extensions defined in this document, HIP end-hosts use
techniques drawn from the Interactive Connectivity Establishment
(ICE) methodology [I-D.ietf-mmusic-ice] to find operational paths for
the HIP control protocol and for ESP encapsulated data traffic. The
hosts test connectivity between different locators and try to
discover a direct end-to-end path between them. However, with some
legacy NATs, utilizing the shortest path between two end-hosts
located behind NATs is not possible without relaying the traffic
through a relay, such as a TURN server [RFC5128]. Because relaying
traffic increases the roundtrip delay and consumes resources from the
relay, with the extensions described in this document, hosts try to
avoid using the TURN server whenever possible.
HIP has defined a Rendezvous Server [RFC5204] to allow for mobile HIP
hosts to establish a stable point-of-contact in the Internet. This
document defines extensions to the Rendezvous Server that solve the
same problems but for both NATed and non-NATed networks. The
extended Rendezvous Server, called a "HIP relay server," forwards all
HIP control packets between an Initiator and Responder, allowing
Responders to be located behind NATs. This behavior is in contrast
to the HIP rendezvous service that forwards only the initial I1
packet of the base exchange, which is less likely to work in a NATed
environment [RFC5128]. Therefore, when using relays to traverse
NATs, HIP uses a HIP relay server for the control traffic and a TURN
server for the data traffic.
The basis for the connectivity checks is ICE [I-D.ietf-mmusic-ice].
[I-D.ietf-mmusic-ice] describes ICE as follows:
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"The Interactive Connectivity Establishment (ICE) methodology is a
technique for NAT traversal for UDP-based media streams (though
ICE can be extended to handle other transport protocols, such as
TCP) established by the offer/answer model. ICE is an extension
to the offer/answer model, and works by including a multiplicity
of IP addresses and ports in SDP offers and answers, which are
then tested for connectivity by peer-to-peer connectivity checks.
The IP addresses and ports included in the SDP and the
connectivity checks are performed using the revised STUN
specification [RFC5389], now renamed to Session Traversal
Utilities for NAT."
The standard ICE [I-D.ietf-mmusic-ice] is specified with SIP in mind
and it has some features that are not necessary or suitable as such
for other protocols. [I-D.rosenberg-mmusic-ice-nonsip] gives
instructions and recommendations on how ICE can be used for other
protocols and this document follows those guidelines.
Two HIP hosts that implement this specification communicate their
locators to each other in the HIP base exchange. The locators are
then paired with the locators of the other endpoint and prioritized
according to recommended and local policies. These locator pairs are
then tested sequentially by both of the end hosts. The tests may
result in multiple operational pairs but ICE procedures determine a
single preferred address pair to be used for subsequent
communication.
In summary, the extensions in this document define:
o UDP encapsulation of HIP packets
o UDP encapsulation of IPsec ESP packets
o registration extensions for HIP relay services
o how the ICE "offer" and "answer" are carried in the base exchange
o interaction with ICE connectivity check messages
o backwards compatibility issues with rendezvous servers
o a number of optimizations (such as when the ICE connectivity tests
can be omitted)
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2. Terminology
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 borrows terminology from [RFC5201], [RFC5206],
[RFC4423], [I-D.ietf-mmusic-ice], and [RFC5389]. Additionally, the
following terms are used:
Rendezvous server:
A host that forwards I1 packets to the Responder.
HIP relay server:
A host that forwards all HIP control packets between the Initiator
and the Responder.
TURN server:
A server that forwards data traffic between two end-hosts as
defined in [I-D.ietf-behave-turn].
Locator:
As defined in [RFC5206]: "A name that controls how the packet is
routed through the network and demultiplexed by the end-host. It
may include a concatenation of traditional network addresses such
as an IPv6 address and end-to-end identifiers such as an ESP SPI.
It may also include transport port numbers or IPv6 Flow Labels as
demultiplexing context, or it may simply be a network address."
It should noted that "address" is used in this document as a
synonym for locator.
LOCATOR (written in capital letters):
Denotes a HIP control message parameter that bundles multiple
locators together.
ICE offer:
The Initiator's LOCATOR parameter in a HIP I2 control message.
ICE answer:
The Responder's LOCATOR parameter in a HIP R2 control message.
Transport address:
Transport layer port and the corresponding IPv4/v6 address.
Candidate:
A transport address that is a potential point of contact for
receiving data.
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Host candidate:
A candidate obtained by binding to a specific port from an IP
address on the host.
Server reflexive candidate:
A translated transport address of a host as observed by a HIP
relay server or a STUN/TURN server.
Peer reflexive candidate:
A translated transport address of a host as observed by its peer.
Relayed candidate:
A transport address that exists on a TURN server. Packets that
arrive at this address are relayed towards the TURN client.
3. Overview of Operation
+-------+
| HIP |
+--------+ | Relay | +--------+
| TURN | +-------+ | STUN |
| Server | / \ | Server |
+--------+ / \ +--------+
/ \
/ \
/ \
/ <- Signaling -> \
/ \
+-------+ +-------+
| NAT | | NAT |
+-------+ +-------+
/ \
/ \
+-------+ +-------+
| Init- | | Resp- |
| iator | | onder |
+-------+ +-------+
Figure 1: Example network configuration
In an example configuration depicted in Figure 1, both Initiator and
Responder are behind one or more NATs, and both private networks are
connected to the public Internet. To be contacted from behind a NAT,
the Responder must be registered with a HIP relay server reachable on
the public Internet, and we assume as a starting point that the
Initiator knows both the Responder's HIT and the address of one of
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its relay servers (how the Initiator learns of the Responder's relay
server is outside of the scope of this document, but may be through
DNS or another name service).
The first steps are for both the Initiator and Responder to register
with a relay server (need not be the same one) and gather a set of
address candidates. Next, the HIP base exchange is carried out by
encapsulating the HIP control packets in UDP datagrams and sending
them through the Responder's relay server. As part of the base
exchange, each HIP host learns of the peer's candidate addresses
through the ICE offer/answer procedure embedded in the base exchange.
