Network Working Group L. Dunbar
Internet Draft A. Malis
Intended status: Informational Huawei
Expires: January 2018 C. Jacquenet
Orange
March 2, 2018
Seamless Interconnect Underlay to Cloud Overlay Problem Statement
draft-dm-net2cloud-problem-statement-00
Abstract
This document describes common approaches deployed by enterprises
for interconnection of workloads & applications hosted in Cloud DCs
with on-premises DCs & branch offices. This document also describes
some of the (network) problems that many enterprises face when they
have workloads & applications & data split among hybrid data
centers, especially for those enterprises with multiple sites that
are already interconnected by VPNs (e.g. MPLS L2VPN/L3VPN) and
leased lines.
Current operational problems in the field are examined to determine
whether there is a need for enhancements to existing protocols or
whether a new protocol is necessary to solve them.
Status of this Memo
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provisions of BCP 78 and BCP 79.
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Internet-Drafts are working documents of the Internet Engineering
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other groups may also distribute working documents as Internet-
Drafts.
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Table of Contents
1. Introduction...................................................3
2. Definition of terms............................................4
3. Current Practices in Interconnecting Enterprise Sites with Cloud
DCs...............................................................5
3.1. Interconnect to Cloud DCs.................................5
3.2. Interconnect to Hybrid Cloud DCs..........................6
3.3. Connecting workloads among hybrid Cloud DCs...............7
4. Desired Properties for Networking that interconnects Hybrid Cloud
DCs...............................................................7
5. Problems with MPLS-based VPNs extending to Hybrid Cloud DCs....8
6. Problem with using IPsec tunnels to Cloud DCs..................9
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6.1. Complexity of multi-point any-to-any interconnection.....10
6.2. Poor performance over long distance......................10
6.3. Scaling Issues with IPsec Tunnels........................11
7. Problems of Using SD-WAN to connect to Cloud DCs..............11
7.1. SD-WAN among branch offices vs. interconnect to Cloud DCs12
8. End-to-End Security Concerns for Data Flows...................14
9. Requirements for Dynamic Cloud Data Center VPNs...............14
10. Security Considerations......................................15
11. IANA Considerations..........................................15
12. References...................................................15
12.1. Normative References....................................15
12.2. Informative References..................................15
13. Acknowledgments..............................................16
1. Introduction
Cloud-based applications and services continue to change how
businesses of all sizes work and share information. "Cloud-based
applications & workloads" are those that are instantiated in third
party DCs that also host services for other customers.
With the advent of widely available third party cloud DCs in diverse
geographic locations and the advancement of tools for monitoring and
predicting application behaviors, it is technically feasible for
enterprises to instantiate applications and workloads in locations
that are geographically closest to their end users. This property
aids in improving end-to-end latency and overall user experience.
Conversely, an enterprise can easily shutdown applications and
workloads when their end users' geographic base changes (therefore
needing to change the networking connection to those relocated
applications and workloads). In addition, an enterprise may wish to
take advantage of more and more business applications offered by
third party private cloud DCs, such as SAP HANA, Oracle Cloud,
Salesforce Cloud, etc.
However, typically, enterprise branch offices & on-premises data
centers are connected via VPNs, such as MPLS based l2VPN/L3VPN, and
therefore connecting to the cloud-based resources may not be
straightforward if the provider of the VPN service does not have
direct connections to the Cloud DCs. Under those circumstances, the
enterprise can upgrade their existing CPEs to utilize SD-WAN to
reach cloud resources, or wait for their VPN service provider to
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make new agreements with data center providers to connect to the
Cloud resources. Either way this is non-trivial and has additional
infrastructure costs, and is slow to operationalize.
In addition, it is an uptrend with more and more enterprises
changing their Apps & workloads so that they can be split among
hybrid DCs to maximize the benefits of geographical convenience &
elasticity and special property of on-premises DCs.
2. Definition of terms
Cloud DC: Off-Premise Data Centers that usually host applications
and workload owned by different organizations or
tenants.
Controller: Used interchangeably with SD-WAN controller to manage
SD-WAN overlay path creation/deletion and monitoring the
path conditions between two or more sites.
DMVPN: Dynamic Multipoint Virtual Private Network. DMVPN is a
secure network that exchanges data between sites without
needing to pass traffic through an organization's
headquarter virtual private network (VPN) server or
router.
Heterogeneous Cloud: applications & workloads split among Cloud DCs
owned & managed by different operators.
