Segment routing for SD-WAN paths over hybrid networks
draft-dunbar-sr-sdwan-over-hybrid-networks-01

' head-
   end selected route traversing through a list of specific nodes of
   multiple network segments without requiring the nodes in each

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   network segment to have the intelligence (or maintaining states) of
   selecting next hop or next domain.

   There may be two approaches here:
   1) Controller installs the entire SID stack at E1.
   2) Controller delivers to E1 a "Key" that the SR ingress PE can use
   to map to the SID stack for the packets arriving at the SR Ingress
   PE. Section 4.2 & 4.3 will describe how the "Key" is carried by the
   packets.

   The Approach 1) requires less processing at the SR Ingress PE nodes,
   but only works if the remote CPEs are in the same Administrative
   domain as the SR domain. SR domain usually is not willing to expose
   its internal binding SIDs to devices in different administration
   domains. This approach also requires more changes to SD-WAN end
   nodes and need more header bytes added to the packets when                            rd        traversing through 3  party internet. Some SD-WAN nodes might not be
   capable of supporting encapsulating packets with the SID stack.

   The Approach 2) above requires SR Ingress PE nodes to map the "Key"
   to the SID Stack and prepend the SID stack to the packets (Same
   processing for other traffic except the mapping is from the received
   "Key" carried in the payload).

4.1. Controller Delivers SID Stack to SD-WAN Head-end

   This approach is straightforward.

         E1  -------------------------- > SD-WAN controller
            request for a SD-WAN path E1<->E2 with a specific SLA

         E1  <--------------------------  SD-WAN controller
            Reply with the Ingress PE Node ID or address
            & the Binding SID.

   Here is the packet header for SD-WAN Source Node to prepend to the
   payload:

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       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

      IPv4 Header:
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |Version|  IHL  |Type of Service|          Total Length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Identification        |Flags|      Fragment Offset    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Time to Live | Prot.=17(UDP) |          Header Checksum      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |               SD-WAN Source IPv4 Address                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |              SR Ingress PE IPv4 Address                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      UDP Header:
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Source Port =              |  Dest. Port = 4754/4755       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           UDP Length          |        UDP Checksum           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      GRE Header:
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |C| |K|S| Reserved0       | Ver |         Protocol Type         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      Checksum (optional)      |       Reserved1 (Optional)    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Key (optional)                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Sequence Number (optional)                    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   To traverse SRv6 domain, SRv6 Header is appended after the GRE
   header [SRv6-SRH]:

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   To traverse MPLS-SR domain, a stack of MPLS labels is appended after
   GRE Header [MPLS-SR].

4.2. Using GRE Key to Differentiate Flows

   This section describes a method of SD-WAN head-end node using GRE
   Key to indicate the desired property for different flows between SD-
   WAN end-points (E1<->E2 in the figure above): such as different
   desired routes through the SR Domain, different egress PEs based on
   cost, performance or other factors.  It might be difficult or
   impossible to DiffServ bits carried by the packets to describe those
   flow properties.

   The SR Domain ingress can map the GRE key to different SID through
   the SR Domain.

   We assume that the SD-WAN Controller can determine which ingress PE
   can lead to the optimal path between E1<->E2. It is beyond the scope
   of this document on how SD-WAN controller computes the paths and how
   & what SD-WAN controller communicates with the SR Domain controller.

   Here is the sequence of the flow:

         E1  -------------------------- > SD-WAN controller
            request for a SD-WAN path E1<->E2 with a specific SLA

         E1  <--------------------------  SD-WAN controller
            Reply with the Ingress PE Node ID or address
            & the GRE Key.

   Note: the GRE key from the SD-WAN controller is for the ingress PE
   to correlate desired Path with the list of SIDs to prepend the
   packet across the SR domain.

   When SD-WAN Controller get the E1<->E2 path request, it will
   communicate with the VPN Controller to get the optimal Ingress PE

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   Node ID (or IP address) and the GRE key to encapsulate the original
   packets between E1 <-> E2 (assuming IPsec Tunnel mode is used).

   Upon receiving the GRE encapsulated packets, the provider ingress
   Edge C1/C3 decapsulates the outer GRE tunnel header, use the GRE key
   to map to the pre-defined (by the network controller) Binding SIDs,
   prepend the Binding SIDs to the packets, and forward its desired
   paths across the provider VPN.

