    Network Working Group                                            M. Wahl
    Request for Comments: 2829                        Sun Microsystems, Inc.
    Category: Standards Track                                  H. Alvestrand
                                                                 EDB Maxware
                                                                   J. Hodges
                                                                 Oblix, Inc.
                                                                   R. Morgan
                                                    University of Washington
                                                                    May 2000

                        Authentication Methods for LDAP

    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 (2000).  All Rights Reserved.

    Abstract

       This document specifies particular combinations of security
       mechanisms which are required and recommended in LDAP [1]
       implementations.

    1. Introduction

       LDAP version 3 is a powerful access protocol for directories.

       It offers means of searching, fetching and manipulating directory
       content, and ways to access a rich set of security functions.

       In order to function for the best of the Internet, it is vital that
       these security functions be interoperable; therefore there has to be
       a minimum subset of security functions that is common to all
       implementations that claim LDAPv3 conformance.

       Basic threats to an LDAP directory service include:

          (1)   Unauthorized access to data via data-fetching operations,

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          (2)   Unauthorized access to reusable client authentication
                information by monitoring others' access,

          (3)   Unauthorized access to data by monitoring others' access,

          (4)   Unauthorized modification of data,

          (5)   Unauthorized modification of configuration,

          (6)   Unauthorized or excessive use of resources (denial of
                service), and

          (7)   Spoofing of directory: Tricking a client into believing that
                information came from the directory when in fact it did not,
                either by modifying data in transit or misdirecting the
                client's connection.

       Threats (1), (4), (5) and (6) are due to hostile clients.  Threats
       (2), (3) and (7) are due to hostile agents on the path between client
       and server, or posing as a server.

       The LDAP protocol suite can be protected with the following security
       mechanisms:

          (1)   Client authentication by means of the SASL [2] mechanism
                set, possibly backed by the TLS credentials exchange
                mechanism,

          (2)   Client authorization by means of access control based on the
                requestor's authenticated identity,

          (3)   Data integrity protection by means of the TLS protocol or
                data-integrity SASL mechanisms,

          (4)   Protection against snooping by means of the TLS protocol or
                data-encrypting SASL mechanisms,

          (5)   Resource limitation by means of administrative limits on
                service controls, and

          (6)   Server authentication by means of the TLS protocol or SASL
                mechanism.

       At the moment, imposition of access controls is done by means outside
       the scope of the LDAP protocol.

       In this document, the term "user" represents any application which is
       an LDAP client using the directory to retrieve or store information.

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       The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
       "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this
       document are to be interpreted as described in RFC 2119 [3].

    2.  Example deployment scenarios

       The following scenarios are typical for LDAP directories on the
       Internet, and have different security requirements. (In the
       following, "sensitive" means data that will cause real damage to the
       owner if revealed; there may be data that is protected but not
       sensitive).  This is not intended to be a comprehensive list, other
       scenarios are possible, especially on physically protected networks.

          (1)   A read-only directory, containing no sensitive data,
                accessible to "anyone", and TCP connection hijacking or IP
                spoofing is not a problem.  This directory requires no
                security functions except administrative service limits.

          (2)   A read-only directory containing no sensitive data; read
                access is granted based on identity.  TCP connection
                hijacking is not currently a problem. This scenario requires
                a secure authentication function.

          (3)   A read-only directory containing no sensitive data; and the
                client needs to ensure that the directory data is
                authenticated by the server and not modified while being
                returned from the server.

          (4)   A read-write directory, containing no sensitive data; read
                access is available to "anyone", update access to properly
                authorized persons.  TCP connection hijacking is not
                currently a problem.  This scenario requires a secure
                authentication function.

          (5)   A directory containing sensitive data.  This scenario
                requires session confidentiality protection AND secure
                authentication.

    3.  Authentication and Authorization:  Definitions and Concepts

       This section defines basic terms, concepts, and interrelationships
       regarding authentication, authorization, credentials, and identity.
       These concepts are used in describing how various security approaches
       are utilized in client authentication and authorization.