Hybrid Cloud: applications & workloads split between on-premises
Data centers and Cloud DCs. In this document Hybrid
Cloud also include heterogeneous cloud as well.
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), https://www.onug.net/software-defined-wide-area-
network-sd-wan/, which is about pooling WAN bandwidth
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from n service providers to get better WAN bandwidth
management, visibility & control.
VPC: Virtual Private Cloud. A service offered by many Cloud
DC operators to allocate a logically isolated cloud
resources, including compute, networking and storage.
3. Current Practices in Interconnecting Enterprise Sites with Cloud DCs
3.1. Interconnect to Cloud DCs
Most Cloud operators offer some type of network gateway through
which an enterprise can reach their workloads hosted in the Cloud
DC. For example, AWS (Amazon Web Services) offers the following
options to reach workloads in AWS Cloud DCs:
- Internet gateway for any external entities to reach the
workloads hosted in AWS Cloud DC via the internet.
- virtual gateway (vGW) to which IPsec tunnels [RFC6071] are
established between an enterprise's own gateways and AWS vGW,
so that the communications between those gateways can be
secured from the underlay (which might be the public internet).
- Direct Connect, which allows enterprises to purchase direct
connect from network service providers to get a private leased
line interconnecting the enterprises gateway(s) and the AWS
Direct Connect routers co-located with the network operators.
+------------------------+
| ,---. ,---. |
| (TN-1 ) ( TN-2)|
| `-+-' +--+ `-+-' |
| +----|vR|-----+ |
| ++-+ |
| | +-+----+
| | /Internet\ For External
| +-------+ Gateway +----------------------
| \ / to reach via Internet
| +-+----+
| |
+------------------------+
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+------------------------+
| ,---. ,---. |
| (TN-1 ) ( TN-2)|
| `-+-' +--+ `-+-' |
| +----|vR|-----+ |
| ++-+ |
| | +-+----+
| | / virtual\ For IPsec Tunnel
| +-------+ Gateway +----------------------
| \ / termination
| +-+----+
| |
+------------------------+
+------------------------+
| ,---. ,---. |
| (TN-1 ) ( TN-2)|
| `-+-' +--+ `-+-' |
| +----|vR|-----+ |
| ++-+ |
| | +-+----+ +------+
| | / \ For Direct /customer\
| +-------+ Gateway +----------+ gateway |
| \ / Connect \ /
| +-+----+ +------+
| |
+------------------------+
Figure 1: Examples of connecting to a Cloud DC
3.2. Interconnect to Hybrid Cloud DCs
According to Gartner, by 2020 "hybrid will be the most common usage
of the cloud" as more enterprises see the benefits of integrating
public and private cloud infrastructures. However, enabling the
growth of hybrid cloud deployments in the enterprise requires fast
and safe interconnection between public and private cloud services.
The Hybrid Cloud scenario also includes heterogeneous Cloud DCs.
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For enterprises to connect to workloads hosted in multiple Cloud
DCs, enterprises can use IPsec tunnels or lease private lines to
connect their own gateways to each of the Cloud DC's gateways or any
other suitable design (including a combination thereof).
Some users prefer to instantiate their own virtual CPEs inside the
public Cloud DC to connect the workloads within the Cloud DC. Then
an overlay path is established between customer gateways to the
virtual CPEs for reaching the workloads inside the cloud DC.
3.3. Connecting workloads among hybrid Cloud DCs
When workloads among different Cloud DCs need to communicate, one
way is to hairpin all the traffic through the customer gateway,
which creates additional transmission delay & incurs cost exiting
Cloud DCs. Another way is to establish direct tunnels among
different VPCs (Virtual Private Clouds), such as using DMVPN
(Dynamic Multipoint Virtual Private Network) or DSVPN (Dynamic Smart
VPN) to establish direct Multi-edge tunnels.
DMVPN (and DSVPN) uses NHRP (Next Hop Resolution Protocol) [RFC2735]
so that spoke nodes can register their IP addresses with the hub
node. The IETF ION WG, Internetworking over NBMA (non-broadcast
multiple access), standardized NHRP for connection-oriented NBMA
network (such as ATM) network address resolution more than two
decades ago.
There are many differences between virtual routers in Public Cloud
DCs and the nodes in an NBMA network. It would be useful for the
IETF community to examine the effectiveness of NHRP as the
registration protocol for registering virtual routers in Cloud DCs
to gateways or entities that connect to enterprise private networks.