   Depending on how the SD-WAN path destination can be reached by the
   egress PE, the egress PE has different processing procedure:

      - If the destination of the SD-WAN path is directly attached to the
        egress VPN PE node, the egress VPN PE decapsulates SR header and
        forward the packets to SD-WAN path destination node, such as the E2
        in the figure above.
      - If the destination of the SD-WAN path is IP reachable via IPv4
        network from the egress VPN PE node, the egress VPN PE node
        decapsulates SR header and forward the packets to SD-WAN path
        destination node via its internet facing port to the SD-WAN path
        destination (i.e. the E2 node in the figure above).
      - If the SD-WAN path is traversing multiple domains owned by different
        network operators, the egress PE processing is described in the next
        session.

   4.3. Using UDP Source Port Number to Differentiate Flows

   [RFC8086] describes how to use GRE-in-UDP source port number as
   entropy for better ECMP performance. When the remotely attached CPEs
   is within very close proximity to the PEs, e.g. only one or two
   hopes away like in LTE access, there is less issue if ECMP put all
   flows with same traffic classifier into one path.  Then, those UDP
   numbers can also be used as a key to SR PE nodes to map to the
   appropriate SID to the packets.

   Same as RFC8086, UDP source port values used as a key for SR PEs to
   map to appropriate SIDs SHOULD be chosen from the ephemeral port
   range (49152-65535) [RFC8085].

   The GRE-in-UDP encapsulation format contains a UDP header [RFC768]
   and a GRE header [RFC2890].  The format is shown as follow
   (presented in bit order):

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       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

      IPv4 Header:
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |Version|  IHL  |Type of Service|          Total Length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Identification        |Flags|      Fragment Offset    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Time to Live | Prot.=17(UDP) |          Header Checksum      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |               SD-WAN Source IPv4 Address                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |              SR Ingress PE IPv4 Address                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      UDP Header:
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Source Port = SIDs key Value |  Dest. Port = 4754/4755       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           UDP Length          |        UDP Checksum           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      GRE Header:
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |C| |K|S| Reserved0       | Ver |         Protocol Type         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      Checksum (optional)      |       Reserved1 (Optional)    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Key (optional)                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Sequence Number (optional)                    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 3: UDP + GRE Headers in IPv4

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   Here is the GRE Header for IPv6 network, i.e. the SD-WAN Source SD-
   WAN Destination, and SR PEs are all in IPv6 domain:

       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

      IPv6 Header:
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |Version| Traffic Class |           Flow Label                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Payload Length        | NxtHdr=17(UDP)|   Hop Limit   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +                                                               +
      |                                                               |
      +                     SD-WAN Source IPv6 Address                +
      |                                                               |
      +                                                               +
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +                                                               +
      |                                                               |
      +               SR Domain Ingress PE IPv6 Address               +
      |                                                               |
      +                                                               +
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      UDP Header:
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Source Port = SIDs key value |  Dest. Port = 4754/4755       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           UDP Length          |        UDP Checksum           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      GRE Header:
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |C| |K|S| Reserved0       | Ver |         Protocol Type         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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      |      Checksum (optional)      |       Reserved1 (Optional)    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Key (optional)                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Sequence Number (optional)                    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 4: GRE+UDP for IPv6

   4.4. GRE Header Extension

   A new protocol type can be added to the GRE header [RFC2890] to make
   it easier for the SR PE to do the proper actions:

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |C|       Reserved0       | Ver |         Protocol Type         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |      Checksum (optional)      |       Reserved1 (Optional)    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      The proposed GRE header will have the following format:

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |C| |K|S| Reserved0       | Ver |         Protocol Type         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      Checksum (optional)      |       Reserved1 (Optional)    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Key (optional)                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Sequence Number (Optional)                    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   New protocol type (value to be assigned by IANA):
     UDP-Key: Using UDP source port value as a Key for SR Ingress PE to
   map to the appropriate SIDs.

     GRE-KEY: Using GRE Key value as a key for SR ingress PE to map to
   the appropriate SIDs

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5. SD-WAN path over multiple SP managed domains
   The following figure shows a SD-WAN Path E1<->E2 over two SP domains
   which are interconnected by public internet.

