L2VPN Workgroup A. Sajassi (Editor)
INTERNET-DRAFT Cisco
Intended Status: Standards Track
J. Drake (Editor)
Y. Rekhter Juniper
R. Shekhar
B. Schliesser Nabil Bitar
Juniper Verizon
S. Salam Aldrin Isaac
K. Patel Bloomberg
D. Rao
S. Thoria James Uttaro
Cisco AT&T
L. Yong W. Henderickx
Huawei Alcatel-Lucent
D. Cai
S. Sinha
Cisco
Wen Lin
Nischal Sheth
Juniper
Expires: August 24, 2015 February 24, 2015
A Network Virtualization Overlay Solution using EVPN
draft-ietf-bess-evpn-overlay-01
Abstract
This document describes how Ethernet VPN (EVPN) [RFC7432] can be used
as an Network Virtualization Overlay (NVO) solution and explores the
various tunnel encapsulation options over IP and their impact on the
EVPN control-plane and procedures. In particular, the following
encapsulation options are analyzed: VXLAN, NVGRE, and MPLS over GRE.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
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 months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/1id-abstracts.html
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html
Copyright and License Notice
Copyright (c) 2012 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
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2 Specification of Requirements . . . . . . . . . . . . . . . . . 5
3 Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4 EVPN Features . . . . . . . . . . . . . . . . . . . . . . . . . 6
5 Encapsulation Options for EVPN Overlays . . . . . . . . . . . . 7
5.1 VXLAN/NVGRE Encapsulation . . . . . . . . . . . . . . . . . 7
5.1.1 Virtual Identifiers Scope . . . . . . . . . . . . . . . 8
5.1.1.1 Data Center Interconnect with Gateway . . . . . . . 8
5.1.1.2 Data Center Interconnect without Gateway . . . . . . 9
5.1.2 Virtual Identifiers to EVI Mapping . . . . . . . . . . . 9
5.1.2.1 Auto Derivation of RT . . . . . . . . . . . . . . . 10
5.1.3 Constructing EVPN BGP Routes . . . . . . . . . . . . . 11
5.2 MPLS over GRE . . . . . . . . . . . . . . . . . . . . . . . 13
6 EVPN with Multiple Data Plane Encapsulations . . . . . . . . . 13
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7 NVE Residing in Hypervisor . . . . . . . . . . . . . . . . . . 14
7.1 Impact on EVPN BGP Routes & Attributes for VXLAN/NVGRE
Encapsulation . . . . . . . . . . . . . . . . . . . . . . . 14
7.2 Impact on EVPN Procedures for VXLAN/NVGRE Encapsulation . . 15
8 NVE Residing in ToR Switch . . . . . . . . . . . . . . . . . . 15
8.1 EVPN Multi-Homing Features . . . . . . . . . . . . . . . . 16
8.1.1 Multi-homed Ethernet Segment Auto-Discovery . . . . . . 16
8.1.2 Fast Convergence and Mass Withdraw . . . . . . . . . . . 16
8.1.3 Split-Horizon . . . . . . . . . . . . . . . . . . . . . 16
8.1.4 Aliasing and Backup-Path . . . . . . . . . . . . . . . . 17
8.1.5 DF Election . . . . . . . . . . . . . . . . . . . . . . 17
8.2 Impact on EVPN BGP Routes & Attributes . . . . . . . . . . . 18
8.3 Impact on EVPN Procedures . . . . . . . . . . . . . . . . . 18
8.3.1 Split Horizon . . . . . . . . . . . . . . . . . . . . . 18
8.3.2 Aliasing and Backup-Path . . . . . . . . . . . . . . . . 19
9 Support for Multicast . . . . . . . . . . . . . . . . . . . . . 19
10 Inter-AS . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
11 Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 21
12 Security Considerations . . . . . . . . . . . . . . . . . . . 21
13 IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
14 References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
14.1 Normative References . . . . . . . . . . . . . . . . . . . 22
14.2 Informative References . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23
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1 Introduction
In the context of this document, a Network Virtualization Overlay
(NVO) is a solution to address the requirements of a multi-tenant
data center, especially one with virtualized hosts, e.g., Virtual
Machines (VMs). The key requirements of such a solution, as described
in [Problem-Statement], are:
- Isolation of network traffic per tenant
- Support for a large number of tenants (tens or hundreds of
thousands)
- Extending L2 connectivity among different VMs belonging to a given
tenant segment (subnet) across different PODs within a data center or
between different data centers
- Allowing a given VM to move between different physical points of
attachment within a given L2 segment
The underlay network for NVO solutions is assumed to provide IP
connectivity between NVO endpoints (NVEs).
This document describes how Ethernet VPN (EVPN) can be used as an NVO
solution and explores applicability of EVPN functions and procedures.
In particular, it describes the various tunnel encapsulation options
for EVPN over IP, and their impact on the EVPN control-plane and
procedures for two main scenarios:
a) when the NVE resides in the hypervisor, and
b) when the NVE resides in a Top of Rack (ToR) device
Note that the use of EVPN as an NVO solution does not necessarily
mandate that the BGP control-plane be running on the NVE. For such
scenarios, it is still possible to leverage the EVPN solution by
using XMPP, or alternative mechanisms, to extend the control-plane to
the NVE as discussed in [L3VPN-ENDSYSTEMS].