Once the base exchange is completed, HIP has established a working
communication session (for signaling) via a relay server, but the
hosts still work to find a better path, preferably without a relay,
for the ESP data flow. For this, ICE connectivity checks are carried
out until a working pair of addresses is discovered. At the end of
the procedure, if successful, the hosts will have enabled a UDP-based
flow that traverses both NATs, with the data flowing directly from
NAT to NAT or via a TURN server. Further HIP signaling can be sent
over the same address/port pair and is demultiplexed from data
traffic via a marker in the payload. Finally, NAT keepalives will be
sent as needed.
If either one of the hosts knows that it is not behind a NAT, hosts
can negotiate during the base exchange a different mode of NAT
traversal that does not use ICE connectivity checks, but only UDP
encapsulation of HIP and ESP. Also, it is possible for the Initiator
to simultaneously try a base exchange with and without UDP
encapsulation. If a base exchange without UDP encapsulation
succeeds, no ICE connectivity checks or UDP encapsulation of ESP are
needed.
4. Protocol Description
This section describes the normative behavior of the protocol
extension. Examples of packet exchanges are provided for
illustration purposes.
4.1. Relay Registration
HIP rendezvous servers operate in non-NATed environments and their
use is described in [RFC5204]. This section specifies a new
middlebox extension, called the HIP relay server, for operating in
NATed environments. A HIP relay server forwards all HIP control
packets between the Initiator and the Responder.
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End-hosts cannot use the HIP relay service for forwarding the ESP
data plane. Instead, they use TURN servers [I-D.ietf-behave-turn]
for that.
A HIP relay server MUST silently drop packets to a HIP relay client
that has not previously registered with the HIP relay. The
registration process follows the generic registration extensions
defined in [RFC5203] and is illustrated in Figure 2.
HIP HIP
Relay Relay
Client Server
| 1. UDP(I1) |
+------------------------------------------------------->|
| |
| 2. UDP(R1(REG_INFO(RELAY_UDP_HIP))) |
|<-------------------------------------------------------+
| |
| 3. UDP(I2(REG_REQ(RELAY_UDP_HIP))) |
+------------------------------------------------------->|
| |
| 4. UDP(R2(REG_RES(RELAY_UDP_HIP), REG_FROM)) |
|<-------------------------------------------------------+
Figure 2: Example Registration to a HIP Relay
In step 1, the relay client (Initiator) starts the registration
procedure by sending an I1 packet over UDP. It is RECOMMENDED that
the Initiator selects a random port number from the ephemeral port
range 49152-65535 for initiating a base exchange. However, the
allocated port MUST be maintained until all of the corresponding HIP
Associations are closed. Alternatively, a host MAY also use a single
fixed port for initiating all outgoing connections. The HIP relay
server MUST listen to incoming connections at UDP port HIPPORT.
In step 2, the HIP relay server (Responder) lists the services that
it supports in the R1 packet. The support for HIP-over-UDP relaying
is denoted by the RELAY_UDP_HIP value.
In step 3, the Initiator selects the services it registers for and
lists them in the REG_REQ parameter. The Initiator registers for HIP
relay service by listing the RELAY_UDP_HIP value in the request
parameter.
In step 4, the Responder concludes the registration procedure with an
R2 packet and acknowledges the registered services in the REG_RES
parameter. The Responder denotes unsuccessful registrations (if any)
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in the REG_FAILED parameter of R2. The Responder also includes a
REG_FROM parameter that contains the transport address of the client
as observed by the relay (Server Reflexive candidate). After the
registration, the client sends NAT keepalives periodically to the
relay to keep possible NAT bindings between the client and the relay
alive.
4.2. ICE Candidate Gathering
If a host is going to use ICE, it needs to gather a set of address
candidates. The candidate gathering SHOULD be done as defined in
Section 4.1 of [I-D.ietf-mmusic-ice]. Candidates need to be gathered
for only one media stream and component. Component ID 1 should be
used for ICE processing, where needed. Initiator takes the role of
the ICE controlling agent.
The candidate gathering can be done at any time, but it needs to be
done before sending an I2 or R2 if ICE is used for the connectivity
checks. It is RECOMMENDED that all three types of candidates (host,
server reflexive and relayed) are gathered to maximize probability of
successful NAT traversal. However, if no TURN server is used, and
the host has only a single local IP address to use, the host MAY use
the local address as the only host candidate and the address from the
REG_FROM parameter discovered during the relay registration as a
server reflexive candidate. In this case, no further candidate
gathering is needed.
4.3. NAT Traversal Mode Negotiation
This section describes the usage of a new non-critical parameter
type. The presence of the parameter in a HIP base exchange means
that the end-host supports NAT traversal extensions described in this
document. As the parameter is non-critical, it can be ignored by an
end-host which means that the host does not support or is not willing
to use these extensions.
The NAT traversal mode parameter applies to a base exchange between
end-hosts, but currently does not apply to a registration with a HIP
relay server. The NAT traversal mode negotiation in base exchange is
illustrated in Figure 3.
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Initiator Responder
| 1. UDP(I1) |
+------------------------------------------------------------->|
| |
| 2. UDP(R1(.., NAT_TRAVERSAL_MODE(list of modes), ..)) |
|<-------------------------------------------------------------+
| |
| 3. UDP(I2(.., NAT_TRAVERSAL_MODE(selected mode), LOCATOR..)) |
+------------------------------------------------------------->|
| |
| 4. UDP(R2(.., LOCATOR, ..)) |
|<-------------------------------------------------------------+
| .... |
Figure 3: Negotiation of NAT Traversal Mode
In step 1, the Initiator sends an I1 to the Responder. In step 2,
the Responder responds with an R1. The R1 contains a list of NAT
traversal modes the Responder supports in the NAT_TRAVERSAL_MODE
parameter as shown in Table 1.