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   +------------+
   |   SDWAN    |                                      /-----------/
   |  Control   |                                     / [SDWAN-C]...
   +---+--------+                                    /           / :
       |                                            /-----------/  :
       |                        SD-WAN Overlay                     :
       |          /-------------------------------------------/    :
       |         /                                           /     :
       |        /    [A]-----[E1]***********[E2]--------[Z] /      :
   +---+       /               *              :            /       :
   |   |      /                *******        :           /        :
   |   |     /-----------------------*--------:----------/         :
   |   |              /----------/   *        .. .. .. .. .. :.    :
   | +-+--------+    /          /    *                        :    :
   | |  SP-1    |   /  [SR-C]  /     *                         :   :
   | |Control   |  /     :    /      *                         :   :
   | +----------+ /------:---/   *****                         :   :
   | +----------+        :   /---*---*-----------------------/ :   :
   | |   SP-1   |        :  /    *   *                      /  :   :
   | |Underlay  |        : /   [C1]-[C3]------[C4]-[C6]    /   :   :
   | +----------+        :/       \           /*   /      /    :   :
   |                     :         \      /--/-*--/      /     :   :
   | +----------+       /:          \    /     *        /      :   :
   +-+  SP-2    |      / :...........[C2]    *         /       :   :
     |Control   |     /-------------**-----*----------/        :   :
     +----------+                  * *   *       .. .. .. .. ..:   :
                                  *    *         :                 :
   +------------+            /---*---*---------:-------------/     :
   |     SP-2   |           /    *   *         :            /      :
   |  Underlay  |          /   [D1]-[D4]------[D2]-[D5]    /       :
   +------------+         /       \           /    /      /        :
                         /         \      /--/----/      /         :
                        /           \    /              /          :
                       /             [D3]..........................:
                      /                               /
                     /-------------------------------/
            Figure 5: SD-WAN path over two different SP domains

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   Let's assume that the SP-1 domain's egress node for the SD-WAN path
   E1<->E2 is C2, which can reach D1 or D4 of SP-2 via public IP
   network (say IPv4 network).

   Let's also assume that the optimal route for some flows over SD-WAN
   path E1<->E2 are C1->C2->D1 and other flows are over C1->C2->D4 (out
   of the scope of this document on how the path is calculated).

   If SP-1 is SR enabled, the mechanism described in Section 4 is
   applicable to the SD-WAN path source node E1 and the SP-1's ingress
   PE (e.g. C1 or C3 in the figure).
   However, the processing at egress node might be different depending
   on how the SP-1's egress edges are connected to the SP-2's ingress
   edge nodes.

5.1. When Both SP domains support SR

   There may be three approaches here:

   1) Controller installs the entire SID stack at E1, and the SID list
   contains SID entries belong to both domains.

   2) Controller delivers to E1 the SID stack that only for the first
   domain, but delivers to C6 (egress node of first domain) the binding
   SID of the second domain.

   3) Controller delivers a "Key" to E1, which can be encoded as GRE
   KEY or represented by the Source UDP port of the GRE encapsulation,
   for Ingress PE of the first SR Domain to map to its own SID stack as
   described in Section 4. The first SR Domain will reserve the "Key"
   through its domain and pass the "Key" to the second SR domain. The
   second SR Domain Ingress node will use the same method to map the
   "Key" to its SID stack.

5.2. When SP-2 does not support SR

   Under this circumstance (which can be caused by SP-2 not supporting
   SR or not willing to share Binding SIDs to SP-1), if the packets
   arriving at SP-1 egress node C6 do not have any metadata indicating
   the types of encrypted payload, C6 does not really have much choice

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   other than simply forwarding the packets to E2 via public IP
   network. This way, the packets may or may not traverse through the
   SP-2 domain. If the distance between C6 and E2 is far, the quality
   of service can be unpredictable.

5.3. When SP-1 and SP-2 don't want to share network information

   If SP-1's ingress node C1 can include the GRE KEY it receives from
   E1 in the data packets' SR header, the SP-1's egress node can map
   the Key to the SP-2's Ingress node and encapsulate the data packet
   in a new GRE header destined towards the SP-2's Ingress node. Then
   the SP-2's Ingress node can follow the procedure described in the
   Section 4 to forward the data packets across its domain.

   If the first SR Domain does not support adding metadata to carry the
   "key" through its domain, the controller can deliver the "key" to
   SP-1's egress node the same time as it delivers the key to E1,
   knowing the SD-WAN path will need to traverse two domains with the
   second one does support SR but the two SPs don't want to exchange
   network information.

5.4. TLV to pass Metadata through SRv6 Domain

   If SP-1 is SRv6 based, the ingress node C1 can append a TLV to the
   end of the SR Header [SRv6-SRH] to carry the KEY it receives from
   E1[Dc1].

   The SP-1 egress node C6 can get the mapping between the KEYs and the
   Node-IDs (or Addresses) of the next domain's ingress edge node (i.e.
   D1 or D4 in the figure 3 above) from its network controller ahead of
   time.

     0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      Type     |     Length    |          RESERVED             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Key ID (4 octets) from the GRE tunnel remote ingress node     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Optional                                                     //
      | Node ID or address for the ingress node Next domain          //
      | Variable length (0~32 octets)                                //
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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   TYPE: (to be assigned by IANA) is to indicate the TLV is for
   carrying the flow identifier of the packet encoded by the SD-WAN
   source node.

