Internet DRAFT - draft-bitar-datacenter-vpn-applicability
draft-bitar-datacenter-vpn-applicability
L2VPN Working Group Nabil Bitar
Internet Draft Verizon
Intended status: Informational
Expires: November 2012 Florin Balus
Marc Lasserre
Wim Henderickx
Alcatel-Lucent
Ali Sajassi
Luyuan Fang
Cisco
Yuichi Ikejiri
NTT Communications
Mircea Pisica
BT
May 18, 2012
Cloud Networking: Framework and VPN Applicability
draft-bitar-datacenter-vpn-applicability-02.txt
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Abstract
Cloud Computing has been attracting a lot of attention from the
networking industry. Some of the most publicized requirements are
related to the evolution of the Cloud Networking Infrastructure to
accommodate a large number of tenants, efficient network utilization,
scalable loop avoidance, and Virtual Machine Mobility.
This draft describes a framework for cloud networking, highlighting
the applicability of existing work in various IETF Working Groups
(e.g., RFCs and drafts developed in IETF L2VPN and L3VPN Working
Groups) to cloud networking, and the gaps and problems that need to
be further addressed. That is, the goal is to understand what may be
re-used from the current protocols and call out requirements specific
to the Cloud space that need to be addressed by new standardization
work with proposed solutions in certain cases.
Table of Contents
1. Introduction...................................................3
2. General terminology............................................4
2.1. Conventions used in this document.........................5
3. Brief overview of Ethernet, L2VPN and L3VPN deployments........5
4. Cloud Networking Framework.....................................6
5. DC problem statement...........................................9
5.1. VLAN Space................................................9
5.2. MAC, IP, ARP Explosion...................................10
5.3. Per VLAN flood containment...............................11
5.4. Convergence and multipath support........................12
5.5. Optimal traffic forwarding...............................12
5.6. Efficient multicast support..............................14
5.7. Connectivity to existing VPN sites.......................14
5.8. DC Inter-connect requirements............................15
5.9. L3 virtualization considerations.........................15
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5.10. VM Mobility requirements................................15
6. L2VPN Applicability to Cloud Networking.......................16
6.1. VLANs and L2VPN toolset..................................16
6.2. PBB and L2VPN toolset....................................17
6.2.1. Addressing VLAN space exhaustion and MAC explosion..18
6.2.2. Fast convergence, L2 multi-pathing..................19
6.2.3. Per ISID flood containment..........................20
6.2.4. Efficient multicast support.........................20
6.2.5. Tunneling options for PBB ELAN: Ethernet, IP, MPLS..20
6.2.6. Use Case examples...................................20
6.2.6.1. PBBN in DC, L2 VPN in DC GW....................20
6.2.6.2. PBBN in VSw, L2VPN in the ToR..................22
6.2.7. Connectivity to existing VPN sites and Internet.....23
6.2.8. DC Interconnect.....................................25
6.2.9. Interoperating with existing DC VLANs...............25
6.3. TRILL and L2VPN toolset..................................27
7. L3VPN applicability to Cloud Networking.......................28
8. Solutions for other DC challenges.............................29
8.1. Addressing IP/ARP explosion..............................29
8.2. Optimal traffic forwarding...............................29
8.3. VM Mobility..............................................29
9. Security Considerations.......................................30
10. IANA Considerations..........................................30
11. References...................................................30
11.1. Normative References....................................30
11.2. Informative References..................................31
12. Acknowledgments..............................................32
1. Introduction
The initial Data Center (DC) networks were built to address the needs
of individual enterprises and/or individual applications. Ethernet
VLANs and regular IP routing are used to provide connectivity between
compute, storage resources and the related customer sites.
The virtualization of compute resources in a DC environment provides
the foundation for selling compute and storage resources to multiple
customers, or selling application services to multiple customers. For
example, a customer may buy a group of Virtual Machines (VMs) that
may reside on server blades distributed throughout a DC or across
DCs. In this latter case, the DCs may be owned and operated by a
cloud service provider connected to one or more network service
providers, two or more cloud service providers each connected to one
or more network service providers, or a hybrid of DCs operated by the
customer and the cloud service provider(s). In addition, multiple
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customers may be assigned resources on the same compute and storage
hardware.
In order to provide access for multiple customers to the virtualized
compute and storage resources, the DC network and DC interconnect
have to evolve from the basic VLAN and IP routing architecture to
provide equivalent connectivity virtualization at a large scale.
This document describes in separate sections existing DC networking
architecture, challenges faced by existing DC network models, and the
applicability of VPN technologies to address such challenges. In
addition, challenges not addressed by existing solutions are called
out to describe the problem or to suggest solutions.
2. General terminology
Some general terminology is defined here; most of the terminology
used is from [802.1ah] and [RFC4026]. Terminology specific to this
memo is introduced as needed in later sections.
DC: Data Center
ELAN: MEF ELAN, multipoint to multipoint Ethernet service
EVPN: Ethernet VPN as defined in [EVPN]
PBB: Provider Backbone Bridging, new Ethernet encapsulation designed
to address VLAN exhaustion and MAC explosion issues; specified in
IEEE 802.1ah [802.1ah]
PBB-EVPN: defines how EVPN can be used to transport PBB frames
BMAC: Backbone MACs, the backbone source or destination MAC address
fields defined in the 802.1ah provider MAC encapsulation header.
CMAC: Customer MACs, the customer source or destination MAC address
fields defined in the 802.1ah customer MAC encapsulation header.
BEB: A backbone edge bridge positioned at the edge of a provider
backbone bridged network. It is usually the point in the network
where PBB encapsulation is added or removed from the frame.
BCB: A backbone core bridge positioned in the core of a provider
backbone bridged network. It performs regular Ethernet switching
using the outer Ethernet header.
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2.1. Conventions used in this document
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].
In this document, these words will appear with that interpretation
only when in ALL CAPS. Lower case uses of these words are not to be
interpreted as carrying RFC-2119 significance.
3. Brief overview of Ethernet, L2VPN and L3VPN deployments
Initial Ethernet networks have been deployed in LAN environments,
where the total number of hosts (hence MAC addresses) to manage was
limited. Physical Ethernet topologies in LANs were pretty simple.
Hence, a simple loop resolution protocol such as the Spanning Tree
Protocol was sufficient in the early days. Efficient utilisation of
physical links was not a major concern in LANs, while at the same
time leveraging existing and mature technologies.
