Internet DRAFT - draft-dmk-rtgwg-multisegment-sdwan
draft-dmk-rtgwg-multisegment-sdwan
Network Working Group K. Majumdar
Internet Draft Microsoft
Intended status: Standard Track L. Dunbar
Expires: August 20, 2024 Futurewei
V.Kasiviswanathan
Arista
A. Ramchandra
Microsoft
A. Choudhary
Aviatrix
February 20, 2024
Multi-segment SD-WAN via Cloud DCs
draft-dmk-rtgwg-multisegment-sdwan-07
Abstract
This document describes a method for SD-WAN CPEs using GENEVE
Encapsulation (RFC8926) to encapsulate the IPsec encrypted
packets and send them to their closest Cloud GWs, who can
steer the IPsec encrypted payload through the Cloud Backbone
without decryption to the egress Cloud GWs which then forward
the original IPsec encrypted payload to the destination CPEs.
This method is for Cloud Backbone to connect multiple
segments of SD-WAN without the Cloud GWs decrypting and re-
encrypting the payloads.
Status of this Memo
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Table of Contents
1. Introduction..............................................3
2. Conventions used in this document.........................5
3. Use Cases.................................................6
3.1. Multi-segment SD-WAN via Single Cloud GW.............6
3.2. Multi-segment SD-WAN via Cloud Backbone..............7
3.3. Analysis of Policy-based Traffic Steering............8
3.4. End to End Encryption................................9
4. Data Plane encoding for SD-WAN Transit....................9
4.1. Multi-Segment SD-WAN Option Class....................9
4.2. SD-WAN Tunnel Endpoint Sub-TLV......................10
4.3. SD-WAN Tunnel Originator Sub-TLV....................11
4.4. Egress GW Sub-TLV...................................12
4.5. Include Transit Sub-TLV.............................12
4.6. Exclude-Transit Sub-TLV.............................13
5. IPsec Flow through Cloud GWs Illustration................14
5.1. Single Hop Cloud GW.................................14
5.2. Multi-hop Transit GWs...............................16
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5.3. Data Authentication and Integrity Check by Cloud GW.18
6. Illustration of Traffic from Private VPN to IPsec Tunnel.19
7. Control Plane considerations.............................21
7.1. Control Plane for CPEs..............................21
7.2. Control Plane between CPEs and Cloud GWs............21
8. Observability Consideration..............................22
9. Security Considerations..................................23
10. Manageability Considerations............................26
11. IANA Considerations.....................................27
12. References..............................................28
12.1. Normative References...............................28
12.2. Informative References.............................29
13. Acknowledgments.........................................29
1. Introduction
SD-WAN is widely deployed to connect enterprises' on-premises
CPEs with services in Cloud DCs. As described in Section 4.1
of [Net2Cloud], there are multiple options for enterprises to
connect to Cloud DCs:
- Direct Interconnect model,
- Direct Interconnect model with Enterprise's virtual
appliances in the Cloud,
- Indirect Interconnect model via SD-WAN paths and
- Managed Hybrid WAN model using Enterprise's existing VPN
connections.
For the enterprise branches with private VPN circuits
interconnecting with a Cloud GW via IXP (Internet
eXchange Point), the Enterprise can extend into Cloud DC
without setting up IPsec paths between their on-premises
CPEs and the Cloud GWs.
Enterprises connecting to Cloud DC may find significant
benefits in leveraging the Cloud Backbone for transporting
traffic between their CPEs, such as
1. Enterprises can benefit from the robust and high-
performance infrastructure cloud service providers provide
by leveraging diverse paths and harnessing cloud backbones'
scalability and global reach to reduce the risk of downtime
or disruptions.
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2. The scalability of the Cloud Backbone allows for efficient
handling of increased data traffic, accommodating the
growing demands of modern enterprises.
3. Cloud Backbone's centralized management and orchestration
capabilities contribute to simplified network
administration, enabling organizations to streamline their
operations and respond more effectively to changing
business requirements.
To ensure security, enterprise traffic between their CPEs is
encrypted and remains inaccessible to any third parties,
including the Cloud DC. For the encrypted packets to be
steered through the Cloud Backbone, the packet header must
contain information indicating the packet's intended route.
Given that the IPsec SA between CPEs is exclusively
maintained between the CPEs and is not accessible to Cloud
GWs, the encrypted packet needs to be carried by a tunnel
between the source CPE and the ingress Cloud GW. This tunnel
can be another layer of IPsec, which adds processing overhead
to the Cloud GW to decrypt the outer IPsec tunnel solely for
steering the encrypted payload.
By steering the encrypted traffic through the Cloud Backbone
without the need for decryption and re-encryption at Cloud
GWs, processing demands at these GWs can be significantly
reduced. This streamlined approach not only maintains the
integrity of the encrypted traffic but also optimizes
processing resources, enhancing overall efficiency within the
cloud infrastructure.
This document introduces a method for SD-WAN CPEs that
utilizes GENEVE Encapsulation [RFC8926] to encapsulate IPsec
encrypted packets, directing them to the nearest Cloud GWs.
