RFC 6081
Teredo Extensions
5. Protocol Details
5.1. Common Processing
The behavior in this section applies to multiple extensions. Packets equivalent to those sent for a peer the first time a connection is being established MAY be generated at other implementation-specific times. (For example, an implementation might choose to do so when its Neighbor Cache Entry for the peer is in the PROBE state.)5.1.1. Refresh Interval
Section 5.2 of [RFC4380] states: The client must regularly perform the maintenance procedure in order to guarantee that the Teredo service port remains usable. The need to use this procedure or not depends on the delay since the last interaction with the Teredo server. The refresh procedure takes as a parameter the "Teredo refresh interval". This parameter is initially set to 30 seconds; it can be updated as a result of the optional "interval determination procedure". The randomized refresh interval is set to a value randomly chosen between 75% and 100% of the refresh interval. This requirement can be problematic when the client is behind a NAT that expires state in less than 30 seconds. The optional interval determination procedure (Section 5.2.7 of [RFC4380]) also does not provide for intervals under 30 seconds. Hence, this document refines the behavior by saying the initial parameter SHOULD be configurable and the default MUST be 30 seconds. An implementation MAY set the randomized refresh interval to a value randomly chosen within an implementation-specific range. Such a range MUST fall within 50% to 150% of the refresh interval. Section 5.2.5 of [RFC4380] states that: At regular intervals, the client MUST check the "date and time of the last interaction with the Teredo server" to ensure that at least one packet has been received in the last Randomized Teredo Refresh Interval. If this is not the case, the client SHOULD send a router solicitation message to the server, as specified in Section 5.2.1;
This document refines the behavior as follows. A Teredo client MAY choose to send additional router solicitation messages to the server at other implementation-specific times. (For example, an implementation might choose to do so when its Neighbor Cache Entry for the router is in the PROBE state.)5.1.2. Trailer Processing
A Teredo client MUST process the sequence of trailers in the same order as they appear in the packet. If the Teredo client does not recognize the trailer Type while processing the trailers in the Teredo packet, the client MUST discard the packet if the highest- order bits of the trailer Type contain 01, or else the Teredo client MUST skip past the trailer. A Teredo client MUST stop processing the trailers as soon as a malformed trailer appears in the sequence of trailers in the packet. A trailer is defined as malformed if it has any of the following properties: o The length in bytes of the remainder of the UDP datagram is less than 2 (the size of the Type and Length fields of a trailer). o The length in bytes of the remainder of the UDP datagram is less than 2 + the value of the Length field of the trailer.5.2. Symmetric NAT Support Extension
Section 5.2.1 of [RFC4380] advises that no Teredo IPv6 address be configured if the Teredo client is positioned behind a symmetric NAT. For Teredo clients positioned behind symmetric NATs, the mapped address/port used by its NAT when communicating with a Teredo peer is different from the mapped address/port embedded in the Teredo client's Teredo IPv6 address. The Symmetric NAT Support Extension provides a solution to this problem. In addition, Section 5.2.9 of [RFC4380] specifies a direct IPv6 connectivity test to determine that the mapped address/port in the Teredo IPv6 address of a peer is not spoofed. It does this through the use of a nonce in ICMPv6 Echo Request and Response messages (which are defined in Section 4 of [RFC4443]). However, the direct IPv6 connectivity test is limited only to communication between Teredo IPv6 addresses and non-Teredo IPv6 addresses. In the following extension, we introduce the use of a nonce in direct and indirect bubbles and provide a mechanism to verify that the mapped address/port are not spoofed. This extension is optional; an implementation SHOULD support it.
5.2.1. Abstract Data Model
This section describes a conceptual model of possible data organization that an implementation maintains to participate in this protocol. The described organization is provided to facilitate the explanation of how the protocol behaves. This document does not mandate that implementations adhere to this model as long as their external behavior is consistent with that described in this document. In addition to the state specified in Section 5.2 of [RFC4380], the following are also required. Peer Entry: The following additional state is required on a per-peer basis: o Nonce Sent: The value of the nonce sent in the last indirect bubble sent to the Teredo peer. o Nonce Received: The value of the nonce received in the last indirect bubble received from the Teredo peer.5.2.2. Timers
No timers are necessary other than those in [RFC4380].5.2.3. Initialization
No initialization is necessary other than that specified in [RFC4380].5.2.4. Message Processing
Except as specified in the following sections, the rules for message processing are as specified in [RFC4380].5.2.4.1. Sending an Indirect Bubble
The rules for when indirect bubbles are sent to a Teredo peer are specified in Section 5.2.6 of [RFC4380]. When a Teredo client sends an indirect bubble, it MUST generate a random 4-byte value and include it in the Nonce field of a Nonce Trailer (Section 4.2) appended to the indirect bubble, and also store it in the Nonce Sent field of its Peer Entry for that Teredo peer.
