Network Working Group G. Zorn Internet-Draft Microsoft Corporation Updates: RFC 2138 D. Leifer Category: Standards Track A. Rubens <draft-ietf-radius-tunnel-auth-04.txt> Ascend Communications J. Shriver Shiva Corporation November 1997 RADIUS Attributes for Tunnel Protocol Support 1. Status of this Memo This document is an Internet-Draft. Internet-Drafts are working docu- ments of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working doc- uments as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as work in progress.'' To learn the current status of any Internet-Draft, please check the ``1id-abstracts.txt'' listing contained in the Internet-Drafts Shadow Directories on ds.internic.net (US East Coast), nic.nordu.net (Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific Rim). The distribution of this memo is unlimited. It is filed as <draft-ietf- radius-tunnel-auth-04.txt>, and expires May 25, 1997. Please send com- ments to the RADIUS Working Group mailing list (ietf-radius@liv- ingston.com) or to the authors (leifer@del.com, acr@del.com, jas@shiva.com and glennz@microsoft.com). 2. Abstract This document defines a set of RADIUS attributes designed to support the provision of compulsory tunneling in dial-up networks. Zorn, Leifer, Rubens & Shriver [Page 1]
INTERNET-DRAFT RADIUS Tunnel Attributes November 1997 3. Motivation Many applications of tunneling protocols such as PPTP and L2TP involve dial-up network access. Some, such as the provision of secure access to corporate intranets via the Internet, are characterized by voluntary tunneling: the tunnel is created at the request of the user for a spe- cific purpose. Other applications involve compulsory tunneling: the tunnel is created without any action from the user and without allowing the user any choice in the matter. Examples of applications that might be implemented using compulsory tunnels are Internet software upgrade servers, software registration servers and banking services. These are all services which, without compulsory tunneling, would probably be pro- vided using dedicated networks or at least dedicated network access servers (NAS), since they are characterized by the need to limit user access to specific hosts. Given the existence of widespread support for compulsory tunneling, however, these types of services could be accessed via any Internet service provider (ISP). The most popular means of authorizing dial-up network users today is through the RADIUS protocol. The use of RADIUS allows the dial-up users' authorization and authenti- cation data to be maintained in a central location, rather than on each NAS. It makes sense to use RADIUS to centrally administer compulsory tunneling, since RADIUS is widely deployed and was designed to carry this type of information. In order to provide this functionality, new RADIUS attributes are needed to carry the tunneling information from the RADIUS server to the tunnel initiator; this document defines those attributes. Specific recommendations for, and examples of, the applica- tion of these attributes for the L2TP and PPTP protocols can be found in draft-ietf-radius-tunnel-imp-XX.txt. 4. Specification of Requirements In this document, the key words "MAY", "MUST, "MUST NOT", "optional", "recommended", "SHOULD", and "SHOULD NOT", are to be interpreted as described in [14]. 5. Attributes Multiple instances of each of the attributes defined below may be included in a single RADIUS packet. In this case, the attributes to be applied to any given tunnel SHOULD all contain the same value in their respective Tag fields; otherwise, the Tag field SHOULD NOT be used. If the RADIUS server returns attributes describing multiple tunnels then the tunnels SHOULD be interpreted by the tunnel initiator as alterna- tives and the server SHOULD include an instance of the Tunnel-Preference Attribute in the set of Attributes pertaining to each alternative Zorn, Leifer, Rubens & Shriver [Page 2]
