HIP Working Group M. Komu, Ed.
Internet-Draft HIIT
Intended status: Experimental S. Schuetz
Expires: January 7, 2008 M. Stiemerling
NEC
July 6, 2007
HIP Extensions for the Traversal of Network Address Translators
draft-ietf-hip-nat-traversal-02
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Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
The Host Identity Protocol (HIP) provides a new namespace that can be
used for uniquely identifying hosts in public and also in private
address realms. Usually, HIP control and data traffic cannot
traverse Network Address Translators (NATs), that hinders general
deployment. This document specifies NAT traversal extensions for
HIP. As HIP is located between network and transport layer, the
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extensions also provide general-purpose NAT traversal support for all
high-layer networking applications that run over HIP. The basic
design concepts for these extensions have been adopted from the
Interactive Connectivity Establishment (ICE) protocol to HIP. Using
the specified extensions, two HIP-capable hosts are able to
communicate with each other even when they are in different private
address realms.
Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. HIP Across NATs . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Port Number Selection . . . . . . . . . . . . . . . . . . 6
3.2. Relay Registration and NAT Detection . . . . . . . . . . . 6
3.3. Base Exchange via Relay . . . . . . . . . . . . . . . . . 8
3.4. Base Exchange without a Relay . . . . . . . . . . . . . . 10
3.5. Connectivity Tests . . . . . . . . . . . . . . . . . . . . 11
3.6. Selecting an Address Pair . . . . . . . . . . . . . . . . 13
3.7. Mobility . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.8. NAT Keepalives . . . . . . . . . . . . . . . . . . . . . . 15
3.9. Closing of HIP Associations . . . . . . . . . . . . . . . 16
3.10. Communication with HIP Hosts without NAT Traversal
Support . . . . . . . . . . . . . . . . . . . . . . . . . 16
4. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . . 17
4.1. HIP Control Packets . . . . . . . . . . . . . . . . . . . 17
4.2. Control Channel Keep-Alives . . . . . . . . . . . . . . . 18
4.3. RELAY_FROM, RELAY_TO and RELAY_VIA Parameters . . . . . . 18
4.4. LOCATOR Parameter . . . . . . . . . . . . . . . . . . . . 19
4.5. RELAY_HMAC . . . . . . . . . . . . . . . . . . . . . . . . 20
4.6. Registration Types . . . . . . . . . . . . . . . . . . . . 20
4.7. ESP Data Packets . . . . . . . . . . . . . . . . . . . . . 21
4.8. UDP Encapsulation/Decapsulation of IPsec BEET-Mode ESP . . 21
5. Firewall Traversal . . . . . . . . . . . . . . . . . . . . . . 23
6. Security Considerations . . . . . . . . . . . . . . . . . . . 23
6.1. A Difference to RFC3948 . . . . . . . . . . . . . . . . . 23
6.2. Privacy Considerations . . . . . . . . . . . . . . . . . . 24
6.3. Opportunistic Mode . . . . . . . . . . . . . . . . . . . . 24
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
8. Acknowlegements . . . . . . . . . . . . . . . . . . . . . . . 25
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26
9.1. Normative References . . . . . . . . . . . . . . . . . . . 26
9.2. Informative References . . . . . . . . . . . . . . . . . . 27
Appendix A. Differences to ICE . . . . . . . . . . . . . . . . . 28
Appendix B. Document Revision History . . . . . . . . . . . . . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29
Intellectual Property and Copyright Statements . . . . . . . . . . 31
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1. Terminology
In general, this document borrows the terminology from
[I-D.ietf-hip-base] and [RFC4423]. Additional terms are defined in
the table below." These draft e.g. define "Initiator" and
"Responder"
+---------------------+---------------------------------------------+
| Term | Explanation |
+---------------------+---------------------------------------------+
| Rendezvous server | A host that forwards I1 packets to the |
| | Responder |
| HIP Relay | A host that forwards all HIP control |
| | packets between an Initiator and Responder |
| ESP Relay | A host that forwards ESP traffic between |
| | two HIP-enabled hosts |
| Locator | A routable IPv4 or IPv6 address |
| Transport locator | Transport layer port and the corresponding |
| | IPv4/v6 address |
| Unreflexive locator | An IPv4 or IPv6 address of a network |
| | interface of a host |
| Relay reflexive | A translated transport locator of a host as |
| transport locator | observed by a relay |
| Peer reflexive | A translated transport locator of a host as |
| transport locator | observed by its peer |
| Leased transport | Transport locator of an ESP relay |
| locator | |
+---------------------+---------------------------------------------+
Table 1: Terminology
2. Introduction
The Host Identity Protocol (HIP) describes a new communication
mechanism for Internet hosts [RFC4423]. It introduces a new
namespace and protocol layer between the network and transport layers
that decouples the identifier and locator roles to support mobility
and multihoming in the Internet architecture. HIP also secures
application layer communications using IPsec ESP [I-D.ietf-hip-esp].
The HIP protocol [I-D.ietf-hip-base] cannot operate across legacy NAT
middleboxes as described in [I-D.irtf-hiprg-nat]. This document
specifies mechanisms that allow HIP to traverse through such NAT
middleboxes that are neither HIP-aware nor ESP-aware, without manual
configuration of the NAT middleboxes.
HIP introduces a new namespace for hosts that decouples the identity
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of a host from its location [RFC4423]. The namespace consists of
Host Identifiers which are public keys. The hosts create the
corresponding private keys by themselves which makes identity theft
more difficult.
The new namespace of HIP has some additional benefits when the
extensions defined in this document are used. First, it is possible
to address hosts behind a single NAT middlebox in a relatively simple
way. The NAT middlebox translates the locators, but the Host
Identifiers remain the same and can be used for uniquely identifying
a host inside the private address realm. Second, multiple services
on different hosts can share the same transport layer port number
behind a single legacy NAT. There is no multiplexing issue as long
as these hosts have different Host Identifiers and UDP encapsulation
is used for traversing the legacy NAT.
Several different types of NATs exist [RFC2663]. This document
describes 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
both types of middleboxes, unless it needs to distinguish between the
two types.
Three basic scenarios exist for NAT traversal. In the first case,
only the Initiator of a HIP base exchange is located behind a NAT.
