IPv6 Operations J. Massar
Internet-Draft Unfix/SixXS
Expires: December 6, 2005 June 4, 2005
SixXS Heartbeat Protocol
draft-massar-v6ops-heartbeat-01
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Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This document proposes a heartbeat protocol for signalling
availability of hosts with a specific emphasis on providing a
signalling protocol for allowing dynamic non-24/7 endnodes to use
tunnel's of the various IPv6 Tunnel Brokers.
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Table of Contents
1. Requirements notation . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. SixXS Heartbeat Protocol . . . . . . . . . . . . . . . . . . . 4
3.1 Heartbeat Command . . . . . . . . . . . . . . . . . . . . 5
3.2 Disable Command . . . . . . . . . . . . . . . . . . . . . 6
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 7
6. Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6.1 Host heartbeat . . . . . . . . . . . . . . . . . . . . . . 7
6.2 IPv6 in IPv4 tunnel heartbeat . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.1 References . . . . . . . . . . . . . . . . . . . . . . . . 9
8.2 Informative References . . . . . . . . . . . . . . . . . . 10
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 10
Intellectual Property and Copyright Statements . . . . . . . . 11
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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
When operating a IPv6 Tunnel Broker [RFC3053] with one or multiple
Tunnel Servers [RFC3053] or any other form of tunneling across the
Internet one doesn't want to send packets out to unsuspecting
endpoints. Unsuspecting endpoints are hosts which don't expect
traffic from the Tunnel Server. This is a common scenario when a
non-static but configured endpoint is used. The user enables the
tunnel to the current endpoint, uses it and then disconnects from the
Internet or gets another IP, due to dhcp policies or various other
reasons. Though the endpoint of the tunnel changes but there
currently is no way of automatically changing that endpoint or
notifying the Tunnel Server that it has changed. Current solutions
include using a script to update the endpoint on the Tunnel Broker's
website and various other non-standardized methods.
Then another host get to use the IP which terminates the tunnel and
suddenly it receives our tunneled packets. This could be seen as a
security risk as the new user of the IP could sniff the packets and
look at them or could even setup the tunnel and take over connections
which where active on that tunnel impersonating the former host using
the tunnel. Many hosts employ so called firewall or logging
facilities that will start complaining about packets being sent from
the Tunnel Server which they perceive as malicious.
The user of this firewall will in turn start complaining about abuse
and hack attempts which takes up time from the staff running the
Tunnel Broker and not even mentioning all the entities that will be
notified by these type of messages.
This protocol resolves this problem by specifying a oneway heartbeat
protocol. As long as the tunnel endpoint is able to send an
authenticated heartbeat packet the tunnel is kept configured on the
side of the Tunnel Server allowing two-way traffic to be sent. This
heartbeat protocol also allows for automatic tunnel reconfiguration
so that in the event of an IP change at the client side the tunnel
will be reconfigured allowing continued service without a (notable)
interruption. If the Tunnel Server doesn't receive a heartbeat for a
certain amount of time it can deem the endpoint as down and
deconfigure the tunnel. Taking these two into consideration will
stop the sending of tunneled packets and will thus avoid the
complaints which could have been brought up before.
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This protocol covers all tunneling protocols which use at least one
set of inner and one set of outer addresses. Note that some of these
protocols already have a heartbeat mechanism in the protocol. In
those cases it is of course advisable to use that mechanism.
3. SixXS Heartbeat Protocol
The heartbeat packet is a UDP [RFC0768] packet to IANA assigned port
3740 of the server to which the signalling is to take place.
Schematically this will look like the following diagram.
+--------+ +--------+
| Client | <--- Internet ---> | Server |
+--------+ +--------+
The heartbeat packet consists out of one single line separated by
spaces and ending in a NULL. The first part is the command thus
allowing extension of this protocol if wanted in the future.
Extensions are allowed to put additional commands on seperate lines,
currently those extensions are not defined but these could be used
for transmitting other informations like load of the client which
could be useful in failover scenario's.
