L2VPN Workgroup Ali Sajassi
INTERNET-DRAFT Samer Salam
Intended Status: Standards Track Samir Thoria
Cisco
Wim Henderickx
Jorge Rabadan Yakov Rekhter
Alcatel-Lucent John Drake
Juniper
Florin Balus
Nuage Networks Lucy Yong
Linda Dunbar
Dennis Cai Huawei
Cisco
Expires: January 4, 2015 July 4, 2014
Integrated Routing and Bridging in EVPN
draft-sajassi-l2vpn-evpn-inter-subnet-forwarding-04
Abstract
EVPN provides an extensible and flexible multi-homing VPN solution
for intra-subnet connectivity among hosts/VMs over an MPLS/IP
network. However, there are scenarios in which inter-subnet
forwarding among hosts/VMs across different IP subnets is required,
while maintaining the multi-homing capabilities of EVPN. This
document describes an Integrated Routing and Bridging (IRB) solution
based on EVPN to address such requirements.
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
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
Sajassi et al. Expires January 4, 2015 [Page 1]
INTERNET DRAFT Integrated Routing & Bridging in EVPN February 13, 2014
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) 2013 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 Inter-Subnet Forwarding Scenarios . . . . . . . . . . . . . . . 5
2.1 Switching among Subnets within a DC . . . . . . . . . . . . 6
2.2 Switching among EVIs in different DCs without route
aggregation . . . . . . . . . . . . . . . . . . . . . . . . 7
2.3 Switching among EVIs in different DCs with route
aggregation . . . . . . . . . . . . . . . . . . . . . . . . 7
2.4 Switching among IP-VPN sites and EVIs with route
aggregation . . . . . . . . . . . . . . . . . . . . . . . . 7
3 Default L3 Gateway Addressing . . . . . . . . . . . . . . . . . 8
3.1 Homogeneous Environment . . . . . . . . . . . . . . . . . . 8
3.1 Heterogeneous Environment . . . . . . . . . . . . . . . . . 9
4 Operational Models for Asymmetric Inter-Subnet Forwarding . . . 9
4.1 Among EVPN NVEs within a DC . . . . . . . . . . . . . . . . 9
4.2 Among EVPN NVEs in Different DCs Without Route Aggregation . 10
4.3 Among EVPN NVEs in Different DCs with Route Aggregation . . 12
4.4 Among IP-VPN Sites and EVPN NVEs with Route Aggregation . . 13
4.5 Use of Centralized Gateway . . . . . . . . . . . . . . . . . 14
5 Operational Models for Symmetric Inter-Subnet Forwarding . . . . 14
5.1 IRB forwarding on NVEs without core-facing IRB Interface . . 14
5.1.1 Control Plane Operation for IRB forwarding without
core-facing I/F . . . . . . . . . . . . . . . . . . . . 15
5.1.2 Data Plane Operation for IRB forwarding without
Sajassi et al. Expires January 4, 2015 [Page 2]
INTERNET DRAFT Integrated Routing & Bridging in EVPN February 13, 2014
core-facing I/F . . . . . . . . . . . . . . . . . . . . 16
5.2 IRB forwarding on NVEs with core-facing IRB Interface . . . 17
5.2.1 Control Plane Operation for IRB forwarding with
core-facing I/F . . . . . . . . . . . . . . . . . . . . 18
5.2.2 Data Plane Operation for IRB forwarding with
core-facing I/F . . . . . . . . . . . . . . . . . . . . 19
6 BGP Encoding . . . . . . . . . . . . . . . . . . . . . . . . . . 20
7 VM Mobility . . . . . . . . . . . . . . . . . . . . . . . . . . 21
7.1 VM Mobility & Optimum Forwarding for VM's Outbound Traffic . 21
7.2 VM Mobility & Optimum Forwarding for VM's Inbound Traffic . 21
7.2.1 Mobility without Route Aggregation . . . . . . . . . . . 22
7.2.2 Mobility with Route Aggregation . . . . . . . . . . . . 22
8 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 22
9 Security Considerations . . . . . . . . . . . . . . . . . . . . 22
10 IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
11 References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
11.1 Normative References . . . . . . . . . . . . . . . . . . . 22
11.2 Informative References . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23
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 [RFC2119].
IRB: Integrated Routing and Bridging
IRB Interface: A virtual interface that connects the bridging module
and the routing module on an NVE.
NVE: Network Virtualization Endpoint
TS: Tenant System
Sajassi et al. Expires January 4, 2015 [Page 3]
INTERNET DRAFT Integrated Routing & Bridging in EVPN February 13, 2014
1 Introduction
EVPN provides an extensible and flexible multi-homing VPN solution
for intra-subnet connectivity among hosts/VMs over an MPLS/IP
network. However, there are scenarios where, in addition to intra-
subnet forwarding, inter-subnet forwarding is required among
hosts/VMs across different IP subnets at the EVPN PE nodes, also
known as EVPN NVE nodes throughout this document, while maintaining
the multi-homing capabilities of EVPN. This document describes an
Integrated Routing and Bridging (IRB) solution based on EVPN to
address such requirements.
The inter-subnet communication is traditionally achieved at
centralized L3 Gateway nodes where all the inter-subnet communication
policies are enforced. When two Tenant Systems belonging to two
different subnets connected to the same PE node wanted to talk to
each other, their traffic needed to be back hauled from the PE node
all the way to the centralized gateway nodes where inter-subnet
switching is performed and then back to the PE node. For today's
large multi-tenant data center, this scheme is very inefficient and
sometimes impractical.
In order to overcome the drawback of centralized approach, IRB
functionality is needed on the PE nodes (i.e., NVE devices) as close
to TS as possible to avoid hair pinning of user traffic
unnecessarily. Under this design, all traffic between hosts attached
to one NVE can be routed and bridged locally, thus avoiding traffic
hair-pinning issue at the centralized L3GW.
There can be scenarios where both centralized and decentralized
approaches may be preferred simultaneously. For example, to allow
NVEs to switch inter-subnet traffic belonging to one tenant or one
security zone locally; whereas, to back haul inter-subnet traffic
belonging to two different tenants or security zones to the
centralized gateway nodes and perform switching there after the
traffic is subjected to Firewall or Deep Packet Inspection (DPI).