In the second case, only the Responder of a HIP base exchange is
located behind a NAT. The respective peer is assumed to be located
at a publicly reachable address in both cases. In the third case,
both peers are located behind (possible different) NATs. All of the
use cases are addressed in the draft in a unified method that has
been adopted from Interactive Connectivity Establishment (ICE)
protocol [I-D.ietf-mmusic-ice] and adapted to HIP.
Legacy NAT devices do not operate consistently although the behavior
for new NAT devices has been unified in [RFC4787]. The HIP protocol
extensions in this document make as little assumptions as possible of
the behavior of the NAT devices so that NAT traversal will work even
with legacy NAT devices in the most general sense. The purpose of
the extensions is to allow two HIP-enabled hosts to communicate with
each other even if one or both communicating hosts are in private
address realms. With some legacy NAT devices, connecting two hosts
behind different address realms is impossible without relaying all
traffic through a third party host [I-D.ietf-behave-p2p-state]. As a
consequence, the relay host introduces additional hops between the
hosts and can become a point of network congestion. In the
extensions described in this document, the peers try to avoid the use
of a relay for data traffic and only make use of it when necessary.
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Hosts that always get a public addresses can use the rendezvous
services as described in [I-D.ietf-hip-rvs]. Hosts that can be
located in private-address realms may use a transport-layer based
relay service as defined in this document. Both rendezvous and relay
services forward HIP control packets, but the main difference is that
the rendezvous service forwards only the initial I1 packet of the
base exchange while all other HIP control packets are sent directly
between the communicating hosts. In contrast, the relay service
relays all HIP control packets because p2p-unfriendly NAT devices
drop the packets otherwise [I-D.ietf-behave-p2p-state]. The peers
use the control channel to communicate their current locators to each
other to find a direct path for carrying ESP encapsulated data
traffic. A direct path between the hosts enables efficient delivery
of data traffic without relaying of ESP packets through an
intermediary ESP relay. The direct path is searched using
connectivity tests.
The basis for the connectivity tests is ICE [I-D.ietf-mmusic-ice].
Two hosts communicate their transport locator (a port and an IP
address) to each other in a base exchange. The local locators are
paired with peer locators and the pairs are prioritized according to
their proximity. The locator pairs are tested sequentially in
priority order using return routability tests [I-D.ietf-hip-mm].
Both sides participate in the connectivity tests. The tests also
determine whether transport layer encapsulation is required or not.
As a result, the hosts either detect that no transport locator pairs
are working, or establish a number of working locator pairs and
select a single pair to be used for communication.
The same connectivity tests are also used in situations when a mobile
host moves to a different network. The mobile host communicates its
new location to the corresponding node through the relay server of
its peer and starts the connectivity tests.
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].
3. HIP Across NATs
This section describes NAT traversal between two HIP end-hosts. A
successful NAT traversal requires at least the Responder located in a
private address realm to register to a relay server. The use of the
relay is optional when the Responder is located in a public address
realm without rendezvous server.
The base exchange is relayed through the relay server. Next, the
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hosts test the reachability between the different locators to
construct a direct route. When a direct route is not possible, the
hosts resort to ESP relays. When locators of a host change, the
hosts test reachability of locators again and select the "optimal"
locator. End-hosts can tear down HIP associations using the CLOSE
mechanism through the relay.
3.1. Port Number Selection
This document defines only UDP encapsulation for HIP and ESP packets.
Further extensions may define bindings for other transport protocols.
The RECOMMENDED transport protocol is UDP.
It is RECOMMENDED that an Initiator selects a random port number
between the ephemeral port ranged 49152-65535 for initiating a base
exchange even for registration. However, the allocated port MUST be
maintained until all of the corresponding Host Associations are
closed. Alternatively, a host MAY also use a single fixed port for
initiating all outgoing connections.
A relay or a Responder without a relay MUST listen at transport port
HIPPORT for incoming UDP-encapsulated HIP control packets.
3.2. Relay Registration and NAT Detection
HIP rendezvous servers are used in non-NATted environments and its
use is described in [I-D.ietf-hip-rvs]. This section defines the
another types middleboxes, called HIP and ESP Relays, which are used
in NATted environments.
A HIP relay forwards UDP-encapsulated traffic, and in future
extensions, a relay may also forward TCP-encapsulated traffic. A
single relay may forward only HIP control packets, ESP traffic or
both. A host acting as a Responder in a private address realm SHOULD
use a HIP relay for NAT traversal. It is RECOMMENDED that the
Responder uses also an ESP relay to guarantee successful NAT
traversal with p2p-unfriendly NAT devices.
A relay MUST NOT forward any packets to a host that has not
successfully registered to the relay. The registration process
follows the generic registration extensions defined in
[I-D.ietf-hip-registration]. The registration process is illustrated
in Figure 1.
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Relay Relay
Client Server
| 1. I1 |
+------------------------------------------------------->|
| |
| 2. R1(LOCATOR,REG_INFO(RELAY_UDP_HIP,RELAY_UDP_ESP)) |
|<-------------------------------------------------------+
| |
| 3. I2(LOCATOR,REG_REQ(RELAY_UDP_HIP,RELAY_UDP_ESP)) |
+------------------------------------------------------->|
| |
| 4. R2(REG_RES(RELAY_UDP_HIP,RELAY_UDP_ESP),REG_FROM) |
|<-------------------------------------------------------|
| |
| 5. Connectivity tests |
|<------------------------------------------------------>|
Figure 1: Example registration to a relay
In the above figure, the end-host is referred to as a relay client
and the relay middlebox as a relay server. The registration is
piggybacked to a base exchange, but it can be done also using HIP
UPDATE control packets as described in [I-D.ietf-hip-registration].
In step 1, the relay client starts the registration procedure by
sending an I1 packet over the transport layer. The port selection
was explained in section Section 3.1.
In step 2, the Responder lists the services that it supports in the
R1 packet. The support for HIP-over-UDP relaying is denoted by
RELAY_UDP_HIP value and the support for ESP-over-UDP relaying is
denoted by a RELAY_UDP_ESP value in the REG_INFO parameter.
In step 3, the Initiator selects the services it registers to and
lists them in the REG_REQ parameter. In this example, the Initiator
registers both to HIP and ESP relay services.