As more hosts got connected to a LAN, or the need arose to create
multiple LANs on the same physical infrastructure, it became
necessary to partition the physical topology into multiple Virtual
LANs (VLANs). STP evolved to cope with multiple VLANs with Multiple-
STP (MSTP). Bridges/Switches evolved to learn behind which VLAN
specific MACs resided, a process known as qualified learning. As
Ethernet LANs moved into the provider space, the 12-bit VLAN space
limitation (i.e. a total of 4k VLANs) led to Q-in-Q and later to
Provider backbone Bridging (PBB).
With PBB, not only can over 16M virtual LAN instances (24-bit Service
I-SID) be supported, but a clean separation between customer and
provider domains has been defined with separate MAC address spaces
(Customer-MACs (CMACs) versus Provider Backbone-MACs (BMACs)). CMACs
are only learned at the edge of the PBB network on PBB Backbone Edge
Bridges (BEBs) in the context of an I-component while only B-MACs are
learnt by PBB Backbone Core Bridges (BCBs). This results in BEB
switches creating MAC-in-MAC tunnels to carry customer traffic,
thereby hiding C-MACs in the core.
In the meantime, interconnecting L2 domains across geographical areas
has become a necessity. VPN technologies have been defined to carry
both L2 and L3 traffic across IP/MPLS core networks. The same
technologies could also be used within the same data center to
provide for scale or for interconnecting services across L3 domains,
as needed. Virtual Private LAN Service (VPLS) has been playing a key
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role to provide transparent LAN services over IP/MPLS WANs while IP
VPNs, including BGP/MPLS IP VPNs and IPsec VPNs, have been used to
provide virtual IP routing instances over a common IP/MPLS core
network.
All these technologies have been combined to maximize their
respective benefits. At the edge of the network, such as in access
networks, VLAN and PBB are commonly used technologies. Aggregation
networks typically use VPLS or BGP/MPLS IP VPNs to groom traffic on a
common IP/MPLS core.
It should be noted that Ethernet has kept evolving because of its
attractive features, specifically its auto-discovery capabilities and
the ability of hosts to physically relocate on the same LAN without
requiring renumbering. In addition, Ethernet switches have become
commodity, creating a financial incentive for interconnecting hosts
in the same community with Ethernet switches. The network layer
(layer3), on the other hand, has become pre-dominantly IP. Thus,
communication across LANs uses IP routing.
4. Cloud Networking Framework
A generic architecture for Cloud Networking is depicted in Figure 1:
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,---------.
,' `.
( IP/MPLS )
`. ,'
`-+------+'
+--+--+ +-+---+
| GW |+-+| GW |
+-+---+ +-----+
/ \
+----+---+ +---+-----+
| Core | | Core |
| SW/Rtr | | SW/Rtr |
+-+----`.+ +-+---+---+
/ \ .' \
+---+--+ +-`.+--+ +--+----+
| ToR | | ToR | | ToR |
+-+--`.+ +-+-`.-+ +-+--+--+
.' \ .' \ .' `.
__/_ _i./ i./_ _\__
:VSw : :VSw : :VSw : :VSw :
'----' '----' '----' '----'
Figure 1 : A Generic Architecture for Cloud Networking
A cloud network is composed of intra-Data Center (DC) networks and
network services, and inter-DC network connectivity. DCs may belong
to a cloud service provider connected to one or more network service
providers, different cloud service providers each connected to one or
more network service providers, or a hybrid of DCs operated by the
enterprise customers and the cloud service provider(s). It may also
provide access to the public and/or enterprise customers.
The following network components are present in a DC:
- VSw or virtual switch - software based Ethernet switch running
inside the server blades. VSw may be single or dual-homed to
the Top of Rack switches (ToRs). The individual VMs appear to a
VSw as IP hosts connected via logical interfaces. The VSw may
evolve to support IP routing functionality.
- ToR or Top of Rack - hardware-based Ethernet switch aggregating
all Ethernet links from the server blades in a rack
representing the entry point in the physical DC network for the
hosts. ToRs may also perform routing functionality. ToRs are
usually dual-homed to the Core SW. Other deployment scenarios
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may use an EoR (End of Row) switch to provide similar function
as a ToR.
- Core SW (switch) - high capacity core node aggregating multiple
ToRs. This is usually a cost effective Ethernet switch. Core
switches can also support routing capabilities.
- DC GW - gateway to the outside world providing DC Interconnect
and connectivity to Internet and VPN customers. In the current
DC network model, this may be a Router with Virtual Routing
capabilities and/or an IPVPN/L2VPN PE.
A DC network also contains other network services, such as firewalls,
load-balancers, IPsec gateways, and SSL acceleration gateways. These
network services are not currently discussed in this draft as the
focus is on the routing and switching services. The usual DC
deployment employs VLANs to isolate different VM groups throughout
the Ethernet switching network within a DC. The VM Groups are mapped
to VLANs in the VSws. The ToRs and Core SWs may employ VLAN trunking
to eliminate provisioning touches in the DC network. In some
scenarios, IP routing is extended down to the ToRs, and may be
further extended to the hypervisor.
Any new DC and cloud networking technology needs to be able to fit as
seamlessly as possible with this existing DC model, at least in a
non-greenfield environment. In particular, it should be possible to
introduce enhancements to various tiers in this model in a phased
approach without disrupting the other elements.
Depending upon the scale, DC distribution, operations model, Capex
and Opex aspects, DC switching elements can act as strict L2 switches
and/or provide IP routing capabilities, including VPN routing and/or
MPLS support. In smaller DCs, it is likely that some tier layers will
be collapsed, and that Internet connectivity, inter-DC connectivity
and VPN support will be handled by Core Nodes which perform the DC GW
role.
The DC network architecture described in this section can be used to
provide generic L2-L3 service connectivity to each tenant as depicted
in Figure 2:
,--+-'. ;-`.--.
..... VRF1 )...... . VRF2 )
| '-----' | '-----'
| Tenant1 |ELAN12 Tenant1|
|ELAN11 ....|........ |ELAN13
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'':'''''''':' | | '':'''''''':'
,'. ,'. ,+. ,+. ,'. ,'.
(VM )....(VM ) (VM )... (VM ) (VM )....(VM )
`-' `-' `-' `-' `-' `-'
Figure 2 : Logical Service connectivity for one tenant
In this example one or more virtual routing contexts distributed on
multiple DC GWs and one or more ELANs (e.g., one per Application)
running on DC switches are assigned for DC tenant 1. ELAN is a
generic term for Ethernet multipoint service, which in the current DC
environment is implemented using 12-bit VLAN tags. Other possible
ELAN technologies are discussed in section 6.
For a multi-tenant DC, this type of service connectivity or a
variation could be used for each tenant. In some cases only L2
connectivity is required, i.e., only an ELAN may be used to
interconnect VMs and customer sites.