As the result of this evaluation, enhancement or new registration
protocols may result.
4. Desired Properties for Networking that interconnects Hybrid Cloud
DCs
The networks that interconnect hybrid Cloud DCs have to enable users
to take advantage of Cloud DCs:
- High availability, any time usage for any length of time.
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Many enterprises incorporate Cloud as their disaster recovery
strategy, e.g. periodically backup data into the cloud, or
running backup applications in the Cloud, etc. Therefore, the
connection to the cloud DCs may not be permanent, but rather
needs to be on-demand.
- Global accessibility in different geographical zones, thereby
facilitating the proximity of applications as a function of the
end users' location, for improved latency.
- Elasticity and mobility, to instantiate additional applications
at Cloud DCs when end users' usages increase and shut down
applications at locations with fewer end users.
Some enterprises have front-end web portals running in Cloud
DCs and Database servers in their on-premises DCs. Those Front-
end web portals need to be reachable from the public Internet.
The backend connection to the sensitive data in database
servers hosted in the on-premises DCs might need secure
connections.
5. Problems with MPLS-based VPNs extending to Hybrid Cloud DCs
Traditional MPLS-based VPNs have been widely deployed as an
effective way to support businesses and organizations that require
network performance and reliability. MPLS shifted the burden of
managing a VPN service from enterprises to service providers. The
CPEs for MPLS VPN are also simpler and less expensive, since they do
not need to manage how to send packets to remote sites; they simply
pass all outbound traffic to the MPLS VPN PEs to which the CPE is
attached (albeit multi-homing scenarios require more processing
logic on CPEs). MPLS has addressed the problems of scale,
availability, and fast recovery from network faults, and
incorporated traffic-engineering capabilities.
However, traditional MPLS-based VPN solutions are not optimized for
connecting end-users to dynamic workloads/applications in cloud DCs
because:
- The Provider Edge (PE) nodes of the enterprise's VPNs might not
have direct connection to the third party cloud DCs that are
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optimal for hosting workloads with the goal of easy access to
enterprises' end users.
- It takes a relatively long time to deploy provider edge (PE)
routers at new locations. When enterprise's workloads are
changed from one cloud DC to another (i.e., removed from one DC
and re-instantiated to another location when demand changes),
the enterprise branch offices need to be connected to the new
cloud DC, but the network service provider might not have PEs
located at the new location.
One of the main drivers for moving workloads into the cloud is
the widely available cloud DCs at geographically diverse
locations, where apps can be instantiated so that they can be
as close to their end users as possible. When the user base
changes, the applications may be moved to a new cloud DC
location closest to the new user base.
- Most of the cloud DCs do not expose their internal networks, so
the provider MPLS based VPNs cannot reach the workloads
natively.
- Many cloud DCs use an overlay to connect their gateways to the
workloads inside the DC. There has not been any standard to
address the interworking between the Cloud Overlay and the
enterprise' existing underlay networks.
Another roadblock is the lack of a standard way to express and
enforce consistent security policies to workloads that not only use
virtual addresses, do not have a port number, but also have a high
chance of placement in different locations within the Cloud DC
[RFC8192]. The traditional VPN path computation and bandwidth
allocation schemes may not be flexible enough to address the need
for enterprises to rapidly connect to dynamically instantiated (or
removed) workloads and applications regardless of their
location/nature (i.e., third party cloud DCs).
6. Problem with using IPsec tunnels to Cloud DCs
As described in the previous section, many Cloud operators expose
their gateways for external entities (which can be enterprises
themselves) to directly establish IPsec tunnels. If there is only
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one enterprise location that needs to reach the Cloud DC, an IPsec
tunnel is a very convenient solution.
However, many medium-to-large enterprises usually have multiple
sites and multiple data centers. For workloads and apps hosted in
Cloud DCs, multiple sites need to communicate securely with those
Cloud workloads and apps. This section documents some of the issues
associated with using IPsec tunnels to connect enterprise' sites
with Cloud operator's Gateways.
6.1. Complexity of multi-point any-to-any interconnection
The dynamic workload instantiated in cloud DC needs to communicate
with multiple branch offices and on-premises data centers. Most
enterprises need multi-point interconnection among multiple
locations, as done by MPLS L2/L3 VPNs.
Using IPsec overlay paths to connect all branches & on-premises data
centers to cloud DCs require CPEs to manage routing among Cloud DCs
gateways and the CPEs located at other branch locations, which can
dramatically increase the complexity of the design, possibly at the
cost of jeopardizing the CPE performance.