5.2.4.2. Sending a Direct Bubble
The rules for when direct bubbles are sent to a Teredo peer are specified in Section 5.2.6 of [RFC4380]. When a Teredo client sends a direct bubble to a peer after receiving an indirect bubble with a Nonce Trailer, it MUST include in the direct bubble a Nonce Trailer with the same nonce value. If the Teredo client is about to send a direct bubble before it has received an indirect bubble from the Teredo peer, the Teredo client MUST NOT include a Nonce Trailer.5.2.4.3. Receiving an Indirect Bubble
The rules for processing an indirect bubble are specified in Section 5.2.3 of [RFC4380]. In addition, when a Teredo client receives an indirect bubble containing a Nonce Trailer, the Teredo client MUST store the nonce in the Nonce Received field of its Peer Entry for that Teredo peer. If an indirect bubble is received without a Nonce Trailer, and the Nonce Received field in the Peer Entry is non-zero, the Nonce Received field SHOULD be set to zero.5.2.4.4. Receiving a Direct Bubble
If the mapped address/port of the direct bubble matches the mapped address/port embedded in the source Teredo IPv6 address, the direct bubble MUST be accepted, as specified in Section 5.2.3 of [RFC4380]. In addition, if the mapped address/port does not match the embedded address/port but the direct bubble contains a Nonce Trailer with a nonce that matches the Nonce Sent field of the Teredo peer, the direct bubble MUST be accepted. If neither of the above conditions is true, the direct bubble MUST be dropped. If the direct bubble is accepted, the Teredo client MUST record the mapped address/port from which the direct bubble is received in the mapped address/port fields of the Teredo peer, as specified in Section 5.2 of [RFC4380].5.3. UPnP-Enabled Symmetric NAT Extension
The UPnP-enabled Symmetric NAT Extension is optional; an implementation SHOULD support it. This extension has the Symmetric NAT Support Extension (Section 5.2) as a dependency. Any node that implements this extension MUST also implement the Symmetric NAT Support Extension.
5.3.1. Abstract Data Model
This section describes a conceptual model of possible data organization that an implementation maintains to participate in this protocol. The described organization is provided to facilitate the explanation of how the protocol behaves. This document does not mandate that implementations adhere to this model as long as their external behavior is consistent with that described in this document. This extension extends the abstract data model in Section 5.2.1 by adding the following additional fields. UPnP-Enabled NAT flag: This is a Boolean value, set to TRUE if the NAT positioned in front of the Teredo client is UPnP enabled. The default value of this flag is FALSE. UPnP-Mapped Address/Port: The mapped address/port assigned via UPnP to the Teredo client by the UPnP-enabled NAT behind which the Teredo client is positioned. Note that this field has a valid value only if the NAT to which the Teredo client is connected is UPnP enabled. Also, note that if the Teredo client is positioned behind a single NAT only (as opposed to a series of nested NATs), this value is the same as the mapped address/port embedded in its Teredo IPv6 address. Symmetric NAT flag: This is a Boolean value, set to TRUE if the Teredo client is positioned behind a symmetric NAT. Peer Entry: The following state needs to be added on a per-peer basis: o Symmetric Peer flag: This is a Boolean value and is TRUE if the Teredo peer is positioned behind a symmetric NAT. A Teredo client SHOULD also maintain the following state that is persisted across reboots: o Persisted UPnP-Mapped Port: The mapped port assigned via UPnP to the Teredo client by the UPnP-enabled NAT behind which the Teredo client is positioned. Note that this value is the same as the UPnP-Mapped Port value when both are non-zero. The default value is all zero bytes.5.3.2. Timers
No timers are necessary other than those in [RFC4380].