These gateways can determine whether the packet needs to
traverse the backbone without decryption by inspecting Sub-
TLVs within the GENEVE header, as specified in Section 4.
Once determined that the packet is intended for backbone
traversal, the IPsec encrypted payload is steered through the
Cloud Backbone without decryption to optimal egress Cloud
GWs. These gateways then forward the original IPsec encrypted
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payload to the destination CPEs. This method facilitates the
Cloud Backbone's connecting multiple SD-WAN segments without
Cloud GWs decrypting and re-encrypting payloads.
GENEVE is selected in this document as the encapsulation
protocol due to its widespread usage in Cloud DC sites.
2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED",
"MAY", and
"OPTIONAL" in this document are to be interpreted as
described in BCP14 [RFC2119] [RFC8174] when, and only when,
they appear in all
capitals, as shown here.
The following acronyms and terms are used in this document:
Cloud DC: Off-Premises Data Center, managed by the third
party, that hosts applications, services, and
workload for different organizations or tenants.
CPE: Customer (Edge) Premises Equipment.
OnPrem: On Premises data centers and branch offices.
RR Route Reflector.
SD-WAN An overlay connectivity service that optimizes
transport of IP Packets over one or more Underlay
Connectivity Services and determining forwarding
behavior by applying Policies to them. [MEF-70.1]
VPN Virtual Private Network.
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3. Use Cases
3.1. Multi-segment SD-WAN via Single Cloud GW
For enterprise branches that have established SD-WAN paths to
a Cloud GW for accessing Cloud services, the Cloud GW can be
utilized to connect those branches, as shown in Figure 1.
Here are some reasons for connecting those branches via a
Cloud GW:
- The public internet among those branches might have limited
bandwidth, unpredictable connection performance, or be
prone to cyber-attacks. In comparison, the network paths
from CPEs to the Cloud GW have more reliable connections
and are constantly monitored by sophisticated network
functions.
- It is easier to utilize Cloud based security functions,
such as Firewall, DDoS, etc., to apply consistent policy
enforcement for workloads/services to the Cloud and across
the branches.
- Proprietary cloud-based tools and SaaS (Software as a
Service) may be available in specific deployments to
collect and analyze the threat to the traffic.
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(^^^^^^^^^^^^)
( Cloud )
( +----+ +----+ )
+ -----(-|Edge| + GW | )
Direct | ( +----+ +/--\+ )
Connect | (^^^^^^^/^^^^\^)
{-+---} / \ SD-WAN Path CPE<->GW
{ VPN } / \
{-+---} / IPsec Tunnel
+-------+----/------+ \
| / | \
++--/+ | +-\--+
|CPE1| +----+CPE2|
+----+ +----+
Client Route: 11.1.1.x 10.1.1.x
21.1.1.x 20.1.1.x
30.1.1.x
Figure 1 Multi-Segment SD-WAN stitching via a Cloud GW
3.2. Multi-segment SD-WAN via Cloud Backbone
For geographic faraway enterprise branches that have
established SD-WAN paths to their corresponding Cloud GWs to
access Cloud services in different geographic locations, the
Cloud backbone can connect those branches, as shown in Figure
2. The reasons to utilize the Cloud Backbone to interconnect
those branches are similar to interconnecting multiple
branches via a single Cloud GW described in the previous
section.
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(^^^^^^^^^^^^^^^)
( Cloud )
( +----+ +----+ ) +-----+
+ ---(-|Edge|==| GW1|=================== GW2 |
Direct | ( +----+ +/--\+ ) +--|--+
Connect | (^^^^^^^/^^^^\^) |
{-+---} / \ |
{ VPN } / \ +-----+
{-+---} / IPsec Tunnel |CPE10|
+-------+--/--------+ \ +-----+
| / | \
10.2.1.x
++/--+ | +\---+
20.2.1.x
|CPE1| +----+CPE2|
30.2.1.x
+----+ +----+
Client Route: 11.1.1.x 10.1.1.x
21.1.1.x 20.1.1.x
30.1.1.x
Figure 2 Multi-Segment SD-WAN Stitching via Cloud Backbone
3.3. Analysis of Policy-based Traffic Steering
There are many well-developed methods, such as SRv6 or
MPLS-TE, to steer traffic through specific nodes. Those
traffic steering methods are effective when the entire
network domain is under one administrative control.
However, the traffic from on-premises CPEs to Cloud GWs via
the public internet can only be forwarded based on the
packets' destination addresses.
SD-WAN allows for the setup of multiple links (paths), some
of which are the Public Internet, from the same SD-WAN
branch CPE to a Cloud GW; each link (or path) represents a
dual tunnel connection from a unique public IP of the SD-
WAN CPE to two different instances of Cloud GW. Using Cloud
GW to interconnect those on-premises CPEs eliminates the
need to manage the multiple ISPs' links/paths between the
CPEs.
