Internet Engineering Task Force (IETF) D. Thaler
Request for Comments: 6081 Microsoft
Updates: 4380 January 2011
Category: Standards Track
ISSN: 2070-1721
Teredo Extensions
Abstract
This document specifies a set of extensions to the Teredo protocol.
These extensions provide additional capabilities to Teredo, including
support for more types of Network Address Translations (NATs) and
support for more efficient communication.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6081.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Direct Bubble: A Teredo bubble that is sent directly to the IPv4 node
whose Teredo address is contained in the Destination field of the
IPv6 header, as specified in Section 2.8 of [RFC4380]. The IPv4
Destination Address and UDP Destination Port fields contain a mapped
address/port.
Echo Test: A mechanism to predict the mapped address/port a
sequential port-symmetric NAT is using for a client behind it.
Hairpinning: A feature that is available in some NATs where two or
more hosts are positioned behind a NAT and each of those hosts is
assigned a specific external (public) address and port by the NAT.
Hairpinning support in a NAT allows these hosts to send a packet to
the external address and port that is assigned to one of the other
hosts, and the NAT automatically routes the packet back to the
correct host. The term hairpinning is derived from the behavior of
the packet, which arrives on, and is sent out to, the same NAT
interface.
Indirect Bubble: A Teredo bubble that is sent indirectly (via the
destination's Teredo server) to another Teredo client, as specified
in Section 5.2.4 of [RFC4380].
Local Address/Port: The IPv4 address and UDP port from which a Teredo
client sends Teredo packets. The local port is referred to as the
Teredo service port in [RFC4380]. The local address of a node may or
may not be globally routable because the node can be located behind
one or more NATs.
Mapped Address/Port: A global IPv4 address and a UDP port that
results from the translation of a node's own local address/port by
one or more NATs. The node learns these values through the Teredo
protocol as specified in [RFC4380]. For symmetric NATs, the mapped
address/port can be different for every peer with which a node tries
to communicate.
Network Address Translation (NAT): The process of converting between
IP addresses used within an intranet or other private network and
Internet IP addresses.
Nonce: A time-variant random value used in the connection setup phase
to prevent message replay and other types of attacks.
Peer: A Teredo client with which another Teredo client needs to
communicate.
Port-Preserving NAT: A NAT that translates a local address/port to a
mapped address/port such that the mapped port has the same value as
the local port, as long as that same mapped address/port has not
already been used for a different local address/port.
Port-Restricted NAT: A restricted NAT that accepts packets from an
external host's IP address X and port Y only if the internal host has
sent a packet destined to IP address X and port Y. In the
terminology of [RFC4787], this is a NAT with Endpoint-Independent
Mapping and Address and Port-Dependent Filtering.
Port-Symmetric NAT: A symmetric NAT that has only a single external
IP address and hence only assigns different ports when communicating
with different external hosts.
Private Address: An IPv4 address that is not globally routable but is
part of the private address space specified in Section 3 of
[RFC1918].
Public Address: An external global address used by a NAT.
Restricted NAT: A NAT where all requests from the same internal IP
address and port are mapped to the same external IP address and port.
Unlike the cone NAT, an external host can send packets to an internal
host (by sending a packet to the external mapped address and port)
only if the internal host has first sent a packet to the external
host. There are two kinds of restricted NATs: address-restricted
NATs and port-restricted NATs.
Sequential Port-Symmetric NAT: A port-symmetric NAT that allocates
external ports sequentially for every {internal IP address and port,
destination IP address and port} tuple. The delta used in the
sequential assignment is typically 1 or 2 for most such NATs.
Symmetric NAT: A NAT where all requests from the same internal IP
address and port and to the same destination IP address and port are
mapped to the same external IP address and port. Requests from the
same internal IP address and port to a different destination IP
address and port may be mapped to a different external IP address and
port. Furthermore, a symmetric NAT accepts packets received from an
external host's IP address X and port Y only if some internal host
has sent packets to IP address X and port Y. In the terminology of
[RFC4787], this is a NAT with a mapping behavior of either Address-
Dependent Mapping or Address- and Port-Dependent Mapping, and a
filtering behavior of either Address-Dependent Filtering or Address-
and Port-Dependent Filtering.
Teredo Bubble: A Teredo control message (specified in Section 2.8 of
[RFC4380]) that is used to create a mapping in a NAT. There are two
types of Teredo bubbles: direct bubbles and indirect bubbles.