In step 4, the relay server concludes the registration procedure with
an R2 packet and acknowledges the registered services in the REG_RES
parameter. The relay may also denote unsuccessful registrations in
the REG_FAILED parameter in R2. After the registration, the hosts
MUST send periodically NAT keepalive packets to each other as defined
later in this document.
In step 5, the client and server handle connectivity tests. The
procedure is described in a later section.
When the ESP relay registration was successful, the relay server uses
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the source IP address and port of the R2 packet (HIPPORT) to relay
ESP traffic with the client. This address-port pair of the relay is
referred to as a "leased transport locator" in this document. As the
port number may be shared by multiple clients, the ESP relay MUST
multiplex the ESP traffic based on SPIs and not the just the port
number.
The R2 packet also includes an REG_FROM parameter that indicates the
transport locator of the client as observed by the server. The
transport locator may be translated by a number of NAT middleboxes
between the client and the server. This locator is referred to as
the "relay reflexive transport locator" later in this document.
A single server can provide multiple HIP middlebox services or the
services can be distributed among multiple servers. The difference
between a HIP rendezvous server [I-D.ietf-hip-rvs] and a HIP relay
server depends on the registration. The rendezvous server processing
rules apply when the Responder has registered to a middlebox with the
RVS registration type. Correspondingly, the middlebox applies the
relay extensions defined in this document when the Responder has
registered using the relay registration types. When a single server
provides both rendezvous and relay services, they are multiplexed
depending on the absence or presence of transport layer
encapsulation.
The Relay Client MUST include a LOCATOR parameter in I2 which lists
all of the locators of the Initiator. The Relay Server MUST include
a LOCATOR parameter in R1, but it is RECOMMENDED that the LOCATOR
parameter includes only the source transport LOCATOR of R1 as the
only locator. The case when the Relay Server includes more locators
may require IP header conversion between IPv4 and IPv6, insertion, or
removal of, UDP header and fragmentation handling. Multiple locators
in R1 is left for further experimentation.
3.3. Base Exchange via Relay
It is RECOMMENDED that the Initiator sends an I1 packet over the
transport layer when it is destined to an IPv4 address of the
Responder. Respectively, the Responder MUST respond to a such 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 be sent over the transport layer. However, the transport layer
encapsulation can be unnecessary when there are no NATs between the
Initiator and Responder. This will be detected in the connectivity
tests described in the next section.
When the Initiator has an IPv6 address and it has discovered only an
IPv6 address for the peer, it MUST send it directly over IP. In such
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a case, the Initiator MUST follow the procedures described in
[I-D.ietf-hip-base]. Otherwise, it is RECOMMENDED that the Initiator
proceeds as shown in Figure 2.
I Relay R
| 1. I1 | |
+------------------------------->| 2. I1(RELAY_FROM) |
| +--------------------------->|
| | |
| | 3. R1(LOCATOR,RELAY_TO) |
| 4. R1(LOCATOR,RELAY_TO) |<---------------------------+
|<-------------------------------+ |
| | |
| 5. I2(LOCATOR) | |
+------------------------------->| |
| | 6. I2(LOCATOR,RELAY_FROM) |
| +--------------------------->|
| | |
| | 7. R2(RELAY_TO) |
| 8. R2(RELAY_TO) |<---------------------------+
|<-------------------------------+ |
| | |
Figure 2: Base Exchange via a relay
In step 1 of the figure, the Initiator discovers the HIT of the
Responder and the IPv4 address of the relay of the Responder. The
Initiator sends an I1 packet over the transport layer to the HIT of
the Responder. The port selection was explained in Section 3.1. The
source address is one of the routable addresses of the host is called
"unreflexive locators" in this document.
In step 2, the relay 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.
The relay MUST append a RELAY_FROM parameter to the I1 packet which
preserves the transport source address and port of the Initiator.
The relay protects the I1 packet with RELAY_HMAC as described in
[I-D.ietf-hip-rvs], except that the parameter type is different. The
relay MUST change the transport source to and destination 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 forwards the packet
to the Responder.
In step 3, the Responder receives the I1 packet at the transport
layer. The Responder MUST process it according to the rules in
[I-D.ietf-hip-base]. In addition, the Responder MUST validate the
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RELAY_HMAC according to [I-D.ietf-hip-rvs] and drop the packet if the
validation fails. The Responder replies with an R1 packet that MUST
contain a LOCATOR parameter that lists the locators of the Responder.
The locator list consists of unreflexive, reflexive and leased
transport locators of the Responder. The R1 packet also contains a
RELAY_TO parameter. The RELAY_TO parameter contains same information
as the RELAY_FROM parameter, i.e., Initiator transport locator, 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-
created R1 packets at the Responder.
In step 4, the relay receives the R1 packet. The relay MUST drop the
packet if the source HIT belongs to an unregistered host. The relay
MAY verify the signature of the R1 packet and drop it when the
signature is invalid. Otherwise, the relay changes the destination
transport header to match RELAY_TO information, recalculates
transport checksum and forwards the packet.
In step 5, the Initiator receives the R1 packet and processes it
accordingly to [I-D.ietf-hip-base]. It replies with an I2 packet
that has the same transport locator as R1, but the source and
destination ports are swapped. The I2 contains a LOCATOR parameter
containing the listing unreflexive, reflexive and leased transport
locators of the Initiator
In step 6, the relay receives the I2 packet. The relay appends a
RELAY_FROM and a RELAY_HMAC to the I2 packet as in the second step.
In step 7, the Responder receives the I2 packet and processes it
according to [I-D.ietf-hip-base]. It replies with an R2 packet and
includes a RELAY_TO parameter as in step three. The RELAY_TO
parameter is protected by the HMAC.
In step 8, the relay processes the R2 as described in step four. The
relay forwards the packet to the Responder.
3.4. Base Exchange without a Relay
A host that has a publicly addressable, fixed IP address MAY exclude
registration to a Relay. As the Relay is not present, the host MUST
listen at HIPPORT for transport-encapsulated HIP and ESP packets. An
UDP-encapsulated base exchange with such an host does not have the
RELAY_TO and RELAY_FROM parameters present. Connectivity tests MUST
be handled as defined in the following section before any ESP traffic
is allowed.
