Network Working Group                                         L. Dunbar
Internet Draft                                                 A. Malis
Intended status: Informational                                   Huawei
Expires: January 2019

                                                           July 2, 2018

        Gap Analysis of Interconnecting Underlay with Cloud Overlay


   This document analyzes the technological gaps when using SD-WAN to
   interconnect workloads & apps hosted in various locations,
   especially cloud data centers when the network service providers do
   not have or have limited physical infrastructure to reach the
   locations [Net2Cloud-problem].

Status of this Memo

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Table of Contents

   1. Introduction...................................................3
   2. Conventions used in this document..............................3
   3. Gap Analysis of CPEs Registration Protocol.....................4
   4. Gap Analysis in aggregating VPN paths and Internet paths.......4
      4.1. Gap analysis of Using BGP to cover SD-WAN paths...........6
      4.2. Gaps in preventing attacks to CPEs from their Internet ports
   5. Gap analysis of CPEs not directly connected to VPN PEs.........8
      5.1. Gap Analysis of Floating PEs to connect to Remote CPEs...10
      5.2. NAT Traversing...........................................10
      5.3. Complication of use BGP between PE and remote CPEs via
      5.4. Designated Forwarder to the remote edges.................11
      5.5. Traffic Path Management..................................12
   6. Manageability Considerations..................................12
   7. Security Considerations.......................................12
   8. IANA Considerations...........................................12
   9. References....................................................12
      9.1. Normative References.....................................13
      9.2. Informative References...................................13

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   10. Acknowledgments..............................................14

1. Introduction

   [Net2Cloud-Problem] describes the problems of enterprises face today
   in transitioning their IT infrastructure to support digital economy,
   such as connecting enterprises' branch offices to dynamic workloads
   in Cloud DCs.

   This document analyzes the technological gaps to interconnect
   dynamic workloads & apps hosted in various locations, especially in
   cloud data centers to which the network service providers may not
   have or have limited physical infrastructure to reach.

2. Conventions used in this document

   Cloud DC:   Off-Premise Data Centers that usually host applications
               and workload owned by different organizations or

   Controller: Used interchangeably with SD-WAN controller to manage
               SD-WAN overlay path creation/deletion and monitoring the
               path conditions between two sites.

   CPE-Based VPN: Virtual Private Secure network formed among CPEs.
               This is to differentiate from most commonly used PE
               based VPNs

   OnPrem:     On Premises data centers and branch offices

   SD-WAN:     Software Defined Wide Area Network, which can mean many
               different things. In this document, "SD-WAN" refers to
               the solutions specified by ONUG (Open Network User
               Group), which build point-to-point IPsec overlay paths
               between two end-points (or branch offices) that need to

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3. Gap Analysis of CPEs Registration Protocol

   SD-WAN, conceived in ONUG (Open Network User Group) a few years ago
   as way to aggregate multiple connections between any two points, has
   emerged as an on-demand technology to securely interconnect the
   OnPrem branches with the workloads instantiated in Cloud DCs that do
   not have MPLS VPN PE co-located or have very limited bandwidths.

   Some SD-WAN networks use the NHRP protocol [RFC2332] to register SD-
   WAN endpoints with a "Controller" (or NHRP server), which then has
   the ability to map a private VPN address to a public IP address of
   the destination node. DSVPN [DSVPN] or DMVPN [DMVPN] are used to
   establish tunnels among SD-WAN endpoints.

   NHRP was originally intended for ATM address resolution, and as a
   result it misses many attributes which are necessary for dynamic end
   point CPE registration to controller, such as:

   - Location identifier, such as Site Identifier, System ID, and/or Port ID.
   - CPE attached GW information. When a CPE is instantiated within Cloud DC,
     the Cloud DC operator' GW to which the CPE is attached.
   - Private <-> Public address mapping, which is needed when the CPEs use
     private addresses.
   - IPsec configuration parameters (from controller to CPEs)

4. Gap Analysis in aggregating VPN paths and Internet paths

   Most likely, enterprises, especially large ones, already have their
   CPEs interconnected by provider VPNs, such as EVPN, L2VPN, or L3VPN.
   The L2VPN or L3VPN can also be formed among all the CPEs directly
   attached to PEs, which is referred to as CPE based VPN as shown in
   the following diagram. The commonly used CPE based VPNs have CPE
   directly attached to PEs via VLANs (Ethernet). Therefore, the
   communication is secure. The BGP is used to distribute routes among

