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Internet Engineering Task Force (IETF)                         P. YeganiRequest for Comments: 6245                              Juniper NetworksCategory: Standards Track                                       K. LeungISSN: 2070-1721                                            Cisco Systems                                                                 A. Lior                                                     Bridgewater Systems                                                            K. Chowdhury                                                               J. Navali                                                           Cisco Systems                                                                May 2011Generic Routing Encapsulation (GRE) Key Extension for Mobile IPv4Abstract   The Generic Routing Encapsulation (GRE) specification contains a Key   field, which MAY contain a value that is used to identify a   particular GRE data stream.  This specification defines a new Mobile   IP extension that is used to exchange the value to be used in the GRE   Key field.  This extension further allows the Mobility Agents to set   up the necessary protocol interfaces prior to receiving the mobile   node traffic.  The new extension allows a Foreign Agent to request   GRE tunneling without disturbing the Home Agent behavior specified   for Mobile IPv4.  GRE tunneling with the Key field allows the   operators to have home networks that consist of multiple Virtual   Private Networks (VPNs), which may have overlapping home addresses.   When the tuple <Care of Address, Home Address, and Home Agent   Address> is the same across multiple subscriber sessions, GRE   tunneling will provide a means for the Foreign Agent and Home Agent   to identify data streams for the individual sessions based on the GRE   key.  In the absence of this key identifier, the data streams cannot   be distinguished from each other -- a significant drawback when using   IP-in-IP tunneling.Status of This Memo   This is an Internet Standards Track document.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Further information on   Internet Standards is available inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc6245.Yegani, et al.               Standards Track                    [Page 1]

RFC 6245                  GRE Key Ext. for MIP4                 May 2011Copyright Notice   Copyright (c) 2011 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.  Code Components extracted from this document must   include Simplified BSD License text as described in Section 4.e of   the Trust Legal Provisions and are provided without warranty as   described in the Simplified BSD License.Table of Contents1. Introduction ....................................................22. Terminology .....................................................33. GRE Key Extension ...............................................34. Operation and Use of the GRE Key Extension ......................34.1. Foreign Agent Requirements for GRE Tunneling Support .......34.2. Home Agent Requirements for GRE Tunneling Support ..........44.3. Mobile Node Requirements for GRE Tunneling Support .........55. GRE Key Extension and Tunneling Procedures ......................56. IANA Considerations .............................................67. Security Considerations .........................................68. Acknowledgements ................................................79. Normative References ............................................71.  Introduction   This document specifies a new extension for use by a Foreign Agent   (FA) operating Mobile IP for IPv4.  The new extension allows a   Foreign Agent to request Generic Routing Encapsulation (GRE)   [RFC2784] tunneling without disturbing the Home Agent (HA) behavior   specified for Mobile IPv4 [RFC5944].  This extension contains the GRE   key [RFC2890] required for establishing a GRE tunnel between the FA   and the HA.   GRE tunneling with the Key field allows the operators to have home   networks that consist of multiple Virtual Private Networks (VPNs),   which may have overlapping home addresses.  When the tuple <Care of   Address, Home Address, and Home Agent Address> is the same acrossYegani, et al.               Standards Track                    [Page 2]

RFC 6245                  GRE Key Ext. for MIP4                 May 2011   multiple subscriber sessions, GRE tunneling will provide a means for   the FA and the HA to identify data streams for the individual   sessions based on the GRE key.  In the absence of this key   identifier, the data streams cannot be distinguished from each other   -- a significant drawback when using IP-in-IP tunneling.2.  Terminology   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this   document are to be interpreted as described in [RFC2119].  Other   terminology is used as already defined in [RFC5944].3.  GRE Key Extension   The format of the GRE Key Extension conforms to the extension format   specified for Mobile IPv4 [RFC5944].  This extension option is used   by the Foreign Agent to supply GRE key and other necessary   information to the Home Agent to establish a GRE tunnel between the   FA and the HA.4.  Operation and Use of the GRE Key Extension4.1.  Foreign Agent Requirements for GRE Tunneling Support   The FA MUST support IP-in-IP tunneling of datagrams for Mobile IPv4   [RFC5944].  The FA may support GRE tunneling that can be used, for   example, to allow for overlapping private home IP addresses   (Section 4.2.2.5 of [X.S0011-E]).  If the FA is capable of supporting   GRE encapsulation, it should set the 'G' (GRE encapsulation) bit in   the Flags field in the Agent Advertisement message sent to the Mobile   Node (MN) during the Mobile IP session establishment.   If the MN does not set the 'G' bit, the FA MAY fall back to using   IP-in-IP encapsulation for the session per [RFC5944].   If the MN does not set the 'G' bit and does not set the 'D'   (Decapsulation by mobile node) bit (i.e., the mobile node does not   request GRE tunneling and is not using a co-located care-of address),   and the local policy allows the FA to override the 'G' bit setting   received from the MN, the FA MUST include the GRE Key Extension as   defined in this memo in the Registration Request (RRQ) that it   propagates to the HA.  The presence of this extension is a request   for GRE encapsulation that takes precedence over the setting of the   'G' bit in the Registration Request.  The FA MUST NOT modify the 'G'   bit in the Registration Request because it is protected by the   Mobile-Home Authentication extension.Yegani, et al.               Standards Track                    [Page 3]