The possible encapsulation options for EVPN overlays that are
analyzed in this document are:
- VXLAN and NVGRE
- MPLS over GRE
Before getting into the description of the different encapsulation
options for EVPN over IP, it is important to highlight the EVPN
solution's main features, how those features are currently supported,
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and any impact that the encapsulation has on those features.
2 Specification of Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
3 Terminology
NVO: Network Virtualization Overlay
NVE: Network Virtualization Endpoint
VNI: Virtual Network Identifier (for VXLAN)
VSID: VIrtual Subnet Identifier (for NVGRE)
EVPN: Ethernet VPN
EVI: An EVPN instance spanning the Provider Edge (PE) devices
participating in that EVPN.
MAC-VRF: A Virtual Routing and Forwarding table for Media Access
Control (MAC) addresses on a PE.
Ethernet Segment (ES): When a customer site (device or network) is
connected to one or more PEs via a set of Ethernet links, then that
set of links is referred to as an 'Ethernet segment'.
Ethernet Segment Identifier (ESI): A unique non-zero identifier that
identifies an Ethernet segment is called an 'Ethernet Segment
Identifier'.
Ethernet Tag: An Ethernet tag identifies a particular broadcast
domain, e.g., a VLAN. An EVPN instance consists of one or more
broadcast domains.
PE: Provider Edge device.
Single-Active Redundancy Mode: When only a single PE, among all the
PEs attached to an Ethernet segment, is allowed to forward traffic
to/from that Ethernet segment for a given VLAN, then the Ethernet
segment is defined to be operating in Single-Active redundancy mode.
All-Active Redundancy Mode: When all PEs attached to an Ethernet
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segment are allowed to forward known unicast traffic to/from that
Ethernet segment for a given VLAN, then the Ethernet segment is
defined to be operating in All-Active redundancy mode.
4 EVPN Features
EVPN was originally designed to support the requirements detailed in
[RFC7209] and therefore has the following attributes which directly
address control plane scaling and ease of deployment issues.
1) Control plane traffic is distributed with BGP and Broadcast and
Multicast traffic is sent using a shared multicast tree or with
ingress replication.
2) Control plane learning is used for MAC (and IP) addresses instead
of data plane learning. The latter requires the flooding of unknown
unicast and ARP frames; whereas, the former does not require any
flooding.
3) Route Reflector is used to reduce a full mesh of BGP sessions
among PE devices to a single BGP session between a PE and the RR.
Furthermore, RR hierarchy can be leveraged to scale the number of BGP
routes on the RR.
4) Auto-discovery via BGP is used to discover PE devices
participating in a given VPN, PE devices participating in a given
redundancy group, tunnel encapsulation types, multicast tunnel type,
multicast members, etc.
5) All-Active multihoming is used. This allows a given customer
device (CE) to have multiple links to multiple PEs, and traffic
to/from that CE fully utilizes all of these links. This set of links
is termed an Ethernet Segment (ES).
6) When a link between a CE and a PE fails, the PEs for that EVI are
notified of the failure via the withdrawal of a single EVPN route.
This allows those PEs to remove the withdrawing PE as a next hop for
every MAC address associated with the failed link. This is termed
'mass withdrawal'.
7) BGP route filtering and constrained route distribution are
leveraged to ensure that the control plane traffic for a given EVI is
only distributed to the PEs in that EVI.
8) When a 802.1Q interface is used between a CE and a PE, each of the
VLAN ID (VID) on that interface can be mapped onto a bridge table
(for upto 4094 such bridge tables). All these bridge tables may be
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mapped onto a single MAC-VRF (in case of VLAN-aware bundle service).
9) VM Mobility mechanisms ensure that all PEs in a given EVI know
the ES with which a given VM, as identified by its MAC and IP
addresses, is currently associated.
10) Route Targets are used to allow the operator (or customer) to
define a spectrum of logical network topologies including mesh, hub &
spoke, and extranets (e.g., a VPN whose sites are owned by different
enterprises), without the need for proprietary software or the aid of
other virtual or physical devices.
11) Because the design goal for NVO is millions of instances per
common physical infrastructure, the scaling properties of the control
plane for NVO are extremely important. EVPN and the extensions
described herein, are designed with this level of scalability in
mind.
5 Encapsulation Options for EVPN Overlays
5.1 VXLAN/NVGRE Encapsulation
Both VXLAN and NVGRE are examples of technologies that provide a data
plane encapsulation which is used to transport a packet over the
common physical IP infrastructure between VXLAN Tunnel End Points
(VTEPs) in VXLAN network and Network Virtualization Endpoints (NVEs)
in NVGRE network. Both of these technologies include the identifier
of the specific NVO instance, Virtual Network Identifier (VNI) in
VXLAN and Virtual Subnet Identifier (VSID) in NVGRE, in each packet.
Note that a Provider Edge (PE) is equivalent to a VTEP/NVE.
VXLAN encapsulation is based on UDP, with an 8-byte header following
the UDP header. VXLAN provides a 24-bit VNI, which typically provides
a one-to-one mapping to the tenant VLAN ID, as described in
[RFC7348]. In this scenario, the ingress VTEP does not include an
inner VLAN tag on the encapsulated frame, and the egress VTEP
discards the frames with an inner VLAN tag. This mode of operation in
[RFC7348] maps to VLAN Based Service in [RFC7432], where a tenant
VLAN ID gets mapped to an EVPN instance (EVI).