5. DC problem statement
This section summarizes the challenges faced with the present mode of
operation described in the previous section and implicitly describes
the requirements for next generation DC network.
With the introduction of Compute virtualization, the DC network must
support multiple customers or tenants that need access to their
respective computing and storage resources in addition to making some
aspect of the service available to other businesses in a B-to-B model
or to the public. Every tenant requires service connectivity to its
own resources with secure separation from other tenant domains.
Connectivity needs to support various deployment models, including
interconnecting customer-hosted data center resources to cloud
service provider hosted resources (Virtualized DC for the customer).
This connectivity may be at layer2 or layer3.
Currently, large DCs are often built on a service architecture where
VLANs configured in Ethernet edge and core switches are
interconnected by IP routing running in a few centralized routers.
There may be some cases though where IP routing might be used in the
core nodes or even in the TORs inside a DC.
5.1. VLAN Space
Existing DC deployments provide customer separation and flood
containment, including support for DC infrastructure
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interconnectivity, using Ethernet VLANs. A 12-bit VLAN tag provides
support for a maximum of 4K VLANs.
4K VLANs are inadequate for a Cloud Provider looking to expand its
customer base. For example, there are a number of VPN deployments
(VPLS and IP VPN) which serve more than 20K customers, each requiring
multiple VLANs. Thus, 4K VLANs will likely support less than 4K
customers.
The cloud networking infrastructure needs to provide support for a
much bigger number of virtual L2 domains.
5.2. MAC, IP, ARP Explosion
Virtual Machines are the basic compute blocks being sold to Cloud
customers. Every server blade supports today 16-40 VMs with 100 or
more VMs per server blade coming in the near future. Every VM may
have multiple interfaces for provider and enterprise management, VM
mobility and tenant access, each with its own MAC and IP addresses.
For a sizable DC, this may translate into millions of VM IP and MAC
addresses. From a cloud network viewpoint, this scale number will be
an order of magnitude higher.
Supporting this amount of IP and MAC addresses, including the
associated dynamic behavior (e.g., ARP), throughout the DC Ethernet
switches and routers is very challenging in an Ethernet VLAN and
regular routing environment. Core Ethernet switches running Ethernet
VLANs learn the MAC addresses for every single VM interface that
sends traffic through that switch. Throwing memory to increase the
MAC Forwarding DataBase (FDB) size affects the cost of these
switches. In addition, as the number of of MACs that switches need to
learn increases, convergence time could increase, and flooding
activity will increase upon a topology change as the core switches
flush and re-learn the MAC addresses. Simple operational mistakes may
lead to duplicate MAC entries within the same VLAN domain and
security issues due to administrative MAC assignment used today for
VM interfaces. Similar concerns about memory requirements and related
cost apply to DC Edge switches (ToRs/EoRs) and DC GWs.
From a router perspective, it is important to maximize the
utilization of available resources in both control and data planes
through flexible mapping of VMs and related VLANs to routing
interfaces. This is not easily done in the current VLAN based
deployment environment where the use of VLAN trunking limits the
allocation of VMs to only local routers.
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The amount of ARP traffic grows linearly with the number of hosts on
a LAN. For 1 million VM hosts, it can be expected that the amount of
ARP traffic will be in the range of half million ARPs per second at
the peak, which corresponds to over 200 Mbps of ARP traffic [MYERS].
Similarly, on a server, the amount of ARP traffic, grows linearly
with the number of virtual L2 domains/ELANs instantiated on that
server and the number of VMs in that domain. Besides the link
capacity wasted, which may be small compared to the link capacities
deployed in DCs, the computational burden may be prohibitive. In a
large-DC environment, the large number of hosts and the distribution
of ARP traffic may lead to a number of challenges:
. Processing overload and overload of ARP entries on the
Server/Hypervisor. This is caused by the increased number of VMs
per server blade and the size of related ELAN domains. For
example, a server blade with 100 VMs, each in a separate L2
domain with 100 VMs each would need to support 10K ARP entries
and the associated ARP processing while performing the other
compute tasks.
. Processing overload and exhaustion of ARP entries on the
Routers/PEs and any other L3 Service Appliances (Firewall (FW),
Load-Balancer (LB) etc). This issue is magnified by the L3
virtualization at the service gateways. For example, a gateway
PE handling 10K ELANs each with 10 VMs will result in 100K hosts
sending/receiving traffic to/from the PE, thus requiring the PE
to learn 100K ARP entries. It should be noted that if the PE
supports Integrated Routing and Bridging (IRB), it must support
the associated virtual IP RIBs/FIBs and MAC FDBs for these hosts
in addition to the ARP entries.
. Flood explosion throughout Ethernet switching network. This is
caused by the use of VLAN trunking and implicitly by the lack of
per VPN flood containment.
DC and DC-interconnect technologies that minimize the negative
impact of ARP, MAC and IP entry explosion on individual network
elements in a DC or cloud network hierarchy are needed.
5.3. Per VLAN flood containment
From an operational perspective, DC operators try to minimize the
provisioning touches required for configuring a VLAN domain by
employing VLAN trunks on the L2 switches. This comes at the cost of
flooding broadcast, multicast and unknown unicast frames outside of
the boundaries of the actual VLAN domain.
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The cloud networking infrastructure needs to prevent unnecessary
traffic from being sent/leaked to undesired locations.
5.4. Convergence and multipath support
Spanning Tree is used in the current DC environment for loop
avoidance in the Ethernet switching domain.
STP can take 30 to 50 seconds to repair a topology. Practical
experience shows that Rapid STP (RSTP) can also take multiple seconds
to converge, such as when the root bridge fails.
STP eliminates loops by disabling ports. The result is that only one
path is used to carry traffic. The capacity of disabled links cannot
be utilized, leading to inefficient use of resources.
In a small DC deployment, multi-chassis LAG (MC-LAG) support may be
sufficient initially to provide for loop-free redundancy as an STP
alternative. However, in medium or large DCs it is challenging to use
MC-LAGs solely across the network to provide for resiliency and loop-
free paths without introducing a layer2 routing protocol: i.e. for
multi-homing of server blades to ToRs, ToRs to Core SWs, Core SWs to
DC GWs. MC-LAG may work as a local mechanism but it has no knowledge
of the end-to-end paths so it does not provide any degree of traffic
steering across the network.
Efficient and mature link-state protocols, such as IS-IS, provide
rapid failover times, can compute optimal paths and can fully utilize
multiple parallel paths to forward traffic between 2 nodes in the
network.
