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Independent Submission                                        N. LeymannRequest for Comments: 8157                                  C. HeidemannCategory: Informational                              Deutsche Telekom AGISSN: 2070-1721                                                 M. Zhang                                                             B. Sarikaya                                                                  Huawei                                                               M. Cullen                                                       Painless Security                                                                May 2017Huawei's GRE Tunnel Bonding ProtocolAbstract   There is an emerging demand for solutions that provide redundancy and   load-sharing across wired and cellular links from a single Service   Provider, so that a single subscriber is provided with bonded access   to heterogeneous connections at the same time.   In this document, GRE (Generic Routing Encapsulation) Tunnel Bonding   is specified as an enabling approach for bonded access to a wired and   a wireless network in customer premises, e.g., homes.  In GRE Tunnel   Bonding, two GRE tunnels, one per network connection, are set up and   bonded together to form a single GRE tunnel for a subscriber.   Compared with each subconnection, the bonded connections promise   increased access capacity and improved reliability.  The solution   described in this document is currently implemented by Huawei and   deployed by Deutsche Telekom AG.  This document will enable other   developers to build interoperable implementations.Status of This Memo   This document is not an Internet Standards Track specification; it is   published for informational purposes.   This is a contribution to the RFC Series, independently of any other   RFC stream.  The RFC Editor has chosen to publish this document at   its discretion and makes no statement about its value for   implementation or deployment.  Documents approved for publication by   the RFC Editor are not a candidate for any level of Internet   Standard; seeSection 2 of RFC 7841.   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/rfc8157.Leymann, et al.               Informational                     [Page 1]

RFC 8157                   GRE Tunnel Bonding                   May 2017Copyright Notice   Copyright (c) 2017 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.Table of Contents1. Introduction ....................................................32. Acronyms and Terminology ........................................43. Use Case ........................................................64. Overview ........................................................74.1. Control Plane ..............................................74.2. Data Plane .................................................74.3. Traffic Classification and Distribution ....................84.4. Traffic Recombination ......................................84.5. Bypass .....................................................94.6. Measurement ................................................94.7. Policy Control Considerations ..............................95. Control Protocol Specification (Control Plane) .................105.1. GRE Tunnel Setup Request ..................................125.1.1. Client Identification Name .........................125.1.2. Session ID .........................................135.1.3. DSL Synchronization Rate ...........................145.2. GRE Tunnel Setup Accept ...................................145.2.1. H IPv4 Address .....................................155.2.2. H IPv6 Address .....................................155.2.3. Session ID .........................................165.2.4. RTT Difference Threshold ...........................165.2.5. Bypass Bandwidth Check Interval ....................175.2.6. Active Hello Interval ..............................175.2.7. Hello Retry Times ..................................185.2.8. Idle Timeout .......................................185.2.9. Bonding Key Value ..................................195.2.10. Configured DSL Upstream Bandwidth .................205.2.11. Configured DSL Downstream Bandwidth ...............215.2.12. RTT Difference Threshold Violation ................215.2.13. RTT Difference Threshold Compliance ...............225.2.14. Idle Hello Interval ...............................235.2.15. No Traffic Monitored Interval .....................23Leymann, et al.               Informational                     [Page 2]

RFC 8157                   GRE Tunnel Bonding                   May 20175.3. GRE Tunnel Setup Deny .....................................245.3.1. Error Code .........................................245.4. GRE Tunnel Hello ..........................................255.4.1. Timestamp ..........................................255.4.2. IPv6 Prefix Assigned by HAAP .......................265.5. GRE Tunnel Tear Down ......................................265.6. GRE Tunnel Notify .........................................275.6.1. Bypass Traffic Rate ................................275.6.2. Filter List Package ................................285.6.3. Switching to DSL Tunnel ............................315.6.4. Overflowing to LTE Tunnel ..........................315.6.5. DSL Link Failure ...................................325.6.6. LTE Link Failure ...................................325.6.7. IPv6 Prefix Assigned to Host .......................335.6.8. Diagnostic Start: Bonding Tunnel ...................335.6.9. Diagnostic Start: DSL Tunnel .......................345.6.10. Diagnostic Start: LTE Tunnel ......................345.6.11. Diagnostic End ....................................355.6.12. Filter List Package ACK ...........................355.6.13. Switching to Active Hello State ...................365.6.14. Switching to Idle Hello State .....................375.6.15. Tunnel Verification ...............................376. Tunnel Protocol Operation (Data Plane) .........................386.1. The GRE Header ............................................386.2. Automatic Setup of GRE Tunnels ............................397. Security Considerations ........................................418. IANA Considerations ............................................419. References .....................................................419.1. Normative References ......................................419.2. Informative References ....................................42   Contributors ......................................................43   Authors' Addresses ................................................441.  Introduction   Service Providers used to provide subscribers with separate access to   their fixed networks and mobile networks.  It has become desirable to   bond these heterogeneous networks together to offer access service to   subscribers; this service will provide increased access capacity and   improved reliability.   This document focuses on the use case where a DSL (Digital Subscriber   Line) connection and an LTE (Long Term Evolution) connection are   bonded together.  When the traffic volume exceeds the bandwidth of   the DSL connection, the excess amount can be offloaded to the LTE   connection.  A Home Gateway (HG) is a Customer Premises Equipment   (CPE) device initiating the DSL and LTE connections.  A Hybrid Access   Aggregation Point (HAAP) is the network function that resides in theLeymann, et al.               Informational                     [Page 3]

RFC 8157                   GRE Tunnel Bonding                   May 2017   provider's networks to terminate these bonded connections.  Note that   if there were more than two connections that need to be bonded, the   GRE Tunnel Bonding mechanism could support that scenario as well.   However, support for more than two connections is out of scope for   this document.  Also, the protocol specified in this document is   limited to the single-operator scenario only, i.e., the two peering   boxes -- the HG and the HAAP -- are operated by a single provider.   The adaptation of the GRE Tunnel Bonding Protocol to the   multi-provider scenario is left for future work.   This document bases the solution on GRE (Generic Routing   Encapsulation [RFC2784] [RFC2890]), since GRE is widely supported in   both fixed and mobile networks.  Approaches specified in this   document might also be used by other tunneling technologies to   achieve tunnel bonding.  However, such variants are out of scope for   this document.   For each heterogeneous connection (DSL and LTE) between the HG and   the HAAP, one GRE tunnel is set up.  The HG and the HAAP,   respectively, serve as the common termination point of the two   tunnels at both ends.  Those GRE tunnels are further bonded together   to form a logical GRE tunnel for the subscriber.  The HG conceals the   GRE tunnels from the end nodes, and end nodes simply treat the   logical GRE tunnel as a single IP link.  This provides an overlay:   the users' IP packets (inner IP) are encapsulated in GRE, which is in   turn carried over IP (outer IP).   The GRE Tunnel Bonding Protocol is developed by Huawei and has been   deployed in networks operated by Deutsche Telekom AG.  This document   makes this protocol available to the public, thereby enabling other   developers to build interoperable implementations.2.  Acronyms and Terminology   GRE: Generic Routing Encapsulation [RFC2784] [RFC2890].   DSL: Digital Subscriber Line.  A family of technologies used to      transmit digital data over telephone lines.   LTE: Long Term Evolution.  A standard for wireless communication of      high-speed data for mobile phones and data terminals.  Commonly      marketed as 4G LTE.   HG: Home Gateway.  A CPE device that is enhanced to support the      simultaneous use of both fixed broadband and 3GPP access      connections.Leymann, et al.               Informational                     [Page 4]

RFC 8157                   GRE Tunnel Bonding                   May 2017   HAAP: Hybrid Access Aggregation Point.  A logical function in an      operator's network, terminating bonded connections while offering      high-speed Internet.   CIR: Committed Information Rate [RFC2697].   RTT: Round-Trip Time.   AAA: Authentication, Authorization, and Accounting [RFC6733].   SOAP: Simple Object Access Protocol.  A protocol specification for      exchanging structured information in the implementation of web      services in computer networks.   FQDN: Fully Qualified Domain Name.  Generally, a host name with at      least one domain label under the top-level domain.  For example,      "dhcp.example.org" is an FQDN [RFC7031].   DSCP: The 6-bit codepoint (DSCP) of the Differentiated Services field      (DS field) in the IPv4 and IPv6 headers [RFC2724].   BRAS: Broadband Remote Access Server.  Routes traffic to and from      broadband remote access devices such as Digital Subscriber Line      Access Multiplexers (DSLAMs) on an Internet Service Provider's      (ISP's) network.   PGW: Packet Data Network Gateway.  In the Long Term Evolution (LTE)      architecture for the Evolved Packet Core (EPC), acts as an anchor      for user-plane mobility.   PDP: Packet Data Protocol.  A packet transfer protocol used in      wireless GPRS (General Packet Radio Service) / HSDPA (High-Speed      Downlink Packet Access) networks.   PPPoE: Point-to-Point over Ethernet.  A network protocol for      encapsulating PPP frames inside Ethernet frames.   DNS: Domain Name System.  A hierarchical distributed naming system      for computers, services, or any resource connected to the Internet      or a private network.   DHCP: Dynamic Host Configuration Protocol.  A standardized network      protocol used on Internet Protocol (IP) networks for dynamically      distributing network configuration parameters, such as IP      addresses for interfaces and services.Leymann, et al.               Informational                     [Page 5]