RFC 6245                  GRE Key Ext. for MIP4                 May 2011   If the FA does not support GRE encapsulation, the FA MUST reset the   'G' bit in the Agent Advertisement message.  In this case, if the MN   sets the 'G' bit in the Registration Request message, the FA returns   a Registration Reply (RRP) message to the MN with code 'requested   encapsulation unavailable' (72) per [RFC5944].   If the FA allows GRE encapsulation, and either the MN requested GRE   encapsulation or local policy dictates using GRE encapsulation for   the session, and the 'D' bit is not set (i.e., the mobile node is not   using a co-located care-of address), the FA MUST include the GRE Key   in the GRE Key Extension in all Mobile IP Registration Requests   (including initial, renewal, and de-registration requests) before   forwarding the request to the HA.  The FA may include a GRE key of   value zero in the GRE Key Extension to signal that the HA assigns GRE   keys in both directions.  The GRE key assignment in the FA and the HA   is outside the scope of this memo.   The GRE Key Extension SHALL follow the format defined in [RFC5944].   This extension SHALL be added after the MN-HA and MN-FA Challenge and   MN-AAA (Mobile Node - Authentication, Authorization, and Accounting)   extensions (if any) and before the FA-HA Auth extension (if any).4.2.  Home Agent Requirements for GRE Tunneling Support   The HA MUST follow the procedures specified in [RFC5944] in   processing this extension in Registration Request messages.   If the HA receives the GRE Key Extension in a Registration Request   and does not recognize this non-skippable extension, it MUST silently   discard the message.  The HA MUST use other alternative forms of   encapsulation (e.g., IP-in-IP tunneling), when requested by the   mobile node per [RFC5944].   If the HA receives the GRE Key Extension in a Registration Request   and recognizes the GRE Key Extension but is not configured to support   GRE encapsulation, it MUST send an RRP with code 'requested   encapsulation unavailable (139)' [RFC3024].   If the HA receives a Registration Request with a GRE Key Extension   but without the 'G' bit set, the HA SHOULD treat this as if the 'G'   bit is set in the Registration Request; i.e., the presence of a GRE   Key Extension indicates a request for GRE encapsulation.   If the HA receives the GRE Key Extension in a Registration Request,   and it recognizes the GRE Key Extension as well as supports GRE   encapsulation, the following procedures should apply:Yegani, et al.               Standards Track                    [Page 4]

RFC 6245                  GRE Key Ext. for MIP4                 May 2011   o  The HA SHOULD accept the RRQ and send an RRP with code      'registration accepted (0)'.   o  The HA MUST assign a GRE key and include the GRE Key Extension in      the RRP before sending it to the FA.   o  The HA MUST include the GRE Key Extension in all RRPs in response      to any RRQ that included the GRE Key Extension, when a GRE key is      available for the registration.   If the HA receives the GRE Key Extension in the initial Registration   Request and recognizes the GRE Key Extension carrying a GRE key value   of zero, it SHOULD accept the RRQ and send an RRP with code   'registration accepted (0)', and the following procedures apply:   o  The HA MUST assign GRE keys for both directions and include these      keys in the GRE Key Extension in the RRP before sending it to      the FA.   o  The HA MUST include the GRE Key Extension in the RRP in response      to the initial RRQ that included the GRE Key Extension, when a GRE      key is available for the registration.4.3.  Mobile Node Requirements for GRE Tunneling Support   If the MN is capable of supporting GRE encapsulation, it SHOULD set   the 'G' bit in the Flags field in the Registration Request per   [RFC5944].5.  GRE Key Extension and Tunneling Procedures   GRE tunneling support for Mobile IP will permit asymmetric GRE   keying; i.e., the FA assigns a GRE key for use in encapsulated   traffic, and the HA can assign its own GRE key.  Once the GRE keys   have been exchanged, the FA uses the HA-assigned key in the   encapsulating GRE header for reverse tunneling, and the HA uses the   FA-assigned key in the encapsulating GRE header.   The format of the GRE Key Extension is as shown below.   The GRE Key Extension MAY be included in Registration Requests or   Registration Replies [RFC5944].  The GRE Key Extension is used to   inform the recipient of the Mobile IP request of the value to be used   in the GRE Key field.Yegani, et al.               Standards Track                    [Page 5]