Unlike OSPF, IS-IS runs directly at L2 (i.e. no reliance on IP) and
does not require any configuration. Therefore, IS-IS based DC
networks are to be favored over STP-based networks. IEEE Shortest
Path Bridging (SPB) based on IEEE 802.1aq and IEEE 802.1Qbp, and IETF
TRILL [RFC6325] are technologies that enable Layer2 networks using
IS-IS for Layer2 routing.
5.5. Optimal traffic forwarding
Optimal traffic forwarding requires (1) efficient utilization of all
available link capacity in a DC and DC-interconnect, and (2) traffic
forwarding on the shortest path between any two communicating VMs
within the DC or across DCs.
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Optimizing traffic forwarding between any VM pair in the same virtual
domain is dependent on (1) the placement of these VMs and their
relative proximity from a network viewpoint, and (2) the technology
used for computing the routing/switching path between these VMs. The
latter is especially important in the context of VMotion, moving a VM
from one network location to another, while maintaining its layer2
and Layer3 addresses.
Ethernet-based forwarding between two VMs relies on the MAC-
destination Address that is unique per VM interface in the context of
a virtual domain. In traditional IEEE technologies (e.g., 802.1ad,
802.1ah) and IETF L2VPN (i.e., VPLS), Ethernet MAC reachability is
always learnt in the data plane. That applies to both B-MACs and C-
MACs. IETF EVPN [EVPN] supports C-MAC learning in the control plane
via BGP. In addition, with newer IEEE technologies (802.1aq and
802.1Qbp) and IETF PBB-EVPN [PBB-EVPN], B-MAC reachability is learnt
in the control plane while C-MACs are learnt in the data plane at
BEBs, and tunneled in PBB frames. In all these cases, it is important
that as a VM is moved from one location to another: (1) VM MAC
reachability convergence happens fast to minimize traffic black-
holing, and (2) forwarding takes the shortest path.
IP-based forwarding relies on the destination IP address. ECMP load
balancing relies on flow-based criteria. An IP host address is unique
per VM interface. However, hosts on a LAN share a subnet mask, and IP
routing entries are based on that subnet address. Thus, when VMs are
on the same LAN and traditional forwarding takes place, these VMs
forward traffic to each other by relying on ARP or IPv6 Neighbor
discovery to identify the MAC address of the destination and on the
underlying layer2 network to deliver the resulting MAC frame to is
destination. However, when VMs, as IP hosts across layer2 virtual
domains, need to communicate they rely on the underlying IP routing
infrastructure.
In addition, when a DC is an all-IP DC, VMs are assigned a host
address with /32 subnet in the IPv4 case, or /64 or /128 host address
in the IPv6 case, and rely on the IP routing infrastructure to route
the IP packets among VMs. In this latter case, there is really no
need for layer2 awareness potentially beyond the hypervisor switch at
the server hosting the VM. In either case, when a VM moves location
from one physical router to another while maintaining its IP identity
(address), the underlying IP network must be able to route the
traffic to the destination and must be able to do that on the
shortest path.
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Thus, in the case of IP address aggregation as in a subnet,
optimality in traffic forwarding to a VM will require reachability to
the VM host address rather than only the subnet. That is what is
often referred to as punching a hole in the aggregate at the expense
of routing and forwarding table size increase.
As in layer2, layer3 may capitalize on hierarchical tunneling to
optimize the routing/FIB resource utilization at different places in
the network. If a hybrid of subnet-based routing and host-based
routing (host-based routing here is used to refer to hole-punching in
the aggregate) is used, then during VMotion, routing transition can
take place, and traffic may be routed to a location based on subnet
reachability or to a location where the VM used to be attached. In
either of these cases, traffic must not be black-holed. It must be
directed potentially via tunneling to the location where the VM is.
This requires that the old routing gateway knows where the VM is
currently attached. How to obtain that information can be based on
different techniques with tradeoffs. However, this traffic
triangulation is not optimal and must only exist in the transition
until the network converges to a shortest path to the destination.
5.6. Efficient multicast support
STP bridges typically perform IGMP and/or PIM snooping in order to
optimize multicast data delivery. However, this snooping is performed
locally by each bridge following the STP topology where all the
traffic goes through the root bridge. This may result in sub-optimal
multicast traffic delivery. In addition, each customer multicast
group is associated with a forwarding tree throughout the Ethernet
switching network. Solutions must provide for efficient Layer2
multicast. In an all-IP network, explicit multicast trees in the DC
network can be built via multicast signaling protocols (e.g., PIM-
SSM) that follows the shortest path between the destinations and
source(s). In an IPVPN context, Multicast IPVPN based on [MVPN] can
be used to build multicast trees shared among IPVPNs, specific to
VPNs, and/or shared among multicast groups across IPVPNs.
5.7. Connectivity to existing VPN sites
It is expected that cloud services will have to span larger
geographical areas in the near future and that existing VPN customers
will require access to VM and storage facilities for virtualized data
center applications. Hence, the DC network virtualization must
interoperate with deployed and evolving VPN solutions - e.g. IP VPN,
VPLS, VPWS, PBB-VPLS, E-VPN and PBB-EVPN.
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5.8. DC Inter-connect requirements
Cloud computing requirements such as VM Mobility across DCs,
Management connectivity, and support for East-West traffic between
customer applications located in different DCs imply that inter-DC
connectivity must be supported. These DCs can be part of a hybrid
cloud operated by the cloud service provider(s) and/or the end-
customers.
Mature VPN technologies can be used to provide L2/L3 DC interconnect
among VLANs/virtual domains located in different DCs.
5.9. L3 virtualization considerations
In order to provide customer L3 separation while supporting
overlapping IP addressing and privacy, a number of schemes were
implemented in the DC environment. Some of these schemes, such as
double NATing are operationally complex and prone to operator errors.
Virtual Routing contexts (or Virtual Device contexts) or dedicated
hardware-routers are positioned in the DC environment as an
alternative to these mechanisms. Every customer is assigned a
dedicated routing context with associated control plane protocols.
For instance, every customer gets an IP Forwarding instance
controlled by its own BGP and/or IGP routing. Assigning virtual or
hardware routers to each customer while supporting thousands of
customers in a DC is neither scalable nor cost-efficient.
5.10. VM Mobility requirements
The ability to move VMs within a resource pool, whether it is a local
move within the same DC to another server or to a distant DC, offers
multiple advantages for a number of scenarios, for example:
- In the event of a possible natural disaster, moving VMs to a safe
DC location decreases downtime and allows for meeting SLA
requirements.