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3.5. Connectivity Tests
The base exchange is completed with an R2 packet. Then, the state of
the HIP associations at both peers is ESTABLISHED, but the peers MUST
NOT allow any ESP traffic until the connectivity tests described in
the next section are performed successfully. All of the locators,
except the relay address, are in UNVERIFIED state. In the
connectivity tests, the hosts test connectivity between different
locator pairs in order to find a working one. The connectivity tests
are illustrated in Figure 3. In this example, both hosts are behind
NATs.
I Relay R
| 2. R2(RELAY_TO) | 1. R2(RELAY_TO) |
+<------------------------------+-------------------------------+
| |
| 3. UPDATE(ECHO_REQUEST,FROM_PEER) NAT-R:DROP|
+------------------------------------------------------------->X|
| |
| 4. UPDATE(ECHO_REQUEST,FROM_PEER) |
|<--------------------------------------------------------------+
| |
| 5. UPDATE(ECHO_RESP,TO_PEER) |
+-------------------------------------------------------------->+
| |
| 6. UPDATE(ECHO_REQUEST,FROM_PEER) |
+-------------------------------------------------------------->|
| |
| 7. UPDATE(ECHO_RESP,TO_PEER) |
|<--------------------------------------------------------------+
| |
Figure 3: Connectivity tests
The connectivity tests are handled as the mobility extensions defined
in [I-D.ietf-hip-mm] and are therefore subject to the same processing
rules. The packets include ESP_INFO, SEQ, ACK, HMAC, SIGNATURE
parameters that are omitted in this section for simplicity. The
differences to the mobility extensions are described in this section.
In steps 1 and 2, the R2 packet is relayed from the Responder through
the Relay to the Responder. After this, both hosts start
connectivity tests using the return routability tests defined in
[I-D.ietf-hip-mm]. The return routability tests are used to probe
for connectivity between each locator pair obtained from the local
and peer locators obtained during base exchange. The return
routability tests are also used as a UDP hole punching mechanism.
The tests are carried in certain order which determined by the
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priorization algorithm defined in the next section.
As an example, let's consider the case where hosts are testing each
others outermost NAT addresses, i.e., relay reflexive transport
locators. In step 3, host I sends an UPDATE message containing an
ECHO_REQUEST to the R. This will punch a hole the NAT of I, but the
NAT of R drops the message because the NAT of R has no state with I.
In step 4, R starts also reachability detection by sending an UPDATE
with ECHO_REQUEST. This traverses the NAT of I successfully because
Initiator had already punched an hole into its NAT in step 3. The
Responder replies using ECHO_RESPONSE in step 5. Upon receiving the
ECHO_RESPONSE, the Responder transitions the address pair to VERIFIED
state.
In step 6, host I starts a new return routability test either due to
a retransmission timer or as a reaction to UPDATE with ECHO_REQUEST
received from R. In step 7, host R receives and sends a response to
I. Upon receiving the response, host R transitions the locator pair
being tested to VERIFIED state.
All locators in UNVERIFIED state MUST be retransmitted RTIME times.
The retransmission packets MUST be paced Ta ms apart as defined in
[I-D.ietf-mmusic-ice]. The retransmission are ordered in a sequence
determined by the priority of the transport locator pairs, as
described in the next section.
The source address of the UPDATE messages containing ECHO_REQUEST
parameter is always an unreflexive IPv4 locator of the host. The
destination locator is the peer's unreflexive, reflexive or leased
transport locator, depending on which address is being tested for
reachability. Implementations may add RTT measurement information to
the ECHO_REQUEST parameter in addition to a nonce.
The UPDATE messages carrying ECHO_REQUEST include a FROM_PEER
parameter. The sender of the UPDATE MUST copy the source address of
the UPDATE to the FROM_PEER parameter. When the peer receives the
UPDATE, it responds with an UPDATE containing and a ECHO_REQUEST and
TO_PEER parameters. The TO_PEER parameter MUST contain the source
address of the UPDATE redundantly. The reason from the FROM_PEER and
TO_PEER parameters is that it is possible to learn new addresses
using them. When there is p2p-unfriendly NAT between the peers, it
may cause translate port number of the UPDATE packets to something
that has not been communicated through the relay before. Such an
addresses are called "peer reflexive transport locators" in this
document. The FROM_PEER and TO_PEER parameters can be used for
detecting peer reflexive locators. The learned locators are added to
the connectivity tests.
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UPDATE packets destined to the unreflexive locators are sent directly
over IP. UPDATE packets destined for reflexive peer, relay and
leased locators are sent transport layer encapsulated.
Hosts proceed sequentially through the locator pairs in the order
described in the next section. A host MUST transition the state of
transport locator pairs verified by the return routability tests to
the ACTIVE state. Keepalive mechanisms described in later sections
MUST be applied to refresh the port state in NAT devices for locators
in the ACTIVE state. A host MUST also set up the Security
Associations for the inbound ESP traffic for such locators. The
selection of a default outbound SA is defined in the next section.
3.6. Selecting an Address Pair
This section describes priority ordering of connectivity tests and
locators pair selection based on ICE [I-D.ietf-mmusic-ice]. As part
of the priority calculation, each locator has a preference based on
its type. The values for these preferences are shown in Table 2.
+-----------------------------------+------------+
| Locator Type | Preference |
+-----------------------------------+------------+
| The preferred locator | 127 |
| Unreflexive locator | 126 |
| Peer reflexive transport locator | 120 |
| Relay reflexive transport locator | 100 |
| Leased transport locator | 0 |
+-----------------------------------+------------+
Table 2: Locator Type Preferences
In addition to the "type" priority, the priority of a locator is also
affected by the "local" priority. A (multihoming) host may have
multiple locators of same type and SHOULD assign a unique local
priority for each locator. Hosts preferring IPv6 communication can
assign higher local preferences for IPv6 locators than for
unreflexive IPv4 locators. ECHO_REQUEST parameters may include RTT
calculation information that an implementation may use to increase
the local priority. A host SHOULD calculate locator priority based
on the local and type priorities as shown in Figure 4. The locator
priority MUST always be included in the type 3 locator fields in
LOCATOR parameters as described in section Section 4.4.
Locator priority = (2^24) * (type preference) +
(2^8) * (local preference)
Figure 4: Locator priority
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A host SHOULD calculate a priority for each locator pair as shown in
Figure 5. I and R denote the priorities of locators of Initiator and
Responder. The use of the same formula at both ends gives more
guarantees that the peers prefer shortest paths between them. It
also converges the selection of the locator pair towards a symmetric
pair instead of an asymmetric pair even though it is not completely
guaranteed. The reasoning for the formula is described in
[I-D.ietf-mmusic-ice].