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    3.1.  Access Control Policy

       An access control policy is a set of rules defining the protection of
       resources, generally in terms of the capabilities of persons or other
       entities accessing those resources.  A common expression of an access
       control policy is an access control list.  Security objects and
       mechanisms, such as those described here, enable the expression of
       access control policies and their enforcement.  Access control
       policies are typically expressed in terms of access control
       attributes as described below.

    3.2.  Access Control Factors

       A request, when it is being processed by a server, may be associated
       with a wide variety of security-related factors (section 4.2 of [1]).
       The server uses these factors to determine whether and how to process
       the request.  These are called access control factors (ACFs).  They
       might include source IP address, encryption strength, the type of
       operation being requested, time of day, etc.  Some factors may be
       specific to the request itself, others may be associated with the
       connection via which the request is transmitted, others (e.g. time of
       day) may be "environmental".

       Access control policies are expressed in terms of access control
       factors.  E.g., a request having ACFs i,j,k can perform operation Y
       on resource Z. The set of ACFs that a server makes available for such
       expressions is implementation-specific.

    3.3.  Authentication, Credentials, Identity

       Authentication credentials are the evidence supplied by one party to
       another, asserting the identity of the supplying party (e.g. a user)
       who is attempting to establish an association with the other party
       (typically a server).  Authentication is the process of generating,
       transmitting, and verifying these credentials and thus the identity
       they assert.  An authentication identity is the name presented in a
       credential.

       There are many forms of authentication credentials -- the form used
       depends upon the particular authentication mechanism negotiated by
       the parties.  For example: X.509 certificates, Kerberos tickets,
       simple identity and password pairs.  Note that an authentication
       mechanism may constrain the form of authentication identities used
       with it.

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    3.4.  Authorization Identity

       An authorization identity is one kind of access control factor.  It
       is the name of the user or other entity that requests that operations
       be performed.  Access control policies are often expressed in terms
       of authorization identities; e.g., entity X can perform operation Y
       on resource Z.

       The authorization identity bound to an association is often exactly
       the same as the authentication identity presented by the client, but
       it may be different.  SASL allows clients to specify an authorization
       identity distinct from the authentication identity asserted by the
       client's credentials.  This permits agents such as proxy servers to
       authenticate using their own credentials, yet request the access
       privileges of the identity for which they are proxying [2].  Also,
       the form of authentication identity supplied by a service like TLS
       may not correspond to the authorization identities used to express a
       server's access control  policy, requiring a server-specific mapping
       to be done.  The method by which a server composes and validates an
       authorization identity from the authentication credentials supplied
       by a client is implementation-specific.

    4. Required security mechanisms

       It is clear that allowing any implementation, faced with the above
       requirements, to pick and choose among the possible alternatives is
       not a strategy that is likely to lead to interoperability. In the
       absence of mandates, clients will be written that do not support any
       security function supported by the server, or worse, support only
       mechanisms like cleartext passwords that provide clearly inadequate
       security.

       Active intermediary attacks are the most difficult for an attacker to
       perform, and for an implementation to protect against.  Methods that
       protect only against hostile client and passive eavesdropping attacks
       are useful in situations where the cost of protection against active
       intermediary attacks is not justified based on the perceived risk of
       active intermediary attacks.

       Given the presence of the Directory, there is a strong desire to see
       mechanisms where identities take the form of a Distinguished Name and
       authentication data can be stored in the directory; this means that
       either this data is useless for faking authentication (like the Unix
       "/etc/passwd" file format used to be), or its content is never passed
       across the wire unprotected - that is, it's either updated outside
       the protocol or it is only updated in sessions well protected against
       snooping.  It is also desirable to allow authentication methods to

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       carry authorization identities based on existing forms of user
       identities for backwards compatibility with non-LDAP-based
       authentication services.

       Therefore, the following implementation conformance requirements are
       in place:

          (1)   For a read-only, public directory, anonymous authentication,
                described in section 5, can be used.

          (2)   Implementations providing password-based authenticated
                access MUST support authentication using the DIGEST-MD5 SASL
                mechanism [4], as described in section 6.1.  This provides
                client authentication with protection against passive
                eavesdropping attacks, but does not provide protection
                against active intermediary attacks.