The basic heartbeat packet looks like the following in ABNF
[RFC2234]. The IPv6address and IPv4address ABNF are defined in
"APPENDIX B: ABNF Description of Text Representations" of the "IP
Version 6 Addressing Architecture" [RFC3513].
packet = command SP epochtime SP md5-signature NULL
command = *%x41-5A [*(SP option)]
option = *VCHAR
epochtime = *DIGIT
md5-signature = 32(HEXDIG)
NULL = %x00
epochtime is the time in seconds since "00:00:00 1970-01-01 UTC"
which corresponds to the output of to unix "date +%s" command. 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 packet must be constructed first with the signature containing
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the password for the tunnel. After construction the md5-signature
should be calculated and then replace the cleartext-password. The
packet 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 command part of
the packet, adding the password and calculating the md5 signature
which can then be compared with the md5-signature which was sent by
the client. If these match the packet can be processed further.
When the md5-signatures don't match the server MUST silently ignore
the packet.
Calculation of the MD5 signature [RFC1321] MUST be done over the
complete string excluding the NULL which is the string terminator in
C and most other programming languages. The scenarios section
demonstrates how this is performed.
The currently defined commands HEARTBEAT and DISABLE both use the
following common options to identify the endpoint for which this
heartbeat is meant:
common-options = ("HOST" endpoint |
"TUNNEL" outer-endpoint SP inner-endpoint)
outer endpoint = endpoint | "sender"
inner endpoint = endpoint
endpoint = IPv4address | IPv6address
An endpoint MAY also be a MAC address or other defined 'address'.
3.1 Heartbeat Command
This command is the main reason for this protocol to exist. It tells
the Tunnel Server that the current endpoint specified by both the
UDP's source address and the common-option's outer endpoint is still
accepting tunneled packets.
Specification:
command = "HEARTBEAT" SP common-options
Example's:
Heartbeat from client host 192.0.2.2 :
HEARTBEAT HOST 192.0.2.2 257209200
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Heartbeat from client host 192.0.2.2 for IPv6 tunnel endpoint 2001:
db8::2 :
HEARTBEAT TUNNEL 2001:db8::2 192.0.2.2 409100400
In this example the server determines the inner-endpoint based on the
sender IP of the packet. This could be used in all cases but is
especially useful when the client is behind a NAT and doesn't know
it's external address. An application MUST not use the 'sender'
replacement when it knows it's public IP address. This because it
adds an extra verification step to the heartbeat.
HEARTBEAT TUNNEL 2001:db8::2 sender 257209200
3.2 Disable Command
The disable command explicitly sets a tunnel 'down' on the Tunnel
Server allowing a gracious and prompt shutdown of the tunnel on the
Tunnel Server. One could even employ this command to stop huge
traffic flows to the local endpoint which maybe could not cope with
the traffic passed over it through the tunnel.
Specification:
command = "DISABLE" SP common-options
Example:
Disable the tunnel endpoint 2001:db8::2 to 192.0.2.2 :
DISABLE TUNNEL 192.0.2.2 2001:db8::2 409100400
4. Acknowledgements
The protocol presented has formed during the existence of IPng [IPNG]
and SixXS [SIXXS] to allow the users of these tunnel broker systems
to have a dynamic non-static IPv4 endpoint. This protocol is already
in use by SixXS since October 2003 and has made a lot of users very
happy and I would like to thank the numerous users requesting the
support for dynamic non 24/7 reachable tunnel's. This was before
this protocol was implemented one of the few requirements of
obtaining a tunnel even when the project only consisted of one Tunnel
Server and was called IPng.
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5. Security Considerations
The password used for creating the MD5 [RFC1321] signature should
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 timestamp 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.
A side effect of this protocol is that whenever the local host cannot
send a heartbeat in time to the Tunnel Server that it will
deconfigure the tunnel. Envision a Denial of Service over the tunnel
to the local endpoint. The local host's heartbeat cannot reach the
Tunnel Server which in turn will automatically disable the tunnel,
allowing the host to catch some breath again and thus effectively
implementing a poor mans rate limiting.
6. Scenarios
6.1 Host heartbeat
This scenario handles the case where a host, the client using either
IPv6 or IPv4, sends notifications of it's aliveness to a server.
