BGP Usage for SDWAN Overlay Networks
draft-ietf-bess-bgp-sdwan-usage-01
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| Last updated | 2020-11-02 | ||
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draft-ietf-bess-bgp-sdwan-usage-01
Network Working Group L. Dunbar
Internet Draft J. Guichard
Intended status: Informational Futurewei
Expires: May 2, 2021 Ali Sajassi
Cisco
J. Drake
Juniper
B. Najem
Bell Canada
Ayan Barnerjee
D. Carrel
Cisco
November 2, 2020
BGP Usage for SDWAN Overlay Networks
draft-ietf-bess-bgp-sdwan-usage-01
Abstract
The document describes three distinct SDWAN scenarios and discusses
the applicability of BGP for each of those scenarios. The goal of
the document is to demonstrate how BGP-based control plane is used
for large scale SDWAN overlay networks with little manual
intervention.
SDWAN edge nodes are commonly interconnected by multiple underlay
networks which can be owned and managed by different network
providers.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. This document may not be modified,
and derivative works of it may not be created, except to publish it
as an RFC and to translate it into languages other than English.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
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other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six
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This Internet-Draft will expire on May 2, 2009.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction...................................................3
2. Conventions used in this document..............................4
3. Use Case Scenario Description and Requirements.................6
3.1. Requirements..............................................6
3.1.1. Supporting Multiple SDWAN Segmentations..............6
3.1.2. Client Service Requirement...........................6
3.1.3. Application Flow Based Segmentation..................7
3.1.4. Zero Touch Provisioning..............................8
3.1.5. Constrained Propagation of SDWAN Edge Properties.....9
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3.2. Scenario #1: Homogeneous WAN.............................10
3.3. Scenario #2: CPE based SDWAN over Hybrid WAN Underlay....11
3.4. Scenario #3: Private VPN PE based SDWAN..................14
4. BGP Walk Through..............................................15
4.1. BGP Walk Through for Homogeneous SDWAN...................15
4.2. BGP Walk Through for Hybrid WAN Underlay.................17
4.3. BGP Walk Through for Application Flow Based Segmentation.18
4.4. Client Service Provisioning Model........................20
4.5. Underlay Network Properties Advertisement................21
4.6. Why BGP as Control Plane for SDWAN?......................21
5. SDWAN Traffic Forwarding Walk Through.........................22
5.1. SDWAN Network Startup Procedures.........................22
5.2. Packet Walk-Through for Scenario #1......................23
5.3. Packet Walk-Through for Scenario #2......................23
5.4. Packet Walk-Through for Scenario #3......................25
6. Manageability Considerations..................................25
7. Security Considerations.......................................25
8. IANA Considerations...........................................26
9. References....................................................26
9.1. Normative References.....................................26
9.2. Informative References...................................26
10. Acknowledgments..............................................28
1. Introduction
Here are some key characteristics of "SDWAN" networks:
- Augment of transport, which refers to utilizing overlay paths
over different underlay networks. Very often there are multiple
parallel overlay paths between any two SDWAN edges, some of
which are private networks over which traffic can traverse with
or without encryption, others require encryption, e.g. over
untrusted public networks.
- Enable direct Internet access from remote sites, instead hauling
all traffic to Corporate HQ for centralized policy control.
- Some traffic flows can be forwarded based on their application
identifiers instead of based on destination IP addresses, by the
edge nodes placing the traffic flows onto specific overlay paths
based on their application requirement.
- The traffic flows forwarding can also be based on specific
performance criteria (e.g. packets delay, packet loos, jitter)
to provide better application performance by choosing the right
underlay that meets or exceeds the specified criteria.
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[Net2Cloud-Problem] describes the network related problems that
enterprises face to connect enterprises' branch offices to dynamic
workloads in different Cloud DCs, including using SDWAN to aggregate
multiple paths provided by different service providers to achieve
better performance and to accomplish application ID based
forwarding.
Even though SDWAN has been positioned as a flexible way to reach
dynamic workloads in third party Cloud data centers over different
underlay networks, scaling becomes a major issue when there are
hundreds or thousands of nodes to be interconnected by an SDWAN
overlay networks.
BGP is widely used by underlay networks. This document describes
using BGP for edge nodes to exchange information across the SDWAN
overlay networks.
2. Conventions used in this document
Cloud DC: Third party data centers that host applications and
workloads owned by different organizations or tenants.
Controller: Used interchangeably with SDWAN controller to manage
SDWAN overlay path creation/deletion and monitor the
path conditions between sites.
CPE: Customer Premise Equipment
CPE-Based VPN: Virtual Private Secure network formed among CPEs.
This is to differentiate from more commonly used PE-
based VPNs [RFC 4364].
Homogeneous SDWAN: A type of SDWAN network in which all traffic
to/from the SDWAN edge nodes has to be encrypted
regardless of underlay networks. For lack of better
terminology, we call this Homogeneous SDWAN throughout
this document.
ISP: Internet Service Provider
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NSP: Network Service Provider. NSP usually provides more
advanced network services, such as MPLS VPN, private
leased lines, or managed Secure WAN connections, many
times within a private trusted domain, whereas an ISP
usually provides plain internet services over public
untrusted domains.
PE: Provider Edge
SDWAN Edge Node: an edge node, which can be physical or virtual,
maps the attached clients' traffic to the wide area
network (WAN) overlay tunnels.