VXLAN also provides an option of including an inner VLAN tag in the
encapsulated frame, if explicitly configured at the VTEP. This mode
of operation can map to VLAN Bundle Service in [RFC7432] because all
the tenant's tagged frames map to a single bridge table / MAC-VRF,
and the inner VLAN tag is not used for lookup by the disposition PE
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when performing VXLAN decapsulation as described in section 6 of
[RFC7348].
[NVGRE] encapsulation is based on [GRE] and it mandates the inclusion
of the optional GRE Key field which carries the VSID. There is a one-
to-one mapping between the VSID and the tenant VLAN ID, as described
in [NVGRE] and the inclusion of an inner VLAN tag is prohibited. This
mode of operation in [NVGRE] maps to VLAN Based Service in
[RFC7432].
As described in the next section there is no change to the encoding
of EVPN routes to support VXLAN or NVGRE encapsulation except for the
use of BGP Encapsulation extended community. However, there is
potential impact to the EVPN procedures depending on where the NVE is
located (i.e., in hypervisor or TOR) and whether multi-homing
capabilities are required.
5.1.1 Virtual Identifiers Scope
Although VNI or VSID are defined as 24-bit globally unique values,
there are scenarios in which it is desirable to use a locally
significant value for VNI or VSID, especially in the context of data
center interconnect:
5.1.1.1 Data Center Interconnect with Gateway
In the case where NVEs in different data centers need to be
interconnected, and the NVEs need to use VNIs or VSIDs as a globally
unique identifiers within a data center, then a Gateway needs to be
employed at the edge of the data center network. This is because the
Gateway will provide the functionality of translating the VNI or VSID
when crossing network boundaries, which may align with operator span
of control boundaries. As an example, consider the network of Figure
1 below. Assume there are three network operators: one for each of
the DC1, DC2 and WAN networks. The Gateways at the edge of the data
centers are responsible for translating the VNIs / VSIDs between the
values used in each of the data center networks and the values used
in the WAN.
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+--------------+
| |
+---------+ | WAN | +---------+
+----+ | +---+ +----+ +----+ +---+ | +----+
|NVE1|--| | | |WAN | |WAN | | | |--|NVE3|
+----+ |IP |GW |--|Edge| |Edge|--|GW | IP | +----+
+----+ |Fabric +---+ +----+ +----+ +---+ Fabric | +----+
|NVE2|--| | | | | |--|NVE4|
+----+ +---------+ +--------------+ +---------+ +----+
|<------ DC 1 ------> <------ DC2 ------>|
Figure 1: Data Center Interconnect with Gateway
5.1.1.2 Data Center Interconnect without Gateway
In the case where NVEs in different data centers need to be
interconnected, and the NVEs need to use locally assigned VNIs or
VSIDs (e.g., as MPLS labels), then there may be no need to employ
Gateways at the edge of the data center network. More specifically,
the VNI or VSID value that is used by the transmitting NVE is
allocated by the NVE that is receiving the traffic (in other words,
this is a "downstream assigned" MPLS label). This allows the VNI or
VSID space to be decoupled between different data center networks
without the need for a dedicated Gateway at the edge of the data
centers.
+--------------+
| |
+---------+ | WAN | +---------+
+----+ | | +----+ +----+ | | +----+
|NVE1|--| | |WAN | |WAN | | |--|NVE3|
+----+ |IP Fabric|---|Edge| |Edge|--|IP Fabric| +----+
+----+ | | +----+ +----+ | | +----+
|NVE2|--| | | | | |--|NVE4|
+----+ +---------+ +--------------+ +---------+ +----+
|<------ DC 1 -----> <---- DC2 ------>|
Figure 2: Data Center Interconnect without Gateway
5.1.2 Virtual Identifiers to EVI Mapping
When the EVPN control plane is used in conjunction with VXLAN or
NVGRE, two options for mapping the VXLAN VNI or NVGRE VSID to an EVI
are possible:
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1. Option 1: Single Subnet per EVI
In this option, a single subnet represented by a VNI or VSID is
mapped to a unique EVI. This corresponds to the VLAN Based service in
[RFC7432], where a tenant VLAN ID gets mapped to an EVPN instance
(EVI). As such, a BGP RD and RT is needed per VNI / VSID on every
VTEP. The advantage of this model is that it allows the BGP RT
constraint mechanisms to be used in order to limit the propagation
and import of routes to only the VTEPs that are interested in a given
VNI or VSID. The disadvantage of this model may be the provisioning
overhead if RD and RT are not derived automatically from VNI or
VSID.
In this option, the MAC-VRF table is identified by the RT in the
control plane and by the VNI or VSID in the data-plane. In this
option, the specific the MAC-VRF table corresponds to only a single
bridge table.
2. Option 2: Multiple Subnets per EVI
In this option, multiple subnets each represented by a unique VNI or
VSID are mapped to a single EVI. For example, if a tenant has
multiple segments/subnets each represented by a VNI or VSID, then all
the VNIs (or VSIDs) for that tenant are mapped to a single EVI -
e.g., the EVI in this case represents the tenant and not a subnet .
This corresponds to the VLAN-Aware Bundle service in [RFC7432]. The
advantage of this model is that it doesn't require the provisioning
of RD/RT per VNI or VSID. However, this is a moot point if option 1
with auto-derivation is used. The disadvantage of this model is that
routes would be imported by VTEPs that may not be interested in a
given VNI or VSID.