Teredo Client: A node that has access to the IPv4 Internet and wants
to gain access to the IPv6 Internet using the Teredo protocol.
Teredo IPv6 Address: An IPv6 address of a Teredo client, as specified
in Section 2.14 of [RFC4380].
Teredo Secondary Server Address: A secondary IPv4 address of a Teredo
server with which a Teredo client is configured, as specified in
Section 5.2 of [RFC4380].
Teredo Server: A node that has a globally routable address on the
IPv4 Internet, and is used as a helper to provide IPv6 connectivity
to Teredo clients.
Teredo Server Address: A (primary) IPv4 address of a Teredo server
with which a Teredo client is configured, as specified in Section 5.2
of [RFC4380].
UPnP-enabled NAT: A NAT that has the UPnP device control protocol
enabled, as specified in [UPNPWANIP]. (Note that today, by default,
most UPnP-capable NATs have the UPnP device control protocol
disabled.)
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 RFC 2119 [RFC2119].
3. Overview
The Teredo protocol (as specified in [RFC4380]) enables nodes located
behind one or more IPv4 NATs to obtain IPv6 connectivity by tunneling
packets over UDP.
When a node behind a NAT needs to communicate with a peer (i.e.,
another node) that is behind a NAT, there are four sets of IPv4
address/port pairs of interest:
o The node's own IPv4 address/port.
o The external IPv4 address/port to which the node's NAT translates.
o The peer's own IPv4 address/port.
o The external IPv4 address/port to which the peer's NAT translates.
When the node sends a packet to a peer, the node needs to send it
from the node's own IPv4 address/port, destined to the peer's
external IPv4 address/port. By the time it arrives at the peer
(i.e., after passing through both NATs), the peer will see the same
packet as coming from the node's external IPv4 address/port, destined
to the peer's own IPv4 address/port.
In this document, the term local address/port refers to a Teredo
client's own IPv4 address/port, and mapped address/port refers to the
external IPv4 address/port to which its NAT translates the local
address/port. That is, the mapped address/port is what the IPv4
Internet sees the Teredo client as.
A Teredo client running on a node communicates with a Teredo server
to discover its mapped address/port. The mapped address/port, along
with the Teredo server address, is used to generate an IPv6 address
known as a Teredo IPv6 address. This allows any peer that gets the
node's IPv6 address to easily determine the external IPv4 address/
port to which to send IPv6 packets encapsulated in IPv4 UDP messages.
This document specifies extensions to the Teredo protocol. These
Teredo extensions are independent of each other and can be
implemented in isolation, except that the UPnP-Symmetric NAT
Extension and the Port-Preserving Symmetric NAT Extension both
require the Symmetric NAT Support Extension to be implemented. An
implementation of this specification can support any combination of
the Teredo extensions, subject to the above-mentioned restriction.
The following matrix outlines the connectivity improvements of some
of the extensions outlined in this document.
No = No connectivity.
Figure 1: Matrix of Connectivity Improvements for Teredo Extensions
Note that as with [RFC4380], if the qualification process is not
successful, Teredo will not be configured with an IPv6 address, and
connectivity will function as if Teredo were not present. Similarly,
for any combination of NAT types that are not supported by Teredo and
the extensions defined herein, the connectivity tests between a
client and a peer will fail within a finite period of time, allowing
the client to handle this case as with any other type of unreachable
destination address (e.g., by trying another address of the
destination such as a native IPv4 address).
3.1. Symmetric NAT Support Extension
The qualification procedure (as specified in Section 5.2.1 of
[RFC4380]) is a process that allows a Teredo client to determine the
type of NAT that it is behind, in addition to its mapped address/port
as seen by its Teredo server. However, Section 5.2.1 of [RFC4380]
suggests that if the client learns it is behind a symmetric NAT, the
Teredo client should go into an "offline state" where it is not able
to use Teredo. The primary reason for doing so is that it is not
easy for Teredo clients to connect to each other if either or both of
them are positioned behind a symmetric NAT. Because of the way a
symmetric NAT works, a peer sees a different mapped address/port in
the IPv4/UDP headers of packets coming from a Teredo client than the
node's Teredo server sees (and hence appears in the node's Teredo
IPv6 address). Consequently, a symmetric NAT does not allow incoming
packets from a peer that are addressed to the mapped address/port
embedded in the node's Teredo IPv6 address. Thus, the incoming
packets are dropped and communication with Teredo clients behind
symmetric NATs is not established.
