IPv6 Operations J. Massar
Internet-Draft Unfix/SixXS
Expires: November 24, 2004 May 26, 2004
AYIYA: Anything In Anything
draft-massar-v6ops-ayiya-00
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Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
This document defines a tunneling protocol that can be encapsulated
in any other protocol. Using authentication tokens multiple tunnels
can be created from behind the same NAT. The tokens allow one to
identify the sender of the packet thus making it possible to
automatically switch over the endpoint. This protocol is intended as
an alternative to the proto-41 protocol in use for tunneling IPv6
over IPv4 packets over the internet. Due to the authentication this
protocol is especially useful for dynamic non-24/7 endnodes which are
located behind NATs and want to use for instance a IPv6 Tunnel
Broker. The protocol can carry any payload and thus is not limited to
only IPv6 over IPv4 but can also be used for IPv4 over IPv6 and many
other combinations of protocols.
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Table of Contents
1. Requirements notation . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. AYIYA Packet format . . . . . . . . . . . . . . . . . . . . . 3
4. Heartbeat . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . 7
7.1 Tunneling to multiple endhosts behind a NAT . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 8
Intellectual Property and Copyright Statements . . . . . . . . 9
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1. Requirements notation
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].
2. Introduction
Many users are currently located behind NAT's which prohibit the
usage of proto-41 IPv6 in IPv4 tunnels unless they manually
reconfigure their NAT setup which in some cases is impossible as the
NAT can't be configured to forward proto-41 ([RFC1933]) to a specific
host. There might also be cases when multiple endpoints are behind
the same NAT, when multiple NAT's are used or when the user has no
control at all on the NAT setup. This is a undesired situation as it
limits the deployment of IPv6, which was meant to solve the problem
of the disturbance in end to end communications by NATs, which where
created because of limited address space, in the first place.
This problem can be solved easily by tunneling the IPv6 packets over
either UDP, TCP or even SCTP. Taking into consideration that multiple
seperate endpoints could be behind the same NAT and/or that the
public endpoint can change on the fly there is also a need to be able
to identify packets as coming from a certain endpoint and to be able
to automatically change the endpoint on the fly. The protocol
described in this document is protocol independent and can be run
over and also encapsulate any protocol. Examples are
IPv6-in-UDP-in-IPv4, which is a typical setup which can be used by
Tunnel Brokers.
This protocol doesn't describe how to determine the identity,
signature type or the inner and outer protocols. These should be
negotiated manually or automatically by eg using TSP or a relevant
protocol which is capable of describing ayiya tunnels.
3. AYIYA Packet format
The AYIYA protocol is put inside the data part of either UDP
[RFC0768], TCP [RFC0793] or SCTP [RFC2960] which are the currently
defined transport protocols, future transport protocols could also be
used. The transport protocol can be run over both IPv4 or IPv6 or any
other future protocol. Schematically this will look like the
following diagram.
+--------+ +--------+
| Client | <--- Internet ---> | Server |
+--------+ +--------+
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A complete on the wire packet will have the following format.
,------------------------------.
| Delivery Header |
| IPv4/IPv6/... |
+-------------------------------+
| Transport Header |
| TCP/UDP/SCTP/... |
+-------------------------------+
| AYIYA Header |
+-------------------------------+
| Payload packet |
`-------------------------------'
The AYIYA protocol header and has the following format.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identity Type | SignatureType | Next Header | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Epoch Time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: Identity :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: Signature :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Epoch Time is the time in seconds since "00:00:00 1970-01-01 UTC".
Both the client and the server are advised to be synchronized using
NTP [RFC2030] to make sure that the system clocks of the hosts don't
differ to much even after travelling the intermediate networks
between the client and the server. The number of seconds since the
above date are stored in a 32 bit unsigned integer in network byte
order.
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The Identity Type specifies what kind of Identity is included in the
header. Currently defined are:
- 0x01 32 bit integer (4 bytes)
- 0x02 64 bit integer (8 bytes)
- 0x03 128 bit integer (16 bytes)
- 0x04 256 bit integer (32 bytes)
- 0x11 4 byte ASCII string
- 0x12 8 byte ASCII string
- 0x13 16 byte ASCII string
- 0x14 32 byte ASCII string
Other values are reserved. The kind of identity used by a tunnel is
negotiated outside this protocol. ASCII strings are NULL padded if
they don't fill the complete identity field.
The Signature Type contains the kind of signature used by the
protocol. Currently defined are:
- 0x01 MD5 (128 bit - 16 bytes)
- 0x01 SHA1 (160 bit - 20 bytes)
The Next Header, like in IPv6, contains the protocol value of the
payload following the Heartbeat Header. There is no length field as
we can deduce that already from the protocol that is carrying this
packet. A Next Header value of 0xffff is special, see the following
Heartbeat section.
The Reserved field is reserved and should be initialized to NULL.
The signature field should contain the hash of the password specified
for the identity in the same hashing method as to be used for hashing
the packet itself. The signature is then made over the complete
packet, thus the header and payload. By hashing the password we allow
arbitrarily lenght passwords to be used. Implementations could choose
to precache the hashed password and thus also requiring having the
cleartext password. The packet, header and payload can then be sent
to the server. This method thus allows verification of the password
without sending the password over the network. The server does the
same thing, taking the header part of the packet, adding the password
and calculating the signature which can then be compared with the
signature which was sent by the client. If these match the packet can
be processed further. When the signatures don't match the server MUST
silently ignore the packet.