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                              |RR | EVPN MAC/IP BGP updates
                      //                      \\
                     //  <-----EVPN-VxLAN----> \\
                  +-+--+  ++-+        ++-+  +--+-+
                  | CPE|--|PE|        |PE+--+ CPE|
               +--|  1 |  |1 |        |x |  | c  |---+
                  +-+--+  ++-+        ++-+  +----+
                           |           |
                           |  VPN    +-+---+    +----+
          +--------+       | Network | PE3 |    |CPE |
          | CPE    |       |         |     |- --| 3  |
          |   c    |       +-----+   +-+---+    +----+
          +------+-+-------+ PE4 |-----+

         === or \\ indicates control plane communications

                      Figure 1: L2 or L3 VPNs over IP WAN

   To use SD-WAN to aggregate Internet paths with the VPN paths, the
   CPEs need to have some ports connected to PEs and other Ports
   connected to the internet. NHRP & DSVPN/DMVPN can be used for the
   CPEs to be registered with their SD-WAN Controllers to establish
   secure tunnels among relevant CPEs.

   That means the CPEs need to participate in two separate control
   planes: EVPN&BGP for CPE based VPN via links directly attached to
   PEs and NHRP & DSVPN/DMVPN. Two separate control planes not only add
   complexity to CPEs, but also increase operational cost.

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               +---------Internet paths--------------+
               |                                     |
               |              +---+                  |
               |              |RR |                  |
               |       +======+---+===========+      |
               |     //                      \\      |
               |    //  <-----EVPN-VxLAN----> \\     |
               |  +-+--+  ++-+        ++-+  +--+-+  (|)
               |  | CPE|--|PE|        |PE+--+ CPE|  (|)
               +--|  1 |  |1 |        |x |  | c  |---+
                  +-+--+  ++-+        ++-+  +----+
                           |           |
                           |  VPN    +-+---+    +----+
          +--------+       | Network | PE3 |    |CPE |
          | CPE    |       |         |     |- --| 3  |
          |   c    |       +-----+   +-+---+    +----+
          +------+-+-------+ PE4 |-----+
            Figure 2: CPEs interconnected by VPN paths and Internet Paths

 4.1. Gap analysis of Using BGP to cover SD-WAN paths

   Since BGP is widely deployed, it is desirable to consider using BGP
   to control the SD-WAN paths instead of NHRP, DSVPN/DMVPN. This
   section analyzes the gaps of using BGP to control SD-WAN.

   RFC5512 and [Tunnel-Encap] describe methods for end points to
   advertise tunnel information and to trigger tunnel Establishment.
   RFC5512 & [Tunnel-Encaps] have the Endpoint Address to indicate IPv4
   or IPv6 address format Tunnel Encapsulation attribute to indicate
   different encapsulation formats, such as L2TPv3, GRE, VxLAN, IP in
   IP, etc. There are sub-TLVs to describe the detailed tunnel
   information for each of the encapsulations.

   There is also Color sub-TLV to describe customer specified
   information about the tunnels (which can be creatively used for SD-

   To express supporting multiple Encap types, multiple Extended
   communities with SAFI value = 7 can be used.

   Here are some of the gaps using RFC5512 and [Tunnel-Encap] to
   control SD-WAN:

   - Doesn't have fields to carry detailed information of the remote CPE:
     such as Site-ID, System-ID, Port-ID

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   - Does not have the proper field to express IPsec configuration
     information from "Controller" (which can be RR) to CPEs.
   - Does not have proper way for two peer CPEs to negotiate IPSec key based
     on the configuration sent from Controller.
   - UDP NAT private address <-> public address mapping
   - CPEs tend to communicate with a few other CPEs, not all the CPEs need to
     form mesh connections.  Using BGP, CPEs can easily get dumped with too
     much information of other CPEs that they never need to communicate.
     NHRP only sends the relevant information for the interested end
     points for establishing tunnels. Therefore, need some form of
     "Registration" methods.

   [VPN-over-Internet] describes a way to securely interconnect CPEs
   via IPsec using BGP. This method is useful, however, it still miss
   some aspects to aggregate CPE based VPN paths with internet paths
   that interconnect the CPEs. In addition:

  -         The draft assumes that CPE "register" with the RR. However, it does not
     say how. Should "NHRP" (modified version) be considered? In SD-WAN, Zero
     Touch Provisioning is expected. It is not acceptable to require manual
     configuration on RR which CPEs are controlled.
  -         The draft assumes that CPE and RR are connected by IPsec tunnel. With
     zero touch provisioning, we need an automatic way to synchronize the
     IPsec SA between CPE and RR. The draft assumes:
          A CPE must also be provisioned with whatever additional information
          is needed in order to set up an IPsec SA with each of the red RRs

  -         IPsec requires periodic refreshment of the keys. How to synchronize the
     refreshment among multiple nodes?
  -         IPsec usually only send configuration parameters to two end points and
     let the two end points to negotiate the KEY. Now we assume that RR is
     responsible for creating the KEY for all end points. When one end point
     is confiscated, all other connections are impacted.