RFC 8157                   GRE Tunnel Bonding                   May 2017   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 inRFC 2119 [RFC2119].3.  Use Case                           Bonding Connection                  +-+ ****************************                  | | *+-+                    +-+*                  | | *|E+-- LTE Connection --+ |*       subscriber |C| *+-+                    |H|*  Internet                  | | *+-+                    | |*                  | | *|D+-- DSL Connection --+ |*                  | | *+-+                    +-+*                  +-+ ****************************                  \______/                    \__/                     HG                       HAAP       C: The service endpoint of the bonding service at the HG.       E: The endpoint of the LTE connection resides in the HG.       D: The endpoint of the DSL connection resides in the HG.       H: The endpoint for each heterogeneous connection at the HAAP.      Figure 1: Offloading from DSL to LTE, Increased Access Capacity   If a Service Provider runs heterogeneous networks, such as fixed and   mobile, subscribers might be eager to use those networks   simultaneously for increased access capacity rather than just using a   single network.  As shown by the reference model in Figure 1, the   subscriber expects a significantly higher access bandwidth from the   bonding connection than from the DSL connection.  In other words,   when the traffic volume exceeds the bandwidth of the DSL connection,   the excess amount may be offloaded to the LTE connection.   Compared to per-flow load-balancing mechanisms, which are widely used   nowadays, the use case described in this document requires a   per-packet offloading approach.  For per-flow load balancing, the   maximum bandwidth that may be used by a traffic flow is the bandwidth   of an individual connection, while for per-packet offloading, a   single flow may use the combined bandwidth of the two connections.Leymann, et al.               Informational                     [Page 6]

RFC 8157                   GRE Tunnel Bonding                   May 20174.  Overview   In this document, the widely supported GRE is chosen as the tunneling   technique.  With the newly defined control protocol, GRE tunnels are   set up on top of the DSL and LTE connections, which are ended at   D and H or at E and H, as shown in Figure 1.  These tunnels are   bonded together to form a single logical bonding connection between   the HG and the HAAP.  Subscribers use this logical connection without   knowing the GRE tunnels.4.1.  Control Plane   A clean-slate control protocol is designed to manage the GRE tunnels   that are set up per heterogeneous connection between the HG and the   HAAP.  The goal is to design a compact control plane for bonding   access instead of reusing existing control planes.   In order to measure the performance of connections, control packets   need to co-route the same path with data packets.  Therefore, a   GRE Channel is opened for the purpose of data-plane forwarding of   control-plane packets.  As shown in Figure 2 (seeSection 5), the GRE   header [RFC2784] with the Key extension specified by [RFC2890] is   being used.  The GRE Protocol Type (0xB7EA) is used to identify this   GRE Channel.  A family of control messages is encapsulated with a GRE   header and carried over this channel.  Attributes, formatted in   Type-Length-Value (TLV) style, are further defined and included in   each control message.   With the newly defined control plane, the GRE tunnels between the HG   and the HAAP can be established, managed, and released without the   involvement of operators.4.2.  Data Plane   Using the control plane defined inSection 4.1, GRE tunnels can be   automatically set up per heterogeneous connection between the HG and   the HAAP.  For the use case described inSection 3, one GRE tunnel is   ended at the DSL WAN interfaces, e.g., the DSL GRE tunnel, and   another GRE tunnel is ended at the LTE WAN interfaces, e.g., the LTE   GRE tunnel.  Each tunnel may carry a user's IP packets as payload,   which forms a typical IP-over-IP overlay.  These tunnels are bonded   together to offer a single access point to subscribers.   As shown in Figure 3 (seeSection 6.1), the GRE header [RFC2784] with   the Key and Sequence Number extensions specified by [RFC2890] is used   to encapsulate data packets.  The Protocol Type is either 0x0800   (listed as "0x800" in [RFC2784]) or 0x86DD [RFC7676], which indicates   that the inner packet is either an IPv4 packet or an IPv6 packet,Leymann, et al.               Informational                     [Page 7]

RFC 8157                   GRE Tunnel Bonding                   May 2017   respectively.  The GRE Key field is set to a unique value for the   entire bonding connection.  The GRE Sequence Number field is used to   maintain the sequence of packets transported in all GRE tunnels as a   single flow between the HG and the HAAP.4.3.  Traffic Classification and Distribution   For the offloading use case, the coloring mechanism specified in   [RFC2697] is being used to classify subscribers' IP packets, both   upstream and downstream, into the DSL GRE tunnel or the LTE GRE   tunnel.  Packets colored as green or yellow will be distributed into   the DSL GRE tunnel, and packets colored as red will be distributed   into the LTE GRE tunnel.  For the scenario that requires more than   two GRE tunnels, multiple levels of token buckets might be realized.   However, that scenario is out of scope for this document.   The Committed Information Rate (CIR) of the coloring mechanism is set   to the total DSL WAN bandwidth minus the bypass DSL bandwidth (seeSection 4.5).  The total DSL WAN bandwidth MAY be configured, MAY be   obtained from the management system (AAA server, SOAP server, etc.),   or MAY be detected in real time using the Access Node Control   Protocol (ANCP) [RFC6320].4.4.  Traffic Recombination   For the offloading use case, the recombination function at the   receiver provides in-order delivery of subscribers' traffic.  The   receiver maintains a small reordering buffer and orders the data   packets in this buffer via the Sequence Number field [RFC2890] of the   GRE header.  All packets carried on GRE tunnels that belong to the   same bonding connection go into a single reordering buffer.   Operators may configure the maximum allowed size (see   MAX_PERFLOW_BUFFER in [RFC2890]) of the buffer for reordering.  They   may also configure the maximum time (see OUTOFORDER_TIMER in   [RFC2890]) that a packet can stay in the buffer for reordering.  The   OUTOFORDER_TIMER must be configured carefully.  Values larger than   the difference of the normal Round-Trip Time (RTT) (e.g., 100 ms) of   the two connections are not recommended.  Implementation and   deployment experiences have demonstrated that there is usually a   large margin for the value of MAX_PERFLOW_BUFFER.  Values larger than   the multiplication of the sum of the line rate of the two connections   and the value of OUTOFORDER_TIMER should be used.Leymann, et al.               Informational                     [Page 8]

RFC 8157                   GRE Tunnel Bonding                   May 20174.5.  Bypass   Service Providers provide some services that should not be delivered   over the bonding connection.  For example, Service Providers may not   expect real-time IPTV to be carried by the LTE GRE tunnel.  It is   required that IPTV traffic bypass the GRE Tunnel Bonding and use the   raw DSL bandwidth.  Bypass traffic is not subject to the traffic   classification and distribution specified above.  The raw connection   used for bypass traffic is not controlled by the HAAP.  It may or may   not go through a device in which the HAAP resides.   The HAAP may announce the service types that need to bypass the   bonded GRE tunnels by using the Filter List Package attribute as   specified inSection 5.6.2.  The HG and the HAAP need to set aside   the DSL bandwidth for bypassing.  The available DSL bandwidth for GRE   Tunnel Bonding is equal to the total DSL bandwidth minus the bypass   bandwidth.4.6.  Measurement   Since control packets are routed using the same paths as the data   packets, the real performance of the data paths (e.g., the GRE   tunnels) can be measured.  The GRE Tunnel Hello messages specified inSection 5.4 are used to carry the timestamp information, and the RTT   value can therefore be calculated based on the timestamp.   Besides the end-to-end delay of the GRE tunnels, the HG and the HAAP   need to measure the capacity of the tunnels as well.  For example,   the HG is REQUIRED to measure the downstream bypassing bandwidth and   report it to the HAAP in real time (seeSection 5.6.1).4.7.  Policy Control Considerations   Operators and users may input policies into the GRE Tunnel Bonding.   These policies will be "interpreted" into parameters or actions that   impact the traffic classification, distribution, combination,   measurement, and bypass.   Operators and users may offer the service types that need to bypass   the bonded GRE tunnels.  Service types defined by operators (seeSection 5.6.2) will be delivered from the HAAP to the HG through the   control plane (seeSection 4.1), and the HG will use the raw   connection to transmit traffic for these service types.  Users may   also define bypass service types on the HG.  Bypass service types   defined by users need not be delivered to the HAAP.Leymann, et al.               Informational                     [Page 9]