INTERNET-DRAFT RADIUS Tunnel Attributes November 1997 tunnel. Similarly, if the RADIUS client includes multiple sets of tun- nel Attributes in an Access-Request packet, all the Attributes pertain- ing to a given tunnel SHOULD contain the same value in their respective Tag fiels and each set SHOULD include an appropriately valued instance of the Tunnel-Preference Attribute. 5.1. Tunnel-Type Description This Attribute indicates the tunneling protocol(s) to be used. It MAY be included in Access-Request, Access-Accept and Accounting- Request packets. If the Tunnel-Type Attribute is present in an Access-Request packet, it SHOULD be taken as a hint to the RADIUS server as to the tunnelling protocols supported by the tunnel ini- tiator; the RADIUS server MAY ignore the hint, however. A tunnel initiator is not required to implement any of these tunnel types; if a tunnel initiator receives an Access-Accept packet which con- tains only unknown or unsupported Tunnel-Types, the tunnel initia- tor MUST behave as though an Access-Reject had been received instead. A summary of the Tunnel-Type Attribute format is shown below. The fields are transmitted from left to right. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Tag | Value +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Value (cont) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 64 for Tunnel-Type Length Always 6. Tag The Tag field is one octet in length and is intended to provide a means of grouping attributes in the same packet which refer to the same tunnel. Valid values for this field are 0x01 through 0x1F, inclusive. If the Tag field is unused, it MUST be zero. Value The Value field is three octets and contains one of the following values, indicating the type of tunnel to be started. Zorn, Leifer, Rubens & Shriver [Page 3]
INTERNET-DRAFT RADIUS Tunnel Attributes November 1997 1 Point-to-Point Tunneling Protocol (PPTP) [1] 2 Layer Two Forwarding (L2F) [2] 3 Layer Two Tunneling Protocol (L2TP) [3] 4 Ascend Tunnel Management Protocol (ATMP) [4] 5 Virtual Tunneling Protocol (VTP) [5] 6 IP Authentication Header in the Tunnel-mode (AH) [6] 7 IP-in-IP Encapsulation (IP-IP) [7] 8 Minimal IP-in-IP Encapsulation (MIN-IP-IP) [8] 9 IP Encapsulating Security Payload in the Tunnel-mode (ESP) [9] 10 Generic Route Encapsulation (GRE) [10] 11 Bay Dial Virtual Services (DVS) 12 IP-in-IP Tunneling [11] 5.2. Tunnel-Medium-Type Description The Tunnel-Medium-Type Attribute indicates which transport medium to use when creating a tunnel for those protocols (such as L2TP) that can operate over multiple transports. It MAY be included in both Access-Request and Access-Accept packets; if it is present in an Access-Request packet, it SHOULD be taken as a hint to the RADIUS server as to the tunnel mediums supported by the tunnel initiator. The RADIUS server MAY ignore the hint, however. A summary of the Tunnel-Medium-Type Attribute format is given below. The fields are transmitted left to right. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Tag | Value | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Value (cont) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 65 for Tunnel-Medium-Type Length 6 Tag The Tag field is one octet in length and is intended to provide a means of grouping attributes in the same packet which refer to the same tunnel. Valid values for this field are 0x01 through 0x1F, inclusive. If the Tag field is unused, it MUST be zero (0x0000). Zorn, Leifer, Rubens & Shriver [Page 4]
INTERNET-DRAFT RADIUS Tunnel Attributes November 1997 Value The Value field is three octets and contains one of the values listed under "Address Family Numbers" in [15]. For the sake of convenience, a relevant excerpt of this list is reproduced below. 