Pair priority = 2^32 * MIN(I,R) + 2 * MAX(I,R) + (I > R ? 1 : 0)
Figure 5: Pair priority
After reachability tests, both hosts SHOULD assign the transport
address pair with the highest pair priority as their default outgoing
SA for ESP.
3.7. Mobility
When one of the hosts changes its locators, it has to notify its
peers of the address change. This is handled as described in the
connectivity tests in Section 3.5 with the exception that the UPDATE
with parameter LOCATOR is used as the trigger to start connectivity
tests instead of the R2. The UPDATE packet contains a LOCATOR
parameter listing unreflexive, reflexive and leased transport
locators of the Initiator. This is illustrated in Figure 6.
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Mobile Relay Corresponding
Node | Node
| | |
| 1. UPDATE(LOCATOR) | 2. UPDATE(LOCATOR,RELAY_TO) |
+-------------------------------+------------------------------>|
| |
| 3. UPDATE(ECHO_REQUEST,FROM_PEER) NAT: DROP|
+------------------------------------------------------------->X|
| |
| 4. UPDATE(ECHO_REQUEST,FROM_PEER) |
|<--------------------------------------------------------------+
| |
| 5. UPDATE(ECHO_RESP,TO_PEER) |
|-------------------------------------------------------------->|
| |
| 6. UPDATE(ECHO_REQUEST,FROM_PEER) |
|<--------------------------------------------------------------|
| |
| 7. UPDATE(ECHO_RESP,TO_PEER) |
|-------------------------------------------------------------->|
| |
Figure 6: Handover
When a mobile host moves from a private address realm to another, it
can obtain the same locator on both networks. To denote that the new
locator requires reachability detection, the mobile host MUST use a
new SPI for the new locator.
A host can also use the UPDATE mechanism can also be used for
switching to a more optimal path after connectivity tests. In the
connectivity tests, the host may implement RTT measurements within
ECHO_REQUEST and ECHO_RESPONSE messages. In some cases the result of
the RTT measurements may indicate that another locator pair is more
optimal than the locator pair resulting from the connectivity and
priority tests. In such a case, the host MAY send UPDATE with
LOCATOR parameter with the optimal locator with the preferred bit on.
This gives the highest priority for the most optimal locator and will
be used if the connectivity tests succeed.
3.8. NAT Keepalives
A NAT can delete the mapping state after a timeout when there is no
traffic refreshing the state. For this reason, both hosts MUST send
keep-alives to each other for all locators pairs that are in the
ACTIVE state. Keepalives MUST be sent every 20 seconds for UDP. The
keepalive is a NOTIFY packet without parameters.
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The keep-alives MAY also be used to implement failure detection
between end-hosts as in [I-D.oliva-hiprg-reap4hip] (XX FIXME: this
needs still more details). The basic idea is to keep track of HIP
control and ESP packets received over a transport port. When there
is no HIP or ESP traffic (not even keep-alives) arriving during a
certain time period, the host switches to an alternative locator
pair. The host transitions the default locator pair to the
UNVERIFIED state and replaces the currently default SA to correspond
to the ACTIVE locator pair with the highest priority. The host may
also try to send an UPDATE packet with the LOCATOR parameter after a
certain time period if connectivity is still broken.
End-host may also used the keep-alives to detect loss of connectivity
with relay server. When this occurs, the end-host can register to a
new relay and replace the IP address of the old relay server with a
new one in DNS or DHT.
3.9. Closing of HIP Associations
A host closes a HIP association as described in [I-D.ietf-hip-base]
except that the CLOSE and CLOSE_ACK packets are sent over transport
layer and through the relay as illustrated in Figure 7. Hosts MUST
transition the corresponding locator pairs to the DEPRECATED state
after a successful CLOSE-CLOSE_ACK exchange. The corresponding
inbound and outbound SAs must be deleted on such occasion.
I Relay R
| 1. CLOSE | |
+---------------------------->| 2. CLOSE |
| +-------------------------------->|
| | |
| | 3. CLOSE_ACK |
| 4. CLOSE_ACK |<--------------------------------+
|<----------------------------+ |
| | |
Figure 7: Closing of a HIP association
The hosts may also use the CLOSE mechanism to remove redundant SAs
remaining from the connectivity tests. However, the removal can
prolong the recovery in the event of connectivity failures.
3.10. Communication with HIP Hosts without NAT Traversal Support
The UDP encapsulation of HIP and ESP control packets has not been
defined in any other IETF document and legacy hosts drop all UDP
encapsulated HIP and ESP traffic. Processing of unknown locator
types terminates the base exchange or UPDATE. As such, the
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extensions defined in this document are not completely backwards
compatible and require a minimal support in implementations.
A minimal implementation MUST provide UDP encapsulation of HIP and
ESP packets. In such a case, the minimal NAT traversal
implementation MUST silently discard the processing of type 3
locators to allow communication with implementations supporting NAT
traversal defined in this document. The minimal implementation MUST
support UDP keepalives to refresh state of the NAT(s).
Hosts that conform to [I-D.ietf-hip-mm] respond to UPDATE messages
containing an ECHO_REQUEST with an UPDATE message containing an
ECHO_RESPONSE. This completes the connectivity tests for the host
supporting the extensions defined in this document. As long as the
implementation supports UDP encapsulation of HIP control packets,
this requires no changes.
The Relay extensions defined in this document do not work with
minimalistic implementations. When there is a Relay between the
hosts, both the Initiator and Responder MUST support the extensions
defined in this document. The presence of RELAY_TO and RELAY_FROM
parameters denotes the precence of a relay.
4. Packet Formats
This section defines an UDP-encapsulation packet format for HIP base
exchange and control traffic, IPsec ESP BEET-mode traffic and NAT
keep-alive packets.
4.1. 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ HIP Header and Parameters ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: Format for UDP-encapsulated HIP control packets
Figure 8 shows how HIP control packets are encapsulated within UDP.
A minimal UDP packet carries a complete HIP packet in its payload.
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Contents of the UDP source and destination ports are described below.
