    Network Working Group                                             D. New
    Request for Comments: 3620                                  October 2003
    Category: Standards Track

                               The TUNNEL Profile

    Status of this Memo

       This document specifies an Internet standards track protocol for the
       Internet community, and requests discussion and suggestions for
       improvements.  Please refer to the current edition of the "Internet
       Official Protocol Standards" (STD 1) for the standardization state
       and status of this protocol.  Distribution of this memo is unlimited.

    Copyright Notice

       Copyright (C) The Internet Society (2003).  All Rights Reserved.

    Abstract

       This memo describes a Blocks Extensible Exchange Protocol (BEEP)
       profile that allows a BEEP peer to serve as an application-layer
       proxy.  It allows authorized users to access services through a
       firewall.

    Table of Contents

       1. Rationale  . . . . . . . . . . . . . . . . . . . . . . . . . .   2
       2. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . .   3
          2.1 One-Hop Example. . . . . . . . . . . . . . . . . . . . . .   3
          2.2 Two-Hop Example. . . . . . . . . . . . . . . . . . . . . .   4
          2.3 Failed Set-Up Example. . . . . . . . . . . . . . . . . . .   5
          2.4 Non-BEEP Example . . . . . . . . . . . . . . . . . . . . .   5
          2.5 Profile Example. . . . . . . . . . . . . . . . . . . . . .   6
          2.6 Endpoint Example . . . . . . . . . . . . . . . . . . . . .   8
       3. Message Syntax.  . . . . . . . . . . . . . . . . . . . . . . .   9
       4. Message Semantics .  . . . . . . . . . . . . . . . . . . . . .  10
       5. Provisioning . . . . . . . . . . . . . . . . . . . . . . . . .  12
       6. Reply Codes. . . . . . . . . . . . . . . . . . . . . . . . . .  13
       7. Security Considerations. . . . . . . . . . . . . . . . . . . .  14
       8. Normative References . . . . . . . . . . . . . . . . . . . . .  15
       A. IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  16
          A.1 Registration: BEEP Profile . . . . . . . . . . . . . . . .  16
          A.2 Registration: A System (Well-Known) TCP
              port number for TUNNEL . . . . . . . . . . . . . . . . . .  16
       B. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  17
          Author's Address . . . . . . . . . . . . . . . . . . . . . . .  17
          Full Copyright Statement . . . . . . . . . . . . . . . . . . .  18

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    RFC 3620                   The TUNNEL Profile               October 2003

    1. Rationale

       The TUNNEL profile provides a mechanism for cooperating BEEP peers to
       form an application-layer tunnel.  The peers exchange "tunnel"
       elements that specify a source route, with the outermost element
       being stripped off and used to decide the next hop.  The innermost,
       empty "tunnel" element tells the final destination that it is,
       indeed, the final destination.  The term "proxy" is used to refer any
       of the BEEP peers other than the initiator and the final destination.

       In one use of this profile, a BEEP peer implementing the TUNNEL
       profile is co-resident with a firewall.  An initiating machine inside
       the firewall makes a connection to the proxy, then ask that proxy to
       make a connection to an endpoint outside the firewall.  Once this
       connection is established, the proxy tells the outside endpoint that
       it will be tunneling.  If the outside machine agrees, the proxy "gets
       out of the way," simply passing octets transparently, and both the
       initiating and terminating machines perform a "tuning reset," not
       unlike the way starting a TLS negotiation discards cached session
       state and starts anew.

       Another use for this profile is to limit connections to outside
       servers based on the user identity negotiated via SASL.  For example,
       a manager may connect to a proxy, authenticate herself with SASL,
       then instruct the proxy to tunnel to an information service
       restricted to managers.  Since each proxy knows the identity of the
       next proxy being requested, it can refuse to tunnel connections if
       inadequate levels of authorization have been established.  It is also
       possible to use the TUNNEL profile to anonymize the true source of a
       BEEP connection, in much the way a NAT translates IP addresses.
       However, detailed discussion of such uses is beyond the scope of this
       document.