SDWAN: Software Defined Wide Area Network. In this document,
"SDWAN" refers to networks that allow augment of
transport, application ID and/or performance based
forwarding, and direct internet breakout at remote
sites.
SDWAN IPsec SA: IPsec Security Association between two SDWAN ports
or nodes.
SDWAN over Hybrid Networks: SDWAN over Hybrid Networks typically
have edge nodes utilizing bandwidth resources from
multiple service providers. In Hybrid SDWAN network,
packets over private networks can go natively without
encryption and are encrypted over the untrusted network,
such as the public Internet.
WAN Port: A Port or Interface facing an ISP or Network Service
Provider (NSP), with address (usually public routable
address) allocated by the ISP or the NSP.
C-PE: SDWAN Edge node, which can be CPE for customer managed
SDWAN, or PE that is for provider managed SDWAN
services).
ZTP: Zero Touch Provisioning
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3. Use Case Scenario Description and Requirements
SDWAN networks can have different topologies and have different
traffic patterns. To make it easier for the focused discussion in
subsequent drafts on SDWAN control plane and data plane, this
section describes several SDWAN scenarios that may have different
impact on their corresponding control planes & data planes.
3.1. Requirements
3.1.1. Supporting Multiple SDWAN Segmentations
The term "network segmentation", a.k.a. SDWAN instances, is
referring to the process of dividing the network into logical sub-
networks using isolation techniques on a forwarding device such as a
switch, router, or firewall. For a homogeneous network, such as MPLS
VPN or Layer 2 network, VRF or VLAN are used to achieve the network
segmentation.
As SDWAN is an overlay network arching over multiple types of
networks, MPLS L2VPN/L3VPN or pure L2 underlay can continue using
the VRF, VN-ID or VLAN to differentiate SDWAN network segmentations.
For public internet, the IPsec inner encapsulation header can carry
the SDWAN Instance Identifier to differentiate the packets belonging
to different SDWAN instances.
BGP already has the capability to differentiate control packets for
different network instances. When using BGP for SDWAN, the SDWAN
segmentations can be differentiated by the SDWAN Target ID in the
BGP Extended Community in the same way as VPN instances being
represented by the Route Target. Same as Route Target, need to use a
different name to differentiate from VPN if a CPE supports
traditional VPN with multiple VRFs and supports multiple SDWAN
Segmentations (instances). The actual SDWAN Target ID encoding is
proposed by [SDWAN-EDGE-Discovery].
3.1.2. Client Service Requirement
Client interface of SDWAN nodes can be IP or Ethernet based.
For Ethernet based client interfaces, SDWAN edge should support
VLAN-based service interfaces (EVI100), VLAN bundle service
interfaces (EVI200), or VLAN-Aware bundling service interfaces. EVPN
service requirements are applicable to the Client traffic, as
described in the Section 3.1 of RFC8388.
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For IP based client interfaces, L3VPN service requirements are
applicable.
3.1.3. Application Flow Based Segmentation
Application Flow based Segmentation, also known as SDWAN Traffic
Segmentation, enables the separation of the traffic based on the
business and the security needs for different users' groups and/or
application requirements. Each user group and/or applications may
need different isolated topology and/or policies to fulfill the
business requirements.
The Application Flow based Segmentation concept is analogous to VLAN
(in L2 network) and VRF (in L3 network).
One can think about the Application Flow based Segmentation as a
feature that can be provided or enabled on a single SDWAN service
(or domain) to a single Subscriber. Each SDWAN Service can have one
or more overlay Segments to support the business requirement; each
Segment has its own policy, topology and application/user groups.
Applications/users' group can belong to more than one Segment.
For example, a retail business requires the point-of-sales (PoS)
application in all stores to be isolated from other applications AND
routed only to the payment processing entity at a hub site (i.e. hub
and spoke); however, the same retail business requires the other
applications to be routed to all sites (i.e. multipoint-to
multipoint) AND isolated from the PoS application.
In the figure below, the traffic from the PoS application follows a
Tree topology, whereas other traffic can be multipoint-to-multipoint
topology.
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+--------+
Payment traffic |Payment |
+------+----+-+gateway +------+----+-----+
/ / | +----+---+ | \ \
/ / | | | \ \
+-+--+ +-+--+ +-+--+ | +-+--+ +-+--+ +-+--+
|Site| |Site| |Site| | |Site| |Site| |Site|
| 1 | | 2 | | 3 | | |4 | | 5 | | 6 |
+--+-+ +--+-+ +--|-+ | +--|-+ +--|-+ +--|-+
| | | | | | |
==+=======+=======+====+======+=======+=======+===
Multi-point connection for Other traffic
Another example is an enterprise who wants to isolate the traffic
for each department and have different topology and policy for
different department; the HR department may need to access certain
applications that are NOT accessible by the engineering department.
In addition, the contractors may have a limited access to the
enterprise resources.
3.1.4. Zero Touch Provisioning
Unlike traditional EVPN or L3VPN whose PEs are deployed for long
term, SDWAN edge nodes (virtual or physical) deployment at a
specific location can be ephemeral. Therefore, Zero Touch
Provisioning (ZTP), or Plug and Play, is a common requirement for
SDWAN. When an SDWAN edge is physically installed at a location or
instantiated on a VM in a Cloud DC, ZTP automates follow-up steps,
including updates to the OS, software version, and configuration
prior to connection. From network control perspective, ZTP includes
the following:
- Upon power up, an SDWAN node can establish transport layer
secure connection (such as TLS, SSL, etc.) to its controller whose
address can be burned or preconfigured on the device.