1 IP (IP version 4) 2 IP6 (IP version 6) 3 NSAP 4 HDLC (8-bit multidrop) 5 BBN 1822 6 802 (includes all 802 media plus Ethernet "canonical format") 7 E.163 8 E.164 (SMDS, Frame Relay, ATM) 9 F.69 (Telex) 10 X.121 (X.25, Frame Relay) 11 IPX 12 Appletalk 13 Decnet IV 14 Banyan Vines 15 E.164 with NSAP format subaddress 5.3. Tunnel-Client-Endpoint Description This Attribute contains the address of the initiator end of the tunnel. It MAY be included in both Access-Request and Access- Accept packets to indicate the address from which a new tunnel is to be initiated. If the Tunnel-Client-Endpoint Attribute is included in an Access-Request packet, the RADIUS server should take the value as a hint; the server is not obligated to honor the hint, however. It SHOULD be included in Accounting-Request pack- ets which contain Acct-Status-Type attributes with values of either Start or Stop, in which case it indicates the address from which the tunnel was initiated. This Attribute, along with the Tunnel-Server-Endpoint and Acct-Tunnel-Connection-ID attributes, may be used to provide a globally unique means to identify a tun- nel for accounting and auditing purposes. A summary of the Tunnel-Client-Endpoint Attribute format is shown below. The fields are transmitted from left to right. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Tag | String ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Zorn, Leifer, Rubens & Shriver [Page 5]
INTERNET-DRAFT RADIUS Tunnel Attributes November 1997 Type 66 for Tunnel-Client-Endpoint. Length >= 2 Tag The Tag field is one octet in length and is intended to provide a means of grouping attributes in the same packet which refer to the same tunnel. Valid values for this field are 0x01 through 0x1F, inclusive. If the value of the Tag field is less than or equal to 0x1F, it SHOULD be interpreted as indicating which tunnel (of sev- eral alternatives) this attribute pertains; otherwise, it SHOULD be interpreted as the first byte of the following String field. String The format of the address represented by the String field depends upon the value of the Tunnel-Medium-Type attribute. If Tunnel-Medium-Type is IP (1) or IP6 (2), then this string is either the fully qualified domain name of the tunnel client machine, or it is a "dotted-decimal" IP address. Conformant implementations MUST support the dotted-decimal format and SHOULD support the FQDN format for IP addresses. If Tunnel-Medium-Type is not IP or IP6, this string is a tag referring to configuration data local to the RADIUS client that describes the interface and medium-specific address to use. 5.4. Tunnel-Server-Endpoint Description This Attribute indicates the address of the server end of the tun- nel. The Tunnel-Server-Endpoint Attribute MAY be included (as a hint to the RADIUS server) in the Access-Request packet and MUST be included in the Access-Accept packet if the initiation of a tunnel is desired. It SHOULD be included in Accounting-Request packets which contain Acct-Status-Type attributes with values of either Start or Stop and which pertain to a tunneled session. This Attribute, along with the Tunnel-Client-Endpoint and Acct- Tunnel-Connection-ID Attributes [12], may be used to provide a globally unique means to identify a tunnel for accounting and auditing purposes. A summary of the Tunnel-Server-Endpoint Attribute format is shown below. The fields are transmitted from left to right. Zorn, Leifer, Rubens & Shriver [Page 6]
INTERNET-DRAFT RADIUS Tunnel Attributes November 1997 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Tag | String ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 67 for Tunnel-Server-Endpoint. Length >= 3 Tag The Tag field is one octet in length and is intended to provide a means of grouping attributes in the same packet which refer to the same tunnel. Valid values for this field are 0x01 through 0x1F, inclusive. If the value of the Tag field is less than or equal to 0x1F, it SHOULD be interpreted as indicating which tunnel (of sev- eral alternatives) this attribute pertains; otherwise, it SHOULD be interpreted as the first byte of the following String field. String The format of the address represented by the String field depends upon the value of the Tunnel-Medium-Type attribute. If Tunnel-Medium-Type is IP (1) or IP6 (2), then this string is either the fully qualified domain name of the tunnel client machine, or it is a "dotted-decimal" IP address. Conformant implementations MUST support the dotted-decimal format and SHOULD support the FQDN format for IP addresses. If Tunnel-Medium-Type is not IP or IP6, this string is a tag referring to configuration data local to the RADIUS client that describes the interface and medium-specific address to use. 5.5. Tunnel-Password Description This Attribute may contain a key or password. It may only be included in an Access-Accept packet. A summary of the Tunnel-Password Attribute format is shown below. The fields are transmitted from left to right. 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 Zorn, Leifer, Rubens & Shriver [Page 7]