       Once both endpoint machines are connected, the tunneling proxy
       machine does no further interpretation of the data.  In particular,
       it does not look for any BEEP framing.  The two endpoint machines may
       therefore negotiate TLS between them, passing certificates
       appropriate to the endpoints rather than the proxy, with the
       assurance that even the proxy cannot access the information
       exchanged.

       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 BCP 14, RFC 2119 [1].

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    2. Examples

       While the semantics described in Section 4 may seem complex, the
       results are actually relatively simple.  A few examples will show the
       operation and use of this profile.  In these examples, the machine
       attempting to establish the connection is named "initial", while the
       intermediate proxies are "proxy1" or "proxy2", and the machine with
       the service that "initial" wishes to access is called "final".  The
       examples also assume that the BEEP framework [2] is implemented on
       top of TCP [3], or some other mapping where one transport connection
       carries all channels.

    2.1 One-Hop Example

       A simple one-hop connection through a single proxy is illustrated
       first.

       initial                   proxy1                     final
          ----- xport connect ----->
         <------- greeting -------->
          --- start TUNNEL [1] ---->
                                    ----- xport connect ------>
                                   <-------- greeting -------->
                                    ---- start TUNNEL [2] ---->
                                   <---------- ok ------------
         <------- ok -------------- [3]
         <------------- greeting [4]-------------------------->

       Notes:

       [1]  The TUNNEL element looks like this:
            <tunnel fqdn='final.example.com' port='604'>
              <tunnel/>
            </tunnel>

       [2]  The TUNNEL element looks like this:
            <tunnel/>

       [3]  At this point, immediately after sending the <ok/> element,
            proxy1 starts passing octets transparently.  It continues to do
            so until either transport connection is closed, after which it
            closes the other.

       [4]  This greeting may include the TLS profile, allowing initial and
            final to communicate without proxy1 understanding or interfering
            without being caught.

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    2.2 Two-Hop Example

       The second example shows the initiator connecting to its proxy, that
       proxy connecting to another, and finally that second proxy finding a
       service outside.

       initial             proxy1                proxy2                final
         --- xport connect -->
        <---- greeting ------>
         --start TUNNEL [1]-->
                              -- xport connect --->
                             <----- greeting ----->
                              --start TUNNEL [2]-->
                                                   --- xport  connect --->
                                                  <------- greeting ----->
                                                   ---start TUNNEL [3]--->
                                                  <-------- ok ----------
                             <------- ok --------- [4]
        <------- ok --------- [5]
        <-------------------------- greeting ---------------------------->

       Notes:

       [1]  The TUNNEL element looks like this:
            <tunnel fqdn='proxy2.example.com' port='604'>
              <tunnel fqdn='final.example.com' port='10290'>
                <tunnel/>
              </tunnel>
            </tunnel>

       [2]  The TUNNEL element looks like this:
            <tunnel fqdn='final.example.com' port='10290'>
              <tunnel/>
            </tunnel>

       [3]  The TUNNEL element looks like this:
            <tunnel/>

       [4]  Proxy2 starts passing octets transparently after sending the
            <ok/>.

       [5]  Proxy1 starts passing octets transparently after sending the
            <ok/>.

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    2.3 Failed Set-Up Example

       The third example shows the initiator connecting through two proxys,
       the second proxy attempting to connect to the specified service and
       finding the destination is not a BEEP server.  (Of course, specifying
       the telnet service can be expected to lead to this error.)  The same
       would result if the destination did not support the TUNNEL profile.

       initial             proxy1                proxy2                final
         --- xport connect -->
        <---- greeting ------>
         --start TUNNEL [1]-->
                              --- xport connect -->
                             <----- greeting ----->
                              --start TUNNEL [2]-->
                                                   ---- xport connect --->
                                                  <------- login: -------
                                                   ----- xport close ---->
                             <---- <error> -------
                              --- xport close ---->
        <---- <error> ------
         --- xport close ---> [3]