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3.4. End to End Encryption
To ensure the confidentiality, integrity, and availability of
communication among CPEs, the traffic between the CPEs should
be encrypted by the IPsec SAs if traversing the public
Internet. When the traffic between the enterprise's CPEs
doesn't terminate within the Cloud DCs, the processing burden
on Cloud GWs can be significantly reduced if the Cloud GWs
don't need to decrypt and re-encrypt transit IPsec encrypted
traffic among CPEs. This document describes the mechanisms
for the IPsec encrypted traffic between CPEs to traverse the
Cloud GWs without being decrypted and re-encrypted by the
Cloud GWs.
4. Data Plane encoding for SD-WAN Transit
For Cloud GWs to differentiate the packets destined towards
their internal hosts/services, which require decryption, and
transit packets to be forwarded to the respective destination
branch CPEs, proper marking is needed in the packets' header.
As the GENEVE Encapsulation [RFC8926] is supported by most
Cloud Service Providers, GENEVE is chosen as the
encapsulation header for Cloud GWs to steer IPsec encrypted
packets among CPEs without decryption.
4.1. Multi-Segment SD-WAN Option Class
Geneve header is specified in Section 3 of [RFC8926].
A new GENEVE Option Class (Type value=TBD) is added to
indicate that the Multi-segment SD-WAN relevant Sub-TLVs are
encoded in the GENEVE header.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| multi-seg-SD-WAN Option Class |C| Type |R|R|R| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ SD-WAN Tunnel Endpoint Sub-TLV ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Optional SD-WAN Tunnel Originator Sub-TLV ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Optional Egress GW Sub-TLV ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// //
// Optional Type Length Value objects (variable) //
// //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4 Multi Segment SD-WAN Option Class
C-bit needs to be set, so that receiving node can drop the
packet if it does not recognize the option [RFC8926].
Type indicates the various types of multi-segment SD-WAN.
Type = Multi-seg-SDWAN_subType1 (To be assigned by IANA):
Single Hop Transit SD-WAN
Type = Multi-seg-SDWAN_subType3 (To be assigned by IANA):
Multi-Hop Transit SD-WAN with explicitly specified egress
Cloud GW.
Type = Multi-seg-SDWAN_subType3 (To be assigned by IANA):
Multi-Hop Transit SD-WAN without specified egress Cloud GW.
Note: the payload after the multi-seg-SD-WAN Option Class can
be IPv4 or IPv6. The IP header protocol type = 50 (ESP)
[RFC4303] indicates the payload is IPsec ESP encrypted.
4.2. SD-WAN Tunnel Endpoint Sub-TLV
The SD-WAN Endpoint sub-TLV indicates the destination CPE of
the IPsec Tunnel.
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For example, for the SD-WAN IPsec SA from CPE1 to CPE2 shown
in Figure 1, the Tunnel Endpoint Sub-TLV of the Geneve Header
has the CPE2's IP address.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|SD-WAN Endpoint| length | Reserved | TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SD-WAN Dst Addr Family | Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (variable) +
~ ~
| SD-WAN end point Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5 SD-WAN Endpoint Sub-TLV
TTL is set by the SD-WAN Tunnel Originator, e.g., CPE1. Each
transit node or transit region/zone (visible to the CPEs) SHOULD
decrement the TTL so that the destination CPE can know the number
of logical transit nodes (cloud regions or zones) the packet has
traversed. Enterprises can also use TTL to set the maximum transit
nodes/regions the packets traverse.
4.3. SD-WAN Tunnel Originator Sub-TLV
The SD-WAN Tunnel Originator Sub-TLV is an optional Sub-TLV
inside the multi-seg-SD-WAN Option Class to indicate the
originating CPE of the IPsec Tunnel.
For example, for the SD-WAN IPsec SA from CPE1 to CPE2 shown
in Figure 1, the Tunnel Originator Sub-TLV inside the Geneve
Header of the packets indicates CPE1's address.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|SDWAN Origin | length | reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SD-WAN Org Addr Family | Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (variable) +
~ ~
| SD-WAN Tunnel Originator Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6 SD-WAN Tunnel Originator Sub-TLV
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The Tunnel Originator Sub-TLV in the GENEVE header can assist
Cloud transit nodes in applying appropriate policies when
forwarding the packet.
4.4. Egress GW Sub-TLV
For the multi-segment SD-WAN via Cloud Backbone scenario, the
originator CPE can use the Egress GW Sub-TLV to specify the
Egress Cloud GW for reaching the destination CPE.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|SDWAN EgressGW | length | reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Egress GW Addr Family | Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (variable) +
~ ~
| Egress GW Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7 SD-WAN Egress GW Sub-TLV
The originator CPE can get the Egress GW address by
configuration or by control plane protocol exchanged with
destination CPEs. The detailed Control Plane protocol
extension is out of the scope of this document.
4.5. Include Transit Sub-TLV
Include-Transit Sub-TLV is an optional Sub-TLV for explicitly
including a list of Cloud Availability Regions or Zones for
reasons like:
- Those regions have certain OAM and security functions for
the improved visibility.