+-------------------+-----------------------------------------------+
| Type | Purpose |
+-------------------+-----------------------------------------------+
| RESERVED | Reserved for future use |
| UDP-ENCAPSULATION | Use only UDP encapsulation of the HIP |
| | signaling traffic and ESP (no ICE |
| | connectivity checks) |
| ICE-STUN-UDP | UDP encapsulated control and data traffic |
| | with ICE-based connectivity checks using STUN |
| | messages |
+-------------------+-----------------------------------------------+
Table 1: NAT Traversal Modes
In step 3, the Initiator sends an I2 that includes a
NAT_TRAVERSAL_MODE parameter. It contains the mode selected by the
Initiator from the list of modes offered by the Responder. The I2
also includes the locators of the Initiator in a LOCATOR parameter.
The locator parameter in I2 is the "ICE offer".
In step 4, the Responder concludes the base exchange with an R2
packet. The Responder includes a LOCATOR parameter in the R2 packet.
The locator parameter in R2 is the "ICE answer".
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4.4. Connectivity Check Pacing Negotiation
As explained in [I-D.ietf-mmusic-ice], when a NAT traversal mode with
connectivity checks is used, new transactions should not be started
too fast to avoid congestion and overwhelming the NATs.
For this purpose, during the base exchange, hosts can negotiate a
transaction pacing value, Ta, using a TRANSACTION_PACING parameter in
I2 and R2 messages. The parameter contains the minimum time
(expressed in milliseconds) the host would wait between two NAT
traversal transactions, such as starting a new connectivity check or
retrying a previous check. If a host does not include this parameter
in the base exchange, a Ta value of 500ms MUST be used as that host's
minimum value. The value that is used by both of the hosts is the
higher out of the two offered values.
Hosts SHOULD NOT use values smaller than 20ms for the minimum Ta,
since such values may not work well with some NATs, as explained in
[I-D.ietf-mmusic-ice].
The minimum Ta value SHOULD be configurable. Guidelines for
selecting a Ta value are given in Appendix A. Currently this feature
applies only to the ICE-STUN-UDP NAT traversal mode.
4.5. Base Exchange via HIP Relay Server
This section describes how Initiator and Responder perform a base
exchange through a HIP relay server. The NAT traversal mode
negotiation (denoted as NAT_TM in the example) was described in the
previous section and shall not be repeated here. If a relay receives
an R1 or I2 packet without the NAT traversal mode parameter, it drops
it and sends a NOTIFY error message to the sender of the R1/I2.
It is RECOMMENDED that the Initiator sends an I1 packet encapsulated
in UDP when it is destined to an IPv4 address of the Responder.
Respectively, the Responder MUST respond to such an I1 packet with an
R1 packet over the transport layer and using the same transport
protocol. The rest of the base exchange, I2 and R2, MUST also use
the same transport protocol.
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I HIP relay R
| 1. UDP(I1) | |
+----------------------------->| 2. UDP(I1(RELAY_FROM)) |
| +------------------------------->|
| | |
| | 3. UDP(R1(RELAY_TO, NAT_TM)) |
| 4. UDP(R1(RELAY_TO),NAT_TM ) |<-------------------------------+
|<-----------------------------+ |
| | |
| 5. UDP(I2(LOCATOR),NAT_TM) | |
+----------------------------->| 6. UDP(I2(LOCATOR,RELAY_FROM),|
| | NAT_TM) |
| +------------------------------->|
| | |
| | 7. UDP(R2(LOCATOR,RELAY_TO)) |
| 8. UDP(R2(LOCATOR,RELAY_TO)) |<-------------------------------+
|<-----------------------------+ |
| | |
Figure 4: Base Exchange via a HIP Relay Server
In step 1 of Figure 4, the Initiator sends an I1 packet over the
transport layer to the HIT of the Responder (and IP address of the
relay). The source address is one of the locators of the Initiator.
In step 2, the HIP relay server receives the I1 packet at port
HIPPORT. If the destination HIT belongs to a registered Responder,
the relay processes the packet. Otherwise, the relay MUST drop the
packet silently. The relay appends a RELAY_FROM parameter to the I1
packet which contains the transport source address and port of the I1
as observed by the relay. The relay protects the I1 packet with
RELAY_HMAC as described in [RFC5204], except that the parameter type
is different (see Section 5.8). The relay changes the source and
destination ports and IP addresses of the packet to match the values
the Responder used when registering to the relay, i.e., the reverse
of the R2 used in the registration. The relay MUST recalculate the
transport checksum and forward the packet to the Responder.
In step 3, the Responder receives the I1 packet. The Responder
processes it according to the rules in [RFC5201]. In addition, the
Responder validates the RELAY_HMAC according to [RFC5204] and
silently drops the packet if the validation fails. The Responder
replies with an R1 packet to which it includes a RELAY_TO parameter.
The RELAY_TO parameter MUST contain same information as the
RELAY_FROM parameter, i.e., the Initiator's transport address, but
the type of the parameter is different. The RELAY_TO parameter is
not integrity protected by the signature of the R1 to allow pre-
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created R1 packets at the Responder.
In step 4, the relay receives the R1 packet. The relay drops the
packet silently if the source HIT belongs to an unregistered host.
The relay MAY verify the signature of the R1 packet and drop it if
the signature is invalid. Otherwise, the relay rewrites the source
address and port, and changes the destination address and port to
match RELAY_TO information. Finally, the relay recalculates
transport checksum and forwards the packet.
In step 5, the Initiator receives the R1 packet and processes it
according to [RFC5201]. It replies with an I2 packet that uses the
destination transport address of R1 as the source address and port.
The I2 contains a LOCATOR parameter that lists all the ICE candidates
(ICE offer) of the Initiator. The candidates are encoded using the
format defined in Section 5.7. The I2 packet MUST also contain the
NAT traversal mode parameter with ICE-STUN-UDP or some other selected
mode.