The complexity of requiring CPEs to maintain routing among other
CPEs is one of the reasons why enterprises migrated from Frame Relay
based services to MPLS-based VPN services.
MPLS-based VPNs have their PEs directly connected to the CPEs.
Therefore, CPEs only need to forward all traffic to the directly
attached PEs, which are therefore responsible for enforcing the
routing policy within the corresponding VPNs. Even for multi-homed
CPEs, the CPEs only need to forward traffic among the directly
connected PEs (note: the complexity may vary for IPv6 network).
However, when using IPsec tunnels between CPEs and Cloud DCs, the
CPEs need to manage the routing for traffic to Cloud DCs, to remote
CPEs via VPN, or directly.
6.2. Poor performance over long distance
When enterprise CPEs or gateways are far away from Cloud DC gateways
or across country/continent boundaries, performance of IPsec tunnels
over the public Internet can be problematic and unpredictable. Even
though there are many monitoring tools available to measure delay
and various performance characteristics of the network, the
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measurement for paths over the Internet is passive and past
measurements may not represent future performance.
Many cloud providers can replicate workloads in different available
zones. An App instantiated in a Cloud DC closest to clients may have
to cooperate with another App (or its mirror image) in another
region or the database server in the on-premises DC. This kind of
coordination requires predicable networking behavior/performance
among those locations.
6.3. Scaling Issues with IPsec Tunnels
IPsec can achieve secure overlay connections between two locations
over any underlay networks, e.g., between CPEs and Cloud DC
Gateways.
If there is only one enterprise location connected to the Cloud
gateway, a small number of IPsec tunnels can be configured on-demand
between the on-premises DC and the Cloud DC, which is an easy and
flexible solution.
However, for multiple enterprise locations to reach workloads hosted
in cloud DCs, the Cloud DC gateway needs to maintain multiple IPsec
tunnels to all those locations (e.g. hub & spoke topology). For a
company with hundreds or thousands of locations, there could be
hundreds (or even thousands) of IPsec tunnels terminating at the
Cloud DC gateway, which is not only very expensive (because Cloud
Operators charge based on connections), but can be very processing
intensive for the gateway. Many cloud operators only allow a limited
number of IPsec tunnels to each customer. Alternatively, you could
use a solution like group encryption where a single IPSec SA is
necessary at the GW but the drawback here is key distribution and
maintenance of a key server etc.
7. Problems of Using SD-WAN to connect to Cloud DCs
SD-WAN enables multiple parallel paths between two locations, for
example, two CPEs interconnected by a traditional MPLS VPN
([RFC4364] or [RFC4664]) as well as overlay tunnels. The overlay,
possibly secured by IPsec tunnels [RFC6071], can traverse over the
public Internet using fiber, cable, DSL-based Internet access, Wi-
Fi, or 4G/Long Term Evolution (LTE).
SD-WAN lets enterprises augment their current VPN network with cost-
effective, readily available Broadband Internet connectivity,
enabling some traffic offloaded to overlay paths based on traffic
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forwarding policy (application-based or otherwise), or when the MPLS
VPN connection between the two locations is congested, or otherwise
undesirable or unavailable.
7.1. SD-WAN among branch offices vs. interconnect to Cloud DCs
SD-WAN interconnection of branch offices is not as simple as it
appears. For an enterprise with multiple sites, using SD-WAN overlay
paths among sites requires each CPE to manage all the addresses that
local hosts have the potential to reach, i.e. map internal VPN
addresses to appropriate SD-WAN paths. This is similar to the
complexity of Frame Relay based VPNs, where each CPE needed to
maintain mesh routing for all destinations if they were to avoid an
extra hop through a hub router. Even though SD-WAN CPEs can get
assistance from a central controller (instead of running a routing
protocol) to resolve the mapping between destinations and SD-WAN
paths, SD-WAN CPEs are still responsible for routing table
maintenance as remote destinations change their attachments, e.g.,
the dynamic workload in other DCs are de-commissioned or added.
Even though originally envisioned for interconnecting branch
offices, SD-WAN offers a very attractive way for enterprises to
connect to Cloud DCs.
The SD-WAN for interconnecting branch offices and the SD-WAN for
interconnecting to Cloud DCs have some differences:
- SD-WAN for interconnecting branch offices usually have two end-
points (e.g. CPEs) controlled by one entity (e.g., a controller
or management system operated by the enterprise).