- To comply with regulations, etc.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Include-Transit| length |Transit_Type |I|Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Transit node ID |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8 Include-Transit Sub-TLV
Multiple Include-Transit Sub-TLVs can be incorporated into a
single GENEVE header to denote multiple nodes or regions
intended for inclusion when steering the packet through the
Cloud Backbone. It's important to note that the multiple
Include-Transit Sub-TLVs constitute a set rather than an
ordered list.
Transit_type:
TBD1: when Transit node ID is represented as a numeric
number, such as a Cloud Availability Region or Zone numeric
identifier that the Cloud Operator provides.
TBD2: when Transit node ID is represented as a string, such
as a Cloud Availability Region or Zone name that the Cloud
Operator provides.
TBD3: when Transit node ID is represented as an IP address.
I-bit:
When set to 0: it indicates it needs best effort to steer
through the transit node ID.
When set to 1, it indicates that the Transit Node ID must be
included through the Cloud Backbone. If the Transit Node ID
cannot be traversed, an alert or alarm must be generated to
the enterprise via an out-of-band channel. It is out of the
scope of this document to specify those alerts or alarms.
4.6. Exclude-Transit Sub-TLV
Exclude-Transit Sub-TLV is an optional Sub-TLV for explicitly
excluding a list of Cloud Availability Regions or Zones for
reasons like
- To comply with regulations,
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- To avoid regions that impose certain risks.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Exclude-Transit| length |Transit_Type |E| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Transit node ID |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9 Exclude-Transit Sub-TLV
Multiple Exclude-Transit Sub-TLVs can be incorporated into a
single GENEVE header to denote multiple nodes or regions to
be exclouded when steering the packet through the Cloud
Backbone. It's important to note that the multiple Enclude-
Transit Sub-TLVs constitute a set rather than an ordered
list.
Transit_type: same as Section 4.6
E-bit:
When set to 0: it indicates it needs best effort to avoid
the transit node ID.
When set to 1, it indicates that the Transit Node ID must be
avoided through the Cloud Backbone. If the Transit Node ID
cannot be avoided, an alert or alarm must be generated to
the enterprise via an out-of-band channel. It is out of the
scope of this document to specify those alerts or alarms.
5. IPsec Flow through Cloud GWs Illustration
This section illustrates Cloud GWs connecting traffic flow
carried by the IPsec tunnels.
5.1. Single Hop Cloud GW
Assuming that all CPEs are under one administrative control
(e.g., iBGP).
Using Figure 1 as an example:
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- There is a bidirectional IPsec tunnel between CPE1 and
Cloud GW; with IPsec SA1 for the traffic from the CPE1
to the Cloud-GW; and IPsec SA2 for the traffic from
the Cloud-GW to the CPE1.
- There is a bidirectional IPsec tunnel between CPE2 and
Cloud GW; with IPsec SA3 for the traffic from the CPE2
to the Cloud-GW; and IPsec SA4 for the traffic from
the Cloud-GW to the CPE2.
- All the CPEs are under one iBGP administrative domain,
with a Route Reflector (RR) as their controller. The
CPEs notify their peers of their corresponding Cloud
GW addresses (which is out of the scope of this
document).
When 11.1.1.x and 10.1.1.x need to communicate with each
other, CPE1 and CPE2 establish a bidirectional IPsec
Tunnel, with SA5 for the traffic from CPE1 to CPE2 and SA6
for the traffic from CPE2 to CPE1. Assume the IPsec ESP
Tunnel Mode is used. A packet from 11.1.1.1 to 10.1.1.2 has
the following outer header:
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Outer IP header:
+---------------------------+
| protocol = 17(UDP) |
| src = CPE1 |
| dst = Cloud GW |
+---------------------------+
| Source Port =xxxx |
| Dst Port = 6081 (GENEVE) |
+===========================+
| GENEVE Header |
| multi-seg-SD-WAN Option |
|GENEVE Proto = 50 (ESP) |
+- - -- -- - - -- - --+
|SD-WAN EndPt SubTLV (CPE2) |
+---------------------------+ < ----------+
|SPI(Security Parameter Idx)| Authenticated
+---------------------------+ |
| sequence number | |
+---------------------------+ <-+ |
| payload IP header: | | |
| src = 11.1.1.1 | | |
| dst = 10.1.1.2 | | |
+---------------------------+ Encrypted |
| TCP header + | | |
~ payload (variable) ~ | |
| | | |
+===========================+ <-+ -------+
| Authentication Data |
+---------------------------+
Figure 8 Packet header illustration of traffic to Cloud GWs
5.2. Multi-hop Transit GWs
Traffic to/from geographic apart CPEs can cross multiple
Cloud DCs via Cloud backbone.
The on-premises CPEs are under one administrative control
(e.g., iBGP).
Using Figure 2 as an example:
- There is a bidirectional IPsec tunnel between CPE1 and
the Cloud GW1; with IPsec SA1 for the traffic from the
CPE1 to the Cloud-GW1; and IPsec SA2 for the traffic
from the Cloud-GW1 to the CPE1.