RFC 8157                   GRE Tunnel Bonding                   May 2017   Operators may specify the interval for sending Hello messages and the   retry times for the HG or the HAAP to send out Hello messages before   the failure of a connection.   Since the GRE tunnels are set up on top of heterogeneous DSL and LTE   connections, if the difference of the transmission delays of these   connections exceeds a given threshold for a certain period, the HG   and the HAAP should be able to stop the offloading behavior and   fall back to a traditional transmission mode, where the LTE GRE   tunnel is disused while all traffic is transmitted over the DSL GRE   tunnel.  Operators are allowed to define this threshold and period.5.  Control Protocol Specification (Control Plane)   Control messages are used to establish, maintain, measure, and   tear down GRE tunnels between the HG and the HAAP.  Also, the control   plane undertakes the responsibility to convey traffic policies over   the GRE tunnels.   For the purpose of measurement, control messages need to be delivered   as GRE encapsulated packets and co-routed with data-plane packets.   The new GRE Protocol Type (0xB7EA) is allocated for this purpose, and   the standard GRE header as per [RFC2784] with the Key extension   specified by [RFC2890] is used.  The Checksum Present bit is set   to 0.  The Key Present bit is set to 1.  The Sequence Number Present   bit is set to 0.  So, the format of the GRE header for control   messages of the GRE Tunnel Bonding Protocol is as follows:    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   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |0| |1|0| Reserved0       | Ver |   Protocol Type 0xB7EA        |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                              Key                              |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Key      For security purposes, the Key field is used to carry a random      number.  The random number is generated by the HAAP, and the HG is      informed of it (seeSection 5.2.9).Leymann, et al.               Informational                    [Page 10]

RFC 8157                   GRE Tunnel Bonding                   May 2017   The general format of the entire control message is as follows:     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    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |0| |1|0|   Reserved0     | Ver |   Protocol Type 0xB7EA        |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |                              Key                              |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |MsgType|T-Type |                                               |    +-+-+-+-+-+-+-+-+           Attributes                          +    ~                                                               ~    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+        Figure 2: Format of Control Messages of GRE Tunnel Bonding   MsgType (4 bits)      Message Type.  The control message family contains the following      six types of control messages (not including "Reserved"):                 Control Message Family         Type                ==========================    =========                 GRE Tunnel Setup Request       1                 GRE Tunnel Setup Accept        2                 GRE Tunnel Setup Deny          3                 GRE Tunnel Hello               4                 GRE Tunnel Tear Down           5                 GRE Tunnel Notify              6                 Reserved                       0, 7-15   T-Type (4 bits)      Tunnel Type.  Set to 0001 if the control message is sent via the      primary GRE tunnel (normally the DSL GRE tunnel).  Set to 0010 if      the control message is sent via the secondary GRE tunnel (normally      the LTE GRE tunnel).  Values 0000 and values from 0011 through      1111 are reserved for future use and MUST be ignored on receipt.Leymann, et al.               Informational                    [Page 11]

RFC 8157                   GRE Tunnel Bonding                   May 2017   Attributes      The Attributes field includes the attributes that need to be      carried in the control message.  Each Attribute has the following      format:      +-+-+-+-+-+-+-+-+      |Attribute Type |                  (1 byte)      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |  Attribute Length             |  (2 bytes)      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |  Attribute Value              ~  (variable)      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      Attribute Type         The Attribute Type specifies the type of the attribute.      Attribute Length         Attribute Length indicates the length of the Attribute Value         in bytes.      Attribute Value         The Attribute Value includes the value of the attribute.   All control messages are sent in network byte order (high-order bytes   first).  The Protocol Type carried in the GRE header for the control   message is 0xB7EA.  Based on this number, the receiver will decide to   consume the GRE packet locally rather than forward it further.5.1.  GRE Tunnel Setup Request   The HG uses the GRE Tunnel Setup Request message to request that the   HAAP establish the GRE tunnels.  It is sent out from the HG's LTE and   DSL WAN interfaces separately.  Attributes that need to be included   in this message are defined in the following subsections.5.1.1.  Client Identification Name   An operator uses the Client Identification Name (CIN) to identify the   HG.  The HG sends the CIN to the HAAP for authentication and   authorization as specified in [TS23.401].  It is REQUIRED that the   GRE Tunnel Setup Request message sent out from the LTE WAN interface   contain the CIN attribute while the GRE Tunnel Setup Request message   sent out from the DSL WAN interface does not contain this attribute.Leymann, et al.               Informational                    [Page 12]

RFC 8157                   GRE Tunnel Bonding                   May 2017   The CIN attribute has the following format:   +-+-+-+-+-+-+-+-+   |Attribute Type |                   (1 byte)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Attribute Length             |   (2 bytes)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+   |  Client Identification Name       (40 bytes)  |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+   Attribute Type      CIN, set to 3.   Attribute Length      Set to 40.   Client Identification Name      This is a 40-byte string value encoded in UTF-8 and set by the      operator.  It is used as the identification of the HG in the      operator's network.5.1.2.  Session ID   This Session ID is generated by the HAAP when the LTE GRE Tunnel   Setup Request message is received.  The HAAP announces the Session ID   to the HG in the LTE GRE Tunnel Setup Accept message.  For those WAN   interfaces that need to be bonded together, the HG MUST use the same   Session ID.  The HG MUST carry the Session ID attribute in each DSL   GRE Tunnel Setup Request message.  For the first time that the LTE   GRE Tunnel Setup Request message is sent to the HAAP, the Session ID   attribute need not be included.  However, if the LTE GRE tunnel fails   and the HG tries to revive it, the LTE GRE Tunnel Setup Request   message MUST include the Session ID attribute.   The Session ID attribute has the following format:   +-+-+-+-+-+-+-+-+   |Attribute Type |                   (1 byte)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Attribute Length             |   (2 bytes)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+   |  Session ID                       (4 bytes)   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+Leymann, et al.               Informational                    [Page 13]

RFC 8157                   GRE Tunnel Bonding                   May 2017   Attribute Type      Session ID, set to 4.   Attribute Length      Set to 4.   Session ID      An unsigned integer generated by the HAAP.  It is used as the      identification of bonded GRE tunnels.5.1.3.  DSL Synchronization Rate   The HG uses the DSL Synchronization Rate to notify the HAAP about the   downstream bandwidth of the DSL link.  The DSL GRE Tunnel Setup   Request message MUST include the DSL Synchronization Rate attribute.   The LTE GRE Tunnel Setup Request message SHOULD NOT include this   attribute.   +-+-+-+-+-+-+-+-+   |Attribute Type |                   (1 byte)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Attribute Length             |   (2 bytes)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+   |  DSL Synchronization Rate         (4 bytes)   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+   Attribute Type      DSL Synchronization Rate, set to 7.   Attribute Length      Set to 4.   DSL Synchronization Rate      An unsigned integer measured in kbps.5.2.  GRE Tunnel Setup Accept   The HAAP uses the GRE Tunnel Setup Accept message as the response to   the GRE Tunnel Setup Request message.  This message indicates   acceptance of the tunnel establishment and carries parameters of the   GRE tunnels.  Attributes that need to be included in this message are   defined below.Leymann, et al.               Informational                    [Page 14]

RFC 8157                   GRE Tunnel Bonding                   May 20175.2.1.  H IPv4 Address   The HAAP uses the H IPv4 Address attribute to inform the HG of the   H IPv4 address.  The HG uses the H IPv4 address as the destination   endpoint IPv4 address of the GRE tunnels (the source endpoint IPv4   addresses of the GRE tunnels are the DSL WAN interface IP address (D)   and the LTE WAN interface IP address (E), respectively, as shown in   Figure 1).  The LTE GRE Tunnel Setup Accept message MUST include the   H IPv4 Address attribute.   +-+-+-+-+-+-+-+-+   |Attribute Type |                   (1 byte)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Attribute Length             |   (2 bytes)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+   |  H IPv4 Address                   (4 bytes)   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+   Attribute Type      H IPv4 Address, set to 1.   Attribute Length      Set to 4.   H IPv4 Address      Set to the pre-configured IPv4 address (e.g., an IP address of a      Line Card in the HAAP), which is used as the endpoint IP address      of GRE tunnels by the HAAP.5.2.2.  H IPv6 Address   The HAAP uses the H IPv6 Address attribute to inform the HG of the   H IPv6 address.  The HG uses the H IPv6 address as the destination   endpoint IPv6 address of the GRE tunnels (the source endpoint IPv6   addresses of the GRE tunnels are the DSL WAN interface IP address (D)   and the LTE WAN interface IP address (E), respectively, as shown in   Figure 1).   The LTE GRE Tunnel Setup Accept message MUST include the H IPv6   Address attribute.   +-+-+-+-+-+-+-+-+   |Attribute Type |                   (1 byte)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Attribute Length             |   (2 bytes)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+   |  H IPv6 Address                   (16 bytes)  |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+Leymann, et al.               Informational                    [Page 15]

RFC 8157                   GRE Tunnel Bonding                   May 2017   Attribute Type      H IPv6 Address, set to 2.   Attribute Length      Set to 16.   H IPv6 Address      Set to the pre-configured IPv6 address (e.g., an IP address of a      Line Card in the HAAP), which is used as the endpoint IP address      of GRE tunnels by the HAAP.5.2.3.  Session ID   The LTE GRE Tunnel Setup Accept message MUST include the Session ID   attribute as defined inSection 5.1.2.5.2.4.  RTT Difference Threshold   The HAAP uses the RTT Difference Threshold attribute to inform the HG   of the acceptable threshold of the RTT difference between the DSL   link and the LTE link.  If the measured RTT difference exceeds this   threshold, the HG SHOULD stop offloading traffic to the LTE GRE   tunnel.  The LTE GRE Tunnel Setup Accept message MUST include the RTT   Difference Threshold attribute.   +-+-+-+-+-+-+-+-+   |Attribute Type |                   (1 byte)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Attribute Length             |   (2 bytes)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+   |  RTT Difference Threshold         (4 bytes)   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+   Attribute Type      RTT Difference Threshold, set to 9.   Attribute Length      Set to 4.   RTT Difference Threshold      An unsigned integer measured in milliseconds.  This value can be      chosen in the range 0 through 1000.Leymann, et al.               Informational                    [Page 16]