 4.2. Gaps in preventing attacks to CPEs from their Internet ports

   When CPEs have ports facing internet, it brings in the security
   risks of potential DDoS attacks to the CPEs from the ports facing
   internet. I.e. the CPE resource are attacked by unwanted traffic.

   To mitigate security risk, it is absolutely necessary to enable
   Anti-DDoS feature on those CPEs to prevent major DDoS attack.

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5. Gap analysis of CPEs not directly connected to VPN PEs

   Because of the ephemeral property of the selected Cloud DCs, an
   enterprise or its network service provider may not have the direct
   links to the Cloud DCs that are optimal for hosting the enterprise's
   specific workloads/Apps. Under those circumstances, SD-WAN is a very
   flexible choice to interconnect the enterprise on-premises data
   centers & branch offices to its desired Cloud DCs.

   However, SD-WAN paths over public internet can have unpredictable
   performance, especially over long distances and cross state/country
   boundaries. Therefore, it is highly desirable to place as much as
   possible the portion of SD-WAN paths over service provider VPN (e.g.
   enterprise's existing VPN) that have guaranteed SLA to minimize the
   distance/segments over public internet.

   MEF Cloud Service Architecture [MEF-Cloud] also describes a use case
   of network operators needing to use SD-WAN over LTE or public
   internet for the last mile access that they do not have physical

   Under those scenarios, one or both of the SD-WAN end points may not
   directly attached to the PEs of a SR Domain.

   Using SD-WAN to connect the enterprise existing sites with the
   workloads in Cloud DC, the enterprise existing sites' CPEs have to
   be upgraded to support SD-WAN.  If the workloads in Cloud DC need to
   be connected to many sites, the upgrade process can be very

   [Net2Cloud-Problem] describes a hybrid network approach that
   integrates SD-WAN with traditional MPLS-based VPNs, to extend the
   existing MPLS-based VPNs to the Cloud DC Workloads over the access
   paths that are not under the VPN provider control. To make it
   working properly, a small number of the PEs of the MPLS VPN can be
   designated to connect to the remote workloads via SD-WAN secure
   IPsec tunnels.  Those designated PEs are shown as fPE (floating PE
   or smart PE) in Figure below. Once the secure IPsec tunnels are
   established, the workloads in Cloud DC can be reached by the
   enterprise's VPN without upgrading all of the enterprise's existing

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   CPEs. The only CPE that needs to support SD-WAN would be a
   virtualized CPE instantiated within the cloud DC.

   +--------+                                             +--------+
   | Host-a +--+                                     +----| Host-b |
   |        |  |                                    (')   |        |
   +--------+  |           +-----------+           (   )  +--------+
               |  +-+--+  ++-+        ++-+  +--+-+  (_)
               |  | CPE|--|PE|        |PE+--+ CPE|   |
               +--|    |  |  |        |  |  |    |---+
                  +-+--+  ++-+        ++-+  +----+
                   /       |           |
                  /        |  MPLS   +-+---+    +--+-++--------+
          +------+-+       | Network |fPE-1|    |CPE || Host   |
          | Host   |       |         |     |- --|    ||   d    |
          |   c    |       +-----+   +-+---+    +--+-++--------+
          +--------+       |fPE-2|-----+
                           +---+-+    (|)
                              (|)     (|) SD-WAN
                              (|)     (|) over any access
                             //   \    | Cloud DC \\
                            //      \ ++-----+       \\
                                      |  CPE |
                                |               |
                            +---+----+      +---+----+
                            | Remote |      | Remote |
                            | App-1  |      | App-2  |
                            +--------+      +--------+

                    Figure 3: VPN Extension to Cloud DC

   In Figure 3 above, the optimal Cloud DC to host the workloads (due
   to proximity, capacity, pricing, or other criteria chosen by the
   enterprises) does not happen to have a direct connection to the PEs
   of the MPLS VPN that interconnects the enterprise's existing sites.

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5.1. Gap Analysis of Floating PEs to connect to Remote CPEs

   To extend MPLS VPN to remote CPEs, it is necessary to establish
   secure tunnels (such as IPsec tunnels) between the Floating PEs and
   the remote CPEs.


   Even though a set of PEs can be manually selected to act as the
   floating PEs for a specific cloud data center, there are no standard
   protocols for those PEs to interact with the remote CPEs (most
   likely virtualized) instantiated in the third party cloud data
   centers (such as exchanging performance information or route

   When there is more than one fPE available for use (as there should
   be for resiliency or the ability to support multiple cloud DCs
   scattered geographically), it is not straight to designate egress
   fPE to remote CPEs based on applications.  There are too much
   applications traffic traversing PEs, it is not feasible for PEs to
   recognize applications carried by the payload.