The UDP length and checksum field MUST be computed as described in
[RFC0768]. The HIP header and parameter follow the conventions
[I-D.ietf-hip-base] 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 [I-D.ietf-hip-base] includes the IP addresses
in the checksum calculation. The NATs unaware of HIP cannot
recompute the HIP checksum after changing IP addresses.
4.2. Control Channel Keep-Alives
The keep-alive for control channel are UDP encapsulated NOTIFY
packets [I-D.ietf-hip-base]. The NOTIFY packets MAY contain HIP
parameters. The NAT traversal mechanisms encapsulate these NOTIFY
packets within the payload of UDP packets.
4.3. RELAY_FROM, RELAY_TO and RELAY_VIA Parameters
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Address |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Port | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type [ TBD by IANA:
RELAY_FROM: (63998 = 2^16 - 2^11 + 2^9 - 2)
RELAY_TO: (64002 = 2^16 - 2^11 + 2^9 + 2)
RELAY_VIA: (64006 = 2^16 - 2^11 + 2^9 + 6) ]
<!-- AG: those are not described?
TO_PEER: (64010 = 2^16 - 2^11 + 2^9 + 10)
REG_FROM: (64010 = 2^16 - 2^11 + 2^9 + 12) ]
-->
Length 18
Address An IPv6 address or an IPv4 address in IPv4-in-IPv6
format.
Port Transport port number
Figure 9: Format for the RELAY_FROM, RELAY_TO and RELAY_VIA
parameters
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Figure 9 shows the format of RELAY_FROM, RELAY_TO and RELAY_VIA
parameters.
4.4. LOCATOR Parameter
The generic LOCATOR parameter format is the same as in
[I-D.ietf-hip-mm]. However, presenting transport locators requires a
new locator type. The generic and NAT specific locator parameters
are illustrated in Figure 10.
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 10: Locator parameter
The individual fields in the LOCATOR parameter are described in
Table 3.
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+------------+----------+-------------------------------------------+
| Field | Value(s) | Purpose |
+------------+----------+-------------------------------------------+
| Type | 193 | Parameter type |
| Length | Variable | Length in octets, excluding Type and |
| | | Length fields, and excluding padding. |
| Traffic | 0-2 | 2 for unreflexive and leased, 1 for relay |
| Type | | reflexive |
| Locator | 3 | Transport locator |
| Type | | |
| Locator | 19 | Length of the Locator field in 4-octet |
| Length | | units |
| Reserved | 0 | Reserved for future extensions |
| Preferred | 0 | Usually zero for type 3 locators |
| (P) bit | | |
| Locator | Variable | Locator lifetime in seconds |
| Lifetime | | |
| Transport | Variable | Zero for unreflexive and greater than |
| Port | | zero otherwise |
| Transport | 0 | Zero for UDP |
| Protocol | | |
| Kind | Variable | 0 for unreflexive, 1 for relay reflexive, |
| | | 2 for leased |
| Priority | Variable | Locator preference, see Section 3.6 |
| SPI | Variable | 0 for relay reflexive, otherwise greater |
| | | than zero |
| Locator | Variable | An IPv6 address or an IPv4-in-IPv6 format |
| | | IPv4 address[RFC2373] |
+------------+----------+-------------------------------------------+
Table 3: Fields of the locator parameter
4.5. RELAY_HMAC
The RELAY_HMAC parameter value has the TLV type 65520 (2^16 - 2^5 +
2^4). It has the same semantics as RVS_HMAC [I-D.ietf-hip-rvs].
4.6. Registration Types
The REG_INFO, REQ_REQ, REG_RESP and REG_FAILED parameters contains
values for relay registration. The value for RELAY_UDP_HIP is 2.
The value for RELAY_UDP_ESP is 3.
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4.7. ESP Data 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ ESP Header ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11: Format for UDP-encapsulated IPsec ESP BEET-mode traffic
Figure 11 shows how IPsec ESP BEET-mode packets are encapsulated
within UDP. Again, a minimal UDP packet carries the ESP packet in
its payload. The contents of the UDP source and destination ports
are described in later sections. The UDP length and checksum field
MUST be computed as described in [RFC0768].
4.8. UDP Encapsulation/Decapsulation of IPsec BEET-Mode ESP
[RFC3948] describes UDP encapsulation of the IPsec ESP transport and
tunnel mode. This section describes the UDP encapsulation of the
BEET mode.
4.8.1. UDP Encapsulation of IPsec BEET-Mode ESP
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 [I-D.ietf-hip-esp]. When two peers perform a
UDP-encapsulated base exchange, they MUST define a pair of IPsec SAs
that produces UDP-encapsulated BEET-mode ESP data traffic.
The management of encryption/authentication protocols and security
parameter indices (SPIs) is defined in [I-D.ietf-hip-esp].
Additional SA parameters, such as IP addresses and UDP ports, MUST be
defined according to this section. Two SAs MUST be defined on each
host for one HIP association; one for outgoing data and another one
for incoming data.
The BEET mode provides limited tunnel mode semantics without the
regular tunnel mode overhead [I-D.nikander-esp-beet-mode]. In the
BEET mode, transport-layer checksums in the payload data are based on
the HITs. The packet MUST then undergo BEET-mode ESP cryptographic
processing as defined in Section 5.3 of [I-D.nikander-esp-beet-mode].
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Next, the resulting BEET-mode packet is UDP encapsulated. For this
purpose, a UDP header MUST be inserted between the IP and ESP header.
The source and destination ports are filled in. The UDP checksum
MUST be calculated based on the outer addresses (locators) of the
IPsec security association. The other fields of the UDP header are
computed as described in [RFC0768].
The resulting UDP packet MUST then undergo BEET IP header processing
as defined in Section 5.4 of [I-D.nikander-esp-beet-mode].
Figure 12 illustrates the BEET-mode UDP encapsulation procedure for a
TCP packet.