5.3.3. Initialization
Prior to beginning the qualification procedure, the Teredo client MUST first perform the uninitialization procedure specified in Section 5.3.5.1 if the Persisted UPnP-Mapped Port is supported and non-zero. The Teredo client MUST then invoke the AddPortMapping function, as specified in Section 2.4.16 of [UPNPWANIP], with the following parameters: o NewRemoteHost: "" (empty string) o NewExternalPort: Local Port value o NewProtocol: UDP o NewInternalPort: Local Port value o NewInternalClient: Local Address value o NewEnabled: TRUE o NewPortMappingDescription: "TEREDO" o NewLeaseDuration: 0 The successful completion of the AddPortMapping function indicates that the NAT has created a port mapping from the external port of the NAT to the internal port of the Teredo client node. The parameters are specified so that any external host should be able to send packets to the Teredo client by sending packets to the mapped address/port. If the AddPortMapping function fails, the Teredo client MUST continue without using this extension. Otherwise, it MUST proceed as follows. The Teredo client MUST set the UPnP-Mapped Port (and Persisted UPnP- Mapped Port, if supported) to the Local Port value specified in AddPortMapping. The Teredo client MUST then call the GetExternalIPAddress function specified in Section 2.4.18 of [UPNPWANIP]. If the GetExternalIPAddress function fails, the Teredo client SHOULD perform the uninitialization procedure specified in Section 5.3.5.1 and continue without using this extension. If the GetExternalIPAddress function succeeds, the Teredo client MUST proceed as follows.
The Teredo client MUST set the UPnP-Mapped Address to the address returned from the GetExternalIPAddress function, and set the UPnP- Enabled NAT flag to TRUE. During the qualification procedure (as specified in Section 5.2.1 of [RFC4380]) when the Teredo client receives a response from the secondary Teredo server, the Teredo client MUST compare the mapped address/port learned from the secondary Teredo server with the mapped address/port associated with the Teredo server. If either the mapped address or the mapped port value is different, the Symmetric NAT flag MUST be set to TRUE. After the qualification procedure, the mapped address/port learned from the Teredo server MUST be compared to the UPnP-Mapped Address/ Port. If both are the same, the Teredo client is positioned behind a single NAT and the UPnP-Mapped Address/Port MUST be zeroed out.5.3.4. Message Processing
Except as specified in the following sections, the rules for message processing are as specified in Section 5.2.3 of [RFC4380].5.3.4.1. Receiving a Direct Bubble
Except as indicated below, the rules for handling a direct bubble are as specified in Section 5.2.4.4. A Teredo client positioned behind a UPnP-enabled NAT (port-restricted NAT as well as symmetric NAT) will receive all packets sent to the mapped address/port embedded in its Teredo IPv6 address. Thus, when a Teredo client receives a direct bubble, it MUST compare the mapped address/port from which the packet was received with the mapped address/port embedded in the Teredo IPv6 address in the source address field of the IPv6 header. If the two are not the same, it indicates that the Teredo peer is positioned behind a symmetric NAT, and it MUST set the Symmetric Peer flag in its Peer Entry.5.3.4.2. Sending a Direct Bubble
The rules for sending a direct bubble are specified in Section 5.2.6 of [RFC4380] and Section 5.2.4.2 of this document. These rules are further refined as follows. If the Teredo client sending the direct bubble meets all of the following criteria: o The Symmetric NAT flag is set to TRUE.
o The UPnP-Enabled NAT flag is set to TRUE. o The UPnP-Mapped Address/Port are set to zero. o The peer's Symmetric Peer flag is set to TRUE. then the Teredo client MUST send the direct bubble to the mapped address/port embedded in the peer's Teredo IPv6 address. This is because Symmetric-to-Symmetric and Port-Restricted-to- Symmetric NAT communication between the Teredo client and the peer would have failed anyway. However, by taking a chance that the peer might also be positioned behind a UPnP-enabled NAT just like the Teredo client itself, the Teredo client can try sending the direct bubble to the mapped address/port in the peer's Teredo IPv6 address. If the packet does go through, communication is established.5.3.4.3. Sending a Data Packet
The rules for sending a data packet are specified in Section 5.2.4 of [RFC4380]. These rules are further refined as follows. If the Teredo client sending the data packet meets all of the following criteria: o The Symmetric NAT flag is set to TRUE. o The UPnP-Enabled NAT flag is set to TRUE. o The UPnP-Mapped Address/Port are set to zero. o The peer's Symmetric Peer flag is set to TRUE. then the Teredo client MUST send the data packet to the mapped address/port embedded in the peer's Teredo IPv6 address.5.3.5. Shutdown
When Teredo client functionality is being shut down, uninitialization MUST be performed as specified in Section 5.3.5.1.5.3.5.1. Uninitialization
First determine the mapped port as follows. If Persisted UPnP-Mapped Port is supported, use it as the mapped port. Otherwise, use the UPnP-Mapped Port.