With the Symmetric NAT Support Extension, Teredo clients begin to use
Teredo even after they detect that they are positioned behind a
symmetric NAT.
Consider the topology shown in Figure 2. Teredo Client B uses Teredo
Server 2 to learn that its mapped address/port is 192.0.2.10:8192,
and constructs a Teredo IPv6 address, as specified in Section 4 of
[RFC4380]. Hence, c633:6476 is the hexadecimal value of the address
of Teredo Server 2 (198.51.100.118), the mapped port is exclusive-
OR'ed with 0xffff to form dfff, and the Mapped Address is exclusive-
OR'ed with 0xffffffff to form 3fff:fdf5.
Teredo Client A uses Teredo Server 1 to learn that its mapped
address/port is 192.0.2.1:4096 and, with this extension, constructs a
Teredo IPv6 address (as specified in Section 4 of [RFC4380]) even
though it learns that it is behind a symmetric NAT. Hence, cb00:7178
is the hexadecimal value of the address of Teredo Server 1
(203.0.113.120), the mapped port is exclusive-OR'ed with 0xffff to
form efff, and the Mapped Address is exclusive-OR'ed with 0xffffffff
to form 3fff:fdfe.
The Symmetric NAT Support Extension enables a Teredo client
positioned behind a symmetric NAT to communicate with Teredo peers
positioned behind a cone or address-restricted NATs as follows,
depending on what side initiates the communication.
--------------------------------------------
/ \
< IPv6 Internet >
\ /
-|----------------------------------------|-
| |
+----------+ +----------+
| Teredo | | Teredo |
| Server 1 | | Server 2 |
+----------+ +----------+
203.0.113.120| 198.51.100.118|
-|----------------------------------------|-
/ \
< IPv4 Internet >
\ /
-|----------------------------------------|-
192.0.2.1| 192.0.2.10|
UDP port 4096| UDP port 8192|
+---------+ +----------+
|Symmetric| |Other type|
| NAT | | of NAT |
+---------+ +----------+
| |
+-----------------+ +-----------------+
| Teredo client A | | Teredo client B |
+-----------------+ +-----------------+
2001:0:cb00:7178:0:efff:3fff:fdfe 2001:0:c633:6476:0:dfff:3fff:fdf5
Teredo Address Teredo Address
Figure 2: Symmetric NAT Example
In the first case, assume that a Teredo Client B (B) positioned
behind a cone or address-restricted NATs initiates communication with
Teredo Client A (A) positioned behind a symmetric NAT. B sends an
indirect bubble via A's server (Teredo Server 1) to A, and A responds
with a direct bubble. This direct bubble reaches B, because it is
positioned behind a cone or address-restricted NAT. However, the
mapped address/port in the IPv4/UDP headers of the direct bubble are
different from the mapped address/port embedded in A's Teredo IPv6
address. B therefore remembers the mapped address/port of the direct
bubble and uses them for future communication with A, and thus
communication is established.
In the second case, assume that A, positioned behind a symmetric NAT,
initiates communication with B, positioned behind a cone or address-
restricted NAT. A sends an indirect bubble to B via B's server
(Teredo Server 2), and B responds with a direct bubble. This direct
bubble is dropped by A's symmetric NAT because the direct bubble is
addressed to the mapped address/port embedded in A's Teredo IPv6
address. However, communication can be established by having B
respond with an indirect bubble via A's server (Teredo Server 1).
Now the scenario is similar to the first case and communication will
be established.
3.2. UPnP-Enabled Symmetric NAT Extension
The UPnP-enabled Symmetric NAT Extension is dependent on the
Symmetric NAT Support Extension. Only if Teredo clients have been
enabled to acquire a Teredo IPv6 address in spite of being behind a
symmetric NAT will this extension help in traversing UPnP-enabled
Symmetric NATs.
The Symmetric NAT Support Extension enables communication between
Teredo clients behind symmetric NATs with Teredo clients behind cone
NATs or address-restricted NATs. However, clients behind symmetric
NATs can still not communicate with clients behind port-restricted
NATs or symmetric NATs.