          (3)   For a directory needing session protection and
                authentication, the Start TLS extended operation [5], and
                either the simple authentication choice or the SASL EXTERNAL
                mechanism, are to be used together.  Implementations SHOULD
                support authentication with a password as described in
                section 6.2, and SHOULD support authentication with a
                certificate as described in section 7.1.  Together, these
                can provide integrity and disclosure protection of
                transmitted data, and authentication of client and server,
                including protection against active intermediary attacks.

       If TLS is negotiated, the client MUST discard all information about
       the server fetched prior to the TLS negotiation.  In particular, the
       value of supportedSASLMechanisms MAY be different after TLS has been
       negotiated (specifically, the EXTERNAL mechanism or the proposed
       PLAIN mechanism are likely to only be listed after a TLS negotiation
       has been performed).

       If a SASL security layer is negotiated, the client MUST discard all
       information about the server fetched prior to SASL.  In particular,
       if the client is configured to support multiple SASL mechanisms, it
       SHOULD fetch supportedSASLMechanisms both before and after the SASL
       security layer is negotiated and verify that the value has not
       changed after the SASL security layer was negotiated.  This detects
       active attacks which remove supported SASL mechanisms from the
       supportedSASLMechanisms list, and allows the client to ensure that it
       is using the best mechanism supported by both client and server
       (additionally, this is a SHOULD to allow for environments where the
       supported SASL mechanisms list is provided to the client through a
       different trusted source, e.g. as part of a digitally signed object).

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    5. Anonymous authentication

       Directory operations which modify entries or access protected
       attributes or entries generally require client authentication.
       Clients which do not intend to perform any of these operations
       typically use anonymous authentication.

       LDAP implementations MUST support anonymous authentication, as
       defined in section 5.1.

       LDAP implementations MAY support anonymous authentication with TLS,
       as defined in section 5.2.

       While there MAY be access control restrictions to prevent access to
       directory entries, an LDAP server SHOULD allow an anonymously-bound
       client to retrieve the supportedSASLMechanisms attribute of the root
       DSE.

       An LDAP server MAY use other information about the client provided by
       the lower layers or external means to grant or deny access even to
       anonymously authenticated clients.

    5.1. Anonymous authentication procedure

       An LDAP client which has not successfully completed a bind operation
       on a connection is anonymously authenticated.

       An LDAP client MAY also specify anonymous authentication in a bind
       request by using a zero-length OCTET STRING with the simple
       authentication choice.

    5.2. Anonymous authentication and TLS

       An LDAP client MAY use the Start TLS operation [5] to negotiate the
       use of TLS security [6].  If the client has not bound beforehand,
       then until the client uses the EXTERNAL SASL mechanism to negotiate
       the recognition of the client's certificate, the client is
       anonymously authenticated.

       Recommendations on TLS ciphersuites are given in section 10.

       An LDAP server which requests that clients provide their certificate
       during TLS negotiation MAY use a local security policy to determine
       whether to successfully complete TLS negotiation if the client did
       not present a certificate which could be validated.

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    6. Password-based authentication

       LDAP implementations MUST support authentication with a password
       using the DIGEST-MD5 SASL mechanism for password protection, as
       defined in section 6.1.

       LDAP implementations SHOULD support authentication with the "simple"
       password choice when the connection is protected against
       eavesdropping using TLS, as defined in section 6.2.

    6.1. Digest authentication

       An LDAP client MAY determine whether the server supports this
       mechanism by performing a search request on the root DSE, requesting
       the supportedSASLMechanisms attribute, and checking whether the
       string "DIGEST-MD5" is present as a value of this attribute.

       In the first stage of authentication, when the client is performing
       an "initial authentication" as defined in section 2.1 of [4], the
       client sends a bind request in which the version number is 3, the
       authentication choice is sasl, the sasl mechanism name is "DIGEST-
       MD5", and the credentials are absent.  The client then waits for a
       response from the server to this request.

       The server will respond with a bind response in which the resultCode
       is saslBindInProgress, and the serverSaslCreds field is present.  The
       contents of this field is a string defined by "digest-challenge" in
       section 2.1.1 of [4].  The server SHOULD include a realm indication
       and MUST indicate support for UTF-8.

