Internet DRAFT - draft-sajassi-drake-l2vpn-evpn-overlay
draft-sajassi-drake-l2vpn-evpn-overlay
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. Samer Aldrin Isaac
Keyur Patel Bloomberg
D. Rao
Cisco James Uttaro
AT&T
L. Yong
Huawei W. Henderickx
Alcatel-Lucent
Expires: June 10, 2013 December 10, 2012
A Network Virtualization Overlay Solution using E-VPN
draft-sajassi-drake-l2vpn-evpn-overlay-00
Abstract
This document describes how E-VPN can be used as an NVO solution and
explores the various tunnel encapsulation options and their impact on
the E-VPN control-plane and procedures. In particular, the following
encapsulation options are analyzed: MPLS over GRE, VXLAN, and NVGRE.
Status of this Memo
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The list of current Internet-Drafts can be accessed at
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http://www.ietf.org/1id-abstracts.html
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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
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described in the Simplified BSD License.
Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 5
2 E-VPN Features . . . . . . . . . . . . . . . . . . . . . . . . . 5
3 Encapsulation Options for E-VPN Overlays . . . . . . . . . . . . 6
3.1 VXLAN/NVGRE Encapsulation . . . . . . . . . . . . . . . . . 6
3.1.1 Constructing E-VPN BGP Routes . . . . . . . . . . . . . 7
3.2 MPLS over GRE . . . . . . . . . . . . . . . . . . . . . . . 8
4 E-VPN with Multiple Data Plane Encapsulations . . . . . . . . . 8
5 NVE Residing in Hypervisor . . . . . . . . . . . . . . . . . . 9
5.1 Impact on E-VPN BGP Routes & Attributes for VXLAN/NVGRE
Encapsulation . . . . . . . . . . . . . . . . . . . . . . . 9
5.2 Impact on E-VPN Procedures for VXLAN/NVGRE Encapsulation . . 10
6 NVE Residing in ToR Switch . . . . . . . . . . . . . . . . . . 10
6.1 E-VPN Multi-Homing Features . . . . . . . . . . . . . . . . 10
6.1.1 Multi-homed Ethernet Segment Auto-Discovery . . . . . . 11
6.1.2 Fast Convergence and Mass Withdraw . . . . . . . . . . . 11
6.1.3 Split-Horizon . . . . . . . . . . . . . . . . . . . . . 11
6.1.4 Aliasing and Backup-Path . . . . . . . . . . . . . . . . 11
6.1.5 DF Election . . . . . . . . . . . . . . . . . . . . . . 12
6.2 Impact on E-VPN BGP Routes & Attributes . . . . . . . . . . 13
6.3 Impact on E-VPN Procedures . . . . . . . . . . . . . . . . . 13
6.3.1 Split Horizon . . . . . . . . . . . . . . . . . . . . . 13
6.3.2 Aliasing and Backup-Path . . . . . . . . . . . . . . . . 14
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7 Support for Multicast . . . . . . . . . . . . . . . . . . . . . 15
8 Inter-AS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
10 Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 16
11 Security Considerations . . . . . . . . . . . . . . . . . . . 16
12 IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
13 References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
11.1 Normative References . . . . . . . . . . . . . . . . . . . 17
11.2 Informative References . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18
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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 to a given instance of L2 connectivity
The underlay network for NVO solutions is assumed to provide IP
connectivity between NVO endpoints (NVEs).
This document describes how E-VPN can be used as an NVO solution and
explores applicability of E-VPN functions and procedures. In
particular, it describes the various tunnel encapsulation options for
E-VPN over IP, and their impact on the E-VPN control-plane and
procedures for two main scenarios:
a) when the NVE resides in the hypervisor, and
b) when the NVE resides in a ToR device
Note that the use of E-VPN 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 E-VPN 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 E-VPN 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 E-VPN over IP, it is important to highlight the E-VPN
solution main features, how those features are currently supported,
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and any impact that the encapsulation has on those features.
1.1 Terminology
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 RFC 2119 [KEYWORDS].
2 E-VPN Features
E-VPN was originally designed to support the requirements detailed in
[EVPN-REQ] 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 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) Active-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) Mass withdraw is used. When a link between a CE and a PE fails,
the PEs in all E-VPNs configured on that failed link are notified via
the withdrawal of a single E-VPN route regardless of how many MAC
addresses are located at the CE.