INTERNET-DRAFT RADIUS Tunnel Attributes November 1997 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Tag | Salt +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Salt (cont) | String ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 69 for Tunnel-Password Length >= 3 Tag The Tag field is one octet in length and is intended to provide a means of grouping attributes in the same packet which refer to the same tunnel. Valid values for this field are 0x01 through 0x1F, inclusive. If the value of the Tag field is less than or equal to 0x1F, it SHOULD be interpreted as indicating which tunnel (of sev- eral alternatives) this attribute pertains; otherwise, it SHOULD be ignored. Salt The Salt field is two octets in length and is used to ensure the uniqueness of the encryption key used to encrypt each instance of the Tunnel-Password attribute occurring in a given Access-Accept packet. The most significant bit (leftmost) of the Salt field MUST be set (1). The contents of each Salt field in a given Access-Accept packet MUST be unique. String The plaintext String field consists of three logical sub-fields: the Data-Length and Password sub-fields (both of which are required), and the optional Padding sub-field. The Data-Length sub-field is one octet in length and contains the length of the unencrypted Password sub-field. The Password sub-field contains the actual tunnel password. If the combined length (in octets) of the unencrypted Data-Length and Password sub-fields is not an even multiple of 16, then the Padding sub-field MUST be present. If it is present, the length of the Padding sub-field is variable, between 1 and 15 octets. The String field MUST be encrypted as follows, prior to transmission: Construct a plaintext version of the String field by concate- nating the Data-Length and Password sub-fields. If necessary, pad the resulting string until its length (in octets) is an even multiple of 16. It is recommended that zero octets (0x00) be used for padding. Call this plaintext P. Zorn, Leifer, Rubens & Shriver [Page 8]
INTERNET-DRAFT RADIUS Tunnel Attributes November 1997 Call the shared secret S, the pseudo-random 128-bit Request Authenticator (from the corresponding Access-Request packet) R, and the contents of the Salt field A. Break P into 16 octet chunks p(1), p(2)...p(i), where i = len(P)/16. Call the ciphertext blocks c(1), c(2)...c(i) and the final ciphertext C. Intermediate values b(1), b(2)...c(i) are required. Encryption is performed in the following manner ('+' indicates concatena- tion): b(1) = MD5(S + R + A) c(1) = p(1) xor b(1) C = c(1) b(2) = MD5(S + c(1)) c(2) = p(2) xor b(2) C = C + c(2) . . . . . . b(i) = MD5(S + c(i-1)) c(i) = p(i) xor b(i) C = C + c(i) The resulting encrypted String field will contain c(1)+c(2)+...+c(i). On receipt, the process is reversed to yield the plaintext String. 5.6. Tunnel-Private-Group-ID Description This Attribute indicates the group ID for a particular tunneled session. The Tunnel-Private-Group-ID Attribute MAY be included in the Access-Request packet if the tunnel initiator can pre-deter- mine the group resulting from a particular connection and SHOULD be included in the Access-Reply packet if this tunnel session is to be treated as belonging to a particular private group. Private groups may be used to associate a tunneled session with a particu- lar group of users. For example, it may be used to facilitate routing of unregistered IP addresses through a particular inter- face. It SHOULD be included in Accounting-Request packets which contain Acct-Status-Type attributes with values of either Start or Stop and which pertain to a tunneled session. A summary of the Tunnel-Private-Group-ID Attribute format is shown below. The fields are transmitted from left to right. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Tag | String ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Zorn, Leifer, Rubens & Shriver [Page 9]