Referring again to Figure 2 (see Section 3.1), assume that Teredo
Client A is positioned behind a symmetric NAT and initiates
communication with Client B, which is positioned behind a port-
restricted NAT. Client A sends a direct bubble and an indirect
bubble to Client B via Client B's server (Teredo Server 2). As per
the characteristics of the symmetric NAT, the IPv4 source of the
direct bubble contains a different mapped address and/or port than
the one embedded in the Teredo server. This direct bubble is dropped
because Client B's NAT does not have state to let it pass through,
and Client B does not learn the mapped address/port used in the IPv4/
UDP headers. In response to the indirect bubble from Client A,
Client B sends a direct bubble destined to the mapped address/port
embedded in Client A's Teredo IPv6 address. This direct bubble is
dropped because Client A's NAT does not have state to accept packets
destined to that mapped address/port. The direct bubble does,
however, cause Client B's NAT to set up outgoing state for the mapped
address/port embedded in Client A's Teredo IPv6 address.
As described in Section 3.1, Client B also sends an indirect bubble
that elicits a direct bubble from Client A. Unlike the case in
Section 3.1, however, the direct bubble from Client A is dropped as
Client B's NAT does not have state for the mapped address/port that
Client A's NAT uses. Note that Client B's NAT is port-restricted and
hence requires both the mapped address and port to be the same as in
its outgoing state, whereas in Section 3.1, Client A's NAT was a cone
or address-restricted NAT which only required the mapped address (but
not port) to be the same. Thus, communication between Client A and
Client B fails. If Client B were behind a symmetric NAT, the problem
is further complicated by Client B's NAT using a different outgoing
mapped address/port than the one embedded in Client B's Teredo IPv6
address.
If a Teredo client is separated from the global Internet by a single
UPnP-enabled symmetric or port-restricted NAT, it can communicate
with other Teredo clients that are positioned behind a single UPnP-
enabled symmetric or port-restricted NAT as follows.
Teredo clients, before communicating with the Teredo server during
the qualification procedure, use UPnP to reserve a translation from a
local address/port to a mapped-address/port. Therefore, during the
qualification procedure, the Teredo server reflects back the reserved
mapped address/port, which then is included in the Teredo IPv6
address. The mapping created by UPnP allows the NAT to forward
packets destined for the mapped address/port to the local address/
port, independent of the source of the packets. It typically does
not, however, cause packets sourced from the local address/port to be
translated to have the mapped address/port as the external source and
hence continues to function as a symmetric NAT in this respect.
Thus, a Teredo client, positioned behind a UPnP-enabled symmetric
NAT, can receive a direct bubble sent by any Teredo peer. The Teredo
client compares the peer's mapped address/port as seen in the IPv4/
UDP headers with the mapped address/port in the peer's Teredo IPv6
address. If the two mappings are different, the packet was sent by
another Teredo client positioned behind a symmetric NAT. The
Symmetric NAT Support Extension suggested that the Teredo client use
the peer's mapped address/port seen in the IPv4/UDP headers for
future communication. However, because symmetric NAT-to-symmetric
NAT communication would not have been possible anyway, the Teredo
client sends back a direct bubble to the mapped port/address embedded
in the peer's Teredo IPv6 address. If the peer is also situated
behind a UPnP-enabled NAT, the direct bubble will make it through and
communication will be established.
Even though communication is established between the two Teredo IPv6
addresses, the mappings will be asymmetric in the two directions of
data transfer. Specifically, incoming packets will be destined to
the reserved mapped address/port that is embedded in the Teredo IPv6
address. Outgoing packets will instead appear to come from a
different mapped address/port due to the symmetric NAT behavior.
3.3. Port-Preserving Symmetric NAT Extension
The Port-Preserving Symmetric NAT Extension is dependent on the
Symmetric NAT Support Extension (Section 3.1). Only if Teredo
clients have been enabled to acquire a Teredo IPv6 address in spite
of being behind a symmetric NAT will this extension help in
traversing port-preserving symmetric NATs.
The Symmetric NAT Support Extension enables communication between
Teredo clients behind symmetric NATs with Teredo clients behind cone
NATs or address-restricted NATs. However, clients behind symmetric
NATs can still not communicate with clients behind port-restricted or
symmetric NATs, as described in Section 3.2. Note that the Port-
Preserving Symmetric NAT Extension described here is independent of
the UPnP-enabled Symmetric NAT Extension, described in Section 3.2.