       Notes:

       [1]  The TUNNEL element looks like this:
            <tunnel fqdn='proxy2.example.com' port='604'>
              <tunnel fqdn='final.example.com' srv='_telnet._tcp'>
                <tunnel/>
              </tunnel>
            </tunnel>

       [2]  The TUNNEL element looks like this:
            <tunnel fqdn='final.example.com' srv='_telnet._tcp'>
              <tunnel/>
            </tunnel>

       [3]  This close is optional. "Initial" may also send another <tunnel>
            element, attempting to contact a different server, for example.

    2.4 Non-BEEP Example

       This example shows the initiator connecting through two proxys, the
       second proxy attempting to connect to the specified service and
       accepting that the destination is not a BEEP server.  The difference
       at the protocol level is two-fold: The "initial" machine does not
       include the innermost "tunnel" element, and the final proxy
       ("proxy2") therefore does not expect a BEEP greeting.

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       initial             proxy1                proxy2                final
         --- xport connect -->
        <---- greeting ------>
         --start TUNNEL [1]-->
                              --- xport connect -->
                             <----- greeting ----->
                              --start TUNNEL [2]-->
                                                   ---- xport connect --->
                                                  <------- login: -------
                              <------ <ok> ------- [3]
                              <----- login: ------ [4]
        <------ <ok> --------- [3]
        <----- login: -------- [4] [5]

       Notes:

       [1]  The TUNNEL element looks like this:
            <tunnel fqdn='proxy2.example.com' port='604'>
              <tunnel fqdn='final.example.com' svc='_telnet._tcp'>
              </tunnel>
            </tunnel>
            Note the lack of an innermost no-attribute <tunnel> element.

       [2]  The TUNNEL element looks like this:
              <tunnel fqdn='final.example.com' srv='_telnet._tcp'>
              </tunnel>
            Note the lack of an innermost no-attribute <tunnel> element.

       [3]  Each proxy starts transparently forwarding octets after this
            <ok>.

       [4]  Each proxy forwards any data it received from the final host,
            even if that data arrived before the <ok> was sent.

       [5]  After receiving the "ok" message, the "initial" peer can expect
            raw, non-BEEP data to be sent to and received from the "final"
            machine.

    2.5 Profile Example

       This example shows the initiator connecting through two proxys.  The
       initial machine knows there is a server offering the SEP2 profile
       somewhere beyond proxy1, but it need not know where.  Proxy1 has been
       locally configured to know that all SEP2 servers are beyond proxy2.
       Proxy2 has been locally configured to chose "final" as the server of
       choice for SEP2 services.  Note that "final" does not necessarily
       need to offer the requested profile in its initial greeting.

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       initial             proxy1                proxy2                final
         --- xport connect -->
        <---- greeting ------>
         --start TUNNEL [1]-->
                              -- xport connect --->
                             <----- greeting ----->
                              --start TUNNEL [2]-->
                                                   --- xport  connect --->
                                                  <------- greeting ----->
                                                   ---start TUNNEL [3]--->
                                                  <-------- ok ----------
                             <------- ok --------- [4]
        <------- ok --------- [5]
        <-------------------------- greeting ---------------------------->

       Notes:

       [1]  The TUNNEL element looks like this:
              <tunnel profile="http://xml.resource/org/profiles/SEP2"/>
            Note the lack of an innermost no-attribute <tunnel> element.

       [2]  Proxy1 maps this to
              <tunnel fqdn="proxy2.example.com" port="604">
                <tunnel profile="http://xml.resource/org/profiles/SEP2"/>
              </tunnel>
            based on local configuration, then processes the new
            element, stripping off the outer element and routing
              <tunnel profile="http://xml.resource/org/profiles/SEP2"/>
            to proxy2.