Some TSes run non-IP protocols in conjunction with their IP traffic.
Therefore, it is important to handle both kinds of traffic optimally
- e.g., to bridge non-IP traffic and to route IP traffic.
Therefore, the solution needs to meet the following requirements:
R1: The solution MUST allow for inter-subnet traffic to be locally
switched at NVEs.
R2: The solution MUST allow for both inter-subnet and intra-subnet
traffic belonging to the same tenant to be locally routed and bridged
Sajassi et al. Expires January 4, 2015 [Page 4]
INTERNET DRAFT Integrated Routing & Bridging in EVPN February 13, 2014
respectively. The solution MUST provide IP routing for inter-subnet
traffic and Ethernet Bridging for intra-subnet traffic.
R3: The solution MUST support bridging non-IP traffic.
R4: The solution MUST allow inter-subnet switching to be disabled on
a per VLAN basis on NVEs where the traffic needs to be back hauled to
another node (e.g., for performing FW or DPI functionality).
2 Inter-Subnet Forwarding Scenarios
The inter-subnet forwarding scenarios performed by an EVPN NVE can be
divided into the following five categories. The last scenario, along
with their corresponding solutions, are described in [EVPN-IPVPN-
INTEROP]. The solutions for the first four scenarios are the focus of
this document.
1. Switching among EVIs (subnets) within a DC
2. Switching among EVIs (subnets) in different DCs without route
aggregation
3. Switching among EVIs (subnets) in different DCs with route
aggregation
4. Switching among IP-VPN sites and EVPN instances with route
aggregation
5. Switching among IP-VPN sites and EVPN instances without route
aggregation
In the above scenario, the term "route aggregation" refers to the
case where a node situated at the WAN edge of the data center network
behaves as a default gateway for all the destinations that are
outside the data center. The absence of route aggregation refers to
the scenario where NVEs within a data center maintain individual
(host) routes that are outside of the data center.
In the case (4) the WAN edge node also performs route aggregation for
all the destinations within its own data center, and acts as an
interworking unit between EVPN and IP VPN (it implements both EVPN
and IP VPN functionality).
Sajassi et al. Expires January 4, 2015 [Page 5]
INTERNET DRAFT Integrated Routing & Bridging in EVPN February 13, 2014
+---+ Enterprise Site 1
|PE1|----- H1
+---+
/
,---------. Enterprise Site 2
,' `. +---+
,---------. /( MPLS/IP )---|PE2|----- H2
' DCN 3 `./ `. Core ,' +---+
`-+------+' `-+------+'
__/__ / / \ \
:NVE4 : +---+ \ \
'-----' ,----|GW |. \ \
| ,' +---+ `. ,---------.
VM6 ( DCN 1 ) ,' `.
`. ,' ( DCN 2 )
`-+------+' `. ,'
__/__ `-+------+'
:NVE1 : __/__ __\__
'-----' :NVE2 : :NVE3 :
| | '-----' '-----'
VM1 VM2 | | |
VM3 VM4 VM5
Figure 2: Interoperability Use-Cases
In what follows, we will describe scenarios 3 through 6 in more
detail.
2.1 Switching among Subnets within a DC
In this scenario, connectivity is required between hosts (e.g. VMs)
in the same data center, where those hosts belong to different IP
subnets. All these subnets belong to the same tenant or are part of
the same IP VPN. Each subnet is associated with a single EVPN
instance, where each such EVI is realized by a collection of MAC-VRFs
(one per NVE) residing on the NVEs configured for that EVI.
As an example, consider VM3 and VM5 of Figure 2 above. Assume that
connectivity is required between these two VMs where VM3 belongs to
the IP-subnet 3 (SN3) whereas VM5 belongs to the IP-subnet 5 (SN5).
Both SN3 and SN5 subnets belong to the same tenant (e.g., are part of
the same IP VPN). NVE2 has an EVI3 associated with the SN3 and this
EVI is represented by a MAC-VRF which is connected to an IP-VRF (for
that IP VPN) via an IRB interface. NVE3 respectively has an EVI5
associated with the SN5 and this EVI is represented by an MAC-VRF
which is connected to an IP-VRF (for the same IP VPN) via an IRB
interface.
Sajassi et al. Expires January 4, 2015 [Page 6]
INTERNET DRAFT Integrated Routing & Bridging in EVPN February 13, 2014
2.2 Switching among EVIs in different DCs without route aggregation
This case is similar to that of section 2.1 above albeit for the fact
that the hosts belong to different data centers that are
interconnected over a WAN (e.g. MPLS/IP PSN). The data centers in
question here are seamlessly interconnected to the WAN, i.e., the WAN
edge devices does not maintain any host/VM-specific addresses in the
forwarding path - e.g., there is no WAN edge GW(s) between these DCs.
As an example, consider VM3 and VM6 of Figure 2 above. Assume that
connectivity is required between these two VMs where VM3 belongs to
the SN3 whereas VM6 belongs to the SN6. NVE2 has an EVI3 associated
with SN3 and NVE4 has an EVI6 associated with the SN6. Both SN3 and
SN6 are part of the same IP VPN.
2.3 Switching among EVIs in different DCs with route aggregation
In this scenario, connectivity is required between hosts (e.g. VMs)
in different data centers, and those hosts belong to different IP
subnets. What makes this case different from that of Section 2.2 is
that (in the context of a given IP-VRF) at least one of the data
centers in question has a gateway as the WAN edge switch. Because of
that, the NVE's IP-VRF within each data center need not maintain
(host) routes to individual VMs outside of the data center.