- SD-WAN for interconnecting to Cloud DCs may have CPEs owned or
managed by the enterprise and remote end-points being managed
or controlled by Cloud DCs (For the ease of description, let's
call it asymmetrically managed CPEs).
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- Cloud DCs may have different entering points (or devices) with
one terminating private direct connect (such as MPLS, or direct
line) and other points being the device terminating the IPsec
tunnels, as shown in the following diagram.
Therefore, the SD-WAN becomes asymmetric.
+------------------------+
| ,---. ,---. |
| (TN-1 ) ( TN-2)|
| `-+-' +---+ `-+-' |
| +----|vR1|----+ |
| ++--+ |
| | +-+----+
| | /Internet\ One path via
| +-------+ Gateway +---------------------+
| \ / Internet \
| +-+----+ \
+------------------------+ \
\
+------------------------+ \
| ,---. ,---. | |
| (TN-3 ) ( TN-4)| |
| `-+-' +--+ `-+-' | | +------+
| +----|vR|-----+ | +------+ CPE |
| ++-+ | | +------+
| | +-+----+ |
| | / virtual\ One path via IPsec Tunnel |
| +-------+ Gateway +-------------------------- +
| \ / |
| +-+----+ |
+------------------------+ |
|
+------------------------+ |
| ,---. ,---. | |
| (TN-5 ) ( TN-6)| |
| `-+-' +--+ `-+-' | |
| +----|vR|-----+ | |
| ++-+ | |
| | +-+----+ +------+ |
| | / \ Via Direct /customer\ |
| +-------+ Gateway +----------+ gateway |-----+
| \ / Connect \ /
| +-+----+ +------+
+------------------------+
Figure 2: Asymmetric Paths SD-WAN
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8. End-to-End Security Concerns for Data Flows
When IPsec tunnels from enterprise on-premises CPEs are terminated
at the Cloud DC gateway where the workloads or applications are
hosted, some enterprises have concerns regarding traffic to/from
their workload being exposed to others behind the data center
gateway (e.g., exposed to other organizations that have workloads
in the same data center).
To ensure that traffic to/from workloads is not exposed to
unwanted entities, it is necessary to have the IPsec tunnels go
all the way to the workload (servers, or VMs) within the DC.
9. Requirements for Dynamic Cloud Data Center VPNs
[Editor's note: this section is only a place holder. The requirement
listed here are only to stimulate more discussions]
In order to address the aforementioned issues, any solution for
enterprise VPNs that includes connectivity to dynamic workloads or
applications in cloud data centers should satisfy a set of
requirements:
- The solution should allow enterprises to take advantage of the
current state-of-the-art in VPN technology, in both traditional
MPLS-based VPNs and IPsec-based VPNs (or any combination
thereof) that run over-the-top of the public Internet.
- The solution should not require an enterprise to upgrade all
their existing CPEs.
- The solution should not require either CPEs or routers to
support a large number of IPsec tunnels simultaneously.
- The solution needs to support easy and fast VPN connections to
dynamic workloads and applications in third party data centers,
and easily allow these workloads to migrate both within a data
center and between data centers.
- Allow VPNs to provide bandwidth and other performance
guarantees.
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- Be a cost-effective solution for enterprises to incorporate
dynamic cloud-based applications and workloads into their
existing VPN environment.
10. Security Considerations
For the most part, we introduce no new security concerns beyond
those of existing MPLS based VPNs, which are widely deployed. The
one addition to MPLS VPNs is selective use of SD-WAN, which uses
IPsec tunnels for the privacy and separation of VPN traffic.
Also see Section 8 for a discussion of end-to-end security for data
flows.
11. IANA Considerations
This document requires no IANA actions. RFC Editor: Please remove
this section before publication.
12. References
12.1. Normative References
12.2. 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.
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[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.
13. Acknowledgments
Many thanks to Ignas Bagdonas, Mehmet Toy, Michael Huang, Liu Yuan
Jiao, Katherine Zhao, and Jim Guichard for the discussion and
contributions.
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Authors' Addresses
Linda Dunbar
Huawei
Email: Linda.Dunbar@huawei.com
Andrew G. Malis
Huawei
Email: agmalis@gmail.com
Christian Jacquenet
France Telecom
Rennes, 35000
France E m i a : l C h r s i i t n a j . a c u q n e t e o @ r a g n . e o c m
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