ORIGINAL TCP PACKET:
+------------------------------------------+
| inner IPv6 hdr | ext hdrs | | |
| with HITs | if present | TCP | Data |
+------------------------------------------+
PACKET AFTER BEET-MODE ESP PROCESSING:
+----------------------------------------------------------+
| inner IPv6 hdr | ESP | dest | | | ESP | ESP |
| with HITs | hdr | opts.| TCP | Data | Trailer | ICV |
+----------------------------------------------------------+
|<------- encryption -------->|
|<----------- integrity ----------->|
FINAL PACKET AFTER BEET_MODE IP HEADER PROCESSING:
+------------------------------------------------------------+
| outer IPv4 | UDP | ESP | dest | | | ESP | ESP |
| hdr | hdr | hdr | opts.| TCP | Data | Trailer | ICV |
+------------------------------------------------------------+
|<------- encryption -------->|
|<----------- integrity ----------->|
Figure 12: UDP encapsulation of an IPsec BEET-mode ESP packet
containing a TCP segment
4.8.2. UDP Decapsulation of IPsec BEET-Mode ESP
An incoming UDP-encapsulated IPsec BEET-mode ESP packet is
decapsulated as follows. First, if the UDP checksum is invalid, then
the packet MUST be dropped. Then, the packet MUST be verified as
defined in [I-D.nikander-esp-beet-mode]. If verified, the ESP data
contained in the payload of the UDP packet MUST be decrypted as
described in [I-D.nikander-esp-beet-mode].
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5. Firewall Traversal
This section describes firewall traversal issues separately from NAT
issues. When the Initiator or the Responder of a HIP association is
behind a firewall, additional issues arise.
The NAT traversal mechanisms described in Section 3 require that the
firewall - stateful or not - allows UDP traffic. At the minimum,
successful firewall control packet traversal requires that the host
behind the firewall is allowed to communicate packets with a HIP
relay (or a Responder without Relay) that is listening on UDP port
HIPPORT. Successful ESP data packet traversal requires the same for
the ESP relay. For unrelayed traffic, the destination port HIPPORT
should be open at the firewall to all hosts behind the firewall.
Most firewall implementations support "UDP connection tracking",
i.e., after a host behind a firewall has initiated UDP communication
to the public Internet, the firewall relays UDP response traffic in
the return direction. If no such return traffic arrives for a
specific period of time, the firewall stops relaying the given IP
address and port pair. The mechanisms described in Section 3 already
enable traversal of such firewalls, if the keep-alive interval used
is less than the refresh interval of the firewall.
When the Initiator is behind a firewall, the NAT traversal mechanisms
described in Section 3 depend on the ability to initiate
communication via UDP to the destination port HIPPORT from arbitrary
source ports and to receive UDP response traffic from that port to
the chosen source port. If the Initiator is behind a firewall that
does not support "UDP connection tracking", the NAT traversal
mechanisms described in Section 3 can still be supported, if the
firewall allows permanently inbound UDP traffic from the port HIPPORT
and destined to arbitrary source IP addresses and UDP ports.
When the Responder is behind a firewall, the NAT traversal mechanisms
described in Section 3 depend on the ability to send and receive UDP
traffic originating from HIPPORT of the HIP and ESP relays. When
unrelayed traffic is preferred, arbitrary source IP addresses and
ports are required.
6. Security Considerations
6.1. A Difference to RFC3948
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
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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 IPsec BEET
mode as described in Section 3, because the Responder use HITs to
distinguish between different communication instances.
6.2. Privacy Considerations
The LOCATORs are sent in plain text. Alternatively, they could be
encrypted. This option was not chosen to allow packet inspection by
middleboxes. Plain text locators may be useful for HIP-aware
middleboxes in the future.
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 unreflexive locators. 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 [I-D.ietf-behave-p2p-state]. With such a legacy NAT,
the only option left would be to use a leased transport locator from
a relay. As a consequence, a host may support locator-based privacy
by leaving out the reflexive locators. Using only unreflexive
locators can produce suboptimal paths possibly causing congestion.
The use of relays can be useful for protection against Denial-of-
Service attacks. If a Responder reveals only its HIP and ESP relay
addresses to malign 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.
6.3. Opportunistic Mode
The use of opportunistic HIP is NOT RECOMMENDED and its use is not
defined in this document. In opportunistic HIP, the Initiator sends
the I1 message with null destination HIT. Private address realms do
not have unique addresses by definition. Therefore, opportunistic
mode is subject to failure even when there are no attackers present.
In a normal HIP base exchange, a well-behaving Responder drops the I1
packet when the destination HIT does not belong to it. An attacker
could respond to the I1, but the base exchange would eventually fail
as the attacker would fail to prove its ownership of the destination
HIT of the I1.
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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
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 Parameters Types by
assigning new HIP Parameter Types values for the new HIP Parameters
defined in Section 4: o RELAY_FROM (defined in Section 4.3) o
RELAY_TO (defined in Section 4.3) o RELAY_VIA (defined in Section
4.3) o RELAY_HMAC (defined in Section 4.5)
8. Acknowlegements
The authors would like to thank Lars Eggert, Vivien Schmitt, Abhinav
Pathak and Andrei Gurtov for their contributions to previous versions
of this draft. Thanks for Philip Matthews on introducing ICE
concepts to the authors and for proposing the initial design. 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
Tobias Heer, Teemu Koponen, Juhana Mattila, Jeffrey M. Ahrenholz,
Thomas Henderson, Kristian Slavov, Janne Lindqvist, Pekka Nikander,
Lauri Silvennoinen, Jukka Ylitalo, Juha Heinanen, Joakim Koskela,
Samu Varjonen, Dan Wing, Hannes Tschofenig and Jani Hautakorpi for
their comments on this document.
[I-D.nikander-hip-path] presented some initial ideas for NAT
traversal of HIP communication. The idea was based on NAT detection
using extra parameters in the base exchange. This document takes a
different approach based on ICE.
Simon Schuetz and Martin Stiemerling are partly funded by Ambient
Networks, a research project supported by the European Commission
under its Sixth Framework Program. The views and conclusions
contained herein are those of the authors and should not be
interpreted as necessarily representing the official policies or
endorsements, either expressed or implied, of the Ambient Networks
project or the European Commission.
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
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Forces and Ericsson. Miika Komu wrote draft-ietf-hip-nat-02 version
from scratch based on ICE-related comments from Philip Matthews.
9. References
9.1. Normative References
[I-D.ietf-hip-base]
Moskowitz, R., "Host Identity Protocol",
draft-ietf-hip-base-08 (work in progress), June 2007.
[I-D.ietf-hip-esp]
Jokela, P., "Using ESP transport format with HIP",
draft-ietf-hip-esp-06 (work in progress), June 2007.