- The SDWAN Controller can designate a Local Network Controller
in the proximity of the SDWAN node; the Local Network Controller
manages and monitor the communication policies of the edge node.
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3.1.5. Constrained Propagation of SDWAN Edge Properties
One SDWAN edge node may only be authorized to communicate with a
small number of other SDWAN edge nodes. Under this circumstance, the
property of the SDWAN edge node cannot be propagated to any other
nodes who are not authorized to communicate. But a remote SDWAN edge
node upon powering up might not have the proper policies to know who
the authorized peers are. Therefore, it is very essential for SDWAN
deployment have a central point to distribute the properties of each
SDWAN edge node to its authorized peers.
BGP is well suited for this purpose. RFC 4684 has specified the
procedure to constrain the distribution of BGP UPDATE to only a
subset of SDWAN edges. Basically, each edge node informs the Route
Reflector (RR) [RFC4456] on its interested SDWAN instances. The RR
only propagates the BGP UPDATE for the relevant SDWAN instances to
the edge.
Usually the connection between a SDWAN edge node and its RR is over
insecure network. Therefore, upon power up, a SDWAN node needs to
establish a secure transport layer connection (TLS, SSL, etc.) to
its designated RR. The BGP UPDATE messages need to be sent over the
secure channel (TLS, SSL, etc.) to the RR.
+---+
Peer Group 1 |RR | Peer Group 2
+======+====+=+ +======+====+=====+
/ / | +---+ | \ \
/ / | | \ \
+-+--+ +-+--+ +-+--+ +-+--+ +-+--+ +-+--+
|C-PE| |C-PE| |C-PE| |C-PE| |C-PE| |C-PE|
| 1 | | 2 | | 3 | |4 | | 5 | | 6 |
+----+ +----+ +----+ +----+ +----+ +----+
Tenant 1 Tenant 2
Figure 1: Peer Groups managed by RR
Tenant separation is achieved by the SDWAN instance identification
represented in control plane and data plane, respectively.
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3.2. Scenario #1: Homogeneous WAN
This is referring to a type of SDWAN network with edge nodes
encrypting all traffic over WAN to other edge nodes, regardless of
whether the underlay is private or public. For lack of better
terminology, we call this Homogeneous SDWAN throughout this
document.
Some typical scenarios for the use of a Homogeneous SDWAN network
are as follows:
- A small branch office connecting to its HQ offices via the
Internet. All sensitive traffic to/from this small branch office has
to be encrypted, which is usually achieved using IPsec SAs.
- A store in a shopping mall may need to securely connect to its
applications in one or more Cloud DCs via the Internet. A common way
of achieving this is to establish IPsec SAs to the Cloud DC gateway
to carry the sensitive data to/from the store.
As described in [SECURE-EVPN], the granularity of the IPsec SAs for
Homogeneous SDWAN can be per site, per subnet, per tenant, or per
address. Once the IPsec SA is established for a specific
subnet/tenant/site, all traffic to/from the subnets/tenants/site are
encrypted.
+---+
+--------------|RR |------------+
/ Untrusted +-+-+ \
/ \
/ \
+----+ +---------+ +------+ +----+
| CN3|--| P1-----+ -------------+------ P1 |--| CN1|
+----+ | C-PE1 P2-----+ | | C-PE2| +----+
+----+ | P3-----+ Wide +------ P2 | +----+
| CN2|--| | | area +------ P3 |--| CN3|
+----+ +---------+ | network | +------+ +----+
| |
+----+ +---------+ | all packets | +------+ +----+
| CN1|--| P1-----+ encrypted +------ P1 |--| CN1|
+----+ | C-PE3 P2-----+ by | | C-PE4| +----+
+----+ | P3-----+ IPsec SAs +------ P2 | +----+
| CN2|--| P4-----+--------------+ | |--| CN2|
+----+ +---------+ +------+ +----+
CN: Client Networks, which is same as Tenant Networks used by NVo3
Figure 2: Homogeneous SDWAN
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One of the key properties of homogeneous SDWAN is that the SDWAN
Local Network Controller (RR)is connected to C-PEs via untrusted
public network, therefore, requiring secure connection between RR
and C-PEs (TLS, DTLS, etc.).
Homogeneous SDWAN has some similarity to commonly deployed IPsec
VPN, albeit the IPsec VPN is usually point-to-point among a small
number of nodes and with heavy manual configuration for IPsec
between nodes, whereas an SDWAN network can have a large number of
edge nodes with an SDWAN controller to manage requiring zero touch
provisioning upon powering up.
Existing Private VPNs (e.g. MPLS based) can use homogeneous SDWAN to
extend over public network to remote sites to which the VPN operator
does not own or lease infrastructural connectivity, as described in
[SECURE-EVPN] and [SECURE-L3VPN]
3.3. Scenario #2: CPE based SDWAN over Hybrid WAN Underlay
In this scenario, SDWAN edge nodes (a.k.a. C-PEs) have some WAN
ports connected to PEs of Private VPNs over which packets can be
forwarded natively without encryption, and some WAN ports connected
to the public Internet over which sensitive traffic have to be
encrypted (usually by IPsec SA).