RFC 8157                   GRE Tunnel Bonding                   May 20175.2.5.  Bypass Bandwidth Check Interval   The HAAP uses the Bypass Bandwidth Check Interval attribute to inform   the HG of how frequently the bypass bandwidth should be checked.  The   HG should check the bypass bandwidth of the DSL WAN interface in each   time period indicated by this interval.  The LTE GRE Tunnel Setup   Accept message MUST include the Bypass Bandwidth Check Interval   attribute.   +-+-+-+-+-+-+-+-+   |Attribute Type |                   (1 byte)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Attribute Length             |   (2 bytes)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+   |  Bypass Bandwidth Check Interval  (4 bytes)   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+   Attribute Type      Bypass Bandwidth Check Interval, set to 10.   Attribute Length      Set to 4.   Bypass Bandwidth Check Interval      An unsigned integer measured in seconds.  This value can be chosen      in the range 10 through 300.5.2.6.  Active Hello Interval   The HAAP uses the Active Hello Interval attribute to inform the HG of   the pre-configured interval for sending out GRE Tunnel Hellos.  The   HG should send out GRE Tunnel Hellos via both the DSL and LTE WAN   interfaces in each time period as indicated by this interval.  The   LTE GRE Tunnel Setup Accept message MUST include the Active Hello   Interval attribute.   +-+-+-+-+-+-+-+-+   |Attribute Type |                   (1 byte)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Attribute Length             |   (2 bytes)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+   |  Active Hello Interval            (4 bytes)   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+Leymann, et al.               Informational                    [Page 17]

RFC 8157                   GRE Tunnel Bonding                   May 2017   Attribute Type      Active Hello Interval, set to 14.   Attribute Length      Set to 4.   Active Hello Interval      An unsigned integer measured in seconds.  This value can be chosen      in the range 1 through 100.5.2.7.  Hello Retry Times   The HAAP uses the Hello Retry Times attribute to inform the HG of the   retry times for sending GRE Tunnel Hellos.  If the HG does not   receive any acknowledgement from the HAAP for the number of GRE   Tunnel Hello attempts specified in this attribute, the HG will   declare a failure of the GRE tunnel.  The LTE GRE Tunnel Setup Accept   message MUST include the Hello Retry Times attribute.   +-+-+-+-+-+-+-+-+   |Attribute Type |                   (1 byte)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Attribute Length             |   (2 bytes)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+   |  Hello Retry Times                (4 bytes)   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+   Attribute Type      Hello Retry Times, set to 15.   Attribute Length      Set to 4.   Hello Retry Times      An unsigned integer that takes values in the range 3 through 10.5.2.8.  Idle Timeout   The HAAP uses the Idle Timeout attribute to inform the HG of the   pre-configured timeout value to terminate the DSL GRE tunnel.  When   an LTE GRE tunnel failure is detected, all traffic will be sent over   the DSL GRE tunnel.  If the failure of the LTE GRE tunnel lasts   longer than the Idle Timeout, subsequent traffic will be sent over   raw DSL rather than over a tunnel, and the DSL GRE tunnel SHOULD be   terminated.  The LTE GRE Tunnel Setup Accept message MUST include the   Idle Timeout attribute.Leymann, et al.               Informational                    [Page 18]

RFC 8157                   GRE Tunnel Bonding                   May 2017   +-+-+-+-+-+-+-+-+   |Attribute Type |                   (1 byte)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Attribute Length             |   (2 bytes)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+   |  Idle Timeout                     (4 bytes)   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+   Attribute Type      Idle Timeout, set to 16.   Attribute Length      Set to 4.   Idle Timeout      An unsigned integer measured in seconds.  It takes values in the      range 0 through 172,800 with a granularity of 60.  The default      value is 86,400 (24 hours).  The value 0 indicates that the idle      timer never expires.5.2.9.  Bonding Key Value   The HAAP uses the Bonding Key Value attribute to inform the HG of the   number that is to be carried as the Key of the GRE header for   subsequent control messages.  The Bonding Key Value is generated by   the HAAP and used for security purposes.   The method used to generate this number is left up to   implementations.  The pseudorandom number generator defined in   ANSI X9.31,Appendix A.2.4 [ANSI-X9.31-1998] is RECOMMENDED.  Note   that random number generation "collisions" are allowed in the GRE   Tunnel Bonding Protocol.   +-+-+-+-+-+-+-+-+   |Attribute Type |                   (1 byte)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Attribute Length             |   (2 bytes)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+   |  Bonding Key Value                (4 bytes)   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+Leymann, et al.               Informational                    [Page 19]

RFC 8157                   GRE Tunnel Bonding                   May 2017   Attribute Type      Bonding Key Value, set to 20.   Attribute Length      Set to 4.   Bonding Key Value      A 32-bit random number generated by the HAAP.5.2.10.  Configured DSL Upstream Bandwidth   The HAAP obtains the upstream bandwidth of the DSL link from the   management system and uses the Configured DSL Upstream Bandwidth   attribute to inform the HG.  The HG uses the received upstream   bandwidth as the CIR [RFC2697] for the DSL link.  The DSL GRE Tunnel   Setup Accept message MUST include the Configured DSL Upstream   Bandwidth attribute.   +-+-+-+-+-+-+-+-+   |Attribute Type |                   (1 byte)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Attribute Length             |   (2 bytes)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+   | Configured DSL Upstream Bandwidth (4 bytes)   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+   Attribute Type      Configured DSL Upstream Bandwidth, set to 22.   Attribute Length      Set to 4.   Configured DSL Upstream Bandwidth      An unsigned integer measured in kbps.Leymann, et al.               Informational                    [Page 20]

RFC 8157                   GRE Tunnel Bonding                   May 20175.2.11.  Configured DSL Downstream Bandwidth   The HAAP obtains the downstream bandwidth of the DSL link from the   management system and uses the Configured DSL Downstream Bandwidth   attribute to inform the HG.  The HG uses the received downstream   bandwidth as the base in calculating the bypassing bandwidth.  The   DSL GRE Tunnel Setup Accept message MUST include the Configured DSL   Downstream Bandwidth attribute.   +-+-+-+-+-+-+-+-+   |Attribute Type |                   (1 byte)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Attribute Length             |   (2 bytes)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+   |Configured DSL Downstream Bandwidth(4 bytes)   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+   Attribute Type      Configured DSL Downstream Bandwidth, set to 23.   Attribute Length      Set to 4.   Configured DSL Downstream Bandwidth      An unsigned integer measured in kbps.5.2.12.  RTT Difference Threshold Violation   The HAAP uses the RTT Difference Threshold Violation attribute to   inform the HG of the number of times in a row that the RTT Difference   Threshold (seeSection 5.2.4) may be violated before the HG MUST stop   using the LTE GRE tunnel.  If the RTT Difference Threshold is   continuously violated for more than the indicated number of   measurements, the HG MUST stop using the LTE GRE tunnel.  The LTE GRE   Tunnel Setup Accept message MUST include the RTT Difference Threshold   Violation attribute.   +-+-+-+-+-+-+-+-+   |Attribute Type |                   (1 byte)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Attribute Length             |   (2 bytes)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+   |  RTT Diff Threshold Violation     (4 bytes)   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+Leymann, et al.               Informational                    [Page 21]

RFC 8157                   GRE Tunnel Bonding                   May 2017   Attribute Type      RTT Difference Threshold Violation, set to 24.   Attribute Length      Set to 4.   RTT Difference Threshold Violation      An unsigned integer that takes values in the range 1 through 25.      A typical value is 3.5.2.13.  RTT Difference Threshold Compliance   The HAAP uses the RTT Difference Threshold Compliance attribute to   inform the HG of the number of times in a row that the RTT Difference   Threshold (seeSection 5.2.4) must be compliant before use of the LTE   GRE tunnel can be resumed.  If the RTT Difference Threshold is   continuously detected to be compliant across more than this number of   measurements, the HG MAY resume using the LTE GRE tunnel.  The LTE   GRE Tunnel Setup Accept message MUST include the RTT Difference   Threshold Compliance attribute.   +-+-+-+-+-+-+-+-+   |Attribute Type |                   (1 byte)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Attribute Length             |   (2 bytes)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+   |  RTT Diff Threshold Compliance    (4 bytes)   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+   Attribute Type      RTT Difference Threshold Compliance, set to 25.   Attribute Length      Set to 4.   RTT Difference Threshold Compliance      An unsigned integer that takes values in the range 1 through 25.      A typical value is 3.Leymann, et al.               Informational                    [Page 22]