- Optimized resource location: VMs can be moved to locations that
offer significant cost reduction (e.g. power savings), or
locations close to the application users. They can also be moved
to simply load-balance across different locations.
When VMs change location, it is often important to maintain the
existing client sessions. The VM MAC and IP addresses must be
preserved, and the state of the VM sessions must be copied to the new
location.
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Current VM mobility tools like VMware VMotion require L2 connectivity
among the hypervisors on the servers participating in a VMotion pool.
This is in addition to "tenant ELAN" connectivity which provides for
communication between the VM and the client(s).
A VMotion ELAN might need to cross multiple DC networks to provide
the required protection or load-balancing. In addition, in the
current VMotion procedure, the new VM location must be part of the
tenant ELAN domain. When the new VM is activated, a Gratuitous ARP is
sent so that the MAC FIB entries in the "tenant ELAN" are updated to
direct traffic destined to that VM to the new VM location. In
addition, if a portion of the path requires IP forwarding, the VM
reachability information must be updated to direct the traffic on the
shortest path to the VM.
VM mobility requirements may be addressed through the use of Inter-DC
VLANs to address VMotion and tenant ELANs. However expanding "tenant
VLANs" across two or more DCs will accelerate VLAN exhaustion and MAC
explosion issues. In addition, STP needs to run across DCs leading to
increased convergence times and the blocking of expensive WAN
bandwidth. VLAN trunking used throughout the network creates
indiscriminate flooding across DCs.
L2 VPN solutions over IP/MPLS are designed to interconnect sites
located across the WAN.
6. L2VPN Applicability to Cloud Networking
The following sections will discuss different solution alternatives,
re-using IEEE and IETF technologies to provide a gradual migration
path from the current Ethernet switching VLAN-based model to more
advanced Ethernet switching and IP/MPLS based models. This evolution
is targeted to address inter-DC requirements, cost considerations and
the efficient use of processing/memory resources on DC networking
components.
6.1. VLANs and L2VPN toolset
One approach to address some of the DC challenges discussed in the
previous section is to gradually deploy additional technologies
within existing DC networks. For example, an operator may start by
breaking its DC VLAN domains into different VLAN islands so that each
island can support up to 4K VLANs. VLAN Domains can then be
interconnected via VPLS using the DC GW as a VPLS PE. An ELAN service
can be identified with one VLAN ID in one island and another VLAN ID
in another island with the appropriate VLAN ID processed at the GW.
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As the number of tenants in individual VLAN islands surpasses 4K, the
operator could push VPLS deployment deeper in the DC network. It is
possible in the end to retain existing VLAN-based solution only in
VSw and to provide L2VPN support starting at the ToRs. The ToR and DC
core elements need to be MPLS enabled with existing VPLS solutions.
However, this model does not solve the MAC explosion issue as ToRs
still need to learn VM MAC addresses. In addition, it requires
management of both VLAN and L2VPN addressing and mapping of service
profiles. Per VLAN, per port and per VPLS configurations are required
at the ToR, increasing the time it takes to bring up service
connectivity and complicating the operational model.
6.2. PBB and L2VPN toolset
As highlighted in the problem statement section, the expected large
number of VM MAC addresses in the DC calls out for a VM MAC hiding
solution so that the ToRs and the Core Switches only need to handle a
limited number of MAC addresses.
PBB IEEE 802.1ah encapsulation is a standard L2 technique developed
by IEEE to achieve this goal. It was designed also to address other
limitations of VLAN-based encapsulations while maintaining the native
Ethernet operational model deployed in the DC network.
A conceptual PBB encapsulation is described in Figure 3 (for detailed
encapsulation see [802.1ah]):
+-------------+
Backbone | BMAC DA,SA |12B
Ethernet |-------------|
Header |BVID optional| 4B
|-------------|
Service ID| PBB I-tag | 6B
|-------------|
Regular |VM MAC DA,SA |
Payload |-------------|
| |
|VM IP Payload|
| |
+-------------+
Figure 3 PBB encapsulation
The original Ethernet packet used in this example for Inter-VM
communication is encapsulated in the following PBB header:
- I-tag field - organized similarly with the 802.1q VLAN tag; it
includes the Ethertype, PCP and DEI bits and a 24 bit ISID tag
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which replaces the 12 bit VLAN tag, extending the number of
virtual L2 domain support to 16 Million. It should be noted
that the PBB I-Tag includes also some reserved bits, and most
importantly the C-MAC DA and SA. What is designated as 6 bytes
in the figure is the I-tag information excluding the C-MAC DA
and SA.
- An optional Backbone VLAN field (BVLAN) may be used if grouping
of tenant domains is desired.
- An outer Backbone MAC header contains the source and
destination MAC addresses for the related server blades,
assuming the PBB encapsulation is done at the hypervisor
virtual switch on the server blade.
- The total resulting PBB overhead added to the VM-originated
Ethernet frame is 18 or 22 Bytes (depending on whether the BVID
is excluded or not)
- Note that the original PBB encapsulation allows the use of
CVLAN and SVLAN in between the VM MACs and IP Payload. These
fields were removed from Figure 3 since in a VM environment
these fields do not need to be used on the VSw, their function
is relegated to the I-SID tag.
6.2.1. Addressing VLAN space exhaustion and MAC explosion
In a DC environment, PBB maintains traditional Ethernet forwarding
plane and operational model. For example, a VSw implementation of PBB
can make use of the 24 bit ISID tag instead of the 12 bit VLAN tag to
identify the virtual bridging domains associated with different VM
groups. The VSw uplink towards the ToR in Figure 1 can still be
treated as an Ethernet backbone interface. A frame originated by a VM
can be encapsulated with the ISID assigned to the VM VSw interface
and with the outer DA and SA MACs associated with the respective
destination and source server blades, and then sent to the ToR
switch. Performing this encapsulation at the VSw distributes the VM
MAC learning to server blades with instances in the corresponding
layer2 domain, and therefore alleviates this load from ToRs that
aggregate multiple server blades. Alternatively, the PBB
encapsulation can be done at the ToR.
With PBB encapsulation, ToRs and Core SWs do not have to handle VM
MAC addresses so the size of their MAC FIB tables may decrease by two
or more orders of magnitude, depending on the number of VMs
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configured in each server blade and the number of VM virtual
interfaces and associated MACs.
The original PBB specification [802.1ah] did not introduce any new
control plane or new forwarding concepts for the PBB core. Spanning
Tree and regular Ethernet switching based on MAC Learning and
Flooding were maintained to provide a smooth technology introduction
in existing Ethernet networks.