As an example, consider VM1 and VM5 of Figure 2 above. Assume that
connectivity is required between these two VMs where VM1 belongs to
the SN1 whereas VM5 belongs to the SN5 thus SN1 and SN5 belong to the
same IP VPN. NVE3 has an EVI5 associated with the SN5 and this EVI is
represented by the MAC-VRF which is connected to the IP-VRF via an
IRB interface. NVE1 has an EVI1 associated with the SN1 and this EVI
is represented by the MAC-VRF which is connected to the IP-VRF
representing the same IP VPN. Due to the gateway at the edge of DCN
1, NVE1's IP-VRF does not need to have the address of VM5 but instead
it has a default route in its IP-VRF with the next-hop being the GW.
2.4 Switching among IP-VPN sites and EVIs with route aggregation
In this scenario, connectivity is required between hosts (e.g. VMs)
in a data center and hosts in an enterprise site that belongs to a
given IP-VPN. The NVE within the data center is an EVPN NVE, whereas
the enterprise site has an IP-VPN PE. Furthermore, the data center in
question has a gateway as the WAN edge switch. Because of that, the
NVE in the data center does not need to maintain individual IP
prefixes advertised by enterprise sites (by IP-VPN PEs).
As an example, consider end-station H1 and VM2 of Figure 2. Assume
Sajassi et al. Expires January 4, 2015 [Page 7]
INTERNET DRAFT Integrated Routing & Bridging in EVPN February 13, 2014
that connectivity is required between the end-station and the VM,
where VM2 belongs to the SN2 that is realized using EVPN, whereas H1
belongs to an IP VPN site connected to PE1 (PE1 maintains an IP-VRF
associated with that IP VPN). NVE1 has an EVI2 associated with the
SN2. Moreover, EVI2 on NVE1 is connected to an IP-VRF associated with
that IP VPN. PE1 originates a VPN-IP route that covers H1. The
gateway at the edge of DCN1 performs interworking function between
IP-VPN and EVPN. As a result of this, a default route in the IP-VRF
on the NVE1, pointing to the gateway as the next hop, and a route to
the VM2 (or maybe SN2) on the PE1's IP-VRF are sufficient for the
connectivity between H1 and VM2. In this scenario, the NVE1's IP-VRF
does not need to maintain a route to H1 because it has the default
route to the gateway.
3 Default L3 Gateway Addressing
3.1 Homogeneous Environment
This is an environment where all NVEs to which an EVPN instance could
potentially be attached (or moved), perform inter-subnet switching.
Therefore, inter-subnet traffic can be locally switched by the EVPN
NVE connecting the VMs belonging to different subnets.
To support such inter-subnet forwarding, the NVE behaves as an IP
Default Gateway from the perspective of the attached end-stations
(e.g. VMs). Two models are possible:
1. All the EVIs of a given EVPN instance use the same anycast default
gateway IP address and the same anycast default gateway MAC address.
On each NVE, this default gateway IP/MAC address correspond to the
IRB interface of the EVI associated with that EVPN instance.
2. Each EVI of a given EVPN instance uses its own default gateway IP
and MAC addresses, and these addresses are aliased to the same
conceptual gateway through the use of the Default Gateway extended
community as specified in [EVPN], which is carried in the EVPN MAC
Advertisement routes. On each NVE, this default gateway IP/MAC
address correspond to the IRB interface of the EVI associated with
that EVPN instance.
Both of these models enable a packet forwarding paradigm for
asymmetric IRB forwarding where a packet can bypass the VRF
processing on the egress (i.e. disposition) NVE. The egress NVE
merely needs to perform a lookup in the associated EVI and forward
the Ethernet frames unmodified, i.e. without rewriting the source MAC
address. This is different from symmetric IRB forwarding where a
packet is forwarded through the bridge module followed by the routing
module on the ingress NVE, and then forwarded through the routing
Sajassi et al. Expires January 4, 2015 [Page 8]
INTERNET DRAFT Integrated Routing & Bridging in EVPN February 13, 2014
module followed by the bridging module on the egress NVE.
It is worth noting that if the applications that are running on the
hosts (e.g. VMs) are employing or relying on any form of MAC
security, then the first model (i.e. using anycast addresses) would
be required to ensure that the applications receive traffic from the
same source MAC address that they are sending to.
3.1 Heterogeneous Environment
For large data centers with thousands of servers and ToR (or Access)
switches, some of them may not have the capability of maintaining or
enforcing policies for inter-subnet switching. Even though policies
among multiple subnets belonging to same tenant can be simpler, hosts
belonging to one tenant can also send traffic to peers belonging to
different tenants or security zones. A L3GW not only needs to enforce
policies for communication among subnets belonging to a single
tenant, but also it needs to know how to handle traffic destined
towards peers in different tenants. Therefore, there can be a mixed
environment where an NVE performs inter-subnet switching for some
EVPN instances but not others.
4 Operational Models for Asymmetric Inter-Subnet Forwarding
4.1 Among EVPN NVEs within a DC
When an EVPN MAC advertisement route is received by the NVE, the IP
address associated with the route is used to populate the IP-VRF
table, whereas the MAC address associated with the route is used to
populate both the MAC-VRF table, as well as the adjacency associated
with the IP route in the IP-VRF table.
When an Ethernet frame is received by an ingress NVE, it performs a
lookup on the destination MAC address in the associated MAC-VRF for
that EVI. If the MAC address corresponds to its IRB Interface MAC
address, the ingress NVE deduces that the packet MUST be inter-subnet
routed. Hence, the ingress NVE performs an IP lookup in the
associated IP-VRF table. The lookup identifies both the next-hop
(i.e. egress) NVE to which the packet must be forwarded, in addition
to an adjacency that contains a MAC rewrite and an MPLS label stack.
The MAC rewrite holds the MAC address associated with the destination
host (as populated by the EVPN MAC route), instead of the MAC address
of the next-hop NVE. The ingress NVE then rewrites the destination
MAC address in the packet with the address specified in the
adjacency. It also rewrites the source MAC address with its IRB
Interface MAC address. The ingress NVE, then, forwards the frame to
the next-hop (i.e. egress) NVE after encapsulating it with the MPLS
Sajassi et al. Expires January 4, 2015 [Page 9]
INTERNET DRAFT Integrated Routing & Bridging in EVPN February 13, 2014
label stack. Note that this label stack includes the LSP label as
well as the EVI label that was advertised by the egress NVE. When the
MPLS encapsulated packet is received by the egress NVE, it uses the
EVI label to identify the MAC-VRF table. It then performs a MAC
lookup in that table, which yields the outbound interface to which
the Ethernet frame must be forwarded. Figure 2 below depicts the
packet flow, where NVE1 and NVE2 are the ingress and egress NVEs,
respectively.