[I-D.ietf-hip-mm]
Henderson, T., "End-Host Mobility and Multihoming with the
Host Identity Protocol", draft-ietf-hip-mm-05 (work in
progress), March 2007.
[I-D.ietf-hip-registration]
Laganier, J., "Host Identity Protocol (HIP) Registration
Extension", draft-ietf-hip-registration-02 (work in
progress), June 2006.
[I-D.ietf-hip-rvs]
Laganier, J. and L. Eggert, "Host Identity Protocol (HIP)
Rendezvous Extension", draft-ietf-hip-rvs-05 (work in
progress), June 2006.
[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-16 (work in progress), June 2007.
[I-D.nikander-esp-beet-mode]
Melen, J. and P. Nikander, "A Bound End-to-End Tunnel
(BEET) mode for ESP", draft-nikander-esp-beet-mode-07
(work in progress), February 2007.
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
August 1980.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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[RFC2373] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 2373, July 1998.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
[RFC4423] Moskowitz, R. and P. Nikander, "Host Identity Protocol
(HIP) Architecture", RFC 4423, May 2006.
9.2. Informative References
[I-D.ietf-behave-p2p-state]
Srisuresh, P., "State of Peer-to-Peer(P2P) Communication
Across Network Address Translators(NATs)",
draft-ietf-behave-p2p-state-03 (work in progress),
July 2007.
[I-D.irtf-hiprg-nat]
Stiemerling, M., "NAT and Firewall Traversal Issues of
Host Identity Protocol (HIP) Communication",
draft-irtf-hiprg-nat-04 (work in progress), March 2007.
[I-D.nikander-hip-path]
Nikander, P., "Preferred Alternatives for Tunnelling HIP
(PATH)", draft-nikander-hip-path-01 (work in progress),
March 2006.
[I-D.oliva-hiprg-reap4hip]
Oliva, A. and M. Bagnulo, "Fault tolerance configurations
for HIP multihoming", draft-oliva-hiprg-reap4hip-00 (work
in progress), July 2007.
[RFC2663] Srisuresh, P. and M. Holdrege, "IP Network Address
Translator (NAT) Terminology and Considerations",
RFC 2663, August 1999.
[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.
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Internet-Draft HIP Extensions for NAT Traversal July 2007
Appendix A. Differences to ICE
The protocol extensions defined in this draft are based on ICE. The
extensions are a rough translation of ICE concepts to HIP protocol.
The translation preserved certain concepts as they are, but there are
subtle differences. This section tries to explain how ICE concepts
were mapped to HIP protocol and what are the differences.
The terminology for this draft is a hybrid of ICE and HIP
terminology. "Agent" was translated to "host" in favour of HIP
terminology. Transport address was changed to transport locator.
Similarly, address pair is denoted as locator pair. This document
does not really talk about "candidate addresses", but just "locators"
which may or may not be verified using the return routability tests,
in favour of mobility terminology in [I-D.ietf-hip-mm]. Host
candidate of ICE became unreflexive locator, server reflexive
candidate was mapped to relay reflexive transport locator, peer
reflexive candidate was mapped to peer reflexive locator and relayed
candidate became leased transport locator.
The component, base and foundation terms are not used in the document
as there is only a single "media stream" for all (ESP) traffic
between two hosts.
There is no "lite" version ICE in this document, just full, as the
full version is the preferred one also for ICE. One specific
scenario defined in this document has some resemblance to the lite
ICE. When a Responder is a publicly accessible server with fixed
address, it may exclude the use of the relay. In that case, it does
not have to handle the RELAY parameters but still has to respond to
the connectivity checks.
A connectivity check is not a STUN Binding Request. Instead, it is
return routability check as defined in [I-D.ietf-hip-mm]. "Triggered
check" occurs when a host receives a UPDATE with ECHO_REQUEST and it
responds using a ECHO_RESPONSE and sends its own ECHO_REQUEST. A
"check list" is effectively a LOCATOR parameter as defined in
[I-D.ietf-hip-mm]. The term "ordinary check" is not really used in
this document as it HIP packets are retransmitted periodically when
the LOCATORs are in UNVERIFIED state. "Valid list" corresponds to
locator pairs that have been verified successfully by the return
routability tests.
The peers trigger the connectivity checks after the base exchange or
after a base exchange. The conclusion of the connectivity checks,
i.e., selection of the final address pair, differs the most as a
result of fitting the ICE nomination algorithm to HIP mobility
mechanisms. There is no "controlling agent" and the end-hosts make a
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local decision on which locator pair to choose. This could lead to
asymmetric address pairs, but the priority algorithm guarantees that
the address pairs converge. Also, there is are no aggressive and
regular nomination modes as a consequence of the lack of controlling
agent.
ICE uses TLS, usernames and passwords as security mechanisms. HIP
has built-in security mechanisms that preferred over the ones that
are used in ICE.
Appendix B. Document Revision History
To be removed upon publication
+------------+------------------------------------------------------+
| Revision | Comments |
+------------+------------------------------------------------------+
| schmitt-00 | Initial version. |
| ietf-00 | Officially adopted as WG item. Solved issues |
| | 1-9,11,12 |
| ietf-01 | Solved remaining issues except that relaying ESP and |
| | mobility were still incomplete. |
| ietf-02 | Miika rewrote almost from scratch based on ICE. |
| | Editorial corrections from Simon and Andrei. |
+------------+------------------------------------------------------+
Authors' Addresses
Miika Komu (editor)
Helsinki Institute for Information Technology
Metsanneidonkuja 4
Espoo
Finland
Phone: +358503841531
Fax: +35896949768
Email: miika@iki.fi
URI: http://www.hiit.fi/
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Simon Schuetz
NEC Network Laboratories
Kurfuerstenanlage 36
Heidelberg 69115
Germany
Phone: +49 6221 4342 165
Fax: +49 6221 4342 155
Email: simon.schuetz@netlab.nec.de
URI: http://www.netlab.nec.de/
Martin Stiemerling
NEC Network Laboratories
Kurfuerstenanlage 36
Heidelberg 69115
Germany
Phone: +49 6221 4342 113
Fax: +49 6221 4342 155
Email: stiemerling@netlab.nec.de
URI: http://www.netlab.nec.de/
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