If the mapped port is non-zero, the Teredo client MUST call the DeletePortMapping function, as specified in Section 2.4.17 of [UPNPWANIP], with the following parameters: o NewRemoteHost: "" (empty string) o NewExternalPort: the mapped port o NewProtocol: UDP5.4. Port-Preserving Symmetric NAT Extension
The Port-Preserving Symmetric NAT Extension is optional; an implementation SHOULD support it. This extension has the Symmetric NAT Support Extension (as specified in Section 5.2) as a dependency. Any node that implements this extension MUST also implement the Symmetric NAT Support Extension.5.4.1. Abstract Data Model
This section describes a conceptual model of possible data organization that an implementation maintains to participate in this protocol. The described organization is provided to facilitate the explanation of how the protocol behaves. This document does not mandate that implementations adhere to this model as long as their external behavior is consistent with that described in this document. The Port-Preserving Symmetric NAT Extension extends the abstract data model in Section 5.2.1 by adding the following additional fields. Port-Preserving NAT flag: This is a Boolean value, set to TRUE if the Teredo client is positioned behind a port-preserving NAT. Symmetric NAT flag: This is a Boolean value, set to TRUE if the Teredo client is positioned behind a symmetric NAT. Peer Entry: The following fields need to be added on a per-peer basis: o Random Port: This field contains the value of the external port that the Teredo client predicts that its NAT has assigned it for communication with the peer. Set to zero by default. o Peer Random Port: This field contains the value of the random port that the peer is using for communication with this Teredo client. Set to zero by default.
o Direct Receive on Primary Port: This is a Boolean value, set to
TRUE if a packet is received from the Teredo peer on the primary
local port. Set to FALSE by default.
o Direct Receive on Random Port: This is a Boolean value, set to
TRUE if a packet is received from the Teredo peer on the Random
Port. Set to FALSE by default.
o Connection Refresh Count: This field contains the number of direct
bubbles that have been sent to the peer since the last time data
was sent to the peer.
o Last Data Packet Sent Timestamp: This field contains the timestamp
of the last data packet sent to the peer. This timestamp is
different from the field that stores the data and time of last
transmission to the peer (as specified in Section 5.2 of
[RFC4380]) because the RFC-defined field is also updated every
time a direct bubble is sent.
5.4.2. Timers
Other than those in [RFC4380], the Port-Preserving Symmetric NAT
Extension requires the following additional timer.
Peer Refresh Timer: A timer to refresh peer connections through the
random port, on which no data has been sent for a while.
5.4.2.1. Peer Refresh Timer Expiry
When the Peer Refresh Timer expires, the Teredo client MUST go
through its list of peers and for each peer to which the Teredo
client is communicating through the random port, the Teredo client
MUST check the Last Data Packet Sent Timestamp to determine if data
has been sent to the peer in the last 30 seconds, and check the
Connection Refresh Count field to determine if the count has reached
the maximum allowed value of 20. If both checks are FALSE, the
Teredo client MUST send a direct bubble (as specified in
Section 5.4.4.3) to the peer and increment the Connection Refresh
Count. This direct bubble is sent as an attempt to keep the port
mappings on all the intermediate NATs alive while the application/
user may be temporarily inactive. If on the other hand, data has
been sent to the peer in the last 30 seconds, the Connection Refresh
Count MUST be reset to zero.
The Peer Refresh Timer MUST then be rescheduled to expire in 30
seconds.
5.4.3. Initialization
In addition to the behavior specified in [RFC4380], the Port- Preserving NAT flag and Symmetric NAT flag MUST be set to FALSE when the Teredo client is started. The Peer Refresh Timer MUST be started and scheduled to expire in 30 seconds. During the qualification procedure (as specified in Section 5.2.1 of [RFC4380]), when the Teredo client receives a response from the Teredo server address, the Teredo client MUST compare the Port value in the origin indication, as specified in Section 5.1.1 of [RFC4380], with the Local Port value. If both values match, the client MUST set the Port-Preserving NAT flag to TRUE.5.4.4. Message Processing
5.4.4.1. Sending a Data Packet
On receiving a data packet to be transmitted to the Teredo peer (in addition to the rules specified in Section 5.2.4 of [RFC4380]), the Teredo client MUST update the Last Data Packet Sent Timestamp when the packet is actually sent.5.4.4.2. Sending an Indirect Bubble
The rules for sending an indirect bubble are as specified in Section 5.2.4.1 of this document and Section 5.2.6 of [RFC4380]. In addition to those rules, if the Port-Preserving NAT flag is TRUE, the Teredo client MUST do the following: o If the Symmetric NAT flag is set, the Teredo peer is not marked as "trusted" (as specified in Section 5.2 of [RFC4380]), and the Random Port is zero, the Teredo client MUST first select a random port number to use, and then begin listening on that port. Since the NAT is port-preserving, the Teredo client can predict that the external port assigned will be equal to the random port chosen, and hence the Teredo client MUST store the random port chosen in the Random Port field of the Peer Entry. o If the Random Port value is non-zero, the Teredo client MUST append a Random Port Trailer to the indirect bubble.