7) Route filtering and constrained route distribution are used to
ensure that the control plane traffic for a given E-VPN is only
distributed to the PEs in that E-VPN.
8) The internal identifier of a broadcast domain, the Ethernet Tag,
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is a 32 bit number, which is mapped into whatever broadcast domain
identifier, e.g., VLAN ID, is understood by the attaching CE device.
This means that when 802.1q interfaces are used, there are up to 4096
distinct VLAN IDs for each attaching CE device in a given E-VPN.
9) VM Mobility mechanisms ensure that all PEs in a given E-VPN 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. E-VPN and the extensions
described herein, are designed with this level of scalability in
mind.
3 Encapsulation Options for E-VPN Overlays
3.1 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 infrastructure between NVEs, VXLAN Tunnel End Point
(VTEPs) in VXLAN and Network Virtualization Endpoint (NVEs) in NVGRE.
Both of these technologies include the identifier of the specific NVO
instance, Virtual Network Identifier (VNI) in VXLAN and Virtual
Subnet Identifier (VSID), NVGRE, in each packet.
Note that an E-VPN Instance (EVI) is equivalent to an NVO instance
and 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 [VXLAN]. In this scenario, the VTEP does not include an
inner VLAN tag on frame encapsulation, and discards decapsulated
frames with an inner VLAN tag. This mode of operation in [VXLAN] maps
to VLAN Based Service in [E-VPN], where a tenant VLAN ID gets mapped
to an Ethernet VPN 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
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of operation maps to VLAN Bundle Service in [E-VPN], where the VLANs
of a given tenant get mapped to an EVI.
[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 [E-VPN].
In other words, [NVGRE] prohibits the application of VLAN Bundle
Service in [E-VPN] and it only requires VLAN Based Service in [E-
VPN].
As described in the next section there is no change to the encoding
of E-VPN routes to support VXLAN or NVGRE encapsulation except for
the use of BGP Encapsulation extended community. However, there is
potential impact to the E-VPN procedures depending on where the NVE
is located (i.e., in hypervisor or TOR) and whether multi-homing
capabilities are required.
3.1.1 Constructing E-VPN BGP Routes
In E-VPN an MPLS label distributed by the egress PE via the E-VPN
control plane and placed in the MPLS header of a given packet by the
ingress PE is used upon receipt of that packet by the egress PE to
disposition 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 and is distributed by
the E-VPN control plane, while a VNI or VSID has global significance.
Although VNI or VSID are defined as 24-bit global value, there are
scenarios in which it is desirable to use a locally significant value
for VNI or VSID and in such such scenarios, MPLS label is advertised
in E-VPN BGP routes and it is used in VXLAN or NVGRE encapsulation as
a 20-bit value for VNI or VSID.
This memo specifies that when E-VPN is to be used with a VXLAN or
NVGRE data plane and when a globally significant VNI or VSID is
desirable, then Ethernet Tag field of E-VPN BGP routes (which is a 4-
octet field) MUST be used and MPLS label field MUST be set to zero;
however, when a locally significant VNI or VSID is desirable, then
MPLS field of E-VPN BGP routes (which is a 3-octet field) MUST be
used and Ethernet Tag field MUST be set to zero.
In order to indicate that a VXLAN or NVGRE data plane encapsulation
rather than MPLS label stack encapsulation is to be used, the BGP
Encapsulation extended community defined in [RFC5512] is included
with E-VPN MAC Advertisement or Per EVI Ethernet AD routes advertised
by an egress PE. Two new values, one for VXLAN and one for NVGRE,
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will be defined.
3.2 MPLS over GRE
The E-VPN data-plane is modeled as an E-VPN MPLS client layer sitting
over an MPLS PSN tunnel. Some of the E-VPN functions (split-horizon,
aliasing and repair-path) are tied to the MPLS client layer. If MPLS
over GRE encapsulation is used, then the E-VPN MPLS client layer can
be carried over an IP PSN tunnel transparently. Therefore, there is
no impact to the E-VPN 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 E-VPN the key field MUST 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.
4 E-VPN with Multiple Data Plane Encapsulations
The use of the BGP Encapsulation extended community allows each PE in
a given E-VPN to know whether the other PEs in that E-VPN support
MPLS label stack, VXLAN, and/or NVGRE data plane encapsulations.