RFC 6245                  GRE Key Ext. for MIP4                 May 2011      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      |   Sub-Type    |            Length             |     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+     |                        Key Identifier                         |     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                        Figure 1: GRE Key Extension   Type      48 - An 8-bit identifier of the GRE Key Extension type      (non-skippable)   Sub-Type      0   Length      4   Key Identifier      This is a four-octet value assigned during registration and      inserted in every GRE packet of the user traffic.6.  IANA Considerations   The GRE Key Extension defined in this memo is a Mobile IP extension   as defined in [RFC5944].  IANA has assigned a Type value (48) for   this extension from the non-skippable range (0-127).   The GRE Key Extension introduces a new sub-type numbering space,   where the value 0 has been assigned from the range 0 to 255.   Approval of new GRE Key Extension sub-type values is to be made   through Expert Review with Specification Required.7.  Security Considerations   This specification does not introduce any new security   considerations, beyond those described in [RFC5944].Yegani, et al.               Standards Track                    [Page 6]

RFC 6245                  GRE Key Ext. for MIP4                 May 2011   Despite its name, the GRE Key Extension has little to do with   security.  The word "Key" here is not used in the cryptographic sense   of a shared secret that must be protected but rather in the sense of   an "index" or demultiplexing value that can be used to distinguish   packets belonging to a given flow within a GRE tunnel.8.  Acknowledgements   Thanks to Jun Wang, Gopal Dommety, and Sri Gundavelli for their   helpful comments, offline discussions, and review of the initial   draft version of this document.  Also, Pete McCann and Simon   Mizikovsky provided valuable review comments.9.  Normative References   [RFC2119]    Bradner, S., "Key words for use in RFCs to Indicate                Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC2784]    Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.                Traina, "Generic Routing Encapsulation (GRE)",RFC 2784,                March 2000.   [RFC2890]    Dommety, G., "Key and Sequence Number Extensions to                GRE",RFC 2890, September 2000.   [RFC3024]    Montenegro, G., Ed., "Reverse Tunneling for Mobile IP,                revised",RFC 3024, January 2001.   [RFC5944]    Perkins, C., Ed., "IP Mobility Support for IPv4,                Revised",RFC 5944, November 2010.   [X.S0011-E]  3rd Generation Partnership Project 2, "cdma2000 Wireless                IP Network Standard: Simple IP and Mobile IP Access                Services", 3GPP2 X.S0011-002-E Version 1.0,                November 2009, <http://www.3gpp2.org/Public_html/specs/X.S0011-002-E_v1.0_091116.pdf>.Yegani, et al.               Standards Track                    [Page 7]

RFC 6245                  GRE Key Ext. for MIP4                 May 2011Authors' Addresses   Parviz Yegani   Juniper Networks   1194 North Mathilda Ave.   Sunnyvale, California  94089   USA   Phone: +1 408-759-1973   EMail: pyegani@juniper.net   Kent Leung   Cisco Systems Incorporated   170 West Tasman Drive   San Jose, California  95134   USA   Phone: +1 408 526 5030   EMail: kleung@cisco.com   Avi Lior   Bridgewater Systems Corporation   303 Terry Fox Drive   Ottawa, Ontario  K2K 3J1   Canada   Phone: +1 613-591-6655   EMail: avi@bridgewatersystems.com   Kuntal Chowdhury   Cisco Systems Incorporated   170 West Tasman Drive   San Jose, California  95134   USA   EMail: kchowdhu@cisco.com   Jay Navali   Cisco Systems Incorporated   170 West Tasman Drive   San Jose, California  95134   USA   EMail: jnavali@cisco.comYegani, et al.               Standards Track                    [Page 8]