       [3]  Proxy2 receives the TUNNEL element with simply the SEP2
            URI specified. Local provisioning maps this to
              <tunnel fqdn='final.example.com' srv='_beep._tcp'>
                <tunnel/>
              </tunnel>
            Note the presence of an innermost no-attribute <tunnel> element.
            Proxy2 then strips the outermost element, looking up the
            appropriate address and port, and forwards the <tunnel/>
            element to the final machine.

       [4]  Proxy2 starts transparently forwarding octets after this <ok>.

       [5]  Proxy1 starts transparently forwarding octets after this <ok>.

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    2.6 Endpoint Example

       This example shows the initiator connecting through two proxys.  The
       initial machine knows there is a server known as "operator console"
       somewhere beyond proxy1, but it needs not know where.  Proxy1 has
       been locally configured to know that "operator console" is beyond
       proxy2.  Proxy2 has been locally configured to use "final" as
       "operator console".  This example is almost identical to the previous
       example, except that "endpoint" is intended to route to a particular
       server, while "profile" is intended to route to a particular service.
       Otherwise, these two attributes are very similar.

       initial             proxy1                proxy2                final
         --- xport connect -->
        <---- greeting ------>
         --start TUNNEL [1]-->
                              -- xport connect --->
                             <----- greeting ----->
                              --start TUNNEL [2]-->
                                                   --- xport  connect --->
                                                  <------- greeting ----->
                                                   ---start TUNNEL [3]--->
                                                  <-------- ok ----------
                             <------- ok --------- [4]
        <------- ok --------- [5]
        <-------------------------- greeting ---------------------------->

       Notes:

       [1]  The TUNNEL element looks like this:
              <tunnel endpoint="operator console">
              </tunnel>
            Note the lack of an innermost no-attribute <tunnel> element.

       [2]  Proxy1 maps this to
              <tunnel fqdn="proxy2.example.com" port="604">
                <tunnel endpoint="operator console">
                </tunnel>
              </tunnel>
            based on local configuration, then processes the new
            element, stripping off the outer element and routing
              <tunnel endpoint="operator console">
              </tunnel>
            to proxy2.

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       [3]  Proxy2 receives the TUNNEL element with simply the endpoint
            specified. Local provisioning maps this to
              <tunnel fqdn='final.example.com' srv='_beep._tcp'>
                <tunnel/>
              </tunnel>
            Note the presence of an innermost no-attribute <tunnel> element.
            Proxy2 then strips the outermost element, looking up the
            appropriate address and port, and forwards the <tunnel/>
            element to the final machine.

       [4]  Proxy2 starts transparently forwarding octets after this <ok>.

       [5]  Proxy1 starts transparently forwarding octets after this <ok>.

    3. Message Syntax

       The only element defined in this profile is the "tunnel" element.  It
       is described in the following DTD, with additional limitations as
       described afterwards.

       <!--
         DTD for the TUNNEL Profile, as of 2001-02-03

         Refer to this DTD as:

            <!ENTITY % TUNNEL PUBLIC "-//IETF//DTD TUNNEL//EN" "">
           %TUNNEL;
         -->

       <!--
         TUNNEL messages

            role           MSG                 RPY
           ======          ===                 ===
           I or L          TUNNEL              +: ok
                                               -: error
         -->

       <!ELEMENT tunnel      (tunnel?)>
       <!ATTLIST tunnel
                 fqdn         CDATA    #IMPLIED
                 ip4          CDATA    #IMPLIED
                 ip6          CDATA    #IMPLIED
                 port         CDATA    #IMPLIED
                 srv          CDATA    #IMPLIED
                 profile      CDATA    #IMPLIED
                 endpoint     CDATA    #IMPLIED
                 >

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    RFC 3620                   The TUNNEL Profile               October 2003

       The format of the "fqdn" attribute is a fully qualified domain name,
       such as "proxy.example.com".  The format of the "ip4" attribute is
       four sets of decimal numbers separated by periods, such as
       "10.23.34.45".  The format of the "ip6" attribute is as specified in
       RFC2373 [4].  The format of the "port" attribute is a decimal number
       between one and 65535, inclusive.  The format of the "srv" attribute
       is a pair of identifiers each starting with an underline and
       separated by a period, such as "_sep._tcp".  The format of the
       "profile" attribute is a URI [5].  The format of the "endpoint"
       attribute is any string that may appear as an attribute value.