5.4.4.3. Sending a Direct Bubble
The rules for when direct bubbles are sent to a Teredo peer are as specified in Section 5.2.6 of [RFC4380]. In addition, Section 5.2.4.2 defines rules for enabling communication for clients positioned behind a symmetric NAT. In addition to the rules defined in both the aforementioned sections, if the Port-Preserving NAT flag is TRUE, the following rules apply also. If the Symmetric NAT flag is set, and the Teredo peer is not marked as "trusted" (as specified in Section 5.2 of [RFC4380]) the Teredo client MUST send a direct bubble destined to the mapped address/port embedded in the Teredo IPv6 address of the Teredo peer. If the peer Random Port field is non-zero, the Teredo client MUST send another direct bubble from its own random port, destined to the peer random port. The IPv4 destination address MUST be the mapped address embedded in the Teredo IPv6 address. In addition, the Teredo client MUST include the Random Port Trailer (Section 4.5).5.4.4.4. Receiving an Indirect Bubble
The rules for processing an indirect bubble are as specified in Section 5.2.4.3 of this document and Section 5.2.3 of [RFC4380]. In addition to these rules, if the incoming indirect bubble has a Random Port Trailer, the following additional processing MUST be done. If the Peer Random Port field of the Peer Entry is zero, the Teredo client MUST store the port from the Random Port Trailer in the Peer Random Port field of the Peer Entry. If the Peer Random Port field is non-zero and if either the Peer Random Port field and the new advertised port have the same value, or if active data has been exchanged between the two Teredo clients in the last 30 seconds (that is, "time of last transmission" or "time of last reception", as specified in Section 5.2 of [RFC4380], is set to a time that is less than 30 seconds ago), the new advertised port value MUST be ignored. If the Peer Random Port field is non-zero and the new advertised port value is different from the Peer Random Port value, and it has been more than 30 seconds since the last exchange of data packets between the two Teredo clients, (that is, "time of last transmission" and "time of last reception" are set to a time that is more than 30 seconds ago), the Teredo client SHOULD store the new advertised port value in the Peer Random Port field and, if the Port-Preserving NAT flag is TRUE, then clear the Random Port field, and stop listening on the old random port. This allows communication to be re-established if either side changes the random port that it is using.
5.4.4.5. Receiving a Direct Bubble
The rules for handling direct bubbles are specified in Section 5.2.4.4 of this document and Section 5.2.3 of [RFC4380]. The rules for whether to accept a direct bubble are extended as follows, when the Port-Preserving NAT flag is TRUE: o If the direct bubble is received on the primary port and the Teredo peer is not "trusted", the status field of the Teredo client MUST be changed to "trusted" and the Direct Receive on Primary Port flag MUST be set to TRUE. The mapped address/port from which the direct bubble was received MUST be recorded in the mapped address/port fields of the Teredo peer, as specified in Section 5.2 of [RFC4380]. The Teredo client MUST then set the Random Port field in the Peer Entry to zero and stop listening on the old random port. o If the direct bubble is received on the primary port, the Teredo peer is "trusted", and the Direct Receive on Primary flag is set to TRUE, the Teredo client MUST compare the mapped address/port of the direct bubble with the mapped address/port of the Peer Entry. If both mappings are the same, the direct bubble MUST be accepted. If the mappings are different and it has been more than 30 seconds since the last packet exchange with the Teredo peer (that is, "time of last transmission" and "time of last reception", as defined in Section 5.2 of [RFC4380], are set to a time that is more than 30 seconds ago), the mapping on the Teredo peer's NAT has changed and communication needs to be re-established. This MUST be done by changing the status of the peer to "not-trusted", setting the Direct Receive on Primary Port flag to FALSE, and sending an indirect bubble to the Teredo peer via its Teredo server. o If the direct bubble is received on the primary port, the Teredo peer is "trusted", the Direct Receive on Primary Port flag is set to FALSE, and the Direct Receive on Random Port flag is set to TRUE, the mapped address/port from which the direct bubble is received MUST be stored in the mapped address/port fields of the Peer Entry. The Direct Receive on Primary Port flag MUST be set to TRUE. The Teredo client MUST then set the Random Port field in the Peer Entry to zero and stop listening on the old random port. Finally, the Direct Receive on Random Port flag MUST be set to FALSE.
o If the direct bubble is received on the random port and the Teredo
peer is not "trusted", the status field of the Teredo client MUST
be changed to "trusted" and the Direct Receive on Random Port flag
MUST be set to TRUE. The mapped address/port from which the
direct bubble was received MUST be recorded in the mapped address/
port fields of the Teredo Peer Entry, as specified in Section 5.2
of [RFC4380].
o If the direct bubble is received on the random port, the Teredo
peer is "trusted", and the Direct Receive on Primary Port flag is
FALSE, the Teredo client MUST compare the mapped address/port in
the direct bubble with the mapped address/port in the Peer Entry.