NVE1 NVE2
+------------+ +------------+
| ... ... | | ... ... |
|(EVI)-(VRF) | |(VRF)-(EVI) |
| .|. .|. | | ... |..| |
+------------+ +------------+
^ v ^ V
| | | |
VM1->-+ +-->--------------+ +->-VM2
Figure 2: Inter-Subnet Forwarding Among EVPN NVEs within a DC
Note that the forwarding behavior on the egress NVE is similar to
EVPN intra-subnet forwarding. In other words, all the packet
processing associated with the inter-subnet forwarding semantics is
confined to the ingress NVE and that is why it is called Asymmetric
IRB.
It should also be noted that [EVPN] provides different level of
granularity for the EVI label. Besides identifying bridge domain
table, it can be used to identify the egress interface or a
destination MAC address on that interface. If EVI label is used for
egress interface or destination MAC address identification, then no
MAC lookup is needed in the egress EVI and the packet can be directly
forwarded to the egress interface just based on EVI label lookup.
4.2 Among EVPN NVEs in Different DCs Without Route Aggregation
When an EVPN MAC advertisement route is received by the NVE, the IP
address associated with the route is used to populate the IP-VRF
table, whereas the MAC address associated with the route is used to
populate both the MAC-VRF table, as well as the adjacency associated
with the IP route in the IP-VRF table.
When an Ethernet frame is received by an ingress NVE, it performs a
lookup on the destination MAC address in the associated EVI. If the
MAC address corresponds to its IRB Interface MAC address, the ingress
Sajassi et al. Expires January 4, 2015 [Page 10]
INTERNET DRAFT Integrated Routing & Bridging in EVPN February 13, 2014
NVE deduces that the packet MUST be inter-subnet routed. Hence, the
ingress NVE performs an IP lookup in the associated IP-VRF table. The
lookup identifies both the next-hop (i.e. egress) Gateway to which
the packet must be forwarded, in addition to an adjacency that
contains a MAC rewrite and an MPLS label stack. The MAC rewrite holds
the MAC address associated with the destination host (as populated by
the EVPN MAC route), instead of the MAC address of the next-hop
Gateway. The ingress NVE then rewrites the destination MAC address in
the packet with the address specified in the adjacency. It also
rewrites the source MAC address with its IRB Interface MAC address.
The ingress NVE, then, forwards the frame to the next-hop (i.e.
egress) Gateway after encapsulating it with the MPLS label stack.
Note that this label stack includes the LSP label as well as an EVI
label. The EVI label could be either advertised by the ingress
Gateway, if inter-AS option B is used, or advertised by the egress
NVE, if inter-AS option C is used. When the MPLS encapsulated packet
is received by the ingress Gateway, the processing again differs
depending on whether inter-AS option B or option C is employed: in
the former case, the ingress Gateway swaps the EVI label in the
packets with the EVI label value received from the egress Gateway. In
the latter case, the ingress Gateway does not modify the EVI label
and performs normal label switching on the LSP label. Similarly on
the egress Gateway, for option B, the egress Gateway swaps the EVI
label with the value advertised by the egress NVE. Whereas, for
option C, the egress Gateway does not modify the EVI label, and
performs normal label switching on the LSP label. When the MPLS
encapsulated packet is received by the egress NVE, it uses the EVI
label to identify the bridge-domain table. It then performs a MAC
lookup in that table, which yields the outbound interface to which
the Ethernet frame must be forwarded. Figure 3 below depicts the
packet flow.
NVE1 GW1 GW2 NVE2
+------------+ +------------+ +------------+ +------------+
| ... ... | | ... | | ... | | ... ... |
|(EVI)-(VRF) | | [LS ] | | [LS ] | |(VRF)-(EVI) |
| .|. .|. | | |..| | | |..| | | ... |..| |
+------------+ +------------+ +------------+ +------------+
^ v ^ V ^ V ^ V
| | | | | | | |
VM1->-+ +-->--------+ +------------+ +---------------+ +->-VM2
Figure 3: Inter-Subnet Forwarding Among EVPN NVEs in Different DCs
without Route Aggregation
Sajassi et al. Expires January 4, 2015 [Page 11]
INTERNET DRAFT Integrated Routing & Bridging in EVPN February 13, 2014
4.3 Among EVPN NVEs in Different DCs with Route Aggregation
In this scenario, the NVEs within a given data center do not have
entries for the MAC/IP addresses of hosts in remote data centers.
Rather, the NVEs have a default IP route pointing to the WAN gateway
for each VRF. This is accomplished by the WAN gateway advertising for
a given EVPN that spans multiple DC a default VPN-IP route that is
imported by the NVEs of that EVPN that are in the gateway's own DC.
When an Ethernet frame is received by an ingress NVE, it performs a
lookup on the destination MAC address in the associated MAC-VRF
table. If the MAC address corresponds to the IRB Interface MAC
address, the ingress NVE deduces that the packet MUST be inter-subnet
routed. Hence, the ingress NVE performs an IP lookup in the
associated IP-VRF table. The lookup, in this case, matches the
default route which points to the local WAN gateway. The ingress NVE
then rewrites the destination MAC address in the packet with the IRB
Interface MAC address of the local WAN gateway. It also rewrites the
source MAC address with its own IRB Interface MAC address. The
ingress NVE, then, forwards the frame to the WAN gateway after
encapsulating it with the MPLS label stack. Note that this label
stack includes the LSP label as well as the IP-VPN label that was
advertised by the local WAN gateway. When the MPLS encapsulated
packet is received by the local WAN gateway, it uses the IP-VPN label
to identify the IP-VRF table. It then performs an IP lookup in that
table. The lookup identifies both the remote WAN gateway (of the
remote data center) to which the packet must be forwarded, in
addition to an adjacency that contains a MAC rewrite and an MPLS
label stack. The MAC rewrite holds the MAC address associated with
the ultimate destination host (as populated by the EVPN MAC route).