INTERNET-DRAFT RADIUS Tunnel Attributes November 1997 Type 81 for Tunnel-Private-Group-ID. Length >= 3 Tag The Tag field is one octet in length and is intended to provide a means of grouping attributes in the same packet which refer to the same tunnel. Valid values for this field are 0x01 through 0x1F, inclusive. If the value of the Tag field is less than or equal to 0x1F, it SHOULD be interpreted as indicating which tunnel (of sev- eral alternatives) this attribute pertains; otherwise, it SHOULD be interpreted as the first byte of the following String field. String This field must be present. The group is represented by the String field. There is no restriction on the format of group IDs. 5.7. Tunnel-Assignment-ID Description This Attribute is used to indicate to the tunnel initiator the particular tunnel to which a session is to be assigned. Some tun- neling protocols, such as PPTP and L2TP, allow for sessions between the same two tunnel endpoints to be multiplexed over the same tunnel and also for a given session to utilize its own dedi- cated tunnel. This attribute provides a mechanism for RADIUS to be used to inform the tunnel initiator (e.g. PAC, LAC) whether to assign the session to a multiplexed tunnel or to a separate tun- nel. Furthermore, it allows for sessions sharing multiplexed tun- nels to be assigned to different multiplexed tunnels. A particular tunneling implementation may assign differing charac- teristics to particular tunnels. For example, different tunnels may be assigned different QOS parameters. Such tunnels may be used to carry either individual or multiple sessions. The Tunnel- Assignment-ID attribute thus allows the RADIUS server to indicate that a particular session is to be assigned to a tunnel that pro- vides an appropriate level of service. It is expected that any QOS-related RADIUS tunneling attributes defined in the future that accompany this attribute will be associated by the tunnel initia- tor with the ID given by this attribute. In the meantime, any semantic given to a particular ID string is a matter left to local configuration in the tunnel initiator. Zorn, Leifer, Rubens & Shriver [Page 10]
INTERNET-DRAFT RADIUS Tunnel Attributes November 1997 The Tunnel-Assignment-ID attribute is of significance only to RADIUS and the tunnel initiator. The ID it specifies is intended to be of only local use to RADIUS and the tunnel initiator. The ID assigned by the tunnel initiator is not conveyed to the tunnel peer. This attribute MAY be included in the Access-Accept. The tunnel initiator receiving this attribute MAY choose to ignore it and assign the session to an arbitrary multiplexed or non-multiplexed tunnel between the desired endpoints. This attribute SHOULD also be included in Accounting-Request packets which contain Acct-Sta- tus-Type attributes with values of either Start or Stop and which pertain to a tunneled session. If a tunnel initiator supports the Tunnel-Assignment-ID Attribute, then it should assign a session to a tunnel in the following man- ner: If this attribute is present and a tunnel exists between the specified endpoints with the specified ID, then the session should be assigned to that tunnel. If this attribute is present and no tunnel exists between the specified endpoints with the specified ID, then a new tunnel should be established for the session and the specified ID should be associated with the new tunnel. If this attribute is not present, then the session is assigned to an unnamed tunnel. If an unnamed tunnel does not yet exist between the specified endpoints then it is established and used for this and subsequent sessions established without the Tun- nel-Assignment-ID attribute. A tunnel initiator MUST NOT assign a session for which a Tunnel-Assignment-ID Attribute was not specified to a named tunnel (i.e. one that was initiated by a session specifying this attribute). Note that the same ID may be used to name different tunnels if such tunnels are between different endpoints. A summary of the Tunnel-Assignment-ID Attribute format is shown below. The fields are transmitted from left to right. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Tag | String ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Zorn, Leifer, Rubens & Shriver [Page 11]