In this scenario, the SDWAN edge nodes' egress WAN ports are all
IP/Ethernet based, either egress to PEs of the VPNs or egress to the
public Internet. Even if the VPN is a MPLS network, the VPN's PEs
have IP/Ethernet links to the SDWAN edge (C-PEs). Throughout this
document, this scenario is also called CPE based SDWAN over Hybrid
Networks.
Even though IPsec SA can secure the packets traversing the Internet,
it does not offer the premium SLA commonly offered by Private VPNs,
especially over long distance. Clients need to have policies to
specify criteria for flows only traversing private VPNs or
traversing either as long as encrypted when over the Internet. For
example, client can have those polices for the flows:
1. A policy or criteria for sending the flows over a private
network without encryption (for better performance),
2. A policy or criteria for sending the flows over any networks
as long as the packets of the flows are encrypted when
traversing untrusted networks, or
3. A policy of not needing encryption at all.
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If a flow traversing multiple segments, such as A<->B<->C<->D, has
either Policy 2 or 3 above, the flow can traverse different
underlays in different network segments, such as over Private
network underlay between A<->B without encryption, or over the
public internet between B<->C in an IPsec SA.
As shown in the figure below, C-PE-1 has two different types of
interfaces (A1 to Internet and A2 & A3 to VPN). The C-PEs' loopback
addresses and addresses attached to C-PEs may or may not be visible
to the ISPs/NSPs. The addresses for the WAN ports can have addresses
allocated by service providers or dynamically assigned (e.g. by
DHCP). One WAN port shown in the figure below (e.g. A1, A2, A3 etc.)
is a logical representation of potential multiple physical ports on
the C-PEs.
+---+
+--------------|RR |----------+
/ Untrusted +-+-+ \
/ \
/ \
+----+ +---------+ packets encrypted over +------+ +----+
| CN3|--| A1-----+ Untrusted +------ B1 |--| CN1|
+----+ | C-PE1 A2-\ | C-PE2| +----+
+----+ | A3--+--+ +---+---B2 | +----+
| CN2|--| | |PE+--------------+PE |---B3 |--| CN3|
+----+ +---------+ +--+ trusted +---+ +------+ +----+
| WAN |
+----+ +---------+ +--+ packets +---+ +------+ +----+
| CN1|--| C1--|PE| go natively |PE |-- D1 |--| CN1|
+----+ | C-PE3 C2--+--+ without encry+---+ | C-PE4| +----+
| | +--------------+ | |
| | | |
+----+ | | without encrypt over | | +----+
| CN2|--| C3--+---- Untrusted --+------D2 |--| CN2|
+----+ +---------+ +------+ +----+
CN: Client Network
Figure 3: Hybrid SDWAN
Some key characteristics of a Hybrid SDWAN overlay network are as
follows:
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- one C-PE may be connected to different ISPs/NSPs, with some of its
WAN ports addresses being assigned by different ISPs/NSPs.
- The WAN ports connected to PEs of trusted private networks (e.g. MPLS
VPN) hand off IP/Ethernet packets, just like today's CPE that do not
handle MPLS packets and do not participate in the underlay VPN networks'
control plane. Traffic can flow natively without encryption when be
forwarded out through those WAN ports for better performance.
- The WAN ports connected to untrusted networks, e.g. the Internet,
requires sensitive traffic to be encrypted, i.e. encrypted by IPsec SA.
- An SDWAN local Network Controller (RR) is connected to C-PEs via
the untrusted public network, therefore, requiring secure
connection between RR and C-PEs via TLS, DTLS, etc.
- The SDWAN nodes' [loopback] addresses might not be routable nor
visible in the underlay ISP/NSP networks. Routes & services
attached to SDWAN edges at the SDWAN overlay layer are in
different address spaces than the underlay networks.
- There could be multiple SDWAN devices sharing a common property,
such as a geographic location. Some applications over SDWAN may
need to traverse specific geographic locations for various
reasons, such as to comply with regulatory rules, to utilize
specific value added services, or others.
- The underlay path selection between sites can be a local decision.
Some policies allow one service from C-PE1 -> C-PE2 -> C-PE3 using
one ISP/NSP underlay in the first segment (C-PE1 -> C-PE2) and
using a different ISP/NSP in the second segment (C-PE2-> CPE3).
- Services may not be congruent, i.e. the packets from A-> B may
traverse one underlay network, and the packets from B -> A may
traverse a different underlay.
- Different services, routes, or VLANs attached to SDWAN nodes can
be aggregated over one underlay path; same service/routes/VLAN can
spread over multiple SDWAN underlays at different times depending
on the policies specified for the service. For example, one
tenant's packets to HQ need to be encrypted when sent over the
Internet or have to be sent over private networks, while the same
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tenant's packets to Facebook can be sent over the Internet without
encryption.
3.4. Scenario #3: Private VPN PE based SDWAN
This scenario refers to existing VPN (e.g. MPLS based VPN, such as
EVPN or IPVPN) adding extra ports facing untrusted public networks
allowing PEs to offload some low priority traffic to ports facing
public networks when the VPN MPLS paths are congested. Throughout
this document, this scenario is also called Internet Offload for
Private VPN, or PE based SDWAN.
In this scenario, the packets offloaded to untrusted public network
must be encrypted.