In this option the MAC-VRF table is identified by the RT in the
control plane and a specific bridge table for that MAC-VRF is
identified by the <RT, Ethernet Tag ID> in the control plane. In this
option, the VNI/VSID in the data-plane is sufficient to identify a
specific bridge table - e.g., no need to do a lookup based on
VNI/VSID and Ethernet Tag ID fields to identify a bridge table.
5.1.2.1 Auto Derivation of RT
When the option of a single VNI or VSID per EVI is used, it is
important to auto-derive RT for EVPN BGP routes in order to simplify
configuration for data center operations. RD can be derived easily as
described in [RFC7432] and RT can be auto-derived as described next.
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Since a gateway PE as depicted in figure-1 participates in both the
DCN and WAN BGP sessions, it is important that when RT values are
auto-derived for VNIs (or VSIDs), there is no conflict in RT spaces
between DCN and WAN networks assuming that both are operating within
the same AS. Also, there can be scenarios where both VXLAN and NVGRE
encapsulations may be needed within the same DCN and their
corresponding VNIs and VSIDs are administered independently which
means VNI and VSID spaces can overlap. In order to ensure that no
such conflict in RT spaces arises, RT values for DCNs are auto-
derived as follow:
0 1 2 3 4
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 2 3 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++
| AS # |A| TYPE| D-ID | Service Instance ID|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++
- 2 bytes of global admin field of the RT is set to the AS number.
- Three least significant bytes of the local admin field of the RT is
set to the VNI or VSID, I-SID, or VID. The most significant bit of
the local admin field of the RT is set as follow:
0: auto-derived
1: manually-derived
- The next 3 bits of the most significant byte of the local admin
field of the RT identifies the space in which the other 3 bytes are
defined. The following spaces are defined:
0 : VID
1 : VXLAN
2 : NVGRE
3 : I-SID
4 : EVI
5 : dual-VID
- The remaining 4 bits of the most significant byte of the local
admin field of the RT identifies the domain-id. The default value of
domain-id is zero indicating that only a single numbering space exist
for a given technology. However, if there are more than one number
space exist for a given technology (e.g., overlapping VXLAN spaces),
then each of the number spaces need to be identify by their
corresponding domain-id starting from 1.
5.1.3 Constructing EVPN BGP Routes
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In EVPN, an MPLS label is distributed by the egress PE via the EVPN
control plane and is placed in the MPLS header of a given packet by
the ingress PE. This label is used upon receipt of that packet by the
egress PE for disposition of that packet. This is very similar to the
use of the VNI or VSID by the egress VTEP or NVE, respectively, with
the difference being that an MPLS label has local significance while
a VNI or VSID typically has global significance. Accordingly, and
specifically to support the option of locally assigned VNIs, the MPLS
label field in the MAC Advertisement, Ethernet AD per EVI, and
Inclusive Multicast Ethernet Tag routes is used to carry the VNI or
VSID. For the balance of this memo, the MPLS label field will be
referred to as the VNI/VSID field. The VNI/VSID field is used for
both local and global VNIs/VSIDs, and for either case the entire 24-
bit field is used to encode the VNI/VSID value.
For the VLAN based mode (a single VNI per MAC-VRF), the Ethernet Tag
field in the MAC/IP Advertisement, Ethernet AD per EVI, and Inclusive
Multicast route MUST be set to zero just as in the VLAN Based service
in [RFC7432].
For the VNI-aware bundle mode (multiple VNIs per MAC-VRF with each
VNI associated with its own bridge table), the Ethernet Tag field in
the MAC Advertisement, Ethernet AD per EVI, and Inclusive Multicast
route MUST identify a bridge table within a MAC-VRF and the set of
Ethernet Tags for that EVI needs to be configured consistently on all
PEs within that EVI. For local VNIs, the value advertised in the
Ethernet Tag field MUST be set to a VID just as in the VLAN-aware
bundle service in [RFC7432]. Such setting must be done consistently
on all PE devices participating in that EVI within a given domain.
For global VNIs, the value advertised in the Ethernet Tag field
SHOULD be set to a VNI as long as it matches the existing semantics
of the Ethernet Tag, i.e., it identifies a bridge table within a MAC-
VRF and the set of VNIs are configured consistently on each PE in
that EVI. It should be noted that if within a single domain, a mix of
local and global VNIs are used for the same VLAN-aware bundle
service, then the Ethernet Tag field in the EVPN BGP route
advertisements SHALL be set to a VID.
In order to indicate that which type of data plane encapsulation
(i.e., VXLAN, NVGRE, MPLS, or MPLS in GRE) is to be used, the BGP
Encapsulation extended community defined in [RFC5512] is included
with all EVPN routes (i.e. MAC Advertisement, Ethernet AD per EVI,
Ethernet AD per ESI, Inclusive Multicast Ethernet Tag, and Ethernet
Segment) advertised by an egress PE. Five new values have been
assigned by IANA to extend the list of encapsulation types defined in
[RFC5512]:
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+ 8 - VXLAN Encapsulation
+ 9 - NVGRE Encapsulation
+ 10 - MPLS Encapsulation
+ 11 - MPLS in GRE Encapsulation
+ 12 - VXLAN GPE Encapsulation
If the BGP Encapsulation extended community is not present, then the
default MPLS encapsulation or a statically configured encapsulation
is assumed.
The Ethernet Segment and Ethernet AD per ESI routes MAY be advertised
with multiple encapsulation types as long as they use the same EVPN
multi-homing procedures - e.g., the mix of VXLAN and NVGRE
encapsulation types is a valid one but not the mix of VXLAN and MPLS
encapsulation types.