       The only allowable combinations of attributes are as follows:

       o  fqdn + port;

       o  fqdn + srv;

       o  fqdn + srv + port;

       o  ip4  + port;

       o  ip6  + port;

       o  profile, but only on the innermost element;

       o  endpoint, but only on the innermost element; or,

       o  no attributes, but only on the innermost element.

    4. Message Semantics

       When a TUNNEL channel is started, the listener expects a "tunnel"
       element from the initiator, either in the "start" element on channel
       zero or on the new channel created.  As usual, if it arrives on
       channel zero, it is processed before the reply is returned.

       In either case, the outermost "tunnel" element is examined.  If it
       has no attributes, then this peer is hosting the BEEP service that
       the initiator wishes to use.  In this case, the listener performs a
       tuning reset:

       o  All channels, including channel zero, are implicitly closed.

       o  Any previously cached information about the BEEP session is
          discarded.

       o  A new plaintext greeting is sent.

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    RFC 3620                   The TUNNEL Profile               October 2003

       If the outermost element has a "port" attribute and an "fqdn"
       attribute but no "srv" attribute, then "fqdn" is looked up as an A
       record via DNS for translation to an IP number.  An "ip4" attribute
       is interpreted as the dotted-quad representation of an IPv4 address.
       An "ip6" attribute is interpreted as a text representation of an IPv6
       address.  In each of these cases, a transport connection is
       established to the so-identified server.  If the outermost element
       has a "srv" attribute, the concatenation of the "srv" attribute and
       the "fqdn" attribute (with a period between) is looked up in the DNS
       for a SRV record [6], and the appropriate server is contacted; if
       that lookup fails and a "port" attribute is present, the connection
       is attempted as if the "srv" attribute were not specified.

       Alternately, if the outermost element has a "profile" attribute, then
       it must have no nested elements.  The proxy processing this element
       is responsible for determining the appropriate routing to reach a
       peer serving the BEEP profile indicated by the URI in the attribute's
       value.  Rather than source routing, this provides a hop-by-hop
       routing mechanism to a desired service.

       Similarly, if the outermost element has an "endpoint" attribute, then
       it must have no nested elements.  The proxy processing this element
       is responsible for determining the appropriate routing to reach a
       peer indicated by the value of the "endpoint" attribute.  Rather than
       source routing, this provides a hop-by-hop routing mechanism to a
       desired machine.  There are no restrictions on how machines are
       identified.

       Then, if the outermost element has no nested elements, but it does
       have attributes other than "profile" or "endpoint", then this peer is
       the final BEEP hop.  (This corresponds to "proxy2" in the "Non-BEEP"
       example above.)  In this case, as soon as the final underlying
       transport connection is established, an "ok" element is returned over
       the listening session, and the tunneling of data starts.  No BEEP
       greeting (or indeed any data) from the final hop is expected.
       Starting with the octet following the END(CR)(LF) trailer of the
       frame with the completion flag set (more=".") of the RPY carrying the
       "ok" element, the proxy begins copying octets directly and without
       any interpretation between the two underlying transport connections.

       If the identified server cannot be contacted, an "error" element is
       returned over the listening channel and any connection established as
       an initiator is closed.  If there is a nested "tunnel" element, and
       the server that has been contacted does not offer a BEEP greeting, or
       the BEEP greeting offered does not include the TUNNEL profile, then
       this too is treated as an error: the initiating transport connection
       is closed, and an error is returned.