In step 6, the relay receives the I2 packet. The relay appends a
RELAY_FROM and a RELAY_HMAC to the I2 packet as explained in step 2.
In step 7, the Responder receives the I2 packet and processes it
according to [RFC5201]. It replies with an R2 packet and includes a
RELAY_TO parameter as explained in step 3. The R2 packet includes a
LOCATOR parameter that lists all the ICE candidates (ICE answer) of
the Responder. The RELAY_TO parameter is protected by the HMAC.
In step 8, the relay processes the R2 as described in step 4. The
relay forwards the packet to the Initiator.
Hosts MAY include the address of their HIP relay server in the
LOCATOR parameter in I2/R2. The traffic type of this address MUST be
"HIP signaling" and it MUST NOT be used as an ICE candidate. This
address MAY be used for HIP signaling also after the base exchange.
If the HIP relay server locator is not included in I2/R2 LOCATOR
parameters, it SHOULD NOT be used after the base exchange, but the
HIP signaling SHOULD use the same path as the data traffic.
4.6. ICE Connectivity Checks
If a HIP relay server was used, the Responder completes the base
exchange with the R2 packet through the relay. When the Initiator
successfully receives and processes the R2, both hosts have
transitioned to ESTABLISHED state. However, the destination address
the Initiator and Responder used for delivering base exchange packets
belonged to the HIP relay server. Therefore, the address of the
relay MUST NOT be used for sending ESP traffic. Instead, if a NAT
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traversal mode with ICE connectivity checks was selected, the
Initiator and Responder MUST start the connectivity checks.
Creating the check list for the ICE connectivity checks should be
performed as described in Section 5.7 of [I-D.ietf-mmusic-ice]
bearing in mind that only one media stream and component is needed
(so there will be only a single checklist and all candidates should
have the same component ID value). The actual connectivity checks
MUST be performed as described in Section 7 of [I-D.ietf-mmusic-ice].
Regular mode SHOULD be used for the candidate nomination.
Section 5.2 defines the details of the STUN control packets. As a
result of the ICE connectivity checks, ICE nominates a single
transport address pair to be used if an operational address pair was
found. The end-hosts MUST use this address pair for the ESP traffic.
The connectivity check messages MUST be paced by the value negotiated
during the base exchange as described in Section 4.4. If neither one
of the hosts announced a minimum pacing value, value of 500ms MUST be
used.
For retransmissions, the RTO value should be calculated as follows:
RTO = MAX (500ms, Ta * P)
In the RTO formula, Ta is the value used for the connectivity check
pacing and P is the number of pairs in the checklist when the
connectivity checks begin. This is identical to the formula in
[I-D.ietf-mmusic-ice] if there is only one checklist.
4.7. NAT Keepalives
To prevent NAT states from expiring, communicating hosts send
periodically keepalives to each other. HIP relay servers MAY refrain
from sending keepalives if it's known that they are not behind a
middlebox that requires keepalives. An end-host MUST send keepalives
every 15 seconds to refresh the UDP port mapping at the NAT(s) when
the control or data channel is idle. To implement failure tolerance,
an end-host SHOULD have shorter keepalive period.
The keepalives are STUN Binding Indications if the hosts have agreed
on ICE-STUN-UDP NAT traversal mode during the base exchange.
Otherwise, HIP NOTIFY messages MAY be used. A HIP relay server MUST
NOT forward the NOTIFY messages.
The communicating hosts MUST send keepalives to each other using the
transport locators they agreed to use for data and signaling when
they are in ESTABLISHED state. Also, the Initiator MUST send a
NOTIFY message to the relay to keep the NAT states alive on the path
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between the Initiator and relay when the Initiator has not received
any response to its I1 or I2 from the Responder in 15 seconds. The
relay MUST NOT forward the NOTIFY messages.
4.8. Base Exchange without ICE Connectivity Checks
In certain network environments, the ICE connectivity checks can be
omitted to reduce initial connection set up latency because base
exchange acts as an implicit connectivity test itself. There are
three assumptions about such as environments. First, the Responder
should have a long-term, fixed locator in the network. Second, the
Responder should not have a HIP relay server configured for itself.
Third, the Initiator can reach the Responder by simply UDP
encapsulating HIP and ESP packets to the host. Detecting and
configuring this particular scenario is prone to administrative
failure unless carefully planned.
In such a scenario, the Responder MAY include only the UDP-
ENCAPSULATION NAT traversal mode in the R1 message. Likewise, if the
Initiator knows that it can receive ESP and HIP signaling traffic by
using simply UDP encapsulation, it can choose the UDP-ENCAPSULATION
mode in the I2 message, if the Responder listed it in the supported
modes. In both of these cases the locators from I2 and R2 packets
will be used also for the UDP encapsulated ESP.
When no ICE connectivity checks are used, locator exchange and return
routability tests for mobility and multihoming are done as specified
in [RFC5206] with the exception that UDP encapsulation is used.
4.9. Simultaneous Base Exchange with and without UDP Encapsulation
The Initiator MAY also try to simultaneously perform a base exchange
with the Responder without UDP encapsulation. In such a case, the
Initiator sends two I1 packets, one without and one with UDP
encapsulation, to the Responder. The Initiator MAY wait for a while
before sending the other I1. How long to wait and in which order to
send the I1 packets can be decided based on local policy. For
retransmissions, the procedure is repeated.
The I1 packet without UDP encapsulation may arrive directly at the
Responder. When the recipient is the Responder, the procedures in
[RFC5201] are followed for the rest of the base exchange. The
Initiator may receive multiple R1 messages, with and without UDP
encapsulation, from the Responder. However, after receiving a valid
R1 and answering to it with an I2, further R1 messages that are not
retransmits of the original R1 MUST be ignored.