If the two mappings are the same, the direct bubble MUST be
accepted. If the mappings are different, it implies that the NAT
had deleted the mapping and when it reassigned the mapping, a
different external port was chosen. In this instance, the Teredo
client SHOULD set the Random Port field to zero, stop listening on
the old random port, and send an indirect bubble to the Teredo
peer as specified in Section 5.4.4.2.
Note that once the Direct Receive on Primary Port flag is TRUE, the
client will stop listening on the random port and hence a direct
bubble cannot be received on the random port. As a result, this case
is intentionally omitted above.
5.5. Sequential Port-Symmetric NAT Extension
The Sequential Port-Symmetric NAT Extension is optional; an
implementation SHOULD support it. This extension has the Symmetric
NAT Support Extension (Section 5.2) as a dependency. Any node that
implements this extension MUST also implement the Symmetric NAT
Support Extension, as well as the Port-Preserving NAT Extension
(Section 5.4).
5.5.1. Abstract Data Model
This section describes a conceptual model of possible data
organization that an implementation maintains to participate in this
protocol. The described organization is provided to facilitate the
explanation of how the protocol behaves. This document does not
mandate that implementations adhere to this model as long as their
external behavior is consistent with that described in this document.
The Sequential Port-Symmetric NAT Extension extends the abstract data
model in Section 5.4.1 by adding the following additional state.
Peer Entry: The following fields need to be added on a per-peer
basis:
o EchoTestNonce1: The value of the nonce sent as part of the
authentication encapsulation, as specified in Section 5.1.1 of
[RFC4380], in the router solicitation packet sent to the Teredo
server address as part of the Echo Test.
o EchoTestNonce2: The value of the nonce sent as part of the
authentication encapsulation in the router solicitation packet
sent to the secondary Teredo server address as part of the Echo
Test.
o EchoTestLowerPort: The value of the external port mapping
extracted from the origin indication of the router advertisement
received from the Teredo server address as part of the Echo Test.
A value of 0 indicates that no such router advertisement has been
received.
o EchoTestUpperPort: The value of the external port mapping
extracted from the origin indication of the router advertisement
received from the secondary Teredo server address as part of the
Echo Test. A value of 0 indicates that no such router
advertisement has been received.
o EchoTestRetryCounter: The number of times an Echo Test has been
attempted.
5.5.2. Timers
In addition to the timers specified in Section 5.4.2, the following
additional timer is required per Peer Entry.
Echo Test Failover Timer: A one-shot timer that runs whenever an Echo
Test is in progress.
5.5.2.1. Peer Refresh Timer Expiry
The processing of the Peer Refresh Timer Expiry MUST be completed as
specified in Section 5.4.2.1. In addition to those rules, the Teredo
client MUST set the EchoTestLowerPort, EchoTestUpperPort, and
EchoTestRetryCounter to zero.
5.5.2.2. Echo Test Failover Timer Expiry
If the Echo Test Failover Timer expires, the Teredo client MUST do
the following.
If the value of the EchoTestRetryCounter is two, then the Teredo client MUST send an indirect bubble as specified in Section 5.2.4.1. If the value of the EchoTestRetryCounter is one, then the Teredo client MUST start another Echo Test as specified in Section 5.5.4.1.1.5.5.3. Initialization
No behavior changes are required beyond what is specified in Section 5.4.3.5.5.4. Message Processing
Except as specified in the following sections, the rules for message processing are as specified in Section 5.4.4.5.5.4.1. Handling a Request to Send an Indirect Bubble
Whenever [RFC4380] or other extensions specified in this document specify that an indirect bubble is to be sent, the following actions apply at that time instead if the Symmetric NAT flag is TRUE and the Port-Preserving NAT flag is FALSE. Note that any behavior specified by [RFC4380] or other extensions in this document still applies to how indirect bubbles are constructed, but such behavior is done at a later time as specified in Section 5.5.4.4. If the Symmetric NAT flag is TRUE, and the Port-Preserving NAT flag is FALSE, and the Teredo peer is not marked as "trusted" (as specified in Section 5.2 of [RFC4380]), and the Random Port is zero, then the Teredo client MUST select a random port number to use, begin listening on that port, and start an Echo Test as specified below.5.5.4.1.1. Starting an Echo Test
To start an Echo Test, the Teredo client MUST send the following three packets from this port: o First, a router solicitation (as specified in Section 5.2.1 of [RFC4380]) MUST be sent to the Teredo server address. The router solicitation MUST include an authentication encapsulation with a randomly generated Nonce field, as specified in Section 5.1.1 of [RFC4380]. The nonce included in the authentication encapsulation MUST then be stored in the EchoTestNonce1 field of the Peer Entry. o Second, a direct bubble MUST be sent to the peer.