RFC 8157                   GRE Tunnel Bonding                   May 20175.2.14.  Idle Hello Interval   The HAAP uses the Idle Hello Interval attribute to inform the HG of   the pre-configured interval for sending out GRE Tunnel Hellos when   the subscriber is detected to be idle.  The HG SHOULD begin to send   out GRE Tunnel Hellos via both the DSL and LTE WAN interfaces in each   time period as indicated by this interval, if the bonded tunnels have   seen no traffic for a period longer than the "No Traffic Monitored   Interval" (seeSection 5.2.15).  The LTE GRE Tunnel Setup Accept   message MUST include the Idle Hello Interval attribute.   +-+-+-+-+-+-+-+-+   |Attribute Type |                    (1 byte)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Attribute Length             |    (2 bytes)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+   |  Idle Hello Interval               (4 bytes)  |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+   Attribute Type      Idle Hello Interval, set to 31.   Attribute Length      Set to 4.   Idle Hello Interval      An unsigned integer measured in seconds.  This value can be chosen      in the range 100 through 86,400 (24 hours) with a granularity of      100.  The default value is 1800 (30 minutes).5.2.15.  No Traffic Monitored Interval   The HAAP uses the No Traffic Monitored Interval attribute to inform   the HG of the pre-configured interval for switching the GRE Tunnel   Hello mode.  If traffic is detected on the bonded GRE tunnels before   this interval expires, the HG SHOULD switch to the Active Hello   Interval.  The LTE GRE Tunnel Setup Accept message MUST include the   No Traffic Monitored Interval attribute.   +-+-+-+-+-+-+-+-+   |Attribute Type |                    (1 byte)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Attribute Length             |    (2 bytes)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+   |  No Traffic Monitored Interval     (4 bytes)  |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+Leymann, et al.               Informational                    [Page 23]

RFC 8157                   GRE Tunnel Bonding                   May 2017   Attribute Type      No Traffic Monitored Interval, set to 32.   Attribute Length      Set to 4.   No Traffic Monitored Interval      An unsigned integer measured in seconds.  This value is in the      range 30 through 86,400 (24 hours).  The default value is 60.5.3.  GRE Tunnel Setup Deny   The HAAP MUST send the GRE Tunnel Setup Deny message to the HG if the   GRE Tunnel Setup Request from this HG is denied.  The HG MUST   terminate the GRE tunnel setup process as soon as it receives the GRE   Tunnel Setup Deny message.5.3.1.  Error Code   The HAAP uses the Error Code attribute to inform the HG of the error   code.  The error code depicts why the GRE Tunnel Setup Request is   denied.  Both the LTE GRE Tunnel Setup Deny message and the DSL GRE   Tunnel Setup Deny message MUST include the Error Code attribute.   +-+-+-+-+-+-+-+-+   |Attribute Type |                    (1 byte)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Attribute Length             |    (2 bytes)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+   |  Error Code                        (4 bytes)  |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+   Attribute Type      Error Code, set to 17.   Attribute Length      Set to 4.   Error Code      An unsigned integer.  The list of codes is as follows:      1:  The HAAP was not reachable over LTE during the GRE Tunnel          Setup Request.      2:  The HAAP was not reachable via DSL during the GRE Tunnel Setup          Request.      3:  The LTE GRE tunnel to the HAAP failed.Leymann, et al.               Informational                    [Page 24]

RFC 8157                   GRE Tunnel Bonding                   May 2017      4:  The DSL GRE tunnel to the HAAP failed.      5:  The given DSL User ID is not allowed to use the GRE Tunnel          Bonding service.      6:  The given User Alias / User ID (Globally Unique Identifier          (GUID)) is not allowed to use the GRE Tunnel Bonding service.      7:  The LTE and DSL User IDs do not match.      8:  The HAAP denied the GRE Tunnel Setup Request because a bonding          session with the same User ID already exists.      9:  The HAAP denied the GRE Tunnel Setup Request because the          user's CIN is not permitted.      10: The HAAP terminated a GRE Tunnel Bonding session for          maintenance reasons.      11: There was a communication error between the HAAP and the          management system during the LTE GRE Tunnel Setup Request.      12: There was a communication error between the HAAP and the          management system during the DSL GRE Tunnel Setup Request.5.4.  GRE Tunnel Hello   After the DSL/LTE GRE tunnel is established, the HG begins to   periodically send out GRE Tunnel Hello messages via the tunnel; the   HAAP acknowledges the HG's messages by returning GRE Tunnel Hello   messages to the HG.  This continues until the tunnel is terminated.5.4.1.  Timestamp   The HAAP uses the Timestamp attribute to inform the HG of the   timestamp value that is used for RTT calculation.  Both the LTE GRE   Tunnel Hello message and the DSL GRE Tunnel Hello message MUST   include the Timestamp attribute.   +-+-+-+-+-+-+-+-+   |Attribute Type |                    (1 byte)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Attribute Length             |    (2 bytes)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+   |  Timestamp                         (8 bytes)  |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+Leymann, et al.               Informational                    [Page 25]

RFC 8157                   GRE Tunnel Bonding                   May 2017   Attribute Type      Timestamp, set to 5.   Attribute Length      Set to 8.   Timestamp      The time since the system restarted.  The high-order 4 bytes      indicate an unsigned integer in units of 1 second; the low-order      4 bytes indicate an unsigned integer in units of 1 millisecond.5.4.2.  IPv6 Prefix Assigned by HAAP   The HAAP uses the IPv6 Prefix Assigned by HAAP attribute to inform   the HG of the assigned IPv6 prefix.  This IPv6 prefix is to be   captured via lawful intercept.  Both the LTE GRE Tunnel Hello message   and the DSL GRE Tunnel Hello message MUST include the IPv6 Prefix   Assigned by HAAP attribute.   +-+-+-+-+-+-+-+-+   |Attribute Type |                    (1 byte)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Attribute Length             |    (2 bytes)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+   |  IPv6 Prefix Assigned by HAAP      (16 bytes) |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+   Attribute Type      IPv6 Prefix Assigned by HAAP, set to 13.   Attribute Length      Set to 17.   IPv6 Prefix Assigned by HAAP      The highest-order 16 bytes encode an IPv6 address.  The      lowest-order 1 byte encodes the prefix length.  These two values      are put together to represent an IPv6 prefix.5.5.  GRE Tunnel Tear Down   The HAAP can terminate a DSL/LTE GRE tunnel by sending the GRE Tunnel   Tear Down message to the HG via the tunnel.  The Error Code attribute   as defined inSection 5.3.1 MUST be included in this message.  After   receiving the GRE Tunnel Tear Down message, the HG removes the IP   address of H, which is the destination IP addresses of the DSL and   LTE GRE tunnels.Leymann, et al.               Informational                    [Page 26]

RFC 8157                   GRE Tunnel Bonding                   May 20175.6.  GRE Tunnel Notify   The HG and the HAAP use the GRE Tunnel Notify message, which is   transmitted through either the DSL GRE tunnel or the LTE GRE tunnel,   to notify each other about their status regarding the DSL/LTE GRE   tunnels, the information for the bonded tunnels, the actions that   need to be taken, etc.   Usually, the receiver just sends the received attributes back as the   acknowledgement for each GRE Tunnel Notify message.  However, there   is an exception for the Filter List Package: since the size of the   Filter List Package attribute can be very large, a special attribute   -- the Filter List Package ACK attribute -- is used as the   acknowledgement (seeSection 5.6.12).   Attributes that need to be included in the GRE Tunnel Notify message   are defined below.5.6.1.  Bypass Traffic Rate   There are a few types of traffic that need to be transmitted over the   raw DSL WAN interface rather than the bonded GRE tunnels.  The HG has   to set aside bypass bandwidth on the DSL WAN interface for these   traffic types.  Therefore, the available bandwidth of the DSL GRE   tunnel is the entire DSL WAN interface bandwidth minus the occupied   bypass bandwidth.   The HG uses the Bypass Traffic Rate attribute to inform the HAAP of   the downstream bypass bandwidth for the DSL WAN interface.  The   Bypass Traffic Rate attribute will be included in the DSL GRE Tunnel   Notify message.  The HAAP calculates the available downstream   bandwidth for the DSL GRE tunnel as the Configured DSL Downstream   Bandwidth minus the bypass bandwidth provided by the HG.  The   available DSL bandwidth will be used as the CIR of the coloring   system [RFC2697].   +-+-+-+-+-+-+-+-+   |Attribute Type |                    (1 byte)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Attribute Length             |    (2 bytes)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+   |  Bypass Traffic Rate               (4 bytes)  |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+Leymann, et al.               Informational                    [Page 27]