The I1 packet without UDP encapsulation may also arrive at a HIP-
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capable middlebox. When the middlebox is a HIP rendezvous server and
the Responder has successfully registered to the rendezvous service,
the middlebox follows rendezvous procedures in [RFC5204].
If the Initiator receives a NAT traversal mode parameter in R1
without UDP encapsulation, the Initiator MAY ignore this parameter
and send an I2 without UDP encapsulation and without any selected NAT
traversal mode. When the Responder receives the I2 without UDP
encapsulation and without NAT traversal mode, it will assume that no
NAT traversal mechanism is needed. The packet processing will be
done as described in [RFC5201]. The Initiator MAY store the NAT
traversal modes for future use e.g., to be used in case of mobility
or multihoming event which causes NAT traversal to be taken in to use
during the lifetime of the HIP association.
4.10. Sending Control Messages after the Base Exchange
After the base exchange, the end-hosts MAY send HIP control messages
directly to each other using the transport address pair established
for data channel without sending the control packets through the HIP
relay server. When a host does not get acknowledgments, e.g., to an
UPDATE or CLOSE message after a timeout based on local policies, the
host SHOULD resend the packet through the relay, if it was listed in
the LOCATOR parameter in the base exchange.
If control messages are sent through a HIP relay server, the sender
MUST include a RELAY_TO parameter to them. Also the HIP relay server
MUST add a RELAY_FROM parameter to the control messages it relays.
5. Packet Formats
The following subsections define the parameter and packet encodings
for the HIP, ESP and ICE connectivity check packets. All values MUST
be in network byte order.
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5.1. HIP Control Packets
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Port | Destination Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 32 bits of zeroes |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ HIP Header and Parameters ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Format of UDP-encapsulated HIP Control Packets
HIP control packets are encapsulated in UDP packets as defined in
Section 2.2 of [RFC3948], "rules for encapsulating IKE messages",
except a different port number is used. Figure 5 illustrates the
encapsulation. The UDP header is followed by 32 zero bits that can
be used to differentiate HIP control packets from ESP packets. The
HIP header and parameters follow the conventions of [RFC5201] with
the exception that the HIP header checksum MUST be zero. The HIP
header checksum is zero for two reasons. First, the UDP header
contains already a checksum. Second, the checksum definition in
[RFC5201] includes the IP addresses in the checksum calculation. The
NATs unaware of HIP cannot recompute the HIP checksum after changing
IP addresses.
A HIP relay server or a Responder without a relay MUST listen at UDP
port HIPPORT for incoming UDP encapsulated HIP control packets.
5.2. Connectivity Checks
The connectivity checks are performed using STUN Binding Requests as
defined in [I-D.ietf-mmusic-ice]. This section describes the details
of the parameters in the STUN messages.
The Binding Requests MUST use STUN short term credentials with HITs
of the Initiator and Responder as the username fragments. The
username is formed from the username fragments as defined in Section
7.1.1.3 of [I-D.ietf-mmusic-ice] with the Initiator being the
"offerer" and the Responder being the "answerer". The HITs are used
as usernames by expressing them in IPv6 hexadecimal ASCII format
[RFC1884], using lowercase letters, each 16 bit HIT fragment
separated by a one byte colon (hex 0x3a). The leading zeroes MUST
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NOT be omitted so that the username's size is fixed.
The STUN password is drawn from the DH keying material. Drawing of
HIP keys is defined in [RFC5201] Section 6.5 and drawing of ESP keys
in [RFC5202] Section 7. Correspondingly, the hosts MUST draw
symmetric keys for STUN according to [RFC5201] Section 6.5. The
hosts draw the STUN key after HIP keys, or after ESP keys if ESP
transform was successfully negotiated in the base exchange. Both
hosts draw a 128 bit key from the DH keying material, express that in
hexadecimal ASCII format using only lowercase letters (resulting in
32 numbers or lowercase letters), and use that as both the local and
peer password. [RFC5389] describes how hosts use the password for
message integrity of STUN messages.
Both the username and password are expressed in ASCII hexadecimal
format to prevent the need to run them through SASLPrep as defined in
[RFC5389].
The connectivity checks MUST contain PRIORITY attribute. They MAY
contain USE-CANDIDATE attribute as defined in Section 7.1.1.1 of
[I-D.ietf-mmusic-ice].
The Initiator is always in the controller role during a base
exchange. Hence, the ICE-CONTROLLED and ICE-CONTROLLING attributes
are not needed and SHOULD NOT be used. When two hosts are initiating
a connection to each other simultaneously, HIP state machine detects
it and assigns the host with the larger HIT as the Responder as
explained in Sections 4.4.2 and 6.7 in [RFC5201].
5.3. Keepalives
The keepalives for HIP associations that are created with ICE are
STUN Binding Indications, as defined in [RFC5389]. In contrast to
the UDP encapsulated HIP header, the non-ESP-marker between the UDP
header and the STUN header is excluded. Keepalives MUST contain the
FINGERPRINT STUN attribute but SHOULD NOT contain any other STUN
attributes and SHOULD NOT utilize any authentication mechanism. STUN
messages are demultiplexed from ESP and HIP control messages using
the STUN markers, such as the magic cookie value and the FINGERPRINT
attribute.
Keepalives for HIP associations created without ICE are HIP control
messages that have NOTIFY as the packet type. The NOTIFY messages do
not contain any parameters.