4. Heartbeat
As the server will disable the tunnel after it has not received a
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packet from the client after a configured time the client should send
packets to the other side of the tunnel with the Next Header field to
0xffff, the payload should contain a 32 bit sequence number and may
be filled with other informations. The server will reply this packet
with the same payload allowing the client to compare the information
and deduce latency information and other statistical information from
it. This packet also allows the client to test if at least the tunnel
to the server works. If the signature is not correct, either because
of the wrong password, wrong hash, wrong identity or connectivity
problems the client won't get a reply and could notify the client of
this situation.
Clients should send these packets once per 60 seconds as the server
is usually configured to disable the tunnel after 120 seconds.
5. Acknowledgements
The protocol presented has formed during the existence of SixXS
[SIXXS] to allow the users of the various tunnel servers provisioned
by SixXS to have a dynamic non-static IPv4 endpoint which could even
be located behind a NAT. This protocol is a combination of the
proto-41 tunneling protocol and the additional SixXS Heartbeat
protocol.
6. Security Considerations
The password used [RFC1321] must never be made publicly available to
3rd parties otherwise that 3rd party could sign a packet and
automatically reconfigure the tunnel endpoint. This could lead into
the 3rd party sending traffic in both directions and thus posing as
the actual user.
The inclusion of the epochtime along with the verification on the
Tunnel Server side should guard against any replay attacks. The
Tunnel Server MUST limit that the local clock compared to the
timestamp from the packet MUST never differ for more than 60 seconds,
this allows for at least some latency and time-desync.
Any packet that is not well formed or contains a invalid signature
MUST be silently dropped, appropriate loggin may be done of these
issues but in that case a ratelimit must be applied to not clutter
the logs with these messages. Invalid signatures MUST be handled as
possibly being spoofed, thus no packet MUST be sent back as these
packets will then go to the spoofed address.
A side effect of this protocol is that whenever the client host
cannot or does not send a packet in time to the Tunnel Server that it
will deconfigure the tunnel. This could be the case when the client's
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connectivity is interrupted.
7. Scenarios
7.1 Tunneling to multiple endhosts behind a NAT
This scenario demonstrates the scenario where this protocol will find
it's main usage: tunneling to multiple endhosts behind a NAT. This
setup allows both clients to change their private IPv4 addresses and
also to allow the NAT to change it's public IPv4 and source port
numbers. The server will notice the change of source IP and port
numbers and can reconfigure it's tunnel to send to the specific
host:port combination for which a mapping will exist at the NAT and
the packet will go through the NAT, not considering firewalling
effects. If firewalls are in place then that is an administrative
policy which should not be tried to be circumvented.
10.0.0.0/8 NAT 192.0.2.0/24
|
,----------. (1) | (2) ,--------.
| Client A |------|------| |
`----------' | | Tunnel |
,----------. | | Server |
| Client B |------|------| |
`----------' (3) | (4) `--------'
|
(1) = src = 10.10.0.1:1234, dst = 192.0.2.42:3740
(2) = src = 192.0.2.5:4321, dst = 192.0.2.42:3740
(3) = src = 10.10.9.2:7890, dst = 192.0.2.42:3740
(4) = src = 192.0.2.5:5678, dst = 192.0.2.42:3740
Note that TEST-NET [RFC3300] addresses could never reach a Tunnel
Server over the public Internet due to filtering of this
documentation prefix.
8 References
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
August 1980.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC
793, September 1981.
[RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
April 1992.
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[RFC1933] Gilligan, R. and E. Nordmark, "Transition Mechanisms for
IPv6 Hosts and Routers", RFC 1933, April 1996.
[RFC2030] Mills, D., "Simple Network Time Protocol (SNTP) Version 4
for IPv4, IPv6 and OSI", RFC 2030, October 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[RFC2960] Stewart, R., Xie, Q., Morneault, K., Sharp, C.,
Schwarzbauer, H., Taylor, T., Rytina, I., Kalla, M.,
Zhang, L. and V. Paxson, "Stream Control Transmission
Protocol", RFC 2960, October 2000.
[RFC3053] Durand, A., Fasano, P., Guardini, I. and D. Lento, "IPv6
Tunnel Broker", RFC 3053, January 2001.
[RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains
via IPv4 Clouds", RFC 3056, February 2001.
[RFC3300] Reynolds, J., Braden, R., Ginoza, S. and A. De La Cruz,
"Internet Official Protocol Standards", RFC 3300, November
2002.
[RFC3513] Hinden, R. and S. Deering, "Internet Protocol Version 6
(IPv6) Addressing Architecture", RFC 3513, April 2003.
[SIXXS] Massar, J. and P. van Pelt, "SixXS - IPv6 Deployment &
Tunnelbroker", <http://www.sixxs.net>.
Author's Address
Jeroen Massar
Unfix/SixXS
Hofpoldersingel 45
Gouda 2807 LW
NL
EMail: jeroen@unfix.org
URI: http://unfix.org/~jeroen/
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