o Third, a router solicitation MUST be sent to the secondary Teredo
server address. The router solicitation MUST include an
authentication encapsulation with a randomly generated Nonce
field, as specified in Section 5.1.1 of [RFC4380]. The nonce
included in the authentication encapsulation MUST then be stored
in the EchoTestNonce2 field of the Peer Entry.
The Teredo client MUST then increment the EchoTestRetryCounter and
set the Echo Test Failover Timer to expire in a number of seconds
equal to EchoTestRetryCounter.
5.5.4.2. Sending an Indirect Bubble
The rules for sending an indirect bubble are as specified in
Section 5.2.4.1 of this document and Section 5.2.6 of [RFC4380]. In
addition to those rules, if the Symmetric NAT flag is TRUE, and the
Port-Preserving NAT flag is FALSE, and the Random Port value is non-
zero, then the Teredo client MUST append a Random Port Trailer to the
indirect bubble.
5.5.4.3. Receiving a Direct Bubble
The processing of the direct bubble MUST be completed as specified in
Section 5.4.4.5, as if the Port-Preserving NAT flag were TRUE. After
the processing is complete, if the Direct Bubble Received on Primary
flag is TRUE, and the Echo Test Failover Timer is running, then the
Echo Test Failover Timer MUST be canceled and EchoTestLowerPort,
EchoTestUpperPort, and EchoTestRetryCounter MUST be set to zero.
5.5.4.4. Receiving a Router Advertisement
The rules for processing a router advertisement are as specified in
Section 5.2.1 of [RFC4380]. In addition to those rules, if the
router advertisement contains an authentication encapsulation, the
Teredo client MUST look for a Peer Entry whose EchoTestNonce1 or
EchoTestNonce2 field matches the nonce in the authentication
encapsulation. If a Peer Entry is found, the Teredo client MUST do
the following.
If the received nonce is equal to EchoTestNonce1 and
EchoTestLowerPort is zero, then EchoTestLowerPort MUST be set to the
external port mapping extracted from the origin indication of this
router advertisement.
If the received nonce is equal to EchoTestNonce2 and
EchoTestUpperPort is zero, then EchoTestUpperPort MUST be set to the
external port mapping extracted from the origin indication of this
router advertisement.
If the EchoTestUpperPort and EchoTestLowerPort are now both non-zero, the Teredo client MUST then set the Random Port field of the Peer Entry to (EchoTestUpperPort + EchoTestUpperPort)/2, rounded down, and send an indirect bubble as specified in Section 5.5.4.2.5.6. Hairpinning Extension
This extension is optional; an implementation SHOULD support it.5.6.1. Abstract Data Model
This section describes a conceptual model of possible data organization that an implementation maintains to participate in this protocol. The described organization is provided to facilitate the explanation of how the protocol behaves. This document does not mandate that implementations adhere to this model as long as their external behavior is consistent with that described in this document. In addition to the state specified in Section 5.2 of [RFC4380], the following are also required: UPnP Mapped Address/Port: The mapped address/port assigned via UPnP to the Teredo client by the UPnP-enabled NAT behind which the Teredo client is positioned. This field has a valid value only if the NAT to which the Teredo client is connected is UPnP enabled. In addition, if the Teredo client is positioned behind a single NAT only (as opposed to a series of nested NATs), this value will be the same as the mapped address/port embedded in its Teredo IPv6 address. Peer Entry: Per-peer state is extended beyond what is described in [RFC4380] by including the following: o Alternate Address/Port list: The list of alternate address/port pairs advertised by the peer.5.6.2. Timers
No timers are necessary other than those in [RFC4380].5.6.3. Initialization
Behavior is as specified in [RFC4380], with the following additions. Prior to beginning the qualification procedure, the Teredo client MUST invoke the AddPortMapping function (as specified in Section 2.4.16 of [UPNPWANIP]) with the parameters specified in Section 5.3.3. If successful, it indicates that the NAT has created a port mapping from the external port of the NAT to the internal port
of the Teredo client node. If the AddPortMapping function is successful, the Teredo client MUST store the mapping assigned by the NAT in its UPnP Mapped Address/Port state. After the qualification procedure, the mapped address/port learned from the Teredo server MUST be compared to the UPnP Mapped Address/ Port. If both are the same, the Teredo client is positioned behind a single NAT and the UPnP Mapped Address/Port MUST be zeroed out.5.6.4. Message Processing
5.6.4.1. Sending an Indirect Bubble