If a Teredo client is positioned behind a port-preserving symmetric
NAT, the client can communicate with other Teredo clients positioned
behind a port-restricted NAT or a port-preserving symmetric NAT as
follows.
Teredo clients compare the mapped port learned during the
qualification procedure with their local port to determine if they
are positioned behind a port-preserving NAT. If both the mapped port
and the local port have the same value, the Teredo client is
positioned behind a port-preserving NAT. At the end of the
qualification procedure, the Teredo client also knows if it is
positioned behind a symmetric NAT, as described in Section 3.1.
Teredo clients positioned behind port-preserving symmetric NATs can
also listen on randomly chosen local ports. If the randomly chosen
local port has not been used by the symmetric NAT as a mapped port in
a prior port-mapping, the NAT uses the same port number as the mapped
port. Thus, the challenge is to get the first direct bubble sent out
from the random port to be destined to a valid destination address
and port. When the mapped address/port is embedded in the
destination's Teredo IPv6 address, this is easy.
The communication setup is more complicated when the destination
Teredo client is also positioned behind a port-preserving symmetric
NAT. In such a case, both Teredo clients need to send their first
direct bubbles to the correct destination mapped address/port. Thus,
the protocol messages, which communicate one Teredo client's random
port number to the other Teredo client, must be exchanged indirectly
(via Teredo servers). When one Teredo client has access to the other
Teredo client's random port number, it can send a direct bubble
destined to the mapped address embedded in the destination's Teredo
IPv6 address, and the mapped port can be the same as the
destination's random port number. If both NATs are port-preserving,
port-preserved mappings are created on both NATs and the second
direct bubble succeeds in reaching the destination.
3.4. Sequential Port-Symmetric NAT Extension
The Sequential Port-Symmetric NAT Extension is dependent on the
Symmetric NAT Support Extension (Section 3.1). This extension helps
in traversing a sequential port-symmetric NAT only if Teredo clients
are enabled to acquire a Teredo IPv6 address even when behind a
symmetric NAT.
When the Sequential Port-Symmetric NAT Extension is used, if a Teredo
client is positioned behind a sequential port-symmetric NAT, the
client can communicate with other Teredo clients that are positioned
behind a port-restricted NAT as follows.
During qualification, if the client discovers it is behind a
symmetric NAT that is not port-preserving, the client assumes by
default that it is behind a sequential port-symmetric NAT. This
assumption is proactive for the following reasons:
o There is no perfect method of discovering whether the client is
behind a sequential port-symmetric NAT.
o These kinds of NATs are notorious for changing their behavior. At
times, they could be sequential port-symmetric and at other times
not.
o There is no other solution for symmetric NAT traversal so this is
a last resort.
Teredo clients positioned behind sequential port-symmetric NATs can
also listen on a randomly chosen local port when communicating with a
peer. To predict the external port being used for a given peer, the
client sends three packets:
o Packet 1 is a router solicitation (as specified in Section 5.2.1
of [RFC4380]) sent to the Teredo server address.
o Packet 2 is a direct bubble sent to the peer.
o Packet 3 is a router solicitation sent to the secondary Teredo
server address.
As part of the normal Teredo protocol, the Teredo server responds to
packets 1 and 3. Based on the information in the responses, the
client now knows that Packet 1 was seen as coming from one external
port, and Packet 3 was seen as coming from another external port.
Assuming the NAT is a sequential port-symmetric NAT, the external
port for Packet 2 is estimated (or predicted) to be midway between
the external ports for Packets 1 and 3. Note that because other
applications might also have been using the NAT between packets 1 and
3, the actual port might not be exactly the midpoint.
The Teredo client then communicates the predicted port to its peer,
which sends a direct bubble to the communicated port. If the
communicated port is indeed the external port for Packet 2, the
direct bubble will reach the Teredo client.
3.5. Hairpinning Extension
Hairpinning support in a NAT routes packets that are sent from a
private (local) address destined to a public (mapped) address of the
NAT, back to another private (local) destination address behind the
same NAT. If hairpinning support is not available in a NAT, two
Teredo clients behind the same NAT are not able to communicate with
each other, as specified in Section 8.3 of [RFC4380].
The Hairpinning Extension enables two clients behind the same NAT to
talk to each other when the NAT does not support hairpinning. This
process is illustrated in the following diagram.