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5.4. NAT Traversal Mode Parameter
Format of the NAT_TRAVERSAL_MODE parameter is similar to the format
of the ESP_TRANSFORM parameter in [RFC5202] and is shown in the
Figure 6. This specification defines traversal mode identifiers UDP-
ENCAPSULATION and ICE-STUN-UDP. The identifier RESERVED is reserved
for future use. Future specifications may define more traversal
modes.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Mode ID #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mode ID #2 | Mode ID #3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mode ID #n | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type [ TBD by IANA: 608 ]
Length length in octets, excluding Type, Length, and padding
Reserved zero when sent, ignored when received
Mode ID defines the NAT traversal mode to be used
The following NAT traversal mode IDs are defined:
ID Value
RESERVED 0
UDP-ENCAPSULATION 1
ICE-STUN-UDP 2
Figure 6: Format of the NAT_TRAVERSAL_MODE parameter
The sender of a NAT_TRAVERSAL_MODE parameter MUST make sure that
there are no more than six (6) Mode IDs in one NAT_TRAVERSAL_MODE
parameter. The limited number of Mode IDs sets the maximum size of
the NAT_TRAVERSAL_MODE parameter.
5.5. Connectivity Check Transaction Pacing Parameter
The TRANSACTION_PACING parameter shown in Figure 7 contains only the
connectivity check pacing value, expressed in milliseconds, as 32 bit
unsigned integer.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Min Ta |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type [ TBD by IANA: 610 ]
Length length in octets, excluding Type and Length
Min Ta the minimum connectivity check transaction pacing
value the host would use
Figure 7: Format of the TRANSACTION_PACING parameter
5.6. Relay and Registration Parameters
Format of the REG_FROM, RELAY_FROM and RELAY_TO parameters is shown
in Figure 8. All parameters are identical except for the type.
REG_FROM is the only parameter covered with the signature.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Port | Protocol | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Address |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type [ TBD by IANA:
REG_FROM: 950
RELAY_FROM: 63998 (2^16 - 2^11 + 2^9 - 2)
RELAY_TO: 64002 (2^16 - 2^11 + 2^9 + 2) ]
Length 20
Port transport port number; zero when plain IP is used
Protocol IANA assigned, Internet Protocol number.
17 for UDP, 0 for plain IP.
Reserved reserved for future use; zero when sent, ignored
when received
Address an IPv6 address or an IPv4 address in "IPv4-Mapped
IPv6 address" format
Figure 8: Format of the REG_FROM, RELAY_FROM and RELAY_TO parameters
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REG_FROM contains the transport address and protocol where the HIP
relay server sees the registration coming from. RELAY_FROM contains
the address where the relayed packet was received from by the relay
server and the protocol that was used. The RELAY_TO contains same
information about the address where a packet should be forwarded to.
5.7. LOCATOR Parameter
The generic LOCATOR parameter format is the same as in [RFC5206].
However, presenting ICE candidates requires a new locator type. The
generic and NAT traversal specific locator parameters are illustrated
in Figure 9.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Traffic Type | Locator Type | Locator Length| Reserved |P|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Locator Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Locator |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Traffic Type | Loc Type = 2 | Locator Length| Reserved |P|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Locator Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Transport Port | Transp. Proto| Kind |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Priority |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SPI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Locator |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: LOCATOR parameter
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The individual fields in the LOCATOR parameter are described in
Table 2.
+-----------+----------+--------------------------------------------+
| Field | Value(s) | Purpose |
+-----------+----------+--------------------------------------------+
| Type | 193 | Parameter type |
| Length | Variable | Length in octets, excluding Type and |
| | | Length fields and padding |
| Traffic | 0-2 | Is the locator for HIP signaling (1), for |
| Type | | ESP (2), or for both (0) |
| Locator | 2 | "Transport address" locator type |
| Type | | |
| Locator | 7 | Length of the fields after Locator |
| Length | | Lifetime in 4-octet units |
| Reserved | 0 | Reserved for future extensions |
| Preferred | 0 | Not used for transport address locators; |
| (P) bit | | MUST be ignored by the receiver. |
| Locator | Variable | Locator lifetime in seconds |
| Lifetime | | |
| Transport | Variable | Transport layer port number |
| Port | | |
| Transport | Variable | IANA Assigned, transport layer Internet |
| Protocol | | Protocol number. Currently only UDP (17) |
| | | is supported. |
| Kind | Variable | 0 for host, 1 for server reflexive, 2 for |
| | | peer reflexive or 3 for relayed address |
| Priority | Variable | Locator's priority as described in |
| | | [I-D.ietf-mmusic-ice] |
| SPI | Variable | SPI value which the host expects to see in |
| | | incoming ESP packets that use this locator |
| Locator | Variable | IPv6 address or an "IPv4-Mapped IPv6 |
| | | address" format IPv4 address [RFC3513] |
+-----------+----------+--------------------------------------------+
Table 2: Fields of the LOCATOR parameter
5.8. RELAY_HMAC Parameter
The RELAY_HMAC parameter value has the TLV type 65520 (2^16 - 2^5 +
2^4). It has the same semantics as RVS_HMAC [RFC5204].
5.9. Registration Types
The REG_INFO, REG_REQ, REG_RESP and REG_FAILED parameters contain
values for HIP relay server registration. The value for
RELAY_UDP_HIP is 2.
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5.10. ESP Data Packets
[RFC3948] describes UDP encapsulation of the IPsec ESP transport and
tunnel mode. On the wire, the HIP ESP packets do not differ from the
transport mode ESP and thus the encapsulation of the HIP ESP packets
is same as the UDP encapsulation transport mode ESP. However, the
(semantic) difference to BEET mode ESP packets used by HIP is that IP
header is not used in BEET integrity protection calculation.
During the HIP base exchange, the two peers exchange parameters that
enable them to define a pair of IPsec ESP security associations (SAs)
as described in [RFC5202]. When two peers perform a UDP-encapsulated
base exchange, they MUST define a pair of IPsec SAs that produces
UDP-encapsulated ESP data traffic.
The management of encryption/authentication protocols and SPIs is
defined in [RFC5202]. The UDP encapsulation format and processing of
HIP ESP traffic is described in Section 6.1 of [RFC5202].
6. Security Considerations
6.1. Privacy Considerations
The locators are in plain text format in favor of inspection at HIP-
aware middleboxes in the future. The current draft does not specify
encrypted versions of LOCATORs even though it could be beneficial for
privacy reasons.