   Upon receiving the packet, the egress node (C6) can

      - find the Node-ID (or the address) for the next domain's ingress
        node,
      - construct a GRE header with the Key received from the TLV above
        and the destination address from the mapping given by the
        controller,
      - encapsulate the GRE header to the data packet (which has
        decapsulated SR header),
      - and forward the packet to the public internet.

   6. Security Considerations

   Remotely attached CPEs might brought the following security risks:

   1) Potential DDoS attack to the PEs with ports facing internet.
     I.e. the PE resourced being attacked by unwanted traffic.
   2) Potential risk of provider VPN network bandwidth being stolen
     by the entities who spoofed the addresses of SD-WAN end nodes.

   To mitigate security risk of 1) above, it is absolutely necessary
   for PEs which accept remotely attached CPEs or simply have ports
   facing internet to enable Anti-DDoS feature to prevent major DDoS
   attack to those PEs.

   To mitigate the security risk of 2) above, RFC7510 defines the use
   of DTLS to authenticate and encrypt the RFC7510 encapsulation.

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   However, for the scenario of SD-WAN source node being remotely
   attached to PEs, using the method recommended by RFC7510  means the
   source node has to perform DTLS on top of the IPSec encryption
   between SD-WAN end points E1<->E2. This can be too processing heavy
   for the SD-WAN end nodes. In addition, if there are many SD-WAN
   flows to traverse through the ingress PE (e.g. C1, C2, C4 in the
   figure 1 above), heavy processing is required on the ingress PEs.

   Since the payload between E2<->E2 is already encrypted, the
   confidentiality of the payload is already ensured.  The network
   operators need to balance between how much they can tolerant some
   percentage of bandwidth being stolen and how much extra cost they
   are willing to pay for completely prevent any unpaid traffic
   traversing through its VPN networks. For operators who opt for lower
   cost ingress PEs and CPEs, but can tolerant some percentage of
   bandwidth being used by unpaid subscribers, a simple approach can be
   considered:

   - Embed a key in the packets, which can be changed periodically,
     like the digital signature used by a certificate authority or
     certification authority (CA).
   - The key can be encoded in the GRE Key field between SD-WAN end
     node and Ingress PE. Since GRE has 24 bits, some fixed bits
     can be used to represent the signature of paid subscribers.

    7. IANA Considerations

   This document requires new protocol type:

   Protocol type to be added to GRE header: SR_Route

8. References

8.1. Normative References
   [RFC2890]   G. Dommety  "Key and Sequence Number Extensions to GRE".
   Sep. 2000.

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    8.2. Informative References

   [RFC2735]   B. Fox, et al "NHRP Support for Virtual Private
   networks". Dec. 1999.

   [RFC8192] S. Hares, et al "Interface to Network Security Functions
             (I2NSF) Problem Statement and Use Cases", July 2017

    [ITU-T-X1036] ITU-T Recommendation X.1036, "Framework for creation,
             storage, distribution and enforcement of policies for
             network security", Nov 2007.

    [RFC6071] S. Frankel and S. Krishnan, "IP Security (IPsec) and
             Internet Key Exchange (IKE) Document Roadmap", Feb 2011.

   [RFC4364] E. Rosen and Y. Rekhter, "BGP/MPLS IP Virtual Private
             Networks (VPNs)", Feb 2006

   [RFC4664] L. Andersson and E. Rosen, "Framework for Layer 2 Virtual
             Private Networks (L2VPNs)", Sept 2006.

   [SR-SD-WAN] D. Dukes, et al, "SR for SDWAN: VPN with Underlay SLA",
             draft-dukes-sr-for-sdwan-00, in progress, Oct 2017

   [SRv6-SRH] S. Previdi, et al, "IPv6 Segment Routing Header (SRH)",
             draft-ietf-6man-segment-routing-header-13, in progress,
             April 2018.

   [MPLS-SR] A. Bashandy, et al, "Segment Routing with MPLS data
             plane", draft-ietf-spring-segment-routing-mpls-13, in
             progress, April 2018.

   [RFC7510] X. Xu, et al, "Encapsulating MPLS in UDP", April 2015.

   [RFC8086] L. Yong, et al, "GRE-in-UDP Encapsulation", March 2017.

   [MEF-Cloud] "Cloud Services Architecture Technical Specification",
             Work in progress, April 2018

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   9. Acknowledgments

   Many thanks to Dean Cheng and Jim Guichard for the discussion and
   contributions.

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Authors' Addresses

   Linda Dunbar
   Huawei
   Email: Linda.Dunbar@huawei.com

   Mehmet Toy
   Verizon
   One Verizon Way
   Basking Ridge, NJ 07920
   Email: mehmet.toy@verizon.com

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