PE based SDWAN can be used by VPN service providers to temporarily
increase bandwidth between sites when they are not sure if the
demand will sustain for long period of time or as a temporary
solution before the permanent infrastructure is built or leased.
+---+
+-------|PE2|
/ +---+
Internet / ^
offload / || VPN
/ VPN v
++--+ ++-+ +---+
|PE1| <====> |RR| <===> |PE3|
+-+-+ +--+ +-+-+
| |
+--- Public Internet -- +
Figure 4: Additional Internet paths added to the VPN
Here are some key properties for PE based SDWAN:
- For MPLS based VPN, PEs continue having MPLS encapsulation
handoff to existing paths.
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- The BGP RR is connected to PEs in the same way as VPN, i.e.
via the trusted network.
- For the added Internet ports, PEs have IP packets handoff,
i.e. sending and receiving IP data frames. Internally, PEs
can have the option to encapsulate the MPLS payload in IP, as
specified by RFC4023.
- The ports facing public internet might get IP addresses
assigned by ISPs, which may not be in the same address domain
as PEs'.
- Ports facing public internet are not as secure as the ports
facing private infrastructure. There could be spoofing, or
DDOS attacks to the ports facing public internet. Extra
consideration must be given when injecting the new routes
learned from public network into VRFs.
- Even though packets are encrypted over public internet, the
performance SLA is not guaranteed over public internet.
Therefore, clients may have policies only allowing some flows
to be offloaded to internet path.
4. BGP Walk Through
4.1. BGP Walk Through for Homogeneous SDWAN
In the figure below, packets destined towards multiple routes
attached to the C-PE2 can be carried by one IPsec tunnel. Then one
BGP UPDATE can be announced by C-PE2 to its RR.
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+---+
+---------|RR |----------+
/ Untrusted+---+ \
/ \
C-PE1/ \
+---------+ +------+
--+---+---------------------------------> |-10.1.x.x/16
| / | |C-PE2 |- VLAN = 15
| / | +-----> |
--|/1.1.1.1 | | | |-12.1.1.x/24
+---------+ | +------+
| 2.2.2.2
|
C-PE3 |
+---------+ |
--|---+---------------------------+
| / |
| / |
--|/3.3.3.3 |
+---------+
Figure 5: Homogeneous SDWAN
The BGP UPDATE Message from C-PE2 to RR should have the client
routes encoded in the MP-NLRI Path Attribute and the IPsec Tunnel
associated information encoded in the Tunnel-Encap Path Attributes
as described in the [SECURE-EVPN].
Alternatively, two separate BGP UPDATEs can be used to optimize the
BGP UPDATE packet size, as described by Section 4 and 8 of [Tunnel-
encap]. UPDATE U1 has its Nexthop to the node loopback address and
is reclusively resolved to the IPsec tunnel detailed attributes
advertised by the UPDATE U2 for the Node Loopback address:
Suppose that:
- a given packet P destined towards the client addresses attached
to C-PE2 (e.g. prefix 10.1.x.x/16) can be carried by any IPsec
tunnels terminated at C-PE2;
- The path along which P is to be forwarded is determined by BGP
UPDATE U1;
- UPDATE U1 does not have a Tunnel Encapsulation attribute;
- UPDATE U1 can include Encapsulation Extended Community and/or
Color Extended Community;
- The address of the next hop of UPDATE U1 is router C-PE2;
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- The best route to router C-PE2 is a BGP route that was
advertised in UPDATE U2;
- UPDATE U2 has a Tunnel Encapsulation attribute to further
describe the IPsec detailed attributes.
UPDATE U1:
- MP-NLRI Path Attribute:
10.1.x.x/16
VLAN #15
12.1.1.x/24
Nexthop: 2.2.2.2 (C-PE2)
- Encapsulation Extended Community: Type = IPsec
UPDATE U2:
- MP-NLRI Path Attribute:
2.2.2.2 (C-PE2)
- Tunnel Encapsulation Path Attributes (as described in the
[SECURE-EVPN])
If different client routes attached to C-PE2 needs to be reached by
separate IPsec tunnels, then The Color-Extended-Community [Tunnel-
encap] is used to associate routes with the tunnels. See Section 8
of [Tunnel-encap].
If C-PE2 doesn't have the policy on authorized peers for the
specific client routes, RR needs to check the client routes policies
to propagate the BGP UPDATE messages to the remote authorized edge
nodes.
4.2. BGP Walk Through for Hybrid WAN Underlay
In this scenario, some client routes can be forwarded by any tunnels
terminated at the edge node and some client routes can be forwarded
by some specific tunnels (such as only MPLS VPN).
Color Extended Community (Section 4 & 8 of [Tunnel-Encap]) can be
used to represent specific tunnels for the client routes.