I.e., PEs in a given E-VPN may support multiple data plane
encapsulations.
If BGP Encapsulation Extended community is not present, then the
default MPLS encapsulation (or statically configured encapsulation)
is used. However, if this attribute is present, then 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 Advertisement or Per
EVI Ethernet AD route, forms a non-empty intersection with the set of
encapsulations supported by the ingress PE, and it is at the
discretion of the ingress PE which encapsulation to choose from this
intersection.
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 E-VPN to ensure
that all of the PEs in that E-VPN 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
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operator and are outside the scope of this document.
5 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 E-VPN
procedures for the case when the NVE resides on the hypervisor and
the VXLAN or NVGRE encapsulation is used.
5.1 Impact on E-VPN BGP Routes & Attributes for VXLAN/NVGRE
Encapsulation
As discussed above, both [NVGRE] and [VXLAN] do not require the
tenant VLAN tag to be sent in BGP routes. Therefore, the 4-octet
Ethernet Tag field in the E-VPN BGP routes can be used to represent
the globally significant value for VXLAN VNI or NVGRE VSID and MPLS
field can be used to represent the locally significant value for VNI
or VSID.
When the VXLAN VNI or NVGRE VSID is assumed to be a global value, one
might question the need for the Route Distinguisher (RD) in the E-VPN
routes. 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 E-VPN 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 [E-VPN].
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.
When the NVEs reside on the hypervisor, the E-VPN BGP routes and
attributes associated with multi-homing are no longer required. This
reduces the required routes and attributes to the following subset of
five out of the set of eight :
- MAC Advertisement Route
- Inclusive Multicast Ethernet Tag Route
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- MAC Mobility Extended Community
- Default Gateway Extended Community
As mentioned in section 3.1.1, BGP Encapsulation Extended Community
attribute as defined in [RFC5512] SHOULD be used along with MAC
Advertisement Route or Ethernet AD Route to indicate the supported
encapsulations.
5.2 Impact on E-VPN Procedures for VXLAN/NVGRE Encapsulation
When the NVEs reside on the hypervisors, the E-VPN procedures
associated with multi-homing are no longer required. This limits the
procedures on the NVE to the following subset of the E-VPN
procedures:
1. Local learning of MAC addresses received from the VMs per section
10.1 of [E-VPN].
2. Advertising locally learned MAC addresses in BGP using the MAC
Advertisement routes.
3. Performing remote learning using BGP per Section 10.2 of [E-VPN].
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 [E-VPN].
6 NVE Residing in ToR Switch
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 Active/Standby 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 E-VPN functionality.
[E-VPN] 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.
6.1 E-VPN Multi-Homing Features
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In this section, we will recap the multi-homing features of E-VPN 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 [E-VPN].
6.1.1 Multi-homed Ethernet Segment Auto-Discovery
E-VPN 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.
6.1.2 Fast Convergence and Mass Withdraw
E-VPN 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).
6.1.3 Split-Horizon
Consider a station that is multi-homed to two or more NVEs on an
Ethernet segment ES1, with all-active redundancy. If the station
sends a multicast, broadcast or unknown unicast packet to a
particular NVE, say NE1, then NE1 will forward that packet to all or
subset of the other NVEs in the E-VPN instance. In this case the
NVEs, other than NE1, that the station is multi-homed to MUST drop
the packet and not forward back to the station. This is referred to
as "split horizon" filtering.
6.1.4 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
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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, E-VPN 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 Active-Standby flag reset.
Backup-Path is a closely related function, albeit it applies to the
case where the redundancy mode is Active/Standby. 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
Active-Standby flag set.
6.1.5 DF Election
Consider a station that is a host or a VM that is multi-homed
directly to more than one NVE in an E-VPN on a given Ethernet
segment. One or more Ethernet Tags may be configured on the Ethernet
segment. In this scenario only one of the PEs, referred to as the
Designated Forwarder (DF), is responsible for certain actions:
- Sending multicast and broadcast traffic, on a given Ethernet Tag on
a particular Ethernet segment, to the station.
- Flooding unknown unicast traffic (i.e. traffic for which an NVE
does not know the destination MAC address), on a given Ethernet Tag
on a particular Ethernet segment to the station, if the environment
requires flooding of unknown unicast traffic.