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- There is a bidirectional IPsec tunnel between CPE10
and the Cloud GW2; with IPsec SA3 for the traffic from
the CPE10 to the Cloud-GW2; and IPsec SA4 for the
traffic from the Cloud-GW2 to the CPE10.
- All the CPEs are under one iBGP administrative domain,
with a Route Reflector (RR) as their controller. CPEs
notify their peers of their corresponding Cloud GW
addresses.
When 11.1.1.x and 10.2.1.x need to communicate with each
other, CPE1 and CPE10 establish a bidirectional IPsec
Tunnel, with SA5 for the traffic from CPE1 to CPE10 and SA6
for the traffic from CPE10 to CPE1. Assume the IPsec ESP
Tunnel Mode is used, a packet from 11.1.1.1 to 10.2.1.2 has
the following outer header:
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Outer IP header:
+---------------------------+
| proto = 17 (UDP) |
| src = CPE1 |
| dst = Cloud GW1 |
+===========================+
| GENEVE Header |
| multi-seg-SD-WAN Option |
|GENEVE Proto = 50 (ESP) |
+- - -- -- - - -- - --+
|SD-WAN EndPt SubTLV (CPE10)|
+---------------------------+
| EgressGW-SubTLV |
+---------------------------+ < ----------+
|SPI(Security Parameter Idx)| Authenticated
+---------------------------+ |
| sequence number | |
+---------------------------+ <-+ |
| payload IP header: | | |
| src = 11.1.1.1 | | |
| dst = 10.2.1.2 | | |
+---------------------------+ Encrypted |
| TCP header + | | |
~ payload (variable) ~ | |
| | | |
+===========================+ <-+ -------+
| Authentication Data |
+---------------------------+
Figure 9 GENEVE header encapsulated IPsec packet
5.3. Data Authentication and Integrity Check by Cloud GW
The IPsec SA already encrypts the client payload between
the CPEs, the Cloud GW doesn't need to decrypt and re-
encrypt the payload when relaying it to the destination
CPE. However, data authentication and integrity check are
needed as the traffic traverse an untrusted network.
[RFC2403] and [RFC2404] define the authentication
algorithms used in AH and ESP. SHA2 224/256/384/512 are
some of the cryptographic hashing algorithms. They are part
of a Hashed Message Authentication Code.
5.4. Packet Header Processing
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In Figure 1, upon receiving a GENEVE encapsulated packet
with the GENEVE Protocol Type = 50 (ESP), the Cloud GW does
the following:
- Authenticate the packet using a preconfigured
authentication method.
- Extract the destination CPE address from the SD-WAN
Endpoint Sub-TLV inside the GENEVE header. Replace the
outer IP destination address with the destination CPE
address.
- Optionally replace the outer IP source address with the
Cloud GW address.
- GENEVE header is unchanged.
- Forward the packet to the destination CPE.
The cloud GW SHOULD drop all packets with the source
addresses or the values in the Sub-TLVs of the GENEVE
header that are not recognized or registered to prevent
unauthorized users from using the Cloud services.
5.5. Error Handling
As traffic through Cloud Backbone takes precious resources,
the Cloud GW SHOULD drop the packets with unregistered source
or destination addresses.
Cloud GW SHOULD drop the packets originated from unpaid (or
unregistered) address (CPE).
Cloud GW SHOULD validate the value of the SD-WAN Endpoint
Sub-TLV and drop the packet if the value of the SD-WAN
Endpoint Sub-TLV is an unpaid (or unregistered) address.
6. Illustration of Traffic from Private VPN to IPsec Tunnel
This section illustrates a Cloud GW connecting client traffic
from a branch CPE via a Private VPN to another CPE via an
IPsec tunnel.
Using Figure 1 as an example:
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- CPE1 send traffic via a Private VPN (Direct Connect to
the Cloud Edge) to the Cloud GW. The traffic is not
encrypted.
- There is a bidirectional IPsec tunnel between CPE2 and
the Cloud GW; with IPsec SA1 for the traffic from the
CPE2 to the Cloud-GW; and IPsec SA2 for the traffic
from the Cloud-GW to the CPE2.
- All the CPEs are under one iBGP administrative domain,
with a Route Reflector (RR) as their controller. CPEs
notify their peers of their corresponding Cloud GW
addresses.