--------------------------------------------
/ \
< IPv6 Internet >
\ /
--------------------|-----------------------
|
+----------+
| Teredo |
| Server |
+----------+
203.0.113.120|
--------------------|-----------------------
/ \
< IPv4 Internet >
\ /
--------------------|-----------------------
198.51.100.118|
NAT +-------+
without | NAT |
hairpinning | E |
support +-------+
|
+------------------+--------------------+
192.168.1.0| 192.168.1.1|
UDP port 4095| UDP port 4096|
+---------+ +----------+
| NAT | | NAT |
| F | | G |
+---------+ +----------+
| |
+-----------------+ +-----------------+
| Teredo client A | | Teredo client B |
+-----------------+ +-----------------+
2001:0:cb00:7178:0:f000:39cc:9b89 2001:0:cb00:7178:0:efff:39cc:9b89
Teredo Address Teredo Address
Figure 3: Hairpinning Example
The Teredo Client A (A) includes, as part of its indirect bubble sent
to Teredo Client B (B), its local address/port. B, upon receiving
the indirect bubble, tries to establish communication by sending
direct bubbles to the mapped address/port of A, and also to the local
address/port of B.
If a Teredo client is part of a multi-NAT hierarchy and the NAT to
which the Teredo client is connected supports the UPnP protocol (as
specified in [UPNPWANIP]), the Teredo client can use UPnP to
determine the mapped address/port assigned to it by the NAT. This
information can be included along with the local address/port when
sending the indirect bubble. The destination Teredo client now tries
to establish a connection by sending direct bubbles to the mapped
address/port in the Teredo IPv6 address, to the local address/port
included in the bubble, and also to the mapped address/port included
in the bubble.
Note that UPnP support is only required if the Teredo clients are
behind different NATs in a multi-NAT hierarchy. Without UPnP
support, the Hairpinning Extension still allows two hosts behind the
same non-hairpinning NAT to communicate using their Teredo IPv6
addresses.
3.6. Server Load Reduction Extension
If communication between a Teredo client and a Teredo peer was
successfully established but at a later stage was silent for a while,
for efficiency, it is best to refresh the mapping state in the NATs
that are positioned between them. To refresh the communication
between itself and a Teredo peer, a Teredo client needs to solicit a
direct bubble response from the Teredo peer. An indirect bubble is
sent to solicit a direct bubble response from a Teredo peer, as
specified in Section 5.2.4 of [RFC4380]. However, these indirect
bubbles increase the load on the Teredo server.
The Server Load Reduction Extension allows Teredo clients to send
direct bubbles most of the time instead of sending indirect bubbles
all of the time in the following way:
1. When a Teredo client tries to refresh its communication with a
Teredo peer, it uses a direct bubble instead of an indirect
bubble. However, because direct bubbles do not normally solicit
a response, the direct bubble format is extended to be able to
solicit a response.
2. When a Teredo client receives a direct bubble that is soliciting
a response, the Teredo client responds with a direct bubble.
3. If attempts to re-establish communication with the help of direct
bubbles fail, the Teredo client starts over the process of
establishing communication with the Teredo peer, as specified in
Section 5.2.4 of [RFC4380].
4. Message Syntax
All Teredo messages are transported over the User Datagram Protocol
(UDP), as specified in Section 3 of [RFC4380].
In addition, Section 5.2.3 of [RFC4380] states:
An IPv6 packet is deemed valid if it conforms to [RFC2460]: the
protocol identifier should indicate an IPv6 packet and the payload
length should be consistent with the length of the UDP datagram in
which the packet is encapsulated. In addition, the client should
check that the IPv6 destination address correspond [sic] to its
own Teredo address.
This document updates the word "consistent" above as follows. The
IPv6 payload length is "consistent" with the length of the UDP
datagram if the IPv6 packet length (i.e., the Payload Length value in
the IPv6 header plus the IPv6 header size) is less than or equal to
the UDP payload length (i.e., the Length value in the UDP header
minus the UDP header size). This allows the use of trailers after
the IPv6 packet, which are defined in the following sections.
4.1. Trailers
Teredo packets can carry a variable number of type-length-value (TLV)
encoded trailers, of the following format (intended to be similar to
the use of IPv6 options defined in [RFC2460] section 4.2):
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 | Value (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type (1 byte): 8-bit identifier of the type of trailer.