6.2.2. Fast convergence and L2 multi-pathing
Additional specification work for PBB control plane has been done
since then in both IEEE and IETF L2VPN.
As stated earlier, STP-based layer2 networks underutilize the
available network capacity as links are put in an idle state to
prevent loops. Similarly, existing VPLS technology for
interconnecting Layer2 network-islands over an IP/MPLS core does not
support active-active dual homing scenarios.
IS-IS controlled layer2 networks allow traffic to flow on multiple
parallel paths between any two servers, spreading traffic among
available links on the path. IEEE 802.1aq Shortest Path Bridging
(SPB) [802.1aq] and emerging IEEE 802.1Qbp [802.1Qbp] are PBB control
plane technologies that utilize different methods to compute parallel
paths and forward traffic in order to maximize the utilization of
available links in a DC. In addition, a BGP based solution [PBB-EVPN]
was submitted and discussed in IETF L2VPN WG.
One or both mechanisms may be employed as required. IS-IS could be
used inside the same administrative domain (e.g., a DC), while BGP
may be employed to provide reachability among interconnected
Autonomous Systems. Similar architectural models have been widely
deployed in the Internet and for large VPN deployments.
IS-IS and/or BGP are also used to advertise Backbone MAC addresses
and to eliminate B-MAC learning and unknown unicast flooding in the
forwarding plane, albeit with tradeoffs. The BMAC FIB entries are
populated as required from the resulting IS-IS or BGP RIBs.
Legacy loop avoidance schemes using Spanning Tree and local
Active/Active MC-LAG are no longer required as their function (layer2
routing) is replaced by the indicated routing protocols (IS-IS and
BGP).
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6.2.3. Per ISID flood containment
Service auto-discovery provided by 802.1aq SPB [802.1aq] and BGP
[PBB-EVPN] is used to distribute ISID related information among DC
nodes, eliminating any provisioning touches throughout the PBB
infrastructure. This implicitly creates backbone distribution trees
that provide per ISID automatic flood and multicast containment.
6.2.4. Efficient multicast support
IS-IS [802.1aq] and BGP [PBB-EVPN] could be used to build optimal
multicast distribution trees. In addition, PBB and IP/MPLS tunnel
hierarchy may be used to aggregate multiple customer multicast trees
sharing the same nodes by associating them with the same backbone
forwarding tree that may be represented by a common Group BMAC and
optionally a P2MP LSP. More details will be discussed in a further
version of the draft.
6.2.5. Tunneling options for PBB ELAN: Ethernet, IP and MPLS
The previous section introduces a solution for DC ELAN domains based
on PBB ISIDs, PBB encapsulation and IS-IS and/or BGP control plane.
IETF L2 VPN specifications [PBB-VPLS] or [PBB-EVPN] enable the
transport of PBB frames using PW/MPLS or simply MPLS, and implicitly
allow the use of MPLS Traffic Engineering and Resiliency toolset to
provide for advanced traffic steering and faster convergence.
Transport over IP/L2TPv3 [RFC 4719] or IP/GRE is also possible as an
alternative to MPLS tunneling. Additional header optimization for PBB
over IP/GRE encapsulated packets may also be feasible. These
specifications would allow for ISID based L2 overlay using a regular
IP backbone.
6.2.6. Use Case examples
6.2.6.1. PBBN in DC, L2VPN in DC GW
DC environments based on VLANs and native Ethernet operational model
may want to consider using the native PBB option to provide L2 multi-
tenancy, in effect the DC ELAN from Figure 2. An example of a network
architecture that addresses this scenario is depicted in Figure 4:
,---------.
,' Inter-DC `.
(L2VPN (PBB-VPLS)
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`.or PBB-EVPN),'
`|-------|-'
+--+--+ +-+---+
|PE GW|+-+|PE GW|
.+-----+ +-----+.
.' `-.
.-' `\
,' `.
+ Intra-DC PBBN \
| +
: ;
`\+------+ +------+ +--+----+-'
| ToR |.. | ToR |..| ToR |
+-+--+-+ +-+--+-+ +-+--+--+
.'PBB `. .'PBB `. .'PBB `.
+--+-+ +-+-++ +-++-+ +-+--+
|VSw | :VSw : :VSw : :VSw :
+----+ +----+ +----+ +----+
Figure 4 PBB in DC, PBB-VPLS or PBB-EVPN for DC Interconnect
PBB inside the DC core interoperates seamlessly with VPLS used for L2
DC-Interconnect to extend ELAN domains across DCs. This expansion may
be required to address VM Mobility requirements or to balance the
load on DC PE gateways. Note than in PBB-VPLS case, just one or a
handful of infrastructure B-VPLS instances are required, providing
Backbone VLAN equivalent function.
PBB encapsulation addresses the expansion of the ELAN service
identification space with 16M ISIDs and solves MAC explosion through
VM MAC hiding from the Ethernet core.
PBB SPB [802.1aq] is used for core routing in the ToRs, Core SWs and
PEs. If the DCs that need to be interconnected at L2 are part of the
same administrative domain, and scaling is not an issue, SPB/IS-IS
may be extended across the VPLS infrastructure. If different AS
domains are present, better load balancing is required between the
DCs and the WAN, or IS-IS extension across DCs causes scaling issues,
then BGP extensions described in [PBB-EVPN] must be employed.
The forwarding plane, MAC FIB requirements and the Layer2 operational
model in the ToR and Core SW are maintained. The VSw sends PBB
encapsulated frames to the ToR as described in the previous section.
ToRs and Core SWs still perform standard Ethernet switching using the
outer Ethernet header.
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From a control plane perspective, VSw uses a default gateway
configuration to send traffic to the ToR, as in regular IP routing
case. VSw BMAC learning on the ToR is done through either LLDP or VM
Discovery Protocol (VDP) described in [802.1Qbg]. Identical
mechanisms may be used for the ISID. Once this information is learned
on the ToR it is automatically advertised through SPB. If PBB-EVPN is
used in the DC GWs, MultiProtcol (MP)-BGP will be used to advertise
the ISID and BMAC over the WAN as described in [PBB-EVPN].
6.2.6.2. PBBN in VSw, L2VPN in the ToR
A variation of the use case example from the previous section is
depicted in Figure 5:
,---------.
,' Inter-DC `.
(L2VPN (PBB-VPLS)
`.or PBB-EVPN),'
`|-------|-'
+--+--+ +-+---+
|PE GW|+-+|PE GW|
.+-----+ +-----+.
.' `-.
.-' `\
,' `.