Assume the IPsec ESP Tunnel Mode is used for the IPsec SA
between Cloud GW and CPE2. For a packet from 11.1.1.1 to
10.2.1.2, the following header is added by CPE1 sending
over the Private VPN:
Outer IP header:
+---------------------------+
| proto = 17 (UDP) |
| src = CPE1 |
| dst = Cloud GW |
+===========================+
| GENEVE Header |
| multi-seg-SD-WAN Option |
|GENEVE Proto =TCP/UDP/etc. |
+- - -- -- - - -- - --+
|SD-WAN EndPt SubTLV (CPE2) |
+---------------------------+ < -+
| payload IP header: | |
| src = 11.1.1.1 | |
| dst = 10.2.1.2 | |
+---------------------------+ Not Encrypted
| TCP header + | |
~ payload (variable) ~ |
| | |
+===========================+ <-+
Figure 10 Illustration of packet through VPN
Upon receiving the GENEVE encapsulated packet with the
"Multi-Segment-SD-WAN" option, the Cloud GW extracts the
destination CPE from the GENEVE header and encrypts the
packet with the IPsec SA2 to forward to the destination
(i.e., CPE2). The GENEVE Header is carried to the CPE2.
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Outer IP header:
+---------------------------+
| proto = 17 (UDP) |
| src = Cloud GW |
| dst = CPE2 |
+===========================+
| GENEVE Header |
| multi-seg-SD-WAN Option |
|GENEVE Proto =50 (ESP) |
+- - -- -- - - -- - --+
|SD-WAN EndPt SubTLV (CPE2) |
+---------------------------+ < ----------+
|SPI(Security Parameter Idx)| Authenticated
+---------------------------+ |
| sequence number | |
+---------------------------+ <-+ |
| payload IP header: | | |
| src = 11.1.1.1 | | |
| dst = 10.2.1.2 | | |
+---------------------------+ Encrypted |
| TCP header + | | |
~ payload (variable) ~ | |
| | | |
+===========================+ <-+ -------+
| Authentication Data |
+---------------------------+
Figure 11 Illustration of packet from the Egress Cloud GW
7. Control Plane considerations
7.1. Control Plane for CPEs
The control plane enables SD-WAN edges to discover their
properties and attached routes. The on-premises CPEs and
their vCPEs (or Virtual Appliances in Cloud DC) can be
controlled by one iBGP instance. [SD-WAN-Edge-Discovery]
describes the mechanism for SD-WAN edges to discover each
other's properties. The IPsec Key Exchange between on-
premises CPEs and the vCPE is via the iBGP Update through RR.
[SD-WAN-Edge-Discovery].
7.2. Control Plane between CPEs and Cloud GWs
It is common to have eBGP sessions between enterprises CPEs
and the Cloud GWs. An enterprise-owned vCPE can establish an
eBGP session with the Cloud VPN GW for accessing the
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workloads hosted in the Cloud DCs. If an IPsec tunnel is
required between the Cloud DC GW and the vCPE, the full suite
of IPSec IKEv2 must be exchanged between the vCPE and the
Cloud GW.
8. Observability Consideration
Observability considerations encompass monitoring, analysis,
and reporting mechanisms to gain insights into the behavior
and performance of the multi-segment SD-WAN infrastructure.
Key observability aspects include:
- Performance Metrics:
Monitor and collect performance metrics related to link
utilization, latency, and packet loss across the SD-WAN
segments and Cloud DC backbone. This data provides insights
into the overall health and efficiency of the network. IP
Flow Information Export (IPFIX) [RFC7011] is one of the
standardized methods to expose traffic flow over the
network.
- Global Network Topology Visualization:
Utilize visualization tools to depict the global network
topology, showcasing the interconnections and traffic flows
between different SD-WAN segments and Cloud DCs.
- Control Plane Monitoring:
Monitor the control plane for both CPEs and the
communication between CPEs and Cloud GWs. This includes
tracking route discovery, path selection, and any changes
in network state to ensure proper functioning of the SD-WAN
control plane.
- Security Event Logging:
The security event logging is to capture and analyze
security-related events, including threat detection,
authentication failures, and any unauthorized access
attempts. Syslog [RFC5424] is a valuable tool for security
monitoring and auditing.
These considerations contribute to the overall success of the
multi-segment SD-WAN deployment connecting edge devices via a
Cloud DC backbone.
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9. Security Considerations
9.1. Threat Analysis
As shown in Figure 3, the information carried by the GENEVE
Header is not encrypted, which is susceptible to Man-in-the-
Middle (MitM) attacks. An attacker can intercept and
potentially alter the information in the GENEVE header
between the branch CPEs and the Cloud GWs without the
enterprise and the Cloud provider's knowledge or consent.
Here is the threat analysis of the MitM attacks between CPEs
and Cloud GWs:
a) Eavesdropping: Attackers can get knowledge of the
enterprise's branch locations and their respective
contracted Cloud GWs. As the payload between the CPEs is
encrypted, attackers can't get any data exchanged between
CPEs. This threat is no different from direct IPsec SAs
between two CPEs.
b) Data Manipulation: Attackers alter the content (Sub-TLVs)
in the GENEVE header. As packets with unrecognized source
addresses or invalid values in the Sub-TLVs of the GENEVE
header are dropped by Cloud GWs, there might be a higher
packet drop rate between the CPEs.