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For example, in the Figure 5 above, suppose that Route 10.1.x.x/16
can be carried by either MPLS or IPsec, and Route 12.1.1.x/24 can
only be carried by MPLS, the following UDPATE messages can be used:
UPDATE #1a for Route Route 10.1.x.x/16:
- MP-NLRI Path Attribute:
10.1.x.x/16
Nexthop: 2.2.2.2 (C-PE2)
- Encapsulation Extended Community: Type = IPsec
- Encapsulation Extended Community: Type= MPLS-in-GRE
- Color Extended Community: RED
UPDATE #1b for Route Route 12.1.1.x/24:
- MP-NLRI Path Attribute:
12.1.1.x/24
Nexthop: 2.2.2.2 (C-PE2)
- Encapsulation Extended Community: Type= MPLS-in-GRE
- Color Extended Community: YELLOW
UPDATE #2a: for IPsec tunnels terminated at the node:
- MP-NLRI Path Attribute:
2.2.2.2 (C-PE2)
- Tunnel Encapsulation Path Attributes: TYPE=IPsec (as described
in the [SECURE-EVPN])
- Color Extended Community: RED
UPDATE #2b: for MPLS-in-GRE terminated at the node:
- MP-NLRI Path Attribute:
2.2.2.2 (C-PE2)
- Tunnel Encapsulation Path Attributes: TYPE=MPLS-in-GRE [Tunnel-
Encap] Section 3
- Color Extended Community: YELLOW
4.3. BGP Walk Through for Application Flow Based Segmentation
If the applications are assigned with unique IP addresses, the
Application Flow based Segmentation described in Section 3.1.2 can
be achieved by advertising different BGP UPDATE messages to
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different nodes. In the Figure below, the following BGP Updates can
be advertised to ensure that Payment Application only communicates
with the Payment Gateway:
BGP UPDATE #1a from C-PE2 to RR for the P2P topology that is only
propagated to Payment GW node:
UPDATE #1a (only to the Payment GW node):
- MP-NLRI Path Attribute:
- 30.1.1.x/24
- Nexthop: 2.2.2.2
- Encapsulation extended community: Tunneltype=IPSEC
- Color Extended Community: BLUE
BGP UPDATE #1b from C-PE2 to RR for the routes to be reached by C-
PE1 and C-PE2:
- MP-NLRI Path Attribute:
- 10.1.x.x
- 12.4.x.x
- Nexthop:2.2.2.2
- Encapsulation extended community: Tunnel-type=IPSEC
- Color Extended Community: RED
BGP UPDATE #2 describes the IPsec detailed attributes for IPsec
tunnels terminated at C-PE2 2.2.2.2.
UPDATE #2a: for all IPsec SAs terminated at the node:
- MP-NLRI Path Attribute:
2.2.2.2 (C-PE2)
- Tunnel Encapsulation Path Attributes: TYPE=IPsec (for all IPsec
SAs)
- Color Extended Community: RED
UPDATE #2b: for the IPsec SA to the Payment Gateway:
- MP-NLRI Path Attribute:
2.2.2.2 (C-PE2)
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- Tunnel Encapsulation Path Attributes: TYPE=IPsec (for the IPsec
SA to Payment GW).
- Color Extended Community: Blue
+-------+
|Payment|
+-------->| GW |<-------+
/Hub-spoke +-------+ \
/for Payment App \
C-PE1 / \ C-PE2
+------/--+ +----\-+
--|-----/ | | -|- 30.1.1.x/24
+ ---------------------------------------> |-10.1.x.x/16
| | | |-
| | +------------> |- 12.1.1.x/24
--|---------------------------+ | |
+---------+ +------> |- VLAN=25;
/ +------+ 22.1.1.x/24
+---------+ /
--| -----------------------------+
| C-PE3 | /
| | /
--| --------------------------+
+---------+
Figure 6: Application Based SDWAN Segmentation
4.4. Client Service Provisioning Model
The provisioning tasks described in Section 4 of RFC8388 are the
same for the SDWAN client traffic. When client traffic is multi-
homed to two (or more) C-PEs, the Non-Service-Specific parameters
need to be provisioned per the Section 4.1.1 of RFC8388.
Since some SDWAN nodes are ephemeral and have small number of IP
subnets or VLANs attached to their client ports, it is recommended
to have default and simplified Service-specific parameters for each
client port, remotely managed by the SDWAN Network Controller via
the secure channel (TLS/DTLS) between the controller and the C-PEs.
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4.5. Underlay Network Properties Advertisement
Since the deployment of PEs to MPLS VPN are for relatively long
term, the common provisioning procedure for PE's WAN ports is via
CLI.
A SDWAN node deployment can be ephemeral and its location can be in
remote locations, manual provisioning for its WAN ports is not
acceptable. In addition, a SDWAN WAN port's IP address can be
dynamically assigned or using private addresses. Therefore, it is
necessary to have a separate control protocol; something like NHRP
did for ATM, for a SDWAN node to advertise its directly connected
underlay network properties to its peers.
Unlike a PE to MPLS based VPN where its WAN ports are homogeneously
facing MPLS private network and all traffic are egressed in MPLS
data frames through its WAN ports, the WAN ports of a SDWAN node can
be connected to a PE of VPN with Ethernet/IP, MPLS private network
directly via MPLS headers, or the public Internet.
For Scenario #1 described in Section 3.2, the WAN ports can face
public internet or VPN.
For Scenario #2 described in Section 3.3, WAN ports are either
configured as connecting to PEs of VPN where traffic can be sent as
IP/Ethernet without encryption, or configured as connecting to
public Internet that requires encryption for packets egress out.
For Scenario #3 described in Section 3.4, the WAN ports are either
configured as VPN egress ports (hand off MPLS data frames), or as
connecting to the public internet that requires MPLS in IP in IPsec
encapsulation.