It is possible that an Initiator or Responder may not want to reveal
all of its locators to its peer. For example, a host may not want to
reveal the internal topology of the private address realm and it
discards host addresses. Such behavior creates non-optimal paths
when the hosts are located behind the same NAT. Especially, this
could be a problem with a legacy NAT that does not support routing
from the private address realm back to itself through the outer
address of the NAT. This scenario is referred to as the hairpin
problem [RFC5128]. With such a legacy NAT, the only option left
would be to use a relayed transport address from a TURN server.
As a consequence, a host may support locator-based privacy by leaving
out the reflexive candidates. However, the trade-off in using only
host candidates can produce suboptimal paths that can congest the
TURN server.
The use of HIP relay servers or TURN relays can be also useful for
protection against Denial-of-Service attacks. If a Responder reveals
only its HIP relay server addresses and Relayed candidates to
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Initiators, the Initiators can only attack the relays. That does not
prevent the Responder from initiating new outgoing connections if a
path around the relay exists.
6.2. Opportunistic Mode
A HIP relay server should have one address per relay client when a
HIP relay is serving more than one relay clients and supports
opportunistic mode. Otherwise, it cannot be guaranteed that the HIP
relay server can deliver the I1 packet to the intended recipient.
6.3. Base Exchange Replay Protection for HIP Relay Server
In certain scenarios, it is possible that an attacker, or two
attackers, can replay an earlier base exchange through a HIP relay
server by masquerading as the original Initiator and Responder. The
attack does not require the attacker(s) to compromise the private
key(s) of the attacked host(s). However, for this attack to succeed,
the Responder has to be disconnected from the HIP relay server.
The relay can protect itself against replay attacks by involving in
the base exchange by introducing nonces that the end-hosts (Initiator
and Responder) have to sign. One way to do this is to add
ECHO_REQUEST_M parameters to the R1 and I2 messages as described in
[I-D.heer-hip-middle-auth] and drop the I2 or R2 messages if the
corresponding ECHO_RESPONSE_M parameters are not present.
6.4. Demuxing Different HIP Associations
Section 5.1 of [RFC3948] describes a security issue for the UDP
encapsulation in the standard IP tunnel mode when two hosts behind
different NATs have the same private IP address and initiate
communication to the same Responder in the public Internet. The
Responder cannot distinguish between two hosts, because security
associations are based on the same inner IP addresses.
This issue does not exist with the UDP encapsulation of HIP ESP
transport format because the Responder uses HITs to distinguish
between different Initiators.
7. IANA Considerations
This section is to be interpreted according to [RFC2434].
This draft currently uses a UDP port in the "Dynamic and/or Private
Port" and HIPPORT. Upon publication of this document, IANA is
requested to register a UDP port and the RFC editor is requested to
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change all occurrences of port HIPPORT to the port IANA has
registered. The HIPPORT number 50500 should be used for initial
experimentation.
This document updates the IANA Registry for HIP Parameter Types by
assigning new HIP Parameter Type values for the new HIP Parameters:
RELAY_FROM, RELAY_TO and REG_FROM (defined in Section 5.6),
RELAY_HMAC (defined in Section 5.8), TRANSACTION_PACING (defined in
Section 5.5), and NAT_TRAVERSAL_MODE (defined in Section 5.4).
8. Contributors
This draft is a product of a design team which also included Marcelo
Bagnulo and Jan Melen who both have made major contributions to this
document.
9. Acknowledgments
Thanks for Jonathan Rosenberg and the rest of the MMUSIC WG folks for
the excellent work on ICE. In addition, the authors would like to
thank Andrei Gurtov, Simon Schuetz, Martin Stiemerling, Lars Eggert,
Vivien Schmitt, Abhinav Pathak for their contributions and Tobias
Heer, Teemu Koponen, Juhana Mattila, Jeffrey M. Ahrenholz, Kristian
Slavov, Janne Lindqvist, Pekka Nikander, Lauri Silvennoinen, Jukka
Ylitalo, Juha Heinanen, Joakim Koskela, Samu Varjonen, Dan Wing and
Jani Hautakorpi for their comments on this document.
Miika Komu is working in the Networking Research group at Helsinki
Institute for Information Technology (HIIT). The InfraHIP project
was funded by Tekes, Telia-Sonera, Elisa, Nokia, the Finnish Defence
Forces, and Ericsson and Birdstep.
10. References
10.1. Normative References
[I-D.ietf-behave-turn]
Rosenberg, J., Mahy, R., and P. Matthews, "Traversal Using
Relays around NAT (TURN): Relay Extensions to Session
Traversal Utilities for NAT (STUN)",
draft-ietf-behave-turn-11 (work in progress),
October 2008.
[I-D.ietf-mmusic-ice]
Rosenberg, J., "Interactive Connectivity Establishment
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(ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols",
draft-ietf-mmusic-ice-19 (work in progress), October 2007.
[RFC1884] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 1884, December 1995.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
[RFC3513] Hinden, R. and S. Deering, "Internet Protocol Version 6
(IPv6) Addressing Architecture", RFC 3513, April 2003.
[RFC4423] Moskowitz, R. and P. Nikander, "Host Identity Protocol
(HIP) Architecture", RFC 4423, May 2006.
[RFC5201] Moskowitz, R., Nikander, P., Jokela, P., and T. Henderson,
"Host Identity Protocol", RFC 5201, April 2008.
[RFC5202] Jokela, P., Moskowitz, R., and P. Nikander, "Using the
Encapsulating Security Payload (ESP) Transport Format with
the Host Identity Protocol (HIP)", RFC 5202, April 2008.
[RFC5203] Laganier, J., Koponen, T., and L. Eggert, "Host Identity
Protocol (HIP) Registration Extension", RFC 5203,
April 2008.