Packet drop is not a new problem. The transport layer, such
as TCP or QUIC, can handle packet drop well.
c) Potential steeling of Cloud Backbone bandwidth:
A threat actor might want to leverage Cloud Backbones to
transport its own traffic between two locations without
paying for the services. For example, a legitimate Cloud
subscriber pays for the Cloud Backbone transport services
for traffic between CPE-A and CPE-B. The attacker, who has
two locations far apart (say Node-A and Node-B), can use
CPE-A's address as the source address and CPE-B as the
value in the SD-WAN Endpoint Sub-TLV for a packet from
Node-A to Node-B before reaching the ingress Cloud GW. When
the packet is sent from the egress Cloud GW via the
Internet towards CPE-B, the actor can change the source
address back to Node-A and the destination address to Node-
B. By doing so, Node-A and Node-B can maintain the IPsec
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tunnel via the Cloud Backbone without paying for the
service.
Therefore, it is necessary to have some level data
integrity and authentication for traffic between CPEs and
Cloud GWs even though it is not necessary for Cloud GWs to
decrypt and re-encrypt the payload between CPEs.
9.2. HMAC-based Integrity and Authentication
HMAC (Hash-based Message Authentication Code), a widely used
cryptographic technique for ensuring both data integrity and
authentication, can be used to ensure the integrity and
authenticity of data between CPEs and Cloud GWs to verify
that GENEVE header has not been tampered with.
The basic idea behind HMAC is to combine a secret key and a
hash function to produce a fixed-size authentication code for
the GENEVE header between CPEs and the Cloud GW. This
authentication code is then sent along with the data itself.
When the Cloud GW and the destination CPEs receive the data
and the authentication code, they can independently compute
the HMAC using the same key and hash function. If the
computed HMAC matches the received authentication code, it
indicates that the data has not been altered, as long as the
secret key remains confidential.
The HMAC authentication code can be carried by an HMAC Sub-
TLV in the GENEVE Header, as specified below:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|MultiSDWAN-HMAC| length | reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
| HMAC Authentication Code for entire GENEVE Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12 Multi Segment SD-WAN HMAC Sub-TLV
The HMAC Authentication Code, a.k.a. the HMAC hash value, is
computed including all the bytes in the GENEVE header and with the
MultiSDWAN-HMAC value field setting to 0.
The advantages of using HMAC are:
- Data Integrity: HMAC provides a strong mechanism for
verifying the integrity of data. By hashing the message
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and using a secret key, it generates a fixed-size hash
value that ensures the data has not been tampered with
during transmission.
- Authentication: HMAC also verifies the authenticity of
the sender. Since HMAC requires a shared secret key
between the sender and receiver, it confirms that the
sender is who they claim to be.
- Efficiency: HMAC is computationally efficient, making it
suitable for real-time and resource-constrained devices.
It uses simple bitwise operations and hash functions.
- Resistance to Tampering: HMAC is designed to resist
various forms of tampering, including replay attacks,
message insertion, and message deletion. Any change in
the message will result in a different HMAC value.
- Flexibility: HMAC can be used with various hash
functions, such as SHA-256 or SHA-512, depending on the
desired level of security requirements.
- Widely Supported: HMAC is a well-established and widely
supported authentication mechanism, making it easy to
integrate into different systems.
Here are some common problems associated with using the HMAC
and why their risks are acceptable in the scenario described
in this draft.
- Key Management: The security of HMAC depends heavily on the
confidentiality and management of the shared secret key. If
the key is compromised, the data packets from CPEs to Cloud
GW can be dropped but not compromised because the user
payloads are protected by IPsec SA encryption.
- Lack of Non-Repudiation: HMAC provides data integrity and
sender authentication but does not provide non-repudiation.
Non-repudiation is the ability to prove that a message was
sent by a specific sender, which HMAC alone cannot
guarantee. This risk is same as two IPsec protected traffic
between CPEs.
- Limited to Symmetric Cryptography: HMAC relies on symmetric
key cryptography, which means that both parties must share
the same secret key. As the Cloud backbone interconnecting
CPEs are paid services, there are established channels to
distribute the symmetric key.
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- No Protection Against Eavesdropping: While HMAC ensures
data integrity and sender authentication, it does not
provide encryption. Eavesdropping does pose additional
risks to payloads encrypted by IPsec SA.
In summary, HMAC-based integrity and authentication offer
strong security benefits in terms of data integrity and
sender authentication. Even though it does not provide non-
repudiation or protection against eavesdropping, the IPsec
encrypted payload between CPEs won't be impacted.
9.3. AH based Integrity and Authentication
For enterprises or Cloud providers worrying about secret HMAC
keys being compromised, they can add another layer of AH
encryption [RFC4301] or ESP-NULL [RFC2410] [RFC6071] on top
of the IPsec encryption between the two CPEs. Both AH and
ESP-NULL IPsec encryption require pairwise IPsec key
management between Cloud GWs and the CPEs, therefore
requiring more processing on Cloud GWs and CPEs. In addition,
the AH encrypted packets can't traverse NAT because of outer
IP address changes.