       The client will send a bind request with a distinct message id, in
       which the version number is 3, the authentication choice is sasl, the
       sasl mechanism name is "DIGEST-MD5", and the credentials contain the
       string defined by "digest-response" in section 2.1.2 of [4].  The
       serv-type is "ldap".

       The server will respond with a bind response in which the resultCode
       is either success, or an error indication.  If the authentication is
       successful and the server does not support subsequent authentication,
       then the credentials field is absent.  If the authentication is
       successful and the server supports subsequent authentication, then
       the credentials field contains the string defined by "response-auth"
       in section 2.1.3 of [4].   Support for subsequent authentication is
       OPTIONAL in clients and servers.

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    6.2. "simple" authentication choice under TLS encryption

       A user who has a directory entry containing a userPassword attribute
       MAY authenticate to the directory by performing a simple password
       bind sequence following the negotiation of a TLS ciphersuite
       providing connection confidentiality [6].

       The client will use the Start TLS operation [5] to negotiate the use
       of TLS security [6] on the connection to the LDAP server.  The client
       need not have bound to the directory beforehand.

       For this authentication procedure to be successful, the client and
       server MUST negotiate a ciphersuite which contains a bulk encryption
       algorithm of appropriate strength.  Recommendations on cipher suites
       are given in section 10.

       Following the successful completion of TLS negotiation, the client
       MUST send an LDAP bind request with the version number of 3, the name
       field containing the name of the user's entry, and the "simple"
       authentication choice, containing a password.

       The server will, for each value of the userPassword attribute in the
       named user's entry, compare these for case-sensitive equality with
       the client's presented password.  If there is a match, then the
       server will respond with resultCode success, otherwise the server
       will respond with resultCode invalidCredentials.

    6.3. Other authentication choices with TLS

       It is also possible, following the negotiation of TLS, to perform a
       SASL authentication which does not involve the exchange of plaintext
       reusable passwords.  In this case the client and server need not
       negotiate a ciphersuite which provides confidentiality if the only
       service required is data integrity.

    7. Certificate-based authentication

       LDAP implementations SHOULD support authentication via a client
       certificate in TLS, as defined in section 7.1.

    7.1. Certificate-based authentication with TLS

       A user who has a public/private key pair in which the public key has
       been signed by a Certification Authority may use this key pair to
       authenticate to the directory server if the user's certificate is
       requested by the server.  The user's certificate subject field SHOULD
       be the name of the user's directory entry, and the Certification
       Authority must be sufficiently trusted by the directory server to

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       have issued the certificate in order that the server can process the
       certificate.  The means by which servers validate certificate paths
       is outside the scope of this document.

       A server MAY support mappings for certificates in which the subject
       field name is different from the name of the user's directory entry.
       A server which supports mappings of names MUST be capable of being
       configured to support certificates for which no mapping is required.

       The client will use the Start TLS operation [5] to negotiate the use
       of TLS security [6] on the connection to the LDAP server.  The client
       need not have bound to the directory beforehand.

       In the TLS negotiation, the server MUST request a certificate.  The
       client will provide its certificate to the server, and MUST perform a
       private key-based encryption, proving it has the private key
       associated with the certificate.

       As deployments will require protection of sensitive data in transit,
       the client and server MUST negotiate a ciphersuite which contains a
       bulk encryption algorithm of appropriate strength.  Recommendations
       of cipher suites are given in section 10.

       The server MUST verify that the client's certificate is valid. The
       server will normally check that the certificate is issued by a known
       CA, and that none of the certificates on the client's certificate
       chain are invalid or revoked.  There are several procedures by which
       the server can perform these checks.

       Following the successful completion of TLS negotiation, the client
       will send an LDAP bind request with the SASL "EXTERNAL" mechanism.

    8. Other mechanisms

       The LDAP "simple" authentication choice is not suitable for
       authentication on the Internet where there is no network or transport
       layer confidentiality.

       As LDAP includes native anonymous and plaintext authentication
       methods, the "ANONYMOUS" and "PLAIN" SASL mechanisms are not used
       with LDAP.  If an authorization identity of a form different from a
       DN is requested by the client, a mechanism that protects the password
       in transit SHOULD be used.