The local WAN gateway then rewrites the destination MAC address in
the packet with the address specified in the adjacency. It also
rewrites the source MAC address with its IRB Interface MAC address.
The local WAN gateway, then, forwards the frame to the remote WAN
gateway after encapsulating it with the MPLS label stack. Note that
this label stack includes the LSP label as well as a EVI label that
was advertised by the remote WAN gateway. When the MPLS encapsulated
packet is received by the remote WAN gateway, it simply swaps the EVI
label and forwards the packet to the egress NVE. This implies that
the GW1 needs to keep the remote host MAC addresses along with the
corresponding EVI labels in the adjacency entries of the IP-VRF
table. The remote WAN gateway then forward the packet to the egress
NVE. The egress NVE then performs a MAC lookup in the MAC-VRF
(identified by the received EVI label) to determine the outbound port
to send the traffic on.
Figure 4 below depicts the forwarding model.
Sajassi et al. Expires January 4, 2015 [Page 12]
INTERNET DRAFT Integrated Routing & Bridging in EVPN February 13, 2014
NVE1 GW1 GW2 NVE2
+------------+ +------------+ +------------+ +------------+
| ... ... | | ... ... | | ... | | ... ... |
|(EVI)-(VRF) | |(VRF)-(EVI) | | [LS ] | |(VRF)-(EVI) |
| .|. .|. | | |..| | | |...| | | ... |..| |
+------------+ +------------+ +------------+ +------------+
^ v ^ V ^ V ^ V
| | | | | | | |
VM1->-+ +-->-----+ +--------------+ +---------------+ +->-VM2
Figure 4: Inter-Subnet Forwarding Among EVPN NVEs in Different DCs
with Route Aggregation
4.4 Among IP-VPN Sites and EVPN NVEs with Route Aggregation
In this scenario, the NVEs within a given data center do not have
entries for the IP addresses of hosts in remote enterprise sites.
Rather, the NVEs have a default IP route pointing the WAN gateway for
each IP-VRF.
When an Ethernet frame is received by an ingress NVE, it performs a
lookup on the destination MAC address in the associated MAC-VRF
table. If the MAC address corresponds to the IRB Interface MAC
address, the ingress NVE deduces that the packet MUST be inter-subnet
routed. Hence, the ingress NVE performs an IP lookup in the
associated IP-VRF table. The lookup, in this case, matches the
default route which points to the local WAN gateway. The ingress NVE
then rewrites the destination MAC address in the packet with the IRB
Interface MAC address of the local WAN gateway. It also rewrites the
source MAC address with its own IRB Interface MAC address. The
ingress NVE, then, forwards the frame to the local WAN gateway after
encapsulating it with the MPLS label stack. Note that this label
stack includes the LSP label as well as the IP-VPN label that was
advertised by the local WAN gateway. When the MPLS encapsulated
packet is received by the local WAN gateway, it uses the IP-VPN label
to identify the VRF table. It then performs an IP lookup in that
table. The lookup identifies the next hop ASBR to which the packet
must be forwarded. The local gateway in this case strips the Ethernet
encapsulation and perform an IP lookup in its IP-VRF and forwards the
IP packet to the ASBR using a label stack comprising of an LSP label
and an IP-VPN label that was advertised by the ASBR. When the MPLS
encapsulated packet is received by the ASBR, it simply swaps the IP-
VPN label with the one advertised by the egress PE. This implies that
the remote WAN gateway must allocate the VPN label at least at the
granularity of a (VRF, egress PE) tuple. The ASBR then forwards the
packet to the egress PE. The egress PE then performs an IP lookup in
the IP-VRF (identified by the received IP-VPN label) to determine
Sajassi et al. Expires January 4, 2015 [Page 13]
INTERNET DRAFT Integrated Routing & Bridging in EVPN February 13, 2014
where to forward the traffic.
Figure 5 below depicts the forwarding model.
NVE1 GW1 ASBR NVE2
+------------+ +------------+ +------------+ +------------+
| ... ... | | ... ... | | ... | | ... |
|(EVI)-(VRF) | |(VRF)-(EVI) | | [LS ] | | (VRF)|
| .|. .|. | | |..| | | |...| | | |..| |
+------------+ +------------+ +------------+ +------------+
^ v ^ V ^ V ^ V
| | | | | | | |
VM1->-+ +-->-----+ +--------------+ +---------------+ +->-H1
Figure 5: Inter-Subnet Forwarding Among IP-VPN Sites and EVPN NVEs
with Route Aggregation
4.5 Use of Centralized Gateway
In this scenario, the NVEs within a given data center need to forward
traffic in L2 to a centralized L3GW for a number of reasons: a) they
don't have IRB capabilities or b) they don't have required policy for
switching traffic between different tenants or security zones. The
centralized L3GW performs both the IRB function for switching traffic
among different EVPN instances as well as it performs interworking
function when the traffic needs to be switched between IP-VPN sites
and EVPN instances.
5 Operational Models for Symmetric Inter-Subnet Forwarding
The following sections describe several main symmetric IRB forwarding
scenarios.
5.1 IRB forwarding on NVEs without core-facing IRB Interface
In this scenario, for a given tenant or IP-VPN, an NVE has an access-
facing EVI for each tenant's subnet (VLAN) that is configured for.
Assuming VLAN-based service which is typically the case for VxLAN and
NVGRE encapsulation, each of these EVIs represent a MAC-VRF with one
bridge domain. In case of MPLS encapsulation with VLAN-aware
bundling, then each EVI may represent a MAC-VRF with multiple bridge
domains (one bridge domain per VLAN). The EVIs (or MAC-VRFs) on an
NVE for a given tenant are connected to an IP-VRF corresponding to
that tenant (or IP-VPN) via their associated IRB interfaces.