INTERNET-DRAFT RADIUS Tunnel Attributes November 1997 Type ?? for Tunnel-Assignment-ID. Length > 3 Tag The Tag field is one octet in length and is intended to provide a means of grouping attributes in the same packet which refer to the same tunnel. Valid values for this field are 0x01 through 0x1F, inclusive. If the value of the Tag field is less than or equal to 0x1F, it SHOULD be interpreted as indicating which tunnel (of sev- eral alternatives) this attribute pertains; otherwise, it SHOULD be interpreted as the first byte of the following String field. String This field must be present. The tunnel ID is represented by the String field. There is no restriction on the format of the ID. 5.8. Tunnel-Preference Description If more than one set of tunneling attributes is returned by the RADIUS server to the tunnel initiator, this Attribute SHOULD be included in each set to indicate the relative preference assigned to each tunnel. For example, suppose that Attributes describing two tunnels are returned by the server, one with a Tunnel-Type of PPTP and the other with a Tunnel-Type of L2TP. If the tunnel ini- tiator supports only one of the Tunnel-Types returned, it will initiate a tunnel of that type. If, however, it supports both tunnel protocols, it SHOULD use the value of the Tunnel-Preference Attribute to decide which tunnel should be started. The tunnel having the numerically lowest value in the Value field of this Attribute SHOULD be given the highest preference. The values assigned to two or more instances of the Tunnel-Preference Attribute within a given Access-Accept packet MAY be identical. In this case, the tunnel initiator SHOULD use locally configured metrics to decide which set of attributes to use. This Attribute MAY be included (as a hint to the server) in Access-Request pack- ets, but the RADIUS server is not required to honor this hint. A summary of the Tunnel-Preference Attribute format is shown below. The fields are transmitted from left to right. 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 Zorn, Leifer, Rubens & Shriver [Page 12]
INTERNET-DRAFT RADIUS Tunnel Attributes November 1997 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Tag | Value +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Value (cont) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type ?? for Tunnel-Preference Length Always 6. Tag The Tag field is one octet in length and is intended to provide a means of grouping attributes in the same packet which refer to the same tunnel. Valid values for this field are 0x01 through 0x1F, inclusive. If the Tag field is unused, it MUST be zero. Value The Value field is three octets in length and indicates the pref- erence to be given to the tunnel to which it refers; higher pref- erence is given to lower values, with 0x000000 being most pre- ferred and 0xFFFFFF least preferred. 6. Table of Attributes The following table provides a guide to which of the above attributes may be found in which kinds of packets, and in what quantity. Request Accept Reject Challenge Acct-Request # Attribute 0+ 0+ 0 0 0-1 64 Tunnel-Type 0+ 0+ 0 0 0-1 65 Tunnel-Medium-Type 0+ 0+ 0 0 0-1 66 Tunnel-Client-Endpoint 0+ 0+ 0 0 0-1 67 Tunnel-Server-Endpoint 0 0+ 0 0 0 69 Tunnel-Password 0+ 0+ 0 0 0-1 81 Tunnel-Private-Group-ID 0 0+ 0 0 0-1 ?? Tunnel-Assignment-ID 0+ 0+ 0 0 0 ?? Tunnel-Preference The following table defines the meaning of the above table entries. 0 This attribute MUST NOT be present in packet. 0+ Zero or more instances of this attribute MAY be present in packet. 0-1 Zero or one instance of this attribute MAY be present in packet. Zorn, Leifer, Rubens & Shriver [Page 13]