Length (1 byte): 8-bit unsigned integer. Length of the Value field
of this trailer, in octets.
Value (variable): Trailer-Type-specific data.
The trailer Type identifiers are internally encoded such that their
highest-order two bits specify the action that is to be taken if the
host does not recognize the trailer Type:
00, 10, 11 - skip over this trailer and continue processing the
packet.
01 - discard the packet.
4.2. Nonce Trailer
The Nonce Trailer is used by the Symmetric NAT Support Extension (and
therefore the UPnP-enabled Symmetric NAT Extension and Port-
Preserving Symmetric NAT Extension also) and the Hairpinning
Extension. The Nonce Trailer can be present in both indirect and
direct bubbles. The nonce in the Nonce Trailer helps authenticate a
Teredo client positioned behind a Symmetric NAT.
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 | Nonce |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type (1 byte): The Trailer Option type. This field MUST be set to
0x01.
Length (1 byte): The length in bytes of the rest of the option. This
field MUST be set to 0x04.
Nonce (4 bytes): The nonce value.
4.3. Alternate Address Trailer
The Alternate Address Trailer is used by the Hairpinning Extension.
The Alternate Address Trailer MUST NOT be present in any packets
other than indirect bubbles sent by a Teredo client. The Alternate
Address Trailer provides another Teredo client positioned behind the
same NAT with more address options that it can use to connect.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Alternate Address/Port List (variable) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type (1 byte): The Trailer Option type. This field MUST be set to
0x03.
Length (1 byte): The length in bytes of the rest of the option. The
value of this field MUST be in the range 8 to 26 (i.e., 2 bytes for
the Reserved field, and 6 bytes for each entry in the Alternate
Address/Port List). This allows for a minimum of one address/port
mapping and a maximum of four address/port mappings to be advertised.
It SHOULD be at most 14 as a maximum of two address/port mappings can
be determined by Teredo: one local address/port and one obtained
using UPnP. Because the length of the alternate address/port is 6
bytes, the valid range of values is only 8, 14, 20, and 26.
Reserved (2 bytes): This field MUST be set to 0x0000 and ignored on
receipt.
Alternate Address/Port List (variable): An array of additional
address/port pairs that can be used by other Teredo clients to
communicate with the sender. Each alternate address/port entry MUST
be formatted as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
IPv4 Address (4 bytes): An IPv4 address in network byte order. This
field MUST contain a valid unicast address.
Port (2 bytes): A port number in network byte order. This field MUST
NOT be zero.
4.4. Neighbor Discovery Option Trailer
The Neighbor Discovery Option Trailer is used by the Server Load
Reduction Extension because it allows direct bubbles to encode an
IPv6 Neighbor Solicitation (Section 4.3 of [RFC4861]), in addition to
an IPv6 Neighbor Advertisement (Section 4.4 of [RFC4861]). This
allows packets to be sent without having to relay them through a
Teredo server. The Neighbor Discovery Option Trailer allows the
receiver to differentiate between a direct bubble that is soliciting
a response versus a regular direct bubble. This allows Teredo
clients to use direct bubbles to refresh inactive connections instead
of using indirect bubbles.
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 | DiscoveryType | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type (1 byte): The Trailer Option type. This field MUST be set to
0x04.
Length (1 byte): The length in bytes of the rest of the option. This
field MUST be set to 0x04.
DiscoveryType (1 byte): This field MUST be set to one of the
following values:
TeredoDiscoverySolicitation (0x00): The receiver is requested to
respond with a direct bubble of DiscoveryType
TeredoDiscoveryAdvertisement.
TeredoDiscoveryAdvertisement (0x01): The direct bubble is in
response to a direct bubble or an indirect bubbles containing
DiscoveryType TeredoDiscoverySolicitation.
Reserved (3 bytes): This field MUST be set to 0x000000 on
transmission and ignored on receipt.
4.5. Random Port Trailer
The Random Port Trailer is used by the Port-Preserving Symmetric NAT
Extension in both indirect and direct bubbles.
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 | Random Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type (1 byte): The Trailer Option type. This field MUST be set to
0x05.
Length (1 byte): The length in bytes of the rest of the option. This
field MUST be set to 0x02.
Random Port (2 bytes): The external port that the sender predicts
that its NAT has assigned it for communication with the destination.
This field MUST be specified in network byte order.