Since in this scenario, there is no core-facing IRB interface, there
Sajassi et al. Expires January 4, 2015 [Page 14]
INTERNET DRAFT Integrated Routing & Bridging in EVPN February 13, 2014
is no need for a core-facing EVI or MAC-VRF. The advantage of not
having a core-facing IRB interface may be operational simplicity as
there is no need to configure an IRB interface and have a MAC-VRF
associated with it and no additional BGP MAC address advertisements
are needed. However, the disadvantage for not having a core-facing
IRB interface is that no QoS or security policies can be enforced for
the core-facing traffic on a per tenant basis.
Since VxLAN and NVGRE encapsulations require inner Ethernet header
(inner MAC SA/DA), and since for inter-subnet traffic, TS MAC address
cannot be used, the ingress NVE's MAC address is used as inner MAC
SA. It should be noted that if there was a core-facing IRB interface,
then the MAC address of IRB interface would have been used as inner
MAC SA. The NVE's MAC address is the device MAC address and the same
MAC address is used across all EVIs and IP-VPNs.
Figure below illustrates this scenario where a given tenant (e.g.,
IP-VPN) has three subnets represented by EVI-1, EVI-2, and EVI3
across two NVEs. There are five TSes connected to these three EVIs -
i.e., TS1, TS5 are connected to EVI-1 on NVE1, TS4 is connected to
EVI-1 on NVE2, TS2 is connected to EVI-2 on NVE1, and TS3 is
connected to EVI3 on NVE2. When TS1, TS5, and TS4 exchange traffic
with each other, only L2 forwarding (bridging) part of the IRB
solution is used because all these TSes sit on the same subnet.
However, when TS1 wants to exchange traffic with TS2 or TS3 which
belong to different subnets, then both bridging and routing parts of
the IRB solution are used. The following subsections describe the
control and data planes operations for this IRB scenario in details.
NVE1 +---------+
+-------------+ | |
TS1-----| MACx| | | NVE2
(IP1/M1) |(EVI-1) | | | +-------------+
TS5-----| \ | | MPLS/ | |MACy (EVI-3)|-----TS3
(IP5/M5) | \ | | VxLAN/ | | / | (IP3/M3)
| (VRF)|----| NVGRE |---|(VRF) |
| / | | | | \ |
TS2-----|(EVI-2) | | | | (EVI-1)|-----TS4
(IP2/M2) +-------------+ | | +-------------+ (IP4/M4)
| |
| |
+---------+
Figure 6: IRB forwarding on NVEs without core-facing IRB Interface
5.1.1 Control Plane Operation for IRB forwarding without core-facing I/F
Sajassi et al. Expires January 4, 2015 [Page 15]
INTERNET DRAFT Integrated Routing & Bridging in EVPN February 13, 2014
Each NVE advertises an RT-2 (MAC/IP Advertisement Route) for each of
its TSes with the following field set:
- RD and ESI per [EVPN]
- Ethernet Tag = 0; assuming VLAN-based service
- MAC Address Length = 48
- MAC Address = Mi ; where i = 1,2,3,4, or 5 in the above example
- IP Address Length = 32 or 128
- IP Address = IPi ; where i = 1,2,3,4, or 5 in the above example
- Label-1 = MPLS Label or VNID corresponding to EVI
- Label-2 = MPLS Label or VNID corresponding to IP-VRF
Each RT-2 route is advertised with two RTs (one corresponding to the
EVI and the other corresponding to the IP-VPN) and with a new BGP
attribute (section 6) that includes the tunnel type and the MAC
address of the NVE (e.g., MACx for NVE1 or MACy for NVE2) .
Upon receiving this advertisement, the receiving NVE performs the
following:
- It uses Route Targets corresponding to EVI and IP-VPN for importing
this route into the corresponding MAC-VRF and IP-VRF tables.
- It imports the MAC address into the MAC-VRF with BGP Next Hop
address as underlay tunnel destination address (e.g., VTEP DA for
VxLAN encapsulation) and Label-1 as EVI VNID for VxLAN encapsulation
or EVPN label for MPLS encapsulation.
- It imports the IP address into IP-VRF with NVE's MAC address (from
the new BGP attribute) as inner MAC DA and BGP Next Hop address as
underlay tunnel destination address (e.g., VTEP DA for VxLAN
encapsulation) and Label-2 as IP-VPN VNID for VxLAN encapsulation or
IP-VPN label for MPLS encapsulation.
5.1.2 Data Plane Operation for IRB forwarding without core-facing I/F
The following description of the data-plane operation describes just
the logical functions and the actual implementation may differ. Lets
consider data-plane operation when TS1 in subnet-1 (EVI-1) on NVE1
wants to send traffic to TS3 in subnet-3 (EVI-3) on NVE2.
- TS1 send an Ethernet frame with MAC DA corresponding to the EVI-1
IRB interface of NVE1, and VLAN-tag corresponding to EVI-1.
- Upon receiving the Ethernet frame, the NVE1 uses VLAN-tag to
identify the MAC-VRF corresponding to EVI-1. It then looks up the MAC
DA and forwards the frame to its IRB interface.
Sajassi et al. Expires January 4, 2015 [Page 16]
INTERNET DRAFT Integrated Routing & Bridging in EVPN February 13, 2014
- The Ethernet header of the frame is stripped and the packet is fed
to the IP-VRF where IP lookup is performed on the destination
address. This lookup yields a MAC address to be used as inner MAC DA
for VxLAN/NVGRE encapsulation, an IP address to be used as VTEP DA
for VxLAN encap or tunnel label for MPLS encap , and a VPN-ID to be
used as VNID for VxLAN encap or IP-VPN label.
- The packet is then encapsulated with the proper header based on
the above info. The inner MAC SA and VTEP SA is set to NVE's MAC and
IP addresses respectively. The packet is then forwarded to the egress
NVE.
- On the egress NVE, if the packet is VxLAN encapsulated, the VxLAN
header is removed. Since the inner MAC DA is that of egress NVE, the
NVE knows that it needs to perform an IP lookup. It uses VNID to
identify the IP-VRF table and then performs an IP lookup which
results in destination TS (TS3) MAC address and the access-facing IRB
interface over which the packet needs to be sent.