[RFC5204] Laganier, J. and L. Eggert, "Host Identity Protocol (HIP)
Rendezvous Extension", RFC 5204, April 2008.
[RFC5206] Nikander, P., Henderson, T., Vogt, C., and J. Arkko, "End-
Host Mobility and Multihoming with the Host Identity
Protocol", RFC 5206, April 2008.
[RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
"Session Traversal Utilities for NAT (STUN)", RFC 5389,
October 2008.
10.2. Informative References
[I-D.heer-hip-middle-auth]
Heer, T., Wehrle, K., and M. Komu, "End-Host
Authentication for HIP Middleboxes",
draft-heer-hip-middle-auth-01 (work in progress),
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July 2008.
[I-D.rosenberg-mmusic-ice-nonsip]
Rosenberg, J., "Guidelines for Usage of Interactive
Connectivity Establishment (ICE) by non Session
Initiation Protocol (SIP) Protocols",
draft-rosenberg-mmusic-ice-nonsip-01 (work in progress),
July 2008.
[RFC3948] Huttunen, A., Swander, B., Volpe, V., DiBurro, L., and M.
Stenberg, "UDP Encapsulation of IPsec ESP Packets",
RFC 3948, January 2005.
[RFC4787] Audet, F. and C. Jennings, "Network Address Translation
(NAT) Behavioral Requirements for Unicast UDP", BCP 127,
RFC 4787, January 2007.
[RFC5128] Srisuresh, P., Ford, B., and D. Kegel, "State of Peer-to-
Peer (P2P) Communication across Network Address
Translators (NATs)", RFC 5128, March 2008.
[RFC5207] Stiemerling, M., Quittek, J., and L. Eggert, "NAT and
Firewall Traversal Issues of Host Identity Protocol (HIP)
Communication", RFC 5207, April 2008.
Appendix A. Selecting a Value for Check Pacing
Selecting a suitable value for the connectivity check transaction
pacing is essential for the performance of connectivity check-based
NAT traversal. The value should not be too small so that the checks
do not cause congestion in the network or overwhelm the NATs. On the
other hand, too high pacing value makes the checks last for a long
time and thus increase the connection setup delay.
The Ta value may be configured by the user in environments where the
network characteristics are known beforehand. However, if the
characteristics are not know, it is recommended that the value is
adjusted dynamically. In this case it's recommended that the hosts
estimate the RTT between them and set the minimum Ta value so that
only two connectivity check messages are sent on every RTT.
One way to estimate the RTT is to use the time it takes for the HIP
relay server registration exchange to complete; this would give an
estimate on the registering host's access link's RTT. Also the I1/R1
exchange could be used for estimating the RTT, but since the R1 can
be cached in the network, or the relaying service can increase the
delay notably, it is not recommended.
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Appendix B. IPv4-IPv6 Interoperability
Currently relay client and server do not have to run any ICE
connectivity tests as described in Section 4.8. However, it could be
useful for IPv4-IPv6 interoperability when the HIP relay server
actually includes both the NAT traversal mode parameter and multiple
locators in R2. The interoperability benefit is that the relay could
support IPv4-based Initiators and IPv6-based Responders by converting
the network headers and recalculating UDP checksums.
Such an approach is underspecified in this document currently. It is
not yet recommended because it may consume resources at the relay and
requires also similar conversion support at the TURN relay for data
packets.
Appendix C. Base Exchange through a Rendezvous Server
When the Initiator looks up the information of the Responder from
DNS, it's possible that it discovers an RVS record [RFC5204]. In
this case, if the Initiator uses NAT traversal methods described in
this document, it uses its own HIP relay server to forward HIP
traffic to the Rendezvous server. The Initiator will send the I1
message using its HIP relay server which will then forward it to the
RVS server of the Responder. In this case, the value of the protocol
field in the RELAY_TO parameter MUST be IP since RVS does not support
UDP encapsulated base exchange packets. The Responder will send the
R1 packet directly to the Initiator's HIP relay server and the
following I2 and R2 packets are also sent directly using the relay.
In case the Initiator is not able to distinguish which records are
RVS address records and which are Responder's address records (e.g.,
if the DNS server did not support HIP extensions), the Initiator
SHOULD first try to contact the Responder directly, without using a
HIP relay server. If none of the addresses is reachable, it MAY try
out them using its own HIP relay server as described above.
Appendix D. Document Revision History
To be removed upon publication
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+-----------------------------+-------------------------------------+
| Revision | Comments |
+-----------------------------+-------------------------------------+
| draft-ietf-nat-traversal-00 | Initial version. |
| draft-ietf-nat-traversal-01 | Draft based on RVS. |
| draft-ietf-nat-traversal-02 | Draft based on Relay proxies and |
| | ICE concepts. |
| draft-ietf-nat-traversal-03 | Draft based on STUN/ICE formats. |
| draft-ietf-nat-traversal-04 | Issues 25-27,29-36 |
| draft-ietf-nat-traversal-05 | Issues 28,40-43,47,49,51 |
+-----------------------------+-------------------------------------+
Authors' Addresses
Miika Komu
Helsinki Institute for Information Technology
Metsanneidonkuja 4
Espoo
Finland
Phone: +358503841531
Fax: +35896949768
Email: miika@iki.fi
URI: http://www.hiit.fi/
Thomas Henderson
The Boeing Company
P.O. Box 3707
Seattle, WA
USA
Email: thomas.r.henderson@boeing.com
Philip Matthews
(Unaffiliated)
Email: philip_matthews@magma.ca
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Hannes Tschofenig
Nokia Siemens Networks
Linnoitustie 6
Espoo 02600
Finland
Phone: +358 (50) 4871445
Email: Hannes.Tschofenig@gmx.net
URI: http://www.tschofenig.com
Ari Keranen (editor)
Ericsson Research Nomadiclab
Hirsalantie 11
02420 Jorvas
Finland
Phone: +358 9 2991
Email: ari.keranen@ericsson.com
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