This could be used for server management and fallover situations. In
combination with extension commands, used on the additional lines in
the packet the client could send along information about cpu load etc
allowing the server to gather information about those factors.
+--------+ +--------+
| Client | <--- Internet ---> | Server |
+--------+ +--------+
Server's IPv6 : 2001:db8::1/64
Client's IPv6 : 2001:db8::2/64
Password : point
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The command, including the password and epochtime would be:
HEARTBEAT HOST 2001:db8::2 409100400 point
The packet to be transmitted, after md5 translation is:
HEARTBEAT HOST 2001:db8::2 409100400
bd72fb8d98b8698fa70cdfeb33bb7342
6.2 IPv6 in IPv4 tunnel heartbeat
This scenario handles the case where a IPv6 in IPv4 tunnel [RFC3056]
is setup between two hosts. This is the normal case for a Tunnel
Broker system with which a IPv4 only host is given acces to a IPv6
network. A tunnel like this can easily be setup using the Tunnel
Setup Protocol [I-D.vg-ngtrans-tsp], SixXS Configuration Service
[TIC] or similar protocols. A diagram of such a setup:
+--------+ +--------+
| Client | <--- IPv6 in IPv4 Tunnel ---> | Server |
+--------+ +--------+
Server's Outer IPv4 : 192.0.2.1
Server's Inner IPv6 : 2001:db8::1/64
Client's Outer IPv4 : 192.0.2.2
Client's Inner IPv6 : 2001:db8::2/64
Password : hartslag
The command would be:
HEARTBEAT TUNNEL 2001:db8::2 192.0.2.2 1051480800 hartslag
The data to be transmitted is:
HEARTBEAT TUNNEL 2001:db8::2 192.0.2.2 1051480800
3f0a026edb1b15e7c1a7a2d92b3c446a
Disabling the same tunnel can be accomplished using:
DISABLE TUNNEL 2001:db8::2 192.0.2.2 1055628000 hartslag
The data to be transmitted is:
DISABLE TUNNEL 2001:db8::2 192.0.2.2 1055628000
53d5bb7bfe4a3a80da01227da02cda24
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The usage for which this protocol was defined in the first place is
signalling the server of the current IPv4 address of the client.
When the server receives a heartbeat packet it looks up the
configuration information based on the supplied Inner IPv6 address,
verifies that the password is correct by constructing the command and
generating the md5 signature. When the md5 signature is incorrect
the server MUST silently discard and ignore the packet. A check MUST
also be made comparing the Inner IPv4 address with the IPv4 address
from which the packet was sent, when incorrect the server MUST
discard and ignore the packet. Logs noting these event MAY be made
depending on the wishes of the administrator. When the password is
correct and thus the md5 verifies the server will configure the IPv6
in IPv4 tunnel to point at the IPv4 address specified by the Inner
IPv4 parameter. When the Inner IPv4 parameter is 'sender' the server
MUST use the IPv4 address from which the packet originates.
Note that TEST-NET [RFC3300] addresses could never reach a Tunnel
Server over the public Internet due to filtering of this
documentation prefix.
7. IANA Considerations
IANA already allocated port 3740 for the Heartbeat Protocol in April
2003. Thus no further actions from IANA are required.
8. References
8.1 References
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
August 1980.
[RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
April 1992.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[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.
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8.2 Informative References
[I-D.vg-ngtrans-tsp]
Blanchet, M., "Tunnel Setup Protocol (TSP)A Control
Protocol to Setup IPv6 or IPv4 Tunnels",
draft-vg-ngtrans-tsp-01 (work in progress), July 2002.
[IPNG] van Pelt, P. and J. Massar, "IPng - IPv6 Enduser
Deployment", <http://www.ipng.nl>.
[RFC2030] Mills, D., "Simple Network Time Protocol (SNTP) Version 4
for IPv4, IPv6 and OSI", RFC 2030, October 1996.
[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>.
[TIC] Massar, J., "TIC - Tunnel Information Control Protocol",
draft-massar-v6ops-tic-00 (work in progress),
January 2004, <http://www.sixxs.net/tools/tic/>.
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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