4.6. Why BGP as Control Plane for SDWAN?
For a small sized SDWAN network, traditional hub & spoke model using
NHRP or DSVPN/DMVPN with a hub node (or controller) managing SDWAN
node WAN ports mapping (e.g. local & public addresses and tunnel
identifiers mapping) can work reasonably well. However, for a large
SDWAN network, say more than 100 nodes with different types of
topologies, the traditional approach becomes very messy, complex and
error prone.
Here are some of the compelling reasons of using BGP instead of
extending NHRP/DSVPN/DMVPN. (Same as the reasons quoted by LSVR on
why using BGP):
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- BGP has the built-in capability to constrain the propagation of
SDWAN edge node properties to a small number of edge nodes
[RFC4684].
- RR already has the capability to apply policies to communications
among peers.
- BGP is widely deployed as sole protocol (see RFC 7938)
- Robust and simple implementation
- Wide acceptance - minimal learning
- Reliable transport
- Guaranteed in-order delivery
- Incremental updates
- Incremental updates upon session restart
- No flooding and selective filtering
5. SDWAN Traffic Forwarding Walk Through
BGP based EVPN control plane are still applicable to routes attached
to the client ports of SDWAN nodes. Section 5 of RFC8388 describes
the BGP EVPN NLRI Usage for various routes of client traffic. The
procedures described in the Section 6 of RFC8388 are same for the
SDWAN client traffic.
The only additional consideration for SDWAN is to control how
traffic egress the SDWAN edge node to various WAN ports.
5.1. SDWAN Network Startup Procedures
A SDWAN network can add or delete SDWAN edge nodes on regular basis
depending on user requests.
- For Scenario #1: a SDWAN edge node in a shopping mall or Cloud DC can
be added or removed on demand. The Zero Touch Provisioning described
in 3.1.2 are required for the node startup.
- For Scenario #2: this can be Data Centers or enterprises upgrading
their CPEs to add extra bandwidth via public internet in addition to
VPN services that they already purchased. Before the node powers up
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or upgraded, there should be links connected to the PEs of a provider
VPNs.
- For Scenario #3, the Internet facing WAN ports are added to (or
removed from) existing VPN PEs.
5.2. Packet Walk-Through for Scenario #1
Upon power up, a SDWAN node can learn client routes from the Client
facing ports, in the same way as EVPN described in RFC8388.
Controller facilitates the IPsec SA establishment and rekey
management as described in [SECURE-EVPN]. Controller manages how
client's routes are associated with individual IPSec SA.
[SECURE-EVPN] describes a solution for SDWAN Scenario #1. It
utilizes the BGP RR to facilitate the key and policy exchange among
PE devices to create private pair-wise IPsec Security Associations
without IKEv2 point-to-point signaling or any other direct peer-to-
peer session establishment messages.
When C-PEs do not support MPLS, the approaches described by RFC8365
can be used, with addition of IPsec encrypting the IP packets when
sending packets over the Black Interfaces.
5.3. Packet Walk-Through for Scenario #2
In this scenario, C-PEs have some WAN ports connected to the public
internet and some WAN ports with direct connect to PEs of trusted
VPN. The C-PEs in Scenario #2 have the plain IP/Ethernet data frames
egress to the PEs of the VPN, encrypted data frames egress the WAN
ports facing the public Internet.
Users specify the policy or criteria on which flows can only egress
WAN ports facing the trusted VPN without encryption, which can
egress the WAN ports facing the public Internet with encryption, or
which can egress WAN ports facing the public Internet without
encryption.
The internet facing WAN ports can face potential DDoS attacks,
additional anti-DDoS mechanism has to be enabled on those WAN ports
and the Control Plane should not learn routes from the Public
Network facing WAN ports.
For the Scenario #2, if a client route can be reached by MPLS VPN
and IPsec Tunnel via public network, the BGP UPDATE for the client
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route should indicate all available tunnels in the Tunnel Path
Attribute of the BGP NLRI.
+---+
+--------------|RR |----------+
/ Untrusted +-+-+ \
/ Network \
/ \
+----+ +---------+ packets encrypted over +--------+ +----+
| CN3|--| A1-----+ Untrusted +------ B1 |--| CN1|
+----+ | C-PE-a A2-----+ +-------B2 C-PE-b| +----+
|10.1.1.1 | |10.1.2.1|
+----+ | | +--+ +---+ | | +----+
| CN2|--| A3 |PE+--------------+PE |---B3 |--| CN3|
+----+ +---------+ +--+ trusted +---+ +--------+ +----+
| VPN |
+--------------+
Figure 8: SDWAN Scenario #2
For example, if the CN1 route can be reached by both VPN and Public
internet, the CN1's BGP route UPDATE should include the following:
- MP-NLRI Path Attribute:
CN1
- Tunnel-Encap Path Attribute:
Tunnel 1: MPLS-in-GRE encapsulation
With the MPLS-in-GRE Sub-TLV specified by Tunnel-Encap;
Tunnel 2: IPsec-GRE encapsulation
With the IPsec Sub-TLVs specified by the [SECURE-EVPN] and
[BGP-EDGE-DISCOVERY]
There could be multiple IPsec SA tunnels terminated at the edge node
loopback address or terminated at WAN ports. For the Scenario #2,
there can be policies to determine which IPsec SA tunnels that the
client route can be carried. When a client route can be carried by
multiple IPsec SA tunnels terminated by two different WAN ports,
multiple Tunnel Path Attributes with different Tunnel-end-point Sub-
TLVs need to be included in the NLRI of the BGP UPDATE for the
client route.