+ Intra-DC L2VPN over \
| IP or MPLS tunneling +
: ;
`\+------+ +------+ +--+----+-'
| ToR |.. | ToR |..| ToR |
+-+--+-+ +-+--+-+ +-+--+--+
.'PBB `. .'PBB `. .'PBB `.
+--+-+ +-+-++ +-++-+ +-+--+
|VSw | :VSw : :VSw : :VSw :
+----+ +----+ +----+ +----+
Figure 5 PBB in VSw, L2VPN at the ToR
The procedures from the previous section are used at the VSw: PBB
encapsulation and Ethernet BVLANs can be used on the VSw uplink.
L2VPN infrastructure is replacing the BVLAN at the ToR enabling the
use of IP (GRE or L2TP) or MPLS tunneling.
L2 networking still has the same control plane choices: IS-IS
[802.1aq] and/or BGP [PBB-EVPN], independently from the tunneling
choice.
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6.2.7. Connectivity to existing VPN sites and Internet
The main reason for extending the ELAN space beyond the 4K VLANs is
to be able to serve multiple DC tenants whereby the total number of
service domains needed exceeds 4K. Figure 6 represents the logical
service view where PBB ELANs are used inside one or multiple DCs to
connect to existing IP VPN sites. It should be noted that the PE GW
should be able to perform integrated routing in a VPN context and
bridging in VSI context:
Tenant 1 sites connected over IP VPN
,--+-'. ;-`.--.
( PE ) VRFs on PEs . PE )
'-----' '-----'
| |
,-------------------------------.
( IP VPN over IP/MPLS WAN )
`---.'-----------------------`.-'
+--+--+ IP VPN VRF on PE GWs +-+---+
.....|PE GW|...... |PE GW|
DC with PBB | +-----+ | +--+--+
Tenant 1 | |PBB ELAN12 |
view PBB|ELAN11 ......|...... PBB|ELAN13
'':'''''''':' | | '':'''''''':'
,'. ,'. ,+. ,+. ,'. ,'.
(VM )....(VM ) (VM )... (VM ) (VM )....(VM )
`-' `-' `-' `-' `-' `-'
Compute Resources inside DC
Figure 6 Logical Service View with IP VPN
DC ELANs are identified with 24-bit ISIDs instead of VLANs. At the PE
GWs, an IP VPN VRF is configured for every DC tenant. Each "ISID
ELAN" for Tenant 1 is seen as a logical Ethernet endpoint and is
assigned an IP interface on the Tenant 1 VRF. Tenant 1 enterprise
sites are connected to IP VPN PEs distributed across the WAN. IP VPN
instances on PE GWs can be automatically discovered and connected to
the WAN IP VPN using standard procedures - see [RFC4364].
In certain cases, the DC GW PEs are part of the IPVPN service
provider network providing IPVPN services to the enterprise
customers. In other cases, DC PEs are operated and managed by the
DC/cloud provider and interconnect to multiple IPVPN service
providers using inter-AS BGP/MPLS models A, B, or C [RFC4364]. The
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same discussion applies to the case of IPSec VPNs from a PBB ELAN
termination perspective.
If tenant sites are connected to the DC using WAN VPLS, the PE GWs
need to implement the BEB function described in the PBB-VPLS PE model
[PBB-VPLS] and the procedures from [PBB-Interop] to perform the
required translation. Figure 7 describes the VPLS WAN scenario:
Customer sites connected over VPLS
,--+-'. ;-`.--.
( PE ) VPLS on PEs . PE )
'-----' '-----'
| |
,-------------------------------.
( VPLS over IP/MPLS WAN )
`---.'-----------------------`.-'
+--+--+ +-+---+
|PE GW| <-- PBB-VPLS/BEB --> |PE GW|
DC with PBB +--+--+ +--+--+
Tenant 1 | |
view PBB|ELAN11 PBB|ELAN13
'':'''''''':' '':'''''''':'
,'. ,'. ,'. ,'.
(VM ) .. (VM ) (VM ) .. (VM )
`-' `-' `-' `-'
Compute Resources inside DC
Figure 7 Logical Service View with VPLS WAN
One VSI is required at the PE GW for every DC ELAN domain. Same as in
the IP VPN case, DC PE GWs may be fully integrated as part of the WAN
provider network or using Inter-AS/Inter-provider models A,B or C.
The VPN connectivity may be provided by one or multiple PE GWs,
depending on capacity need and/or the operational model used by the
DC/cloud operator.
If a VM group is serving Internet connected customers, the related
ISID ELAN will be terminated into a routing context (global public
instance or another VRF) connected to the Internet. Same as in the IP
VPN case, the 24bit ISID will be represented as a logical Ethernet
endpoint on the Internet routing context and an IP interface will be
allocated to it. Same PE GW may be used to provide both VPN and
Internet connectivity with the routing contexts separated internally
using the IP VPN models.
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6.2.8. DC Interconnect
L2 DC interconnect may be required to expand the ELAN domains for
Management, VM Mobility or when a VM Group needs to be distributed
across DCs.
PBB may be used to provide ELAN extension across multiple DCs as
depicted in Figure 8:
,-------------------------------.
( IP/MPLS WAN )
`---.'------------------------`.'
+--+--+ +-+---+
|PE GW| <----- PBB BCB ----> |PE GW|
DC with PBB +--+--+ +--+--+
Tenant 1 | |
view PBB|ELAN11 PBB|ELAN11
'':'''''''':' '':'''''''':'
,'. ,'. ,'. ,'.
(Hvz) .. (Hvz) (Hvz) .. (Hvz)
`-' `-' `-' `-'
Compute Resources inside DC
Figure 8 PBB BCB providing VMotion ELAN
ELAN11 is expanded across DC to provide interconnect for the pool of
server blades assigned to the same VMotion domain. This time
Hypervisors are connected directly to ELAN11. The PE GW operates in
this case as a PBB Backbone Core Bridge (BCB) [PBB-VPLS] combined
with PBB-EVPN capabilities [PBB-EVPN]. The ISID ELANs do not require
any additional provisioning touches and do not consume additional
MPLS resources on the PE GWs. Per ISID auto-discovery and flood
containment is provided by IS-IS/SPB [802.1aq] and BGP [PBB-EVPN].
6.2.9. Interoperating with existing DC VLANs
While green field deployments will definitely benefit from all the
advantages described in the previous sections, in many other
scenarios, existing DC VLAN environments will have to be gradually
migrated to the new architecture. Figure 9 depicts an example of a
possible migration scenario where both PBB and VLAN technologies are
present:
,---------.
,' Inter-DC `.
(L2VPN (PBB-VPLS)
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`.or PBB-EVPN),'
`-/------\-'
+---+-+ +-+---+
|PE GW|+-+|PE GW|
.-+-----+ +-----+:-.