The Next Hop field of the MP_REACH_NLRI attribute of the route MUST
be set to the IPv4 or IPv6 address of the NVE. The remaining fields
in each route are set as per [RFC7432].
5.2 MPLS over GRE
The EVPN data-plane is modeled as an EVPN MPLS client layer sitting
over an MPLS PSN tunnel. Some of the EVPN functions (split-horizon,
aliasing, and backup-path) are tied to the MPLS client layer. If MPLS
over GRE encapsulation is used, then the EVPN MPLS client layer can
be carried over an IP PSN tunnel transparently. Therefore, there is
no impact to the EVPN procedures and associated data-plane
operation.
The existing standards for MPLS over GRE encapsulation as defined by
[RFC4023] can be used for this purpose; however, when it is used in
conjunction with EVPN the key field SHOULD be present, and SHOULD be
used to provide a 32-bit entropy field. The Checksum and Sequence
Number fields are not needed and their corresponding C and S bits
MUST be set to zero.
6 EVPN with Multiple Data Plane Encapsulations
The use of the BGP Encapsulation extended community allows each PE in
a given EVI to know each of the encapsulations supported by each of
the other PEs in that EVI. I.e., each of the PEs in a given EVI may
support multiple data plane encapsulations. An ingress PE can send a
frame to an egress PE only if the set of encapsulations advertised by
the egress PE in the subject MAC/IP Advertisement or per EVI Ethernet
AD route, forms a non-empty intersection with the set of
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encapsulations supported by the ingress PE, and it is at the
discretion of the ingress PE which encapsulation to choose from this
intersection. (As noted in section 5.1.3, if the BGP Encapsulation
extended community is not present, then the default MPLS
encapsulation or a statically configured encapsulation is assumed.)
An ingress node that uses shared multicast trees for sending
broadcast or multicast frames MUST maintain distinct trees for each
different encapsulation type.
It is the responsibility of the operator of a given EVI to ensure
that all of the PEs in that EVI support at least one common
encapsulation. If this condition is violated, it could result in
service disruption or failure. The use of the BGP Encapsulation
extended community provides a method to detect when this condition is
violated but the actions to be taken are at the discretion of the
operator and are outside the scope of this document.
7 NVE Residing in Hypervisor
When a PE and its CEs are co-located in the same physical device,
e.g., when the PE resides in a server and the CEs are its VMs, the
links between them are virtual and they typically share fate; i.e.,
the subject CEs are typically not multi-homed or if they are multi-
homed, the multi-homing is a purely local matter to the server
hosting the VM, and need not be "visible" to any other PEs, and thus
does not require any specific protocol mechanisms. The most common
case of this is when the NVE resides in the hypervisor.
In the sub-sections that follow, we will discuss the impact on EVPN
procedures for the case when the NVE resides on the hypervisor and
the VXLAN or NVGRE encapsulation is used.
7.1 Impact on EVPN BGP Routes & Attributes for VXLAN/NVGRE Encapsulation
In the scenario where all data centers are under a single
administrative domain, and there is a single global VNI/VSID space,
the RD MAY be set to zero in the EVPN routes. However, in the
scenario where different groups of data centers are under different
administrative domains, and these data centers are connected via one
or more backbone core providers as described in [NOV3-Framework], the
RD must be a unique value per EVI or per NVE as described in
[RFC7432]. In other words, whenever there is more than one
administrative domain for global VNI or VSID, then a non-zero RD MUST
be used, or whenever the VNI or VSID value have local significance,
then a non-zero RD MUST be used. It is recommend to use a non-zero RD
at all time.
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When the NVEs reside on the hypervisor, the EVPN BGP routes and
attributes associated with multi-homing are no longer required. This
reduces the required routes and attributes to the following subset of
four out of the set of eight :
- MAC Advertisement Route
- Inclusive Multicast Ethernet Tag Route
- MAC Mobility Extended Community
- Default Gateway Extended Community
However, as noted in section 8.6 of [RFC7432] in order to enable a
single-homed ingress PE to take advantage of fast convergence,
aliasing, and backup-path when interacting with multi-homed egress
PEs attached to a given Ethernet segment, a single-homed ingress PE
SHOULD be able to receive and process Ethernet AD per ES and Ethernet
AD per EVI routes."
7.2 Impact on EVPN Procedures for VXLAN/NVGRE Encapsulation
When the NVEs reside on the hypervisors, the EVPN procedures
associated with multi-homing are no longer required. This limits the
procedures on the NVE to the following subset of the EVPN procedures:
1. Local learning of MAC addresses received from the VMs per section
10.1 of [RFC7432].
2. Advertising locally learned MAC addresses in BGP using the MAC
Advertisement routes.
3. Performing remote learning using BGP per Section 10.2 of
[RFC7432].
4. Discovering other NVEs and constructing the multicast tunnels
using the Inclusive Multicast Ethernet Tag routes.
5. Handling MAC address mobility events per the procedures of Section
16 in [RFC7432].
However, as noted in section 8.6 of [RFC7432] in order to enable a
single-homed ingress PE to take advantage of fast convergence,
aliasing, and back-up path when interacting with multi-homed egress
PEs attached to a given Ethernet segment, a single-homed ingress PE
SHOULD implement the ingress node processing of Ethernet AD per ES
and Ethernet AD per EVI routes as defined in sections 8.2 Fast
Convergence and 8.4 Aliasing and Backup-Path of [RFC7432].