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.
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6.2 Impact on E-VPN BGP Routes & Attributes
Since multi-homing is supported in this scenario, then the entire set
of BGP routes and attributes defined in [E-VPN] are used. As
discussed in Section 3.1, the VSID or VNI is encoded in the Ethernet
Tag field of the routes if globally significant or in the MPLS label
field if locally significant.
As mentioned in section 3.1.1, BGP Encapsulation Extended Community
attribute as defined in [RFC5512] SHOULD be used along with MAC
Advertisement Route or Ethernet AD Route to indicate the supported
encapsulations.
6.3 Impact on E-VPN Procedures
Two cases need to be examined here, depending on whether the NVEs are
operating in Active/Standby or in All-Active redundancy.
First, let's 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 Aliasing functions are not required
but other functions such as multi-homed Ethernet segment auto-
discovery, fast convergence and mass withdraw, repair path, and DF
election are required. In this case, the impact of the use of the
VXLAN/NVGRE encapsulation on the E-VPN procedures is when the Backup-
Path function is supported, as discussed next:
In E-VPN, the NVEs connected to a multi-homed site using
Active/Standby redundancy optionally advertise a VPN label, in the
Ethernet A-D Route per EVI, used to send traffic to the backup NVE in
the case where the primary NVE fails. In the case where VXLAN or
NVGRE encapsulation is used, some alternative means that does not
rely on MPLS labels is required to support Backup-Path. This is
discussed in Section 4.3.2 below. If the Backup-Path function is not
used, then the VXLAN/NVGRE encapsulation would have no impact on the
E-VPN procedures.
Second, let's consider the case of All-Active redundancy. In this
case, out of the E-VPN multi-homing features listed in section 4.1,
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.
6.3.1 Split Horizon
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In E-VPN, an MPLS label is used for split-horizon filtering to
support active/active multi-homing where an ingress ToR switch adds a
label corresponding to the site of origin (aka ESI MPLS Label) when
encapsulating the packet. The egress ToR switch checks the ESI MPLS
label when attempting to forward a multi-destination frame out an
interface, and 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 MPLS
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 [E-VPN] and the local bias procedures described
in this memo, 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. 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.
6.3.2 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). The same two routes are used when VXLAN or NVGRE encapsulation
is used with the difference that when Ethernet AD route is used for
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Aliasing with VPN scope, the Ethernet Tag field is set to VNI or VSID
to indicate VPN scope (and MPLS field may be set to a VPN label if
needed).
7 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 or VSID. This route is tagged with the PMSI Tunnel
attribute, which is used to encode the type of multicast tunnel to be
used as well as the multicast tunnel identifier. The following tunnel
types can be used for VXLAN/NVGRE:
- PIM-SSM Tree
- PIM-SM Tree
- BIDIR-PIM Tree
- 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.
8 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.
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,
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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
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. This subject will be further expanded in
the future revision.
Even 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 E-VPN.
10 Acknowledgement
The authors would like to thank David Smith, John Mullooly, Thomas
Nadeau for their valuable comments and feedback.
11 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]. 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.
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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
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.
12 IANA Considerations
13 References
11.1 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.
11.2 Informative References
[EVPN-REQ] Sajassi et al., "Requirements for Ethernet VPN (E-VPN)",
draft-ietf-l2vpn-evpn-req-01.txt, work in progress, October 21, 2012.
[NVGRE] Sridhavan, M., et al., "NVGRE: Network Virtualization using
Generic Routing Encapsulation", draft-sridharan-virtualization-nvgre-
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01.txt, July 8, 2012.
[VXLAN] Dutt, D., et al, "VXLAN: A Framework for Overlaying
Virtualized Layer 2 Networks over Layer 3 Networks", draft-
mahalingam-dutt-dcops-vxlan-02.txt, August 22, 2012.
[E-VPN] Sajassi et al., "BGP MPLS Based Ethernet VPN", draft-ietf-
l2vpn-evpn-02.txt, work in progress, February, 2012.
[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
595 Burrard Street
Vancouver, BC V7X 1J1, Canada
Email: ssalam@cisco.com
Keyur Patel
Cisco
Email: Keyupate@cisco.com
Dhananjaya Rao
Cisco
Email: dhrao@cisco.com
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