INTERNET-DRAFT RADIUS Tunnel Attributes November 1997 7. Security Considerations The Tunnel-Password Attribute may contain information which should only be known to a tunnel endpoint. However, the method used to hide the value of the attribute is such that intervening RADIUS proxies will have knowledge of the contents. For this reason, the Tunnel-Password Attribute SHOULD NOT be included in Access-Accept packets which may pass through (relatively) untrusted RADIUS proxies. In addition, the Tunnel- Password Attribute SHOULD NOT be returned to an unauthenticated client; if the corresponding Access-Request packet did not contain a verified instance of the Signature Attribute [16], the Access-Accept packet SHOULD NOT contain an instance of the Tunnel-Password Attribute. 8. References [1] Hamzeh, et. al., "Point-to-Point Tunneling Protocol -- PPTP", draft-ietf-pppext-pptp-02.txt (work in progress), July 1997 [2] Valencia, Littlewood and Kolar, "Layer Two Forwarding (Protocol) 'L2F'", draft-valencia-l2f-00.txt (work in progress), October 1997 [3] Hamzeh, et. al., "Layer Two Tunnelling Protocol (L2TP)", work in progress, draft-ietf-pppext-l2tp-08.txt, Movember 1997 [4] Hamzeh, "Ascend Tunnel Management Protocol - ATMP", RFC 2107, February 1997 [5] Calhoun and Wong, "Virtual Tunneling Protocol (VTP)", draft-cal- houn-vtp-protocol-00.txt (work in progress), July 1996 (expired) [6] Kent and Atkinson, "IP Authentication Header", draft-ietf-ipsec- auth-header-02.txt (work in progress), October 1997 [7] Perkins, "IP Encapsulation within IP", RFC 2003, October 1996 [8] Perkins, "Minimal Encapsulation within IP", RFC 2004, October 1996 [9] Atkinson, "IP Encapsulating Security Payload (ESP)", RFC 1827, August 1995 [10] Hanks, et. al., "Generic Routing Encapsulation (GRE)", RFC 1701, October 1994 [11] Simpson, "IP in IP Tunneling", RFC 1853, October 1995 [12] Zorn and Mitton, "RADIUS Accounting Modifications for Tunnel Proto- col Support", draft-ietf-radius-tunnel-acct-00.txt (work in Zorn, Leifer, Rubens & Shriver [Page 14]
INTERNET-DRAFT RADIUS Tunnel Attributes November 1997 progress), November 1997 [13] Rigney, et. al., "Remote Authentication Dialin User Service (RADIUS)", RFC 2138, April 1997 [14] Bradner, "Key words for use in RFCs to Indicate Requirement Lev- els", RFC 2119, March 1997 [15] Reynolds and Postel, "Assigned Numbers", STD 2, RFC 1700, October 1994 [16] Rigney and Willats, "RADIUS Extensions", draft-ietf-radius- ext-01.txt (work in progress), September 1997 9. Acknowledgements Thanks to Dave Mitton (dmitton@baynetworks.com) for pointing out a nasty circular dependency in the original Tunnel-Password attribute definition and (in no particular order) to Kory Hamzeh (kory@ascend.com), Bertrand Buclin (Bertrand.Buclin@att.ch), Dave Mitton (dmitton@baynetworks.com), Andy Valencia (vandys@cisco.com), Bill Westfield (billw@cisco.com), Kris Michielsen (kmichiel@cisco.com), Gurdeep Singh Pall (gur- deep@microsoft.com), Ran Atkinson (rja@home.net), Aydin Edguer (edguer@MorningStar.com) and Bernard Aboba (aboba@internaut.com) for useful input and review. 10. Chair's Address The RADIUS Working Group can be contacted via the current chair: Carl Rigney Livingston Enterprises 4464 Willow Road Pleasanton, California 94588 Phone: +1 510 426 0770 E-Mail: cdr@livingston.com 11. Authors' Addresses Questions about this memo can also be directed to: Glen Zorn Microsoft Corporation One Microsoft Way Zorn, Leifer, Rubens & Shriver [Page 15]
INTERNET-DRAFT RADIUS Tunnel Attributes November 1997 Redmond, Washington 98052 Phone: +1 425 703 1559 E-Mail: glennz@microsoft.com Dory Leifer Ascend Communications 1678 Broadway Ann Arbor, MI 48105 Phone: +1 313 747 6152 E-Mail: leifer@ascend.com John Shriver Shiva Corporation 28 Crosby Drive Bedford, MA 01730 Phone: +1 781 687 1329 E-Mail: jas@shiva.com Allan Rubens Ascend Communications 1678 Broadway Ann Arbor, MI 48105 Phone: +1 313 761 6025 E-Mail: acr@del.com 12. Expiration Date This memo is filed as <draft-ietf-radius-tunnel-auth-04.txt>, and expires May 25, 1997. Zorn, Leifer, Rubens & Shriver [Page 16]