- The IP packet is encapsulated with an Ethernet header with MAC SA
set to that of NVE-2 MAC address(MACy) and MAC DA set to that of
destination TS (TS3) MAC address. The packet is sent to the
corresponding MAC-VRF and after a lookup of MAC DA, is forwarded to
the destination TS (TS3) over the corresponding interface.
5.2 IRB forwarding on NVEs with core-facing IRB Interface
The only difference between this scenario and the previous scenario
is that there is a core-facing IRB interface per tenant (or IP-VPN)
on each NVE. Each core-facing IRB interface has a MAC and IP
addresses associated with it and it allows for QoS/security policies
to be configured on a per tenant basis on this interface.
Furthermore, it allows for better OAM coverage (e.g., fault
isolation) by running OAM on this interface. Other than that, the
rest of the functionality is the same as the solution describe in
section 5.1.
This core-facing IRB interface results in additional control-plane
processing (e.g., BGP routes advertisements) and additional data-
plane processing as detail in the next two sub-sections.
Sajassi et al. Expires January 4, 2015 [Page 17]
INTERNET DRAFT Integrated Routing & Bridging in EVPN February 13, 2014
NVE1 +--------------+
+---------------------+ | |
TS1-----|(EVI-1) | | |
(IP1/M1) | \ | | |
| (VRF)-(EVI-x)|------| |
| / | | |
TS2-----|(EVI-2) | | MPLS/ |
(IP2/M2) +---------------------+ | VxLAN/ |
| NVGRE |
+---------------------+ | |
TS3-----|(EVI-1) | | |
(IP3/M3) | \ | | |
| (VRF)-(EVI-x)|------| |
| / | | |
TS4-----|(EVI-3) | | |
(IP4/M4) +---------------------+ | |
NVE2 +--------------+
Figure 7: IRB forwarding on NVEs with core-facing IRB Interface
5.2.1 Control Plane Operation for IRB forwarding with core-facing I/F
Each NVE advertises an RT-2 (MAC/IP Advertisement Route) for each of
its TSes and it also advertises a single RT-2 for core-facing IRB
interface (which is per tenant or per IP-VPN).
The fields of RT-2 for each TS are set as follow:
- RD and ESI per [EVPN]
- Ethernet Tag = 0; assuming VLAN-based service
- MAC Address Length = 48
- MAC Address = Mi ; MAC address of TS
- IP Address Length = 32 or 128
- IP Address = IPi ; IP address of TS
- Label-1 = MPLS Label or VNID corresponding to access-facing EVI
Furthermore, this RT-2 is also advertised with two RTs (one
corresponding to the EVI and the other corresponding to the IP-VPN)
as described in section 5.1.1. The main difference in terms of BGP
advertisement for this per-TS RT-2 is that it is advertised with a
new BGP attribute (section 6) that includes the tunnel type and the
IP address of the core-facing IRB interface (which is per tenant).
Upon receiving this per-TS RT-2 advertisement, the receiving NVE
performs the following:
- It uses the Route Targets corresponding to EVI and IP-VPN for
Sajassi et al. Expires January 4, 2015 [Page 18]
INTERNET DRAFT Integrated Routing & Bridging in EVPN February 13, 2014
importing this route into the corresponding MAC-VRF and IP-VRF tables
similar to section 5.1.1.
- It imports the MAC address into the MAC-VRF just like section
5.1.1.
- It imports the IP address into IP-VRF with next hop pointing to the
IP address of core-facing IRB interface (carried in the new BGP
attribute).
The fields of RT-2 advertised for core-facing IRB interface, are set
as follow. This RT-2 is advertised with an RT corresponding to the
core-facing EVI (e.g., EVI-x). This RT-2 is also advertised as a
sticky MAC per section 15.2 of [EVPN] in order to ensure mis-
configuration is caught quickly.
- RD per [EVPN]
- ESI = 0
- Ethernet Tag = 0
- MAC Address Length = 48
- MAC Address = Ma ; MAC address of core-facing IRB interface
- IP Address Length = 32 or 128
- IP Address = IPa ; IP address of core-facing IRB interface
- Label-1 = MPLS Label or VNID corresponding to core-facing EVI
Upon receiving the RT-2 advertisement corresponding to core-facing
IRB interface, the receiving NVE performs the following:
- It uses the Route Target corresponding to the EVI-x, to identify
MAC-VRF associated with EVI-x.
- It imports the MAC address into the MAC-VRF associated with EVI-x
with BGP Next Hop address as underlay tunnel destination address
(e.g., VTEP DA for VxLAN encapsulation) and Label-1 as EVI VNID for
VxLAN encapsulation or EVPN label for MPLS encapsulation.
- It imports (MAC/IP ) pair associated with core-facing IRB interface
into the overlay ARP table. This overlay ARP table is used to resolve
per-TS IP addresses imported into the IP-VRF table previously.
5.2.2 Data Plane Operation for IRB forwarding with core-facing I/F
The following description of the data-plane operation describes just
the logical functions and the actual implementation may differ. Lets
consider data-plane operation when TS1 in subnet-1 (EVI-1) on NVE1
wants to send traffic to TS4 in subnet-3 (EVI-3) on NVE2.
Sajassi et al. Expires January 4, 2015 [Page 19]
INTERNET DRAFT Integrated Routing & Bridging in EVPN February 13, 2014
- TS1 send an Ethernet frame with MAC DA corresponding to the EVI-1
IRB interface of NVE1, and VLAN-tag corresponding to EVI-1 just like
section 5.1.1.
- Upon receiving the Ethernet frame, the ingress NVE1 uses VLAN-tag
to identify the MAC-VRF corresponding to EVI-1. It then looks up the
MAC DA and forwards the frame to its IRB interface just like section
5.1.1.
- The Ethernet header of the frame is stripped and the packet is fed
to the IP-VRF where IP lookup is performed on the destination
address. This lookup yield a MAC address (corresponding to the
destination core-facing IRB interface) and its local core-facing IRB
interface over which the packet is sent.