10. Manageability Considerations
The following manageability considerations are crucial for
the successful deployment and ongoing operation of the
proposed strategies outlined in this document:
- Centralized Orchestration:
A centralized orchestration system is needed to manage
and authenticate multiple SD-WAN segments through the
Cloud GWs.
- Policy-based Configuration:
Utilize policy-driven configurations to streamline the
deployment of SD-WAN segments and their connectivity
options. This approach allows for efficient management
of network policies, ensuring consistent and coherent
behavior across diverse deployment scenarios. [RFC8192]
can be used to automate the security policy
configurations.
- Real-time Monitoring and Analytics:
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Integrate robust monitoring and analytics tools to
provide real-time visibility into the performance and
health of SD-WAN segments. This includes monitoring
bandwidth utilization, latency, packet loss, and other
key performance indicators to promptly identify and
address any issues.
- Automated Alerting and Reporting:
Implement automated alerting mechanisms to promptly
notify network administrators of potential issues or
anomalies within the SD-WAN infrastructure.
Additionally, generate regular reports to facilitate
performance analysis, capacity planning, and compliance
monitoring.
11. IANA Considerations
IANA is requested to assign a new GENEVE Option Class from
the IETF Review range as shown below:
Option
Class Description Assignee/Contact Reference
------ ------------------- ------------- -----------
TBD Multi Segment SD-WAN IETF [this document]
Multi-seg-
SDWAN_subType Description Assignee/Contact Reference
------ -------------- ------------- -----------
TBD1 Single Hop Transit IETF [this document]
TBD2 MultiHopTransit IETF [this document]
TBD3 MultiHop wo egress IETF [this document]
IANA is requested to create a registry as below with the
initial values shown in the Multi Segment SD-WAN Geneve
Option Class registry group:
Registry: Multi Segment SD-WAN Sub-TLVs
Assignment Policy: IETF Review
Reference: [this document]
Sub-TLV Type Description Reference
------------ ---------------------- ---------------
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0 Reserved
1 SD-WAN Endpoint [this document]
2 SD-WAN Originator [this document]
3 SD-WAN Egress GW [this document]
4 Multi SD-WAN-HMAC [this document]
5-254 Unassigned
255 Reserved
12. References
12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2403] C. Madson, R. Glenn, "The Use of HMAC-MD5-96 within
ESP and AH", RFC2403, Nov. 1998.
[RFC2404] C. Madson, R. Glenn, "The Use of HMAC-SHA-1-96
within ESP and AH", RFC2404, Nov. 1998.
[RFC4301] S. Kent and K. Seo, "Security Architecture for the
Internet Protocol", RFC4301, Dec. 2005.
[RFC4303] S. Kent, "IP Encapsulating Security Payload (ESP)".
RFC4303, Dec. 2005.
[RFC5424] R. Gerhards, "The Syslog Protocol", RFC5424, March
2009.
[RFC7011] B. Claise, B. Trammell, and P. Aitken,
"Specification of the IP Flow Information Export
(IPFIX) Protocol for the Exchange of Flow
Information", RFC7011, Sept 2013.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in
RFC 2119 Key Words", BCP 14, RFC 8174, DOI
10.17487/RFC8174, May 2017, <https://www.rfc-
editor.org/info/rfc8174>.
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[RFC8926] J. Gross, et al, "Geneve: Generic Network
Virtualization Encapsulation", RFC8926, Nov 2020.
12.2. Informative References
[RFC2410] R. Glenn and S. Kent, "The NULL encryption
Algorithm and Its Use with IPsec", RFC2310, Nov.
1998.
[RFC6071] S. Frankel and S. Krishnan, "IP Security (IPsec)
and Internet Key Exchange (IKE) Document Roadmap",
Feb. 2011.
[RFC8192] S. Hares, et al, "Interface to Network Security
Functions (I2NSF) Problem Statement and Use Cases",
July 2017
[MEF-70.1] MEF 70.1 SD-WAN Service Attributes and Service
Framework. Nov. 2021.
[Net2Cloud] L. Dunbar and A. Malis, "Dynamic Networks to
Hybrid Cloud DCs Problem Statement", draft-ietf-
rtgwg-net2cloud-problem-statement-34, Jan, 2024.
[SD-WAN-Edge-Discovery] L. Dunbar, et al, "BGP UPDATE for SD-
WAN Edge Discovery", draft-ietf-idr-sdwan-edge-
discovery-12, Oct. 2023.
13. Acknowledgments
Acknowledgements to Adrian Farrel, Donald Eastlake, Stephen
Farrell for their extensive review and suggestions.
This document was prepared using 2-Word-v2.0.template.dot.
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Authors' Addresses
Linda Dunbar
Futurewei
Email: ldunbar@futurewei.com
Kausik Majumdar
Microsoft
Email: kmajumdar@microsoft.com
Venkit Kasiviswanathan
Arista
Email: venkit@arista.com
Ashok Ramchandra
Microsoft
Email: aramchandra@microsoft.com
Aseem Choudhary
Aviatrix
Email: achoudhary@aviatrix.com
Contributors' Addresses
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