RFC 8157                   GRE Tunnel Bonding                   May 2017   Attribute Type      Bypass Traffic Rate, set to 6.   Attribute Length      Set to 4.   Bypass Traffic Rate      An unsigned integer measured in kbps.5.6.2.  Filter List Package   The HAAP uses the Filter List Package attribute to inform the HG of   the service types that need to bypass the bonded GRE tunnels.  The   full list of all Filter Items may be given by a series of Filter List   Package attributes with each specifying a partial list.  At the HG, a   full list of Filter Items is maintained.  Also, the HG needs to   maintain an exception list of Filter Items.  For example, the packets   carrying the control messages defined in this document should be   excluded from the filter list.   Incoming packets that match a Filter Item in the filter list while   not matching any item in the exception list MUST be transmitted over   raw DSL rather than the bonded GRE tunnels.  Both the LTE GRE Tunnel   Notify message and the DSL GRE Tunnel Notify message MAY include the   Filter List Package attribute.  The DSL GRE Tunnel Notify message is   preferred.   +-+-+-+-+-+-+-+-+   |Attribute Type |                    (1 byte)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Attribute Length             |    (2 bytes)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+   |  Filter List TLV                   (variable) ~   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+   Attribute Type      Filter List Package, set to 8.   Attribute Length      The total length of the Filter List TLV.  The maximum allowed      length is 969 bytes.Leymann, et al.               Informational                    [Page 28]

RFC 8157                   GRE Tunnel Bonding                   May 2017   Filter List TLV      The Filter List TLV occurs one time in a Filter List Package      attribute.  It has the following format:    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   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                  Commit_Count                                 |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |      Packet_Sum               |         Packet_ID             |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                         Filter Item (1)                       |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                         ......                                |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |                         Filter Item (n)                       |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   where each Filter Item is of the following format:   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |         Type                  |          Length               |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |         Enable                |     Description Length        |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   ~                 Description Value                             ~   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   ~                        Value                                  ~   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      Commit_Count         An unsigned integer that identifies the version of the Filter         Item list.  The version is shared by all Filter List Packages         and increases monotonically by one for each new Filter Item         list.  The HG MUST refresh its Filter Item list when a new         Commit_Count is received.      Packet_Sum         If a single Filter List Package attribute might make the         control message larger than the MTU, fragmentation is used.         The Packet_Sum indicates the total number of fragments.      Packet_ID         The fragmentation index for this Filter List Package attribute.         Each fragment is numbered starting at 1 and increasing by one         up to Packet_Sum.Leymann, et al.               Informational                    [Page 29]

RFC 8157                   GRE Tunnel Bonding                   May 2017      Type         The Type of the Filter Item.  Currently, the following types         are supported:                       Filter Item                  Type                   ===========================   ============                   FQDN [RFC7031]                    1                   DSCP [RFC2724]                    2                   Destination Port                  3                   Destination IP                    4                   Destination IP & Port             5                   Source Port                       6                   Source IP                         7                   Source IP & Port                  8                   Source MAC                        9                   Protocol                          10                   Source IP Range                   11                   Destination IP Range              12                   Source IP Range & Port            13                   Destination IP Range & Port       14         Other values are reserved for future use and MUST be ignored on         receipt.      Length         The length of the Filter Item in bytes.  Type and Length are         excluded.      Enable         An integer that indicates whether or not the Filter Item is         enabled.  A value of 1 means "enabled", and a value of 0 means         "disabled".  Other possible values are reserved and MUST be         ignored on receipt.      Description Length         The length of the Description Value in bytes.      Description Value         A variable-length string value encoded in UTF-8 that describes         the Filter List TLV (e.g., "FQDN").      Value         A variable-length string encoded in UTF-8 that specifies the         value of the Filter Item (e.g., "www.yahoo.com").  As an         example, Type = 1 and Value = "www.yahoo.com" mean that packets         whose FQDN field equals "www.yahoo.com" match the Filter Item.         "Source MAC" (source Media Access Control address) values are         specified using hexadecimal numbers.  Port numbers are decimalsLeymann, et al.               Informational                    [Page 30]

RFC 8157                   GRE Tunnel Bonding                   May 2017         as assigned by IANA in [Port-NO].  For the "Protocol" type, the         value could be either a decimal or a keyword specified by IANA         in [Pro-NO].  The formats for IP addresses and IP address         ranges are defined in [RFC4632] and [RFC4291] for IPv4 and         IPv6, respectively.  A Filter Item of Type 5, 8, 13, or 14 is a         combination of two parameters; values for the two parameters         are separated by a colon (":").5.6.3.  Switching to DSL Tunnel   If the RTT difference is continuously detected to be in violation of   the RTT Difference Threshold (seeSection 5.2.4) more than the number   of times specified in the RTT Difference Threshold Violation   attribute (seeSection 5.2.12), the HG uses the Switching to DSL   Tunnel attribute to inform the HAAP to use the DSL GRE tunnel only.   When the HAAP receives this attribute, it MUST begin to transmit   downstream traffic to this HG solely over the DSL GRE tunnel.  The   DSL GRE Tunnel Notify message MAY include the Switching to DSL Tunnel   attribute.   +-+-+-+-+-+-+-+-+   |Attribute Type |                    (1 byte)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Attribute Length             |    (2 bytes)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Attribute Type      Switching to DSL Tunnel, set to 11.   Attribute Length      Set to 0.5.6.4.  Overflowing to LTE Tunnel   If the RTT difference is continuously detected to not be in violation   of the RTT Difference Threshold (seeSection 5.2.4) more than the   number of times specified in the RTT Difference Threshold Compliance   attribute (seeSection 5.2.13), the HG uses the Overflowing to LTE   Tunnel attribute to inform the HAAP that the LTE GRE tunnel can be   used again.  The DSL GRE Tunnel Notify message MAY include the   Overflowing to LTE Tunnel attribute.   +-+-+-+-+-+-+-+-+   |Attribute Type |                    (1 byte)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Attribute Length             |    (2 bytes)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+Leymann, et al.               Informational                    [Page 31]

RFC 8157                   GRE Tunnel Bonding                   May 2017   Attribute Type      Overflowing to LTE Tunnel, set to 12.   Attribute Length      Set to 0.5.6.5.  DSL Link Failure   When the HG detects that the DSL WAN interface status is "down", it   MUST tear down the DSL GRE tunnel.  It informs the HAAP about the   failure by using the DSL Link Failure attribute.  The HAAP MUST   tear down the DSL GRE tunnel upon receipt of the DSL Link Failure   attribute.  The DSL Link Failure attribute SHOULD be carried in the   LTE GRE Tunnel Notify message.   +-+-+-+-+-+-+-+-+   |Attribute Type |                    (1 byte)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Attribute Length             |    (2 bytes)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Attribute Type      DSL Link Failure, set to 18.   Attribute Length      Set to 0.5.6.6.  LTE Link Failure   When the HG detects that the LTE WAN interface status is "down", it   MUST tear down the LTE GRE tunnel.  It informs the HAAP about the   failure by using the LTE Link Failure attribute.  The HAAP MUST   tear down the LTE GRE tunnel upon receipt of the LTE Link Failure   attribute.  The LTE Link Failure attribute SHOULD be carried in the   DSL GRE Tunnel Notify message.   +-+-+-+-+-+-+-+-+   |Attribute Type |                    (1 byte)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Attribute Length             |    (2 bytes)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Attribute Type      LTE Link Failure, set to 19.   Attribute Length      Set to 0.Leymann, et al.               Informational                    [Page 32]

RFC 8157                   GRE Tunnel Bonding                   May 20175.6.7.  IPv6 Prefix Assigned to Host   If the HG changes the IPv6 prefix assigned to the host, it uses the   IPv6 Prefix Assigned to Host attribute to inform the HAAP.  Both the   LTE GRE Tunnel Notify message and the DSL GRE Tunnel Notify message   MAY include the IPv6 Prefix Assigned to Host attribute.   +-+-+-+-+-+-+-+-+   |Attribute Type |                    (1 byte)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Attribute Length             |    (2 bytes)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+   |  IPv6 Prefix Assigned to Host      (16 bytes) |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+   Attribute Type      IPv6 Prefix Assigned to Host, set to 21.   Attribute Length      Set to 17.   IPv6 Prefix Assigned to Host      The highest-order 16 bytes encode an IPv6 address.  The      lowest-order 1 byte encodes the prefix length.  These two values      are put together to represent an IPv6 prefix.5.6.8.  Diagnostic Start: Bonding Tunnel   The HG uses the Diagnostic Start: Bonding Tunnel attribute to inform   the HAAP to switch to diagnostic mode to test the performance of the   entire bonding tunnel.  The Diagnostic Start: Bonding Tunnel   attribute SHOULD be carried in the DSL GRE Tunnel Notify message.   +-+-+-+-+-+-+-+-+   |Attribute Type |                    (1 byte)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Attribute Length             |    (2 bytes)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Attribute Type      Diagnostic Start: Bonding Tunnel, set to 26.   Attribute Length      Set to 0.Leymann, et al.               Informational                    [Page 33]