8 NVE Residing in ToR Switch
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In this section, we discuss the scenario where the NVEs reside in the
Top of Rack (ToR) switches AND the servers (where VMs are residing)
are multi-homed to these ToR switches. The multi-homing may operate
in All-Active or Single-Active redundancy mode. If the servers are
single-homed to the ToR switches, then the scenario becomes similar
to that where the NVE resides in the hypervisor, as discussed in
Section 5, as far as the required EVPN functionality.
[RFC7432] defines a set of BGP routes, attributes and procedures to
support multi-homing. We first describe these functions and
procedures, then discuss which of these are impacted by the
encapsulation (such as VXLAN or NVGRE) and what modifications are
required.
8.1 EVPN Multi-Homing Features
In this section, we will recap the multi-homing features of EVPN to
highlight the encapsulation dependencies. The section only describes
the features and functions at a high-level. For more details, the
reader is to refer to [RFC7432].
8.1.1 Multi-homed Ethernet Segment Auto-Discovery
EVPN NVEs (or PEs) connected to the same Ethernet Segment (e.g. the
same server via LAG) can automatically discover each other with
minimal to no configuration through the exchange of BGP routes.
8.1.2 Fast Convergence and Mass Withdraw
EVPN defines a mechanism to efficiently and quickly signal, to remote
NVEs, the need to update their forwarding tables upon the occurrence
of a failure in connectivity to an Ethernet segment (e.g., a link or
a port failure). This is done by having each NVE advertise an
Ethernet A-D Route per Ethernet segment for each locally attached
segment. Upon a failure in connectivity to the attached segment, the
NVE withdraws the corresponding Ethernet A-D route. This triggers all
NVEs that receive the withdrawal to update their next-hop adjacencies
for all MAC addresses associated with the Ethernet segment in
question. If no other NVE had advertised an Ethernet A-D route for
the same segment, then the NVE that received the withdrawal simply
invalidates the MAC entries for that segment. Otherwise, the NVE
updates the next-hop adjacencies to point to the backup NVE(s).
8.1.3 Split-Horizon
If a server is multi-homed to two or more NVEs on an Ethernet segment
ES1 operating in all-active redundancy mode sends a multicast,
broadcast or unknown unicast packet to a one of these NVEs, then it
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is important to ensure the packet is not looped back to the server
via another NVE connected to this server. The filtering mechanism on
the NVE to prevent such loop and packet duplication is called "split
horizon filtering'.
8.1.4 Aliasing and Backup-Path
In the case where a station is multi-homed to multiple NVEs, it is
possible that only a single NVE learns a set of the MAC addresses
associated with traffic transmitted by the station. This leads to a
situation where remote NVEs receive MAC advertisement routes, for
these addresses, from a single NVE even though multiple NVEs are
connected to the multi-homed station. As a result, the remote NVEs
are not able to effectively load-balance traffic among the NVEs
connected to the multi-homed Ethernet segment. This could be the
case, for e.g. when the NVEs perform data-path learning on the
access, and the load-balancing function on the station hashes traffic
from a given source MAC address to a single NVE. Another scenario
where this occurs is when the NVEs rely on control plane learning on
the access (e.g. using ARP), since ARP traffic will be hashed to a
single link in the LAG.
To alleviate this issue, EVPN introduces the concept of Aliasing.
This refers to the ability of an NVE to signal that it has
reachability to a given locally attached Ethernet segment, even when
it has learnt no MAC addresses from that segment. The Ethernet A-D
route per EVI is used to that end. Remote NVEs which receive MAC
advertisement routes with non-zero ESI SHOULD consider the MAC
address as reachable via all NVEs that advertise reachability to the
relevant Segment using Ethernet A-D routes with the same ESI and with
the Single-Active flag reset.
Backup-Path is a closely related function, albeit it applies to the
case where the redundancy mode is Single-Active. In this case, the
NVE signals that it has reachability to a given locally attached
Ethernet Segment using the Ethernet A-D route as well. Remote NVEs
which receive the MAC advertisement routes, with non-zero ESI, SHOULD
consider the MAC address as reachable via the advertising NVE.
Furthermore, the remote NVEs SHOULD install a Backup-Path, for said
MAC, to the NVE which had advertised reachability to the relevant
Segment using an Ethernet A-D route with the same ESI and with the
Single-Active flag set.
8.1.5 DF Election
If a CE is multi-homed to two or more NVEs on an Ethernet segment
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operating in all-active redundancy mode, then for a given EVI only
one of these NVEs, termed the Designated Forwarder (DF) is
responsible for sending it broadcast, multicast, and, if configured
for that EVI, unknown unicast frames.
This is required in order to prevent duplicate delivery of multi-
destination frames to a multi-homed host or VM, in case of all-active
redundancy.
8.2 Impact on EVPN BGP Routes & Attributes
Since multi-homing is supported in this scenario, then the entire set
of BGP routes and attributes defined in [RFC7432] are used. As
discussed in Section 3.1.3, the VSID or VNI is carried in the
VNI/VSID field in the MAC Advertisement, Ethernet AD per EVI, and
Inclusive Multicast Ethernet Tag routes.
8.3 Impact on EVPN Procedures
Two cases need to be examined here, depending on whether the NVEs are
operating in Active/Standby or in All-Active redundancy.