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5.4. Packet Walk-Through for Scenario #3
The behavior described in [SECURE-L3VPN] applies to this scenario.
[SECURE-L3VPN] describes how to extend the RFC4364 VPN to allow some
PEs being connected to other PEs via public networks. In this
scenario, the PEs is the SDWAN Edge nodes. [SECURE-L3VPN] introduces
the concept of RED Interface & Black Interface on those PEs. RED
interfaces face the VPN over which packets can be forwarded natively
without encryption. Black Interfaces face public network over which
only IPsec-protected packets are forwarded. [SECURE-L3VPN] assumes
PEs terminate MPLS packets, and use MPLS over IPsec when sending
over the Black Interfaces.
The C-PEs not only have RED interfaces facing clients but also have
RED interface facing MPLS backbone, with additional BLACK interfaces
facing the untrusted public networks for the WAN side. The C-PEs
cannot mix the routes learned from the Black Interfaces with the
Routes from RED Interfaces. The routes learned from core-facing RED
interfaces are for underlay and cannot be mixed with the routes
learned over access-facing RED interfaces that are for overlay.
Furthermore, the routes learned over core-facing interfaces (both
RED and BLACK) can be shared in the same GLOBAL route table.
There may be some added risks of the packets from the ports facing
the Internet. Therefore, special consideration has to be given to
the routes from WAN ports facing the Internet. RFC4364 describes
using an RD to create different routes for reaching same system. A
similar approach can be considered to force packets received from
the Internet facing ports to go through special security functions
before being sent over to the VPN backbone WAN ports.
6. Manageability Considerations
SDWAN overlay networks utilize the SDWAN controller to facilitate
route distribution, central configurations, and others. SDWAN Edge
nodes need to advertise the attached routes to their controller
(i.e. RR in BGP case).
7. Security Considerations
Having WAN ports facing the public Internet introduces the following
security risks:
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1) Potential DDoS attack to the C-PEs with ports facing internet.
2) Potential risk of provider VPN network being injected with
illegal traffic coming from the public Internet WAN ports on the C-
PEs.
8. IANA Considerations
None
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4364] E. rosen, Y. Rekhter, "BGP/MPLS IP Virtual Private
networks (VPNs)", Feb 2006.
[RFC7296] C. Kaufman, et al, "Internet Key Exchange Protocol Version
2 (IKEv2)", Oct 2014.
[RFC7432] A. Sajassi, et al, "BGP MPLS-Based Ethernet VPN", Feb
2015.
[RFC8365] A. Sajassi, et al, "A network Virtualization Overlay
Solution Using Ethernet VPN (EVPN)", March 2018.
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.
[BGP-SDWAN-Port] L. Dunbar, H. Wang, W. Hao, "BGP Extension for
SDWAN Overlay Networks", draft-dunbar-idr-bgp-sdwan-
overlay-ext-03, work-in-progress, Nov 2018.
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[Net2Cloud-Gap] L. Dunbar, A. Malis, C. Jacquenet, "Gap Analysis of
Interconnecting Underlay with Cloud Overlay", draft-dm-
net2cloud-gap-analysis-02, work in progress, Oct. 2018.
[SDWAN-EDGE-Discovery] L. Dunbar, S. Hares, R. Raszuk, K. Majumdar,
"BGP UPDATE for SDWAN Edge Discovery", draft-dunbar-idr-
sdwan-edge-discovery-00, work-in-progress, July 2020.
[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:
https://www.cisco.com/c/en/us/products/security/dynamic-
multipoint-vpn-dmvpn/index.html
[DSVPN] Dynamic Smart VPN:
http://forum.huawei.com/enterprise/en/thread-390771-1-
1.html
[SECURE-EVPN] A. Sajassi, et al, "Secure EVPN", draft-sajassi-bess-
secure-evpn-01, Work-in-progress, March 2019.
[SECURE-L3VPN] E. Rosen, R. Bonica, "Secure Layer L3VPN over Public
Infrastructure", draft-rosen-bess-secure-l3vpn-00, Work-
in-progress, June 2018.
[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
[Net2Cloud-gap] L. Dunbar, A. Malis, and C. Jacquenet, "Gap Analysis
of Interconnecting Underlay with Cloud Overlay", draft-dm-
net2cloud-gap-analysis-02, work-in-progress, Aug 2018.
[Tunnel-Encap] E. Rosen, et al "The BGP Tunnel Encapsulation
Attribute", draft-ietf-idr-tunnel-encaps-10, Aug 2018.
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10. Acknowledgments
Acknowledgements to Adrian Farrel, Joel Halpern, John Scudder,
Darren Dukes, Andy Malis and Donald Eastlake for their review and
contributions.
This document was prepared using 2-Word-v2.0.template.dot.
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Authors' Addresses
Linda Dunbar
Futurewei
Email: ldunbar@futurewei.com
James Guichard
Futurewei
Email: james.n.guichard@futurewei.com
Ali Sajassi
Cisco
Email: sajassi@cisco.com
John Drake
Juniper
Email: jdrake@juniper.net
Basil Najem
Bell Canada
Email: basil.najem@bell.ca
David Carrel
Cisco
Email: carrel@cisco.com
Ayan Banerjee
Cisco
Email: ayabaner@cisco.com
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