       The following SASL-based mechanisms are not considered in this
       document: KERBEROS_V4, GSSAPI and SKEY.

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       The "EXTERNAL" SASL mechanism can be used to request the LDAP server
       make use of security credentials exchanged by a lower layer. If a TLS
       session has not been established between the client and server prior
       to making the SASL EXTERNAL Bind request and there is no other
       external source of authentication credentials (e.g.  IP-level
       security [8]), or if, during the process of establishing the TLS
       session, the server did not request the client's authentication
       credentials, the SASL EXTERNAL bind MUST fail with a result code of
       inappropriateAuthentication.  Any client authentication and
       authorization state of the LDAP association is lost, so the LDAP
       association is in an anonymous state after the failure.

    9. Authorization Identity

       The authorization identity is carried as part of the SASL credentials
       field in the LDAP Bind request and response.

       When the "EXTERNAL" mechanism is being negotiated, if the credentials
       field is present, it contains an authorization identity of the
       authzId form described below.

       Other mechanisms define the location of the authorization identity in
       the credentials field.

       The authorization identity is a string in the UTF-8 character set,
       corresponding to the following ABNF [7]:

       ; Specific predefined authorization (authz) id schemes are
       ; defined below -- new schemes may be defined in the future.

       authzId    = dnAuthzId / uAuthzId

       ; distinguished-name-based authz id.
       dnAuthzId  = "dn:" dn
       dn         = utf8string    ; with syntax defined in RFC 2253

       ; unspecified userid, UTF-8 encoded.
       uAuthzId   = "u:" userid
       userid     = utf8string    ; syntax unspecified

       A utf8string is defined to be the UTF-8 encoding of one or more ISO
       10646 characters.

       All servers which support the storage of authentication credentials,
       such as passwords or certificates, in the directory MUST support the
       dnAuthzId choice.

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       The uAuthzId choice allows for compatibility with client applications
       which wish to authenticate to a local directory but do not know their
       own Distinguished Name or have a directory entry.  The format of the
       string is defined as only a sequence of UTF-8 encoded ISO 10646
       characters, and further interpretation is subject to prior agreement
       between the client and server.

       For example, the userid could identify a user of a specific directory
       service, or be a login name or the local-part of an RFC 822 email
       address. In general a uAuthzId MUST NOT be assumed to be globally
       unique.

       Additional authorization identity schemes MAY be defined in future
       versions of this document.

    10. TLS Ciphersuites

       The following ciphersuites defined in [6] MUST NOT be used for
       confidentiality protection of passwords or data:

             TLS_NULL_WITH_NULL_NULL
             TLS_RSA_WITH_NULL_MD5
             TLS_RSA_WITH_NULL_SHA

       The following ciphersuites defined in [6] can be cracked easily (less
       than a week of CPU time on a standard CPU in 1997).  The client and
       server SHOULD carefully consider the value of the password or data
       being protected before using these ciphersuites:

             TLS_RSA_EXPORT_WITH_RC4_40_MD5
             TLS_RSA_EXPORT_WITH_RC2_CBC_40_MD5
             TLS_RSA_EXPORT_WITH_DES40_CBC_SHA
             TLS_DH_DSS_EXPORT_WITH_DES40_CBC_SHA
             TLS_DH_RSA_EXPORT_WITH_DES40_CBC_SHA
             TLS_DHE_DSS_EXPORT_WITH_DES40_CBC_SHA
             TLS_DHE_RSA_EXPORT_WITH_DES40_CBC_SHA
             TLS_DH_anon_EXPORT_WITH_RC4_40_MD5
             TLS_DH_anon_EXPORT_WITH_DES40_CBC_SHA

       The following ciphersuites are vulnerable to man-in-the-middle
       attacks, and SHOULD NOT be used to protect passwords or sensitive
       data, unless the network configuration is such that the danger of a
       man-in-the-middle attack is tolerable:

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             TLS_DH_anon_EXPORT_WITH_RC4_40_MD5
             TLS_DH_anon_WITH_RC4_128_MD5
             TLS_DH_anon_EXPORT_WITH_DES40_CBC_SHA
             TLS_DH_anon_WITH_DES_CBC_SHA
             TLS_DH_anon_WITH_3DES_EDE_CBC_SHA

       A client or server that supports TLS MUST support at least
       TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA.