RFC 8157                   GRE Tunnel Bonding                   May 20175.6.9.  Diagnostic Start: DSL Tunnel   The HG uses the Diagnostic Start: DSL Tunnel attribute to inform the   HAAP to switch to diagnostic mode to test the performance of the DSL   GRE tunnel.  The Diagnostic Start: DSL Tunnel attribute SHOULD be   carried in the DSL GRE Tunnel Notify message.   +-+-+-+-+-+-+-+-+   |Attribute Type |                    (1 byte)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Attribute Length             |    (2 bytes)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Attribute Type      Diagnostic Start: DSL Tunnel, set to 27.   Attribute Length      Set to 0.5.6.10.  Diagnostic Start: LTE Tunnel   The HG uses the Diagnostic Start: LTE Tunnel attribute to inform the   HAAP to switch to diagnostic mode to test the performance of the   LTE GRE tunnel.  The Diagnostic Start: LTE Tunnel attribute SHOULD be   carried in the DSL GRE Tunnel Notify message.   +-+-+-+-+-+-+-+-+   |Attribute Type |                    (1 byte)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Attribute Length             |    (2 bytes)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Attribute Type      Diagnostic Start: LTE Tunnel, set to 28.   Attribute Length      Set to 0.Leymann, et al.               Informational                    [Page 34]

RFC 8157                   GRE Tunnel Bonding                   May 20175.6.11.  Diagnostic End   The HG uses the Diagnostic End attribute to inform the HAAP to stop   operating in diagnostic mode.  The Diagnostic End attribute SHOULD be   carried in the DSL GRE Tunnel Notify message.   +-+-+-+-+-+-+-+-+   |Attribute Type |                    (1 byte)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Attribute Length             |    (2 bytes)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Attribute Type      Diagnostic End, set to 29.   Attribute Length      Set to 0.5.6.12.  Filter List Package ACK   The HG uses the Filter List Package ACK attribute to acknowledge the   Filter List Package sent by the HAAP.  Both the LTE GRE Tunnel Notify   message and the DSL GRE Tunnel Notify message MAY include the Filter   List Package ACK attribute.   +-+-+-+-+-+-+-+-+   |Attribute Type |                    (1 byte)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Attribute Length             |    (2 bytes)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+   |  Filter List Package ACK           (5 bytes)  |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+   Attribute Type      Filter List Package ACK, set to 30.   Attribute Length      Set to 5.Leymann, et al.               Informational                    [Page 35]

RFC 8157                   GRE Tunnel Bonding                   May 2017   Filter List Package ACK      The highest-order 4 bytes are the Commit_Count as defined inSection 5.6.2.  The lowest-order 1 byte encodes the following      error codes:      0: The Filter List Package is acknowledged.      1: The Filter List Package is not acknowledged.  The HG is a new         subscriber and has not ever received a Filter List Package.  In         this case, the HAAP SHOULD tear down the bonding tunnels and         force the HG to re-establish the GRE tunnels.      2: The Filter List Package is not acknowledged.  The HG has         already gotten a valid Filter List Package.  The filter list on         the HG will continue to be used, while the HAAP need not do         anything.5.6.13.  Switching to Active Hello State   If traffic is being sent/received over the bonding GRE tunnels before   the "No Traffic Monitored Interval" expires (seeSection 5.2.15), the   HG sends the HAAP a GRE Tunnel Notify message containing the   Switching to Active Hello State attribute.   The HAAP will switch to Active Hello State and send the HG a GRE   Tunnel Notify message carrying the Switching to Active Hello State   attribute as the ACK.   When the HG receives the ACK, it will switch to Active Hello State,   start RTT detection, and start sending GRE Tunnel Hello messages with   the Active Hello Interval (seeSection 5.2.6).   +-+-+-+-+-+-+-+-+   |Attribute Type |                    (1 byte)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Attribute Length             |    (2 bytes)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Attribute Type      Switching to Active Hello State, set to 33.   Attribute Length      Set to 0.Leymann, et al.               Informational                    [Page 36]

RFC 8157                   GRE Tunnel Bonding                   May 20175.6.14.  Switching to Idle Hello State   The HG initiates switching to Idle Hello State when the bonding of   GRE tunnels is successfully established and the LTE GRE Tunnel Setup   Accept message carrying the Idle Hello Interval attribute (seeSection 5.2.14) is received.  The HG sends the HAAP a GRE Tunnel   Notify message containing the Switching to Idle Hello State   attribute.   The HAAP will switch to Idle Hello State, clear RTT state, and send   the HG a GRE Tunnel Notify message carrying the Switching to Idle   Hello State attribute as the ACK.   When the HG receives the ACK, it will (1) switch to Idle Hello State,   (2) stop RTT detection and clear RTT state, and (3) start sending GRE   Tunnel Hello messages with the Idle Hello Interval (seeSection 5.2.14).   +-+-+-+-+-+-+-+-+   |Attribute Type |                    (1 byte)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Attribute Length             |    (2 bytes)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Attribute Type      Switching to Idle Hello State, set to 34.   Attribute Length      Set to 0.5.6.15.  Tunnel Verification   The HAAP uses the Tunnel Verification attribute to inform the HG to   verify whether an existing LTE GRE tunnel is still functioning.  The   Tunnel Verification attribute SHOULD be carried in the LTE GRE Tunnel   Notify message.  It provides a means to detect the tunnel faster than   the GRE Tunnel Hello, especially when the LTE GRE tunnel is in the   Idle Hello State and it takes a much longer time to detect this   tunnel.   When the HAAP receives an LTE GRE Tunnel Setup Request and finds that   the requested tunnel conflicts with an existing tunnel, the HAAP   initiates tunnel verification.  The HAAP drops all conflicting LTE   GRE Tunnel Setup Request messages and sends GRE Tunnel Notify   messages carrying the Tunnel Verification attribute until the   verification ends.  The HG MUST respond to the HAAP with the same   Tunnel Verification attribute as the ACK if the tunnel is still   functioning.Leymann, et al.               Informational                    [Page 37]

RFC 8157                   GRE Tunnel Bonding                   May 2017   If the ACK of the Tunnel Verification attribute is received from the   HG, the HAAP determines that the existing tunnel is still   functioning.  An LTE GRE Tunnel Deny message (with Error Code = 8)   will be sent to the HG.  The HG SHOULD terminate the GRE Tunnel Setup   Request process immediately.   If the HAAP does not receive a tunnel verification ACK message after   three attempts (one initial attempt and two retries), it will regard   the existing tunnel as failed, and the LTE GRE Tunnel Setup Request   will be accepted.   +-+-+-+-+-+-+-+-+   |Attribute Type |                    (1 byte)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Attribute Length             |    (2 bytes)   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Attribute Type      Tunnel Verification, set to 35.   Attribute Length      Set to 0.6.  Tunnel Protocol Operation (Data Plane)   GRE tunnels are set up over heterogeneous connections, such as LTE   and DSL, between the HG and the HAAP.  Users' IP (inner) packets are   encapsulated in GRE packets that are in turn carried in IP (outer)   packets.  The general structure of data packets of the GRE Tunnel   Bonding Protocol is shown below.                  +--------------------------------+                  |          Media Header          |                  +--------------------------------+                  |         Outer IP Header        |                  +--------------------------------+                  |           GRE Header           |                  +--------------------------------+                  |         Inner IP Packet        |                  +--------------------------------+6.1.  The GRE Header   The GRE header was first standardized in [RFC2784].  [RFC2890] added   the optional Key and Sequence Number fields.   The Checksum and the Reserved1 fields are not used in the GRE Tunnel   Bonding; therefore, the C bit is set to 0.Leymann, et al.               Informational                    [Page 38]

RFC 8157                   GRE Tunnel Bonding                   May 2017   The Key bit is set to 1 so that the Key field is present.  The Key   field is used as a 32-bit random number.  It is generated by the HAAP   per bonding connection, and the HG is notified (seeSection 5.2.9).   The S bit is set to 1, and the Sequence Number field is present and   used for in-order delivery as per [RFC2890].   The Protocol Type field in the GRE header MUST be set to 0x0800 for   IPv4 or 0x86DD for IPv6.  So, the GRE header used by data packets of   the GRE Tunnel Bonding Protocol has the following format:      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     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+     |0| |1|1| Reserved0       | Ver |  Protocol Type 0x0800/86DD    |     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+     |                              Key                              |     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+     |                        Sequence Number                        |     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+        Figure 3: GRE Header for Data Packets of GRE Tunnel Bonding6.2.  Automatic Setup of GRE Tunnels   The HG gets the DSL WAN interface IP address (D) from the Broadband   Remote Access Server (BRAS) via the Point-to-Point Protocol over   Ethernet (PPPoE) and gets the LTE WAN interface IP address (E)   through the Packet Data Protocol (PDP) from the Packet Data Network   Gateway (PGW).  The domain name of a HAAP group may be configured or   obtained via the DSL/LTE WAN interface based on gateway configuration   protocols such as [TR-069], where the HAAP group comprises one or   multiple HAAPs.  The Domain Name System (DNS) resolution of the HAAP   group's domain name is requested via the DSL/LTE WAN interface.  The   DNS server will reply with an anycast HAAP IP address (G), which MAY   be pre-configured by the operator.   After the interface IP addresses have been acquired, the HG starts   the following GRE Tunnel Bonding procedure.  It is REQUIRED that the   HG first set up the LTE GRE tunnel and then set up the DSL GRE   tunnel.   The HG sends the GRE Tunnel Setup Request message to the HAAP via the   LTE WAN interface.  The outer source IP address for this message is   the LTE WAN interface IP address (E), while the outer destination IP   address is the anycast HAAP IP address (G).  The HAAP with the   highest priority (e.g., the one that the HG has the least-cost path   to reach) in the HAAP group, which receives the GRE Tunnel SetupLeymann, et al.               Informational                    [Page 39]