- The packet is encapsulated with an Ethernet header where MAC SA is
set to that of the local core-facing IRB interface and MAC DA is set
to that of the remote core-facing IRB interface. The packet is then
sent to the core-facing EVI of the ingress NVE.
- MAC DA lookup is performed in the core-facing IRB of the ingress
NVE. This lookup yields an IP address to be used as VTEP DA for VxLAN
encap or tunnel label for MPLS encap , and a VPN-ID to be used as
VNID for VxLAN encap or IP-VPN label.
- The packet is then encapsulated with the proper header based on
the above info and is forwarded to the egress NVE.
- On the egress NVE, if the packet is VxLAN encapsulated, the VxLAN
header is removed and the resultant Ethernet frame is fed into the
core-facing MAC-VRF associated with that tenant based on the VNID.
- The MAC DA lookup yields the core-facing IRB interface of the
egress NVE over which the frame is sent. Next, the Ethernet header is
removed and a lookup is performed based on IP DA in the associated
IP-VRF for that tenant. The IP lookup yields the destination TS (TS3)
MAC address and the access-facing IRB interface over which the packet
needs to be sent.
- The IP packet is encapsulated with an Ethernet header with the MAC
SA set to that of the access-facing IRB interface of the egress NVE
(NVE2) and the MAC DA is set to that of destination TS (TS4) MAC
address. The packet is sent to the corresponding MAC-VRF and after a
lookup of MAC DA, is forwarded to the destination TS (TS3) over the
corresponding interface.
6 BGP Encoding
Sajassi et al. Expires January 4, 2015 [Page 20]
INTERNET DRAFT Integrated Routing & Bridging in EVPN February 13, 2014
A new BGP attribute with the following encoding is introduced.
0 1 2 3
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tunnel Type (2 Octets) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Addr len | Address (IPv4, MAC, or IPv6) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Tunnel Type (2 octets): identifies the type of tunneling technology
being signaled. This document specifies the following types:
This document defines the following types:
- VXLAN: Tunnel Type = 8
- NVGRE: Tunnel Type = 9
- GTP: Tunnel Type = 10
Unknown types MUST be ignored and skipped upon receipt.
Length (2 octets): the total number of octets of the value field.
Address Length - Addr len (1 octet): Length of Address. Set to 4
bytes for an IPv4 address, 6 bytes for MAC address, and 16 bytes for
an IPv6 address.
7 VM Mobility
7.1 VM Mobility & Optimum Forwarding for VM's Outbound Traffic
Optimum forwarding for the VM's outbound traffic, upon VM mobility,
can be achieved using either the anycast default Gateway MAC and IP
addresses, or using the address aliasing as discussed in [DC-
MOBILITY].
7.2 VM Mobility & Optimum Forwarding for VM's Inbound Traffic
For optimum forwarding of the VM's inbound traffic, upon VM mobility,
all the NVEs and/or IP-VPN PEs need to know the up to date location
of the VM. Two scenarios must be considered, as discussed next.
In what follows, we use the following terminology:
- source NVE refers to the NVE behind which the VM used to reside
prior to the VM mobility event.
Sajassi et al. Expires January 4, 2015 [Page 21]
INTERNET DRAFT Integrated Routing & Bridging in EVPN February 13, 2014
- target NVE refers to the new NVE behind which the VM has moved
after the mobility event.
7.2.1 Mobility without Route Aggregation
In this scenario, when a target NVE detects that a MAC mobility event
has occurred, it initiates the MAC mobility handshake in BGP as
specified in [EVPN]. The WAN Gateways, acting as ASBRs in this case,
re-advertise the MAC route of the target NVE with the MAC Mobility
extended community attribute unmodified. Because the WAN Gateway for
a given data center re-advertises BGP routes received from the WAN
into the data center, the source NVE will receive the MAC
Advertisement route of the target NVE (with the next hop attribute
adjusted depending on which inter-AS option is employed). The source
NVE will then withdraw its original MAC Advertisement route as a
result of evaluating the Sequence Number field of the MAC Mobility
extended community in the received MAC Advertisement route. This is
per the procedures already defined in [EVPN].
7.2.2 Mobility with Route Aggregation
This section will be completed in the next revision.
8 Acknowledgements
The authors would like to thank Sami Boutros for his valuable
comments.
9 Security Considerations
10 IANA Considerations
11 References
11.1 Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
11.2 Informative References
[EVPN] Sajassi et al., "BGP MPLS Based Ethernet VPN", draft-ietf-
l2vpn-evpn-04.txt, work in progress, July, 2014.
Sajassi et al. Expires January 4, 2015 [Page 22]
INTERNET DRAFT Integrated Routing & Bridging in EVPN February 13, 2014
[EVPN-IPVPN-INTEROP] Sajassi et al., "EVPN Seamless Interoperability
with IP-VPN", draft-sajassi-l2vpn-evpn-ipvpn-interop-01, work in
progress, October, 2012.
[DC-MOBILITY] Aggarwal et al., "Data Center Mobility based on
BGP/MPLS, IP Routing and NHRP", draft-raggarwa-data-center-mobility-
05.txt, work in progress, June, 2013.
Authors' Addresses
Ali Sajassi
Cisco
Email: sajassi@cisco.com
Samer Salam
Cisco
Email: ssalam@cisco.com
Yakov Rekhter
Juniper Networks
Email: yakov@juniper.net
John E. Drake
Juniper Networks
Email: jdrake@juniper.net
Lucy Yong
Huawei Technologies
Email: lucy.yong@huawei.com
Linda Dunbar
Huawei Technologies
Email: linda.dunbar@huawei.com
Wim Henderickx
Alcatel-Lucent
Email: wim.henderickx@alcatel-lucent.com
Florin Balus
Alcatel-Lucent
Sajassi et al. Expires January 4, 2015 [Page 23]
INTERNET DRAFT Integrated Routing & Bridging in EVPN February 13, 2014
Email: Florin.Balus@alcatel-lucent.com
Samir Thoria
Cisco
Email: sthoria@cisco.com
Sajassi et al. Expires January 4, 2015 [Page 24]