First, lets consider the case of Active/Standby redundancy, where the
hosts are multi-homed to a set of NVEs, however, only a single NVE is
active at a given point of time for a given VNI or VSID. In this
case, the split-horizon and the aliasing functions are not required
but other functions such as multi-homed Ethernet segment auto-
discovery, fast convergence and mass withdraw, backup path, and DF
election are required.
Second, let's consider the case of All-Active redundancy. In this
case, out of the EVPN multi-homing features listed in section 8.1,
the use of the VXLAN or NVGRE encapsulation impacts the split-horizon
and aliasing features, since those two rely on the MPLS client layer.
Given that this MPLS client layer is absent with these types of
encapsulations, alternative procedures and mechanisms are needed to
provide the required functions. Those are discussed in detail next.
8.3.1 Split Horizon
In EVPN, an MPLS label is used for split-horizon filtering to support
active/active multi-homing where an ingress NVE adds a label
corresponding to the site of origin (aka ESI Label) when
encapsulating the packet. The egress NVE checks the ESI label when
attempting to forward a multi-destination frame out an interface, and
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if the label corresponds to the same site identifier (ESI) associated
with that interface, the packet gets dropped. This prevents the
occurrence of forwarding loops.
Since the VXLAN or NVGRE encapsulation does not include this ESI
label, other means of performing the split-horizon filtering function
MUST be devised. The following approach is recommended for split-
horizon filtering when VXLAN or NVGRE encapsulation is used.
Every NVE track the IP address(es) associated with the other NVE(s)
with which it has shared multi-homed Ethernet Segments. When the NVE
receives a multi-destination frame from the overlay network, it
examines the source IP address in the tunnel header (which
corresponds to the ingress NVE) and filters out the frame on all
local interfaces connected to Ethernet Segments that are shared with
the ingress NVE. With this approach, it is required that the ingress
NVE performs replication locally to all directly attached Ethernet
Segments (regardless of the DF Election state) for all flooded
traffic ingress from the access interfaces (i.e. from the hosts).
This approach is referred to as "Local Bias", and has the advantage
that only a single IP address needs to be used per NVE for split-
horizon filtering, as opposed to requiring an IP address per Ethernet
Segment per NVE.
In order to prevent unhealthy interactions between the split horizon
procedures defined in [RFC7432] and the local bias procedures
described in this document, a mix of MPLS over GRE encapsulations on
the one hand and VXLAN/NVGRE encapsulations on the other on a given
Ethernet Segment is prohibited.
8.3.2 Aliasing and Backup-Path
The Aliasing and the Backup-Path procedures for VXLAN/NVGRE
encapsulation is very similar to the ones for MPLS. In case of MPLS,
two different Ethernet AD routes are used for this purpose. The one
used for Aliasing has a VPN scope and carries a VPN label but the one
used for Backup-Path has Ethernet segment scope and doesn't carry any
VPN specific info (e.g., Ethernet Tag and MPLS label are set to
zero).
9 Support for Multicast
The E-VPN Inclusive Multicast BGP route is used to discover the
multicast tunnels among the endpoints associated with a given VXLAN
VNI or NVGRE VSID. The Ethernet Tag field of this route is used to
encode the VNI for VLXAN or VSID for NVGRE. The Originating router's
IP address field is set to the NVE's IP address. This route is tagged
with the PMSI Tunnel attribute, which is used to encode the type of
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multicast tunnel to be used as well as the multicast tunnel
identifier. The tunnel encapsulation is encoded by adding the BGP
Encapsulation extended community as per section 3.1.1. The following
tunnel types as defined in [RFC6514] can be used in the PMSI tunnel
attribute for VXLAN/NVGRE:
+ 3 - PIM-SSM Tree
+ 4 - PIM-SM Tree
+ 5 - BIDIR-PIM Tree
+ 6 - Ingress Replication
Except for Ingress Replication, this multicast tunnel is used by the
PE originating the route for sending multicast traffic to other PEs,
and is used by PEs that receive this route for receiving the traffic
originated by CEs connected to the PE that originated the route.
In the scenario where the multicast tunnel is a tree, both the
Inclusive as well as the Aggregate Inclusive variants may be used. In
the former case, a multicast tree is dedicated to a VNI or VSID.
Whereas, in the latter, a multicast tree is shared among multiple
VNIs or VSIDs. This is done by having the NVEs advertise multiple
Inclusive Multicast routes with different VNI or VSID encoded in the
Ethernet Tag field, but with the same tunnel identifier encoded in
the PMSI Tunnel attribute.
10 Inter-AS
For inter-AS operation, two scenarios must be considered:
- Scenario 1: The tunnel endpoint IP addresses are public
- Scenario 2: The tunnel endpoint IP addresses are private
In the first scenario, inter-AS operation is straight-forward and
follows existing BGP inter-AS procedures. However, in the first
scenario where the tunnel endpoint IP addresses are public, there may
be security concern regarding the distribution of these addresses
among different ASes. This security concern is one of the main
reasons for having the so called inter-AS "option-B" in MPLS VPN
solutions such as EVPN.