RFC 8157                   GRE Tunnel Bonding                   May 2017   Request message, will initiate the procedure for authentication and   authorization, as specified in [TS23.401], to check whether the HG is   trusted by the PGW.   If the authentication and authorization succeed, the HAAP sets the   LTE WAN interface IP address (E), which is obtained from the GRE   Tunnel Setup Request message (i.e., its outer source IP address), as   the destination endpoint IP address of the GRE tunnel and replies to   the HG's LTE WAN interface with the GRE Tunnel Setup Accept message   in which an IP address (H) of the HAAP (e.g., an IP address of a Line   Card in the HAAP) and a Session ID randomly generated by the HAAP are   carried as attributes.  The outer source IP address for this message   is the IP address (H) or the anycast HAAP IP address (G), while the   outer destination IP address is the LTE WAN interface IP address (E).   Otherwise, the HAAP MUST send to the HG's LTE WAN interface the GRE   Tunnel Setup Deny message, and the HG MUST terminate the tunnel setup   process once it receives the GRE Tunnel Setup Deny message.   After the LTE GRE tunnel is successfully set up, the HG will obtain   the C address (see Figure 1) over the tunnel from the HAAP through   the Dynamic Host Configuration Protocol (DHCP).  After that, the HG   starts to set up the DSL GRE tunnel.  It sends a GRE Tunnel Setup   Request message via the DSL WAN interface, carrying the   aforementioned Session ID received from the HAAP.  The outer source   IP address for this message is the DSL WAN interface IP address (D),   while the outer destination IP address is the IP address (H) of the   HAAP.  The HAAP, which receives the GRE Tunnel Setup Request message,   will initiate the procedure for authentication and authorization in   order to check whether the HG is trusted by the BRAS.   If the authentication and authorization succeed, the HAAP sets the   DSL WAN interface IP address (D), which is obtained from the GRE   Tunnel Setup Request message (i.e., its outer source IP address), as   the destination endpoint IP address of the GRE tunnel and replies to   the HG's DSL WAN interface with the GRE Tunnel Setup Accept message.   The outer source IP address for this message is the IP address (H) of   the HAAP, while the outer destination IP address is the DSL WAN   interface IP address (D).  In this way, the two tunnels with the same   Session ID can be used to carry traffic from the same user.  That is   to say, the two tunnels are "bonded" together.  Otherwise, if the   authentication and authorization fail, the HAAP MUST send to the HG's   DSL WAN interface the GRE Tunnel Setup Deny message.  Meanwhile, it   MUST send to the HG's LTE WAN interface the GRE Tunnel Tear Down   message.  The HG MUST terminate the tunnel setup process once it   receives the GRE Tunnel Setup Deny message and MUST tear down the LTE   GRE tunnel that has been set up once it receives the GRE Tunnel   Tear Down message.Leymann, et al.               Informational                    [Page 40]

RFC 8157                   GRE Tunnel Bonding                   May 20177.  Security Considerations   Malicious devices controlled by attackers may intercept the control   messages sent on the GRE tunnels.  Later on, the rogue devices may   fake control messages to disrupt the GRE tunnels or attract traffic   from the target HG.   As a security feature, the Key field of the GRE header of the control   messages and the data packets is generated as a 32-bit cleartext   password, except for the first GRE Setup Request message per bonding   connection sent from the HG to the HAAP, whose Key field is filled   with all zeros.  The HAAP and the HG validate the Key value and the   outer source IP address, and they discard any packets with invalid   combinations.   Moreover, GRE over IP Security (IPsec) could be used to enhance   security.8.  IANA Considerations   IANA need not assign anything for the GRE Tunnel Bonding Protocol.   The GRE Protocol Type, the Ethertype for the GRE Channel, is set to   0xB7EA, which is under the control of the IEEE Registration   Authority.  However, IANA has updated the "IEEE 802 Numbers" IANA web   page [802Type], which is of primarily historic interest.9.  References9.1.  Normative References   [Port-NO]  IANA, "Service Name and Transport Protocol Port Number              Registry", <http://www.iana.org/assignments/service-names-port-numbers>.   [Pro-NO]   IANA, "Assigned Internet Protocol Numbers",              <http://www.iana.org/assignments/protocol-numbers>.   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119,              DOI 10.17487/RFC2119, March 1997,              <http://www.rfc-editor.org/info/rfc2119>.   [RFC2697]  Heinanen, J. and R. Guerin, "A Single Rate Three Color              Marker",RFC 2697, DOI 10.17487/RFC2697, September 1999,              <http://www.rfc-editor.org/info/rfc2697>.Leymann, et al.               Informational                    [Page 41]

RFC 8157                   GRE Tunnel Bonding                   May 2017   [RFC2784]  Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.              Traina, "Generic Routing Encapsulation (GRE)",RFC 2784,              DOI 10.17487/RFC2784, March 2000,              <http://www.rfc-editor.org/info/rfc2784>.   [RFC2890]  Dommety, G., "Key and Sequence Number Extensions to GRE",RFC 2890, DOI 10.17487/RFC2890, September 2000,              <http://www.rfc-editor.org/info/rfc2890>.   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing              Architecture",RFC 4291, DOI 10.17487/RFC4291,              February 2006, <http://www.rfc-editor.org/info/rfc4291>.   [RFC4632]  Fuller, V. and T. Li, "Classless Inter-domain Routing              (CIDR): The Internet Address Assignment and Aggregation              Plan",BCP 122,RFC 4632, DOI 10.17487/RFC4632,              August 2006, <http://www.rfc-editor.org/info/rfc4632>.   [TR-069]   Broadband Forum, "CPE WAN Management Protocol", Issue: 1              Amendment 5, November 2013,              <https://www.broadband-forum.org/technical/download/TR-069_Amendment-5.pdf>.   [TS23.401] 3GPP TS23.401, "General Packet Radio Service (GPRS)              enhancements for Evolved Universal Terrestrial Radio              Access Network (E-UTRAN) access", v11.7.0, September 2013.9.2.  Informative References   [802Type]  IANA, "IEEE 802 Numbers",              <http://www.iana.org/assignments/ieee-802-numbers>.   [ANSI-X9.31-1998]              ANSI Standard X9.31-1998, "Digital Signatures Using              Reversible Public Key Cryptography for the Financial              Services Industry (rDSA)", 1998.   [RFC2724]  Handelman, S., Stibler, S., Brownlee, N., and G. Ruth,              "RTFM: New Attributes for Traffic Flow Measurement",RFC 2724, DOI 10.17487/RFC2724, October 1999,              <http://www.rfc-editor.org/info/rfc2724>.   [RFC6320]  Wadhwa, S., Moisand, J., Haag, T., Voigt, N., and T.              Taylor, Ed., "Protocol for Access Node Control Mechanism              in Broadband Networks",RFC 6320, DOI 10.17487/RFC6320,              October 2011, <http://www.rfc-editor.org/info/rfc6320>.Leymann, et al.               Informational                    [Page 42]

RFC 8157                   GRE Tunnel Bonding                   May 2017   [RFC6733]  Fajardo, V., Ed., Arkko, J., Loughney, J., and G. Zorn,              Ed., "Diameter Base Protocol",RFC 6733,              DOI 10.17487/RFC6733, October 2012,              <http://www.rfc-editor.org/info/rfc6733>.   [RFC7031]  Mrugalski, T. and K. Kinnear, "DHCPv6 Failover              Requirements",RFC 7031, DOI 10.17487/RFC7031,              September 2013, <http://www.rfc-editor.org/info/rfc7031>.   [RFC7676]  Pignataro, C., Bonica, R., and S. Krishnan, "IPv6 Support              for Generic Routing Encapsulation (GRE)",RFC 7676,              DOI 10.17487/RFC7676, October 2015,              <http://www.rfc-editor.org/info/rfc7676>.Contributors   Li Xue   Individual   Email: xueli_jas@163.com   Zhongwen Jiang   Huawei Technologies   Email: jiangzhongwen@huawei.comLeymann, et al.               Informational                    [Page 43]

RFC 8157                   GRE Tunnel Bonding                   May 2017Authors' Addresses   Nicolai Leymann   Deutsche Telekom AG   Winterfeldtstrasse 21-27   Berlin  10781   Germany   Phone: +49-170-2275345   Email: n.leymann@telekom.de   Cornelius Heidemann   Deutsche Telekom AG   Heinrich-Hertz-Strasse 3-7   Darmstadt  64295   Germany   Phone: +49-6151-5812721   Email: heidemannc@telekom.de   Mingui Zhang   Huawei Technologies   No. 156 Beiqing Rd.   Haidian District   Beijing  100095   China   Email: zhangmingui@huawei.com   Behcet Sarikaya   Huawei USA   5340 Legacy Dr. Building 3   Plano, TX  75024   United States of America   Email: sarikaya@ieee.org   Margaret Cullen   Painless Security   14 Summer St. Suite 202   Malden, MA  02148   United States of America   Email: margaret@painless-security.comLeymann, et al.               Informational                    [Page 44]