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    RFC 3620                   The TUNNEL Profile               October 2003

       If there is a nested "tunnel" element, and the identified server is
       contacted and offers a BEEP greeting including the TUNNEL profile,
       then the outermost element from the "tunnel" element received is
       stripped off, a new TUNNEL channel is started on the initiating
       session, and the stripped (inner) element is sent to start the next
       hop.  In this case, the peer is considered a "proxy" (meaning that
       the next paragraph is applicable).

       Once the proxy has passed the "tunnel" element on the TUNNEL channel,
       it awaits an "error" or an "ok" element in response.  If it receives
       an "error" element, it closes the initiated session and its
       underlying transport connection.  It then passes the "error" element
       unchanged back on the listening session.  If, on the other hand, it
       receives an "ok" element, it passes the "ok" element back on the
       listening session.  Starting with the octet following the END(CR)(LF)
       trailer of the frame with the completion flag set (more=".") of the
       RPY carrying the "ok" element, the proxy begins copying octets
       directly and without any interpretation between the two underlying
       transport connections.

    5. Provisioning

       While the BEEP Framework [2] is used, the attributes described are
       sufficient for the TCP mapping [3] of BEEP.  The attributes on the
       "tunnel" element may need to be extended to handle other transport
       layers.

       In a mapping where multiple underlying transport connections are
       used, once the "ok" element is passed, all channels are closed,
       including channel zero.  Thus, only the underlying transport
       connection initially established remains, and all other underlying
       transport connections for the session should be closed as well.

       If a transport security layer (such as TLS) has been negotiated over
       the session, the semantics for the TUNNEL profile are ill-defined.
       The TUNNEL profile MUST NOT be advertised in any greetings after
       transport security has been negotiated.

       An SRV identifier of "_tunnel" is reserved by IANA for use with this
       profile.  Hence, the "srv" attribute "_tunnel._tcp" MAY be used as a
       default for finding the appropriate address for tunneling into a
       particular domain.

       System port number 604 has been allocated by the IANA for TUNNEL.

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    6. Reply Codes

       This section lists the three-digit error codes the TUNNEL profile may
       generate.

       code   meaning
       ====   =======
        421   Service not available
              (E.g., the proxy does not have sufficient resources.)

        450   Requested action not taken
              (E.g., DNS lookup failed or connection could not
              be established. See too 550.)

        500   General syntax error (E.g., poorly-formed XML)

        501   Syntax error in parameters
              (E.g., non-valid XML, letters in "ip4" attribute, etc.)

        504   Parameter not implemented

        530   Authentication required

        534   Authentication mechanism insufficient
              (E.g., too weak, sequence exhausted, etc.)

        537   Action not authorized for user

        538   Encryption already enabled
              (E.g., TLS already negotiated, or a SASL that
              provides encryption already negotiated.)

        550   Requested action not taken
              (E.g., next hop could be contacted, but
              malformed greeting or no TUNNEL profile advertised.)

        553   Parameter invalid

        554   Transaction failed (E.g., policy violation)

       Note that the 450 error code is appropriate when the destination
       machine could not be contacted, while the 550 error code is
       appropriate when the destination machine could be contacted but the
       next phase of the protocol could not be negotiated.  It is suggested
       that the beginning of any reply from the destination machine be
       included as part of the CDATA text of the error element, for
       debugging purposes.

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    7. Security Considerations

       The TUNNEL profile is a profile of BEEP.  In BEEP, transport
       security, user authentication, and data exchange are orthogonal.
       Refer to Section 8 of [2] for a discussion of this.

       However, the intent of the TUNNEL profile is to allow bidirectional
       contact between two machines normally separated by a firewall.  Since
       TUNNEL allows this connection between BEEP peers, and BEEP peers can
       offer a range of services with appropriate greetings, the TUNNEL
       profile should be configured with care.  It is reasonable to strictly
       limit the hosts and services that a proxy is allowed to contact.  It
       is also reasonable to limit the use of the TUNNEL profile to
       authorized users, as identified by a SASL profile.