The second scenario is more challenging, because the absence of the
MPLS client layer from the VXLAN encapsulation creates a situation
where the ASBR has no fully qualified indication within the tunnel
header as to where the tunnel endpoint resides. To elaborate on this,
recall that with MPLS, the client layer labels (i.e. the VPN labels)
are downstream assigned. As such, this label implicitly has a
connotation of the tunnel endpoint, and it is sufficient for the ASBR
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to look up the client layer label in order to identify the label
translation required as well as the tunnel endpoint to which a given
packet is being destined. With the VXLAN encapsulation, the VNI is
globally assigned and hence is shared among all endpoints. The
destination IP address is the only field which identifies the tunnel
endpoint in the tunnel header, and this address is privately managed
by every data center network. Since the tunnel address is allocated
out of a private address pool, then we either need to do a lookup
based on VTEP IP address in context of a VRF (e.g., use IP-VPN) or
terminate the VXLAN tunnel and do a lookup based on the tenant's MAC
address to identify the egress tunnel on the ASBR. This effectively
mandates that the ASBR to either run another overlay solution such as
IP-VPN over MPLS/IP core network or to be aware of the MAC addresses
of all VMs in its local AS, at the very least.
If VNIs/VSIDs have local significance, then the inter-AS operation
can be simplified to that of MPLS and thus MPLS inter-AS option B and
C can be leveraged in here. That's why the use of local significance
VNIs/VSIDs (e.g., MPLS labels) are recommended for inter-AS operation
of DC networks without gateways.
11 Acknowledgement
The authors would like to thank David Smith, John Mullooly, Thomas
Nadeau for their valuable comments and feedback.
12 Security Considerations
This document uses IP-based tunnel technologies to support data
plane transport. Consequently, the security considerations of those
tunnel technologies apply. This document defines support for VXLAN
and NVGRE encapsulations. The security considerations from those
documents as well as [RFC4301] apply to the data plane aspects of
this document.
As with [RFC5512], any modification of the information that is used
to form encapsulation headers, to choose a tunnel type, or to choose
a particular tunnel for a particular payload type may lead to user
data packets getting misrouted, misdelivered, and/or dropped.
More broadly, the security considerations for the transport of IP
reachability information using BGP are discussed in [RFC4271] and
[RFC4272], and are equally applicable for the extensions described
in this document.
If the integrity of the BGP session is not itself protected, then an
imposter could mount a denial-of-service attack by establishing
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numerous BGP sessions and forcing an IPsec SA to be created for each
one. However, as such an imposter could wreak havoc on the entire
routing system, this particular sort of attack is probably not of
any special importance.
It should be noted that a BGP session may itself be transported over
an IPsec tunnel. Such IPsec tunnels can provide additional security
to a BGP session. The management of such IPsec tunnels is outside
the scope of this document.
13 IANA Considerations
IANA has allocated the following BGP Tunnel Encapsulation Attribute
Tunnel Types:
8 VXLAN Encapsulation
9 NVGRE Encapsulation
10 MPLS Encapsulation
11 MPLS in GRE Encapsulation
12 VXLAN GPE Encapsulation
14 References
14.1 Normative References
[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4271] Y. Rekhter, Ed., T. Li, Ed., S. Hares, Ed., "A Border
Gateway Protocol 4 (BGP-4)", January 2006.
[RFC4272] S. Murphy, "BGP Security Vulnerabilities Analysis.",
January 2006.
[RFC4301] S. Kent, K. Seo., "Security Architecture for the
Internet Protocol.", December 2005.
[RFC5512] Mohapatra, P. and E. Rosen, "The BGP Encapsulation
Subsequent Address Family Identifier (SAFI) and the BGP
Tunnel Encapsulation Attribute", RFC 5512, April 2009.
[RFC7432] Sajassi et al., "BGP MPLS Based Ethernet VPN", RFC 7432,
February 2014
14.2 Informative References
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[RFC7209] Sajassi et al., "Requirements for Ethernet VPN (EVPN)", RFC
7209, May 2014
[RFC7348] Mahalingam, M., et al, "VXLAN: A Framework for Overlaying
Virtualized Layer 2 Networks over Layer 3 Networks", RFC 7348, August
2014
[NVGRE] Garg, P., et al., "NVGRE: Network Virtualization using
Generic Routing Encapsulation", draft-sridharan-virtualization-nvgre-
07.txt, November 11, 2014
[Problem-Statement] Narten et al., "Problem Statement: Overlays for
Network Virtualization", draft-ietf-nvo3-overlay-problem-statement-
01, September 2012.
[L3VPN-ENDSYSTEMS] Marques et al., "BGP-signaled End-system IP/VPNs",
draft-ietf-l3vpn-end-system, work in progress, October 2012.
[NOV3-FRWK] Lasserre et al., "Framework for DC Network
Virtualization", draft-ietf-nvo3-framework-01.txt, work in progress,
October 2012.
Authors' Addresses
Ali Sajassi
Cisco
Email: sajassi@cisco.com
John Drake
Juniper Networks
Email: jdrake@juniper.net
Nabil Bitar
Verizon Communications
Email : nabil.n.bitar@verizon.com
Aldrin Isaac
Bloomberg
Email: aisaac71@bloomberg.net
James Uttaro
AT&T
Email: uttaro@att.com
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Wim Henderickx
Alcatel-Lucent
e-mail: wim.henderickx@alcatel-lucent.com
Ravi Shekhar
Juniper Networks
Email: rshekhar@juniper.net
Samer Salam
Cisco
Email: ssalam@cisco.com
Keyur Patel
Cisco
Email: Keyupate@cisco.com
Dhananjaya Rao
Cisco
Email: dhrao@cisco.com
Samir Thoria
Cisco
Email: sthoria@cisco.com
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