5.2. NAT Traversing

   Most cloud DCs only assign private IP addresses to the workloads
   instantiated. Therefore, the traffic to/from the workload usually
   need to traverse NAT.

5.3. Complication of use BGP between PE and remote CPEs via Internet

   Even though EBGP (external BGP) Multihop method can be used to
   connect peers that are not directly connected to each other, there
   are still some complications/gaps in extending BGP from MPLS VPN PEs
   to remote CPEs via any access paths (e.g. internet):

   EBGP Multi-hop scheme requires static configuration on both peers.
   To use EBGP between a PE and remote CPEs, the PE has to be
   statically configured with "next-hop" to the IP addresses of the
   CPEs. When remote CPEs, especially remote virtualized CPEs

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   dynamically instantiated or removed, the configuration on the PE
   Multi-Hop EBGP has to be changed accordingly.


     Egress peering engineering (EPE) is not enough. Running BGP on
     virtualized CPE in Cloud DC requires GRE tunnels being established
     first, which requires address and key management for the remote
     CPEs. RFC 7024 (Virtual Hub & Spoke) and Hierarchical VPN is not

     Also need a method to automatically trigger configuration changes
     on PE when remote CPEs' are instantiated or moved (IP address
     change) or deleted.

     EBGP Multi-hop scheme does not have embedded security mechanism.
     The PE and remote CPEs needs secure communication channel when
     connected via public internet.

   Remote CPEs, if instantiated in Cloud DC, might have to traverse NAT
   to reach PE. It is not clear how BGP can be used between devices
   outside the NAT and the entities behind the NAT. It is not clear how
   to configure the Next Hop on the PEs to reach private addresses.

5.4. Designated Forwarder to the remote edges

   Among multiple floating PEs available for a remote CPE, multicast
   traffic from the remote CPE towards the MPLS VPN can be broadcasted
   back to the remote CPE due to the PE receiving the broadcast data
   frame forwarding the multicast/broadcast frame to other PEs that in
   turn send to all attached CPEs. This process may cause a traffic

   Therefore, it is necessary to designate one floating PE as the CPE's
   Designated Forwarder, similar to TRILL's Appointed Forwarders

   Gap: the MPLS VPN does not have features like TRILL's Appointed

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5.5. Traffic Path Management

   When there are multiple floating PEs that have established IPsec
   tunnels to the remote CPE, the remote CPE can forward the outbound
   traffic to the Designated Forwarder PE, which in turn forwards the
   traffic to egress PEs to the destinations. However, it is not
   straightforward for the egress PE to send back the return traffic to
   the Designated Forwarder PE.

   Example of Return Path management using Figure 3 above.

   - fPE-1 is desired for communication between App-1 <-> Host-a due to
   latency, pricing or other criteria.
   - fPE-2 is desired for communication between App-1 <-> Host-b.

6. Manageability Considerations


7. Security Considerations

     The intention of this draft is to identify the gaps in current and
     proposed SD-WAN approaches to the requirements identified in

     Several of these approaches have gaps in meeting enterprise
     security requirements when tunneling their traffic over the
     Internet, as is the general intention of SD-WAN. See the
     individual sections above for further discussion of these security

8. IANA Considerations

   This document requires no IANA actions. RFC Editor: Please remove
   this section before publication.

9. References

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 9.1. Normative References

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.

 9.2. Informative References

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

   [RFC5521] P. Mohapatra, E. Rosen, "The BGP Encapsulation Subsequent
             Address Family Identifier (SAFI) and the BGP Tunnel
             Encapsulation Attribute", April 2009.

   [Tunnel-Encap]E. Rosen, et al, "The BGP Tunnel Encapsulation
             Attribute", draft-ietf-idr-tunnel-encaps-09, Feb 2018.

   [VPN-over-Internet] E. Rosen, "Provide Secure Layer L3VPNs over
             Public Infrastructure", draft-rosen-bess-secure-l3vpn-00,
             work-in-progress, July 2018

   [DMVPN] Dynamic Multi-point VPN:

   [DSVPN] Dynamic Smart VPN:

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

    [Net2Cloud-Problem] L. Dunbar and A. Malis, "Seamless Interconnect
             Underlay to Cloud Overlay Problem Statement", draft-dm-
             net2cloud-problem-statement-02, June 2018

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10. Acknowledgments

   Acknowledgements to xxx for his review and contributions.

   This document was prepared using 2-Word-v2.0.template.dot.

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Authors' Addresses

   Linda Dunbar
   Email: Linda.Dunbar@huawei.com

   Andrew G. Malis
   Email: agmalis@gmail.com

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