The rules for when indirect bubbles are sent to a Teredo peer are as specified in Section 5.2.6 of [RFC4380]. If communication between a Teredo client and a Teredo peer has not been established, the Teredo client MUST include the Alternate Address Trailer in the indirect bubble. The Alternate Address Trailer MUST include the node's local address/port in the Alternate Address/Port list. If the UPnP Mapped Address/Port is non-zero, the Alternate Address Trailer MUST also include it in the list. Hairpinning requires "direct IPv6 connectivity tests" (as specified in Section 5.2.9 of [RFC4380]) to succeed before it can accept packets from an IPv4 address and port not embedded in the Teredo IPv6 address. Hence, the indirect bubble MUST also include a Nonce Trailer.5.6.4.2. Receiving an Indirect Bubble
The rules for processing indirect bubbles are as specified in Section 5.2.3 of [RFC4380]. In addition to those rules, when a Teredo client receives an indirect bubble with the Alternate Address Trailer, it SHOULD first verify that the Alternate Address Trailer is correctly formed (as specified in Section 4.3), and drop the bubble if not. Otherwise, it MUST set the Alternate Address/Port list in its Peer Entry to the list in the trailer. The Teredo client, besides sending direct bubbles to the mapped address/port embedded in the Teredo IPv6 address (as specified in Section 5.2.6 of [RFC4380]), MUST also send a direct bubble to each mapped address/port advertised in the Alternate Address Trailer. In each of the direct bubbles, the Teredo client MUST include a Nonce Trailer with the nonce value received in the indirect bubble.
5.6.4.3. Receiving a Direct Bubble
If the mapped address/port of the direct bubble matches the mapped address/port embedded in the source Teredo IPv6 address, the direct bubble MUST be accepted, as specified in Section 5.2.3 of [RFC4380]. If the mapped address/port does not match the embedded address/port, but the direct bubble contains a Nonce Trailer with a nonce that matches the Nonce Sent field of the Teredo peer, the direct bubble MUST be accepted. If neither of the above rules match, the direct bubble MUST be dropped.5.7. Server Load Reduction Extension
This extension is optional; an implementation SHOULD support it.5.7.1. Abstract Data Model
This section describes a conceptual model of possible data organization that an implementation maintains to participate in this protocol. The described organization is provided to facilitate the explanation of how the protocol behaves. This document does not mandate that implementations adhere to this model as long as their external behavior is consistent with that described in this document. In addition to the state specified in Section 5.2 of [RFC4380], the following are also required. Peer Entry: The following state needs to be added on a per-peer basis: o Count of Solicitations Transmitted: The number of Solicitation packets sent.5.7.2. Timers
Retransmission Timer: A timer used to retransmit Teredo Neighbor Solicitation packets. When the retransmission timer expires, the Teredo client MUST retransmit a direct bubble with a Neighbor Discovery Option Trailer, and increment the Count of Solicitations Transmitted. If the count is less than three, it MUST then reset the timer to expire in two seconds. Otherwise (if the count is now three), it MUST send an
indirect bubble to the Teredo peer to re-establish connectivity as if no communication between the Teredo client and the Teredo peer had been established.5.7.3. Initialization
No initialization is necessary other than that specified in [RFC4380].5.7.4. Message Processing
Except as specified below, processing is the same as specified in [RFC4380].5.7.4.1. Sending a Data Packet
Upon receiving a data packet to be transmitted to the Teredo peer, the Teredo client MUST determine whether data has been exchanged between the Teredo client and peer in either direction in the last 30 seconds (using the state as specified in Section 5.2 of [RFC4380]). If not, the Teredo client MUST send a direct bubble with a Neighbor Discovery Option Trailer having the DiscoveryType field set to TeredoDiscoverySolicitation. The Count of Solicitations Transmitted field MUST be set to 1. The retransmission timer MUST be set to expire in two seconds.5.7.4.2. Receiving a Direct Bubble
The rules for processing direct bubbles are as specified in Section 5.2.3 of [RFC4380]. In addition to those rules, upon receiving a direct bubble containing a Neighbor Discovery Option Trailer with DiscoveryType field set to TeredoDiscoverySolicitation, the Teredo client MUST respond with a direct bubble with the Neighbor Discovery Option Trailer having the DiscoveryType field set to TeredoDiscoveryAdvertisement.
(page 42 continued on part 3)