       Negotiation of a TLS profile in an end-to-end manner after a TUNNEL
       has been established will prevent intermediate proxies from observing
       or modifying the cleartext information exchanged, but only if TLS
       certificates are properly configured during the negotiation.  The
       proxy could mount a "man in the middle" attack if public key
       infrastructure is not deployed.

       In some environments, it is undesirable to expose the names of
       machines on one side of a firewall in unencrypted messages on the
       other side of that firewall.  In this case, source routing (using the
       "fqdn", "ip4", "ip6", "port" and "srv" attributes) can route a
       connection to the firewall proxy, with an innermost "profile" or
       "endpoint" attribute which the firewall proxy understands.  Local
       provisioning can allow a  proxy to translate a particular "profile"
       or "endpoint" element into a new source route to reach the desired
       service.  This can prevents two attacks:

       o  Attackers sniffing packets on one side of the firewall cannot see
          IP addresses or FQDNs of machines on the other side of the
          firewall; and,

       o  Attackers cannot exhaustively attempt to connect to many FQDNs or
          IP addresses via source routing and use the error messages as an
          indication of whether the queried machine exists.  For this attack
          to be prevented, the proxy must allow only "profile" or "endpoint"
          connections, always refusing to even attempt source-routed
          connections.  This latter attack can also be thwarted by requiring
          a SASL identification before allowing a TUNNEL channel to be
          started, but this can have higher overhead.

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    RFC 3620                   The TUNNEL Profile               October 2003

    8. Normative References

       [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
            Levels", BCP 14, RFC 2119, March 1997.

       [2]  Rose, M., "The Blocks Extensible Exchange Protocol Core", RFC
            3080, March 2001.

       [3]  Rose, M., "Mapping the BEEP Core onto TCP", RFC 3081, March
            2001.

       [4]  Hinden, R. and S. Deering, "IP Version 6 Addressing
            Architecture", RFC 2373, July 1998.

       [5]  Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource
            Identifiers (URI): Generic Syntax", RFC 2396, August 1998.

       [6]  Gulbrandsen, A., Vixie, P. and L. Esibov, "A DNS RR for
            specifying the location of services (DNS SRV)", RFC 2782,
            February 2000.

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    RFC 3620                   The TUNNEL Profile               October 2003

    Appendix A. IANA Considerations

    A.1 Registration: BEEP Profile

       The IANA has registered the profiles specified in this section and
       has selected an IANA-specific URI: "http://iana.org/beep/TUNNEL".

       Profile identification: http://iana.org/beep/TUNNEL

       Message exchanged during channel creation: "tunnel"

       Messages starting one-to-one exchanges: "tunnel"

       Messages in positive replies: "ok"

       Messages in negative replies: "error"

       Messages in one-to-many exchanges: None.

       Message syntax: See Section 3 of this document.

       Message semantics: See Section 4 of this document.

       Contact information: See the Author's Address appendix of this
       document.

       Any extensions to this protocol MUST be documented in a Standards
       track RFC.

    A.2 Registration: The System (Well-Known) TCP port number for TUNNEL

       A single well-known port, 604, is allocated by the IANA to the TUNNEL
       profile.

       Protocol Number: TCP

       Message Formats, Types, Opcodes, and Sequences: See Section 3.

       Functions: See Section 4.

       Use of Broadcast/Multicast: none

       Proposed Name: TUNNEL Profile

       Short name: tunnel

       Contact Information: See the "Authors' Addresses" section of this
       memo

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    RFC 3620                   The TUNNEL Profile               October 2003

    Appendix B. Acknowledgements

       The author gratefully acknowledges the contributions of  Marshall
       Rose, Greg Matthews, and Ben Feinstein.

       Inspiration for this profile comes from the Intrusion Detection
       Working Group of the IETF.

    Author's Address

       Darren New
       5390 Caminito Exquisito
       San Diego, CA  92130
       US

       Phone: +1 858 350 9733
       EMail: dnew@san.rr.com

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    RFC 3620                   The TUNNEL Profile               October 2003

    Full Copyright Statement

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