    11. SASL service name for LDAP

       For use with SASL [2], a protocol must specify a service name to be
       used with various SASL mechanisms, such as GSSAPI.  For LDAP, the
       service name is "ldap", which has been registered with the IANA as a
       GSSAPI service name.

    12. Security Considerations

       Security issues are discussed throughout this memo; the
       (unsurprising) conclusion is that mandatory security is important,
       and that session encryption is required when snooping is a problem.

       Servers are encouraged to prevent modifications by anonymous users.
       Servers may also wish to minimize denial of service attacks by timing
       out idle connections, and returning the unwillingToPerform result
       code rather than performing computationally expensive operations
       requested by unauthorized clients.

       A connection on which the client has not performed the Start TLS
       operation or negotiated a suitable SASL mechanism for connection
       integrity and encryption services is subject to man-in-the-middle
       attacks to view and modify information in transit.

       Additional security considerations relating to the EXTERNAL mechanism
       to negotiate TLS can be found in [2], [5] and [6].

    13. Acknowledgements

       This document is a product of the LDAPEXT Working Group of the IETF.
       The contributions of its members is greatly appreciated.

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    14. Bibliography

       [1] Wahl, M., Howes, T. and S. Kille, "Lightweight Directory Access
           Protocol (v3)", RFC 2251, December 1997.

       [2] Myers, J., "Simple Authentication and Security Layer (SASL)", RFC
           2222, October 1997.

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

       [4] Leach, P. and C. Newman, "Using Digest Authentication as a SASL
           Mechanism", RFC 2831, May 2000.

       [5] Hodges, J., Morgan, R. and M. Wahl, "Lightweight Directory Access
           Protocol (v3): Extension for Transport Layer Security", RFC 2830,
           May 2000.

       [6] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC
           2246, January 1999.

       [7] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
           Specifications: ABNF", RFC 2234, November 1997.

       [8] Kent, S. and R. Atkinson, "Security Architecture for the Internet
           Protocol", RFC 2401, November 1998.

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    15. Authors' Addresses

       Mark Wahl
       Sun Microsystems, Inc.
       8911 Capital of Texas Hwy #4140
       Austin TX 78759
       USA

       EMail: M.Wahl@innosoft.com

       Harald Tveit Alvestrand
       EDB Maxware
       Pirsenteret
       N-7462 Trondheim, Norway

       Phone: +47 73 54 57 97
       EMail: Harald@Alvestrand.no

       Jeff Hodges
       Oblix, Inc.
       18922 Forge Drive
       Cupertino, CA 95014
       USA

       Phone: +1-408-861-6656
       EMail: JHodges@oblix.com

       RL "Bob" Morgan
       Computing and Communications
       University of Washington
       Seattle, WA 98105
       USA

       Phone: +1-206-221-3307
       EMail: rlmorgan@washington.edu

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    16.  Full Copyright Statement

       Copyright (C) The Internet Society (2000).  All Rights Reserved.

       This document and translations of it may be copied and furnished to
       others, and derivative works that comment on or otherwise explain it
       or assist in its implementation may be prepared, copied, published
       and distributed, in whole or in part, without restriction of any
       kind, provided that the above copyright notice and this paragraph are
       included on all such copies and derivative works.  However, this
       document itself may not be modified in any way, such as by removing
       the copyright notice or references to the Internet Society or other
       Internet organizations, except as needed for the purpose of
       developing Internet standards in which case the procedures for
       copyrights defined in the Internet Standards process must be
       followed, or as required to translate it into languages other than
       English.

       The limited permissions granted above are perpetual and will not be
       revoked by the Internet Society or its successors or assigns.

       This document and the information contained herein is provided on an
       "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
       TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
       BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
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    Acknowledgement

       Funding for the RFC Editor function is currently provided by the
       Internet Society.

    Wahl, et al.                Standards Track                    [Page 16]