.-' `-.
,' `-:.
+ PBBN/SPB DC \
| +
: ;
`-+------+ +------+ +--+----+-'
| ToR |.. | ToR |..| ToR |
+-+--+-+ +-+--+-+ +-+--+--+
.'PBB `. .' `. .'VLAN`.
+--+-+ +-+-++ +-++-+ +-+--+
|VSw | :VSw : :VSw : :VSw :
+----+ +----+ +----+ +----+
Figure 9 DC with PBB and VLANs
This example assumes that the two VSWs on the right do not support
PBB but the ToRs do. The VSw on the left side are running PBB while
the ones on the right side are still using VLANs. The left ToR is
performing only Ethernet switching whereas the one on the right is
translating from VLANs to ISIDs and performing PBB encapsulation
using the BEB function [802.1ah] and [PBB-VPLS]. The ToR in the
middle is performing both functions: core Ethernet tunneling for the
PBB VSw and BEB function for the VLAN VSw.
The SPB control plane is still used between the ToRs, providing the
benefits described in the previous section. The VLAN VSw must use
regular multi-homing functions to the ToRs: for example STP or Multi-
chassis-LAG.
DC VLANs may be also present initially on some of the legacy ToRs or
Core SWs. PBB interoperability will be performed as follows:
. If VLANs are used in the ToRs, PBB BEB function may be
performed by the Core SW(s) where the ToR uplink is connected
. If VLANs are used in the Core SW, PBB BEB function may be
performed by the PE GWs where the Core SW uplink is connected
It is possible that some DCs may run PBB or PBB-VLAN combination
while others may still be running VLANs. An example of this
interoperability scenario is described in Figure 10:
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,-------------------------------.
( IP/MPLS WAN )
`------/-----------------\-------'
+--/--+ +--\--+
|PE GW|PBB-VPLS |PE GW|VPLS
.'+-----+-' .'+-----+'.
/ \ / \
| | | |
| PBB DC | | VLAN DC |
\ / \ /
+---+ +---+ +---+ +---+
|VSw|.|VSw| |VSw|.|VSw|
+---+ +---+ +---+ +---+
Figure 10 Interoperability to a VLAN-based DC
Interoperability with existing VLAN DC is required for DC
interconnect. The PE-GW in the PBB DC or the PE GW in the VLAN DC
must implement PBB-VPLS PE model described in [PBB-VPLS]. This
interoperability scenario is addressed in detail in [PBB-Interop].
Connectivity to existing VPN customer sites (IP VPN, VPLS, IPSec) or
Internet does not require any additional procedures beyond the ones
described in the VPN connectivity section. The PE GW in the DC VLAN
will aggregate DC ELANs through IP interfaces assigned to VLAN
logical endpoints whereas the PE GW in the PBB DC will assign IP
interfaces to ISID logical endpoints.
If EVPN is used to interconnect the two DCs, PBB-EVPN functions
described in [PBB-EVPN] must be implemented in one of the PE-GWs.
6.3. TRILL and L2VPN toolset
TRILL and SPB control planes provide similar functions. IS-IS is the
base protocol used in both specifications to provide multi-pathing
and fast convergence for core networking. [PBB-EVPN] describes how
seamless Inter-DC connectivity can be provided over an MPLS/IP
network for both TRILL [RFC6325] and SPB [802.1aq]/[802.1Qbp]
networks.
The main differences exist in the encapsulation and data plane
forwarding. TRILL encapsulation [RFC6325] was designed initially for
large enterprise and campus networks where 4k VLANs are sufficient.
As a consequence the ELAN space in [RFC6325] is limited to 4K VLANs;
however, this VLAN scale issue is being addressed in [Fine-Grained].
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7. L3VPN applicability to Cloud Networking
This section discusses the role of IP VPN technology in addressing
the L3 Virtualization challenges described in section 5.
IP VPN technology defined in L3VPN working group may be used to
provide L3 virtualization in support of multi-tenancy in the DC
network as depicted in Figure 11.
,-------------------------------.
( IP VPNs over IP/MPLS WAN )
`----.'------------------------`.'
,--+-'. ;-`.--.
..... VRF1 )...... . VRF2 )
| '-----' | '-----'
| Tenant1 |ELAN12 Tenant1|
|ELAN11 ....|........ |ELAN13
'':'''''''':' | | '':'''''''':'
,'. ,'. ,+. ,+. ,'. ,'.
(VM )....(VM ) (VM )... (VM ) (VM )....(VM )
`-' `-' `-' `-' `-' `-'
Figure 11 Logical Service View with IP VPN
Tenant 1 might buy Cloud Services in different DC locations and
choose to associate the VMs in 3 different groups, each mapped to a
different ELAN: ELAN11, ELAN12 and ELAN13. L3 interconnect between
the ELANs belonging to tenant1 is provided using an IP/MPLS VPN and
associated VRF1 and VRF2, possibly located in different DCs. Each
tenant that requires L3 virtualization will be allocated a different
IP VPN instance. Using full fledge IP VPN for L3 Virtualization
inside a DC presents the following advantages compared with existing
DC technologies like Virtual Routing:
- Interoperates with existing WAN VPN technology
- Deployment tested, provides a full networking toolset
- Scalable core routing - only one BGP-MP routing instance is
required compared with one per customer/tenant in the Virtual
Routing case
- Service Auto-discovery - automatic discovery and route
distribution between related service instances
- Well defined and deployed Inter-Provider/Inter-AS models
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- Supports a variety of VRF-to-VRF tunneling options
accommodating different operational models: MPLS [RFC4364], IP
or GRE [RFC4797]
To provide Cloud services to related customer IP VPN instances
located in the WAN the following connectivity models may be employed:
- DC IP VPN instance may participate directly in the WAN IP VPN
- Inter-AS Options A, B or C models may be employed with
applicability to both Intra and Inter-Provider use cases
[RFC4364]
8. Solutions for other DC challenges
This section touches on some of the DC challenges that may be
addressed by a combination of IP VPN, L2VPN and IP toolset.
Additional details will be provided in a future revision.
8.1. Addressing IP/ARP explosion
Possible solutions for IP/ARP explosion are discussed in [EVPN],
[PBB-EVPN], [ARPproxy] and in ARMD WG that address certain aspects.
More discussion is required to clarify the requirements in this
space, taking into account the different network elements potentially
impacted by ARP.
8.2. Optimal traffic forwarding
IP networks, built using links-state protocols such as OSPF or ISIS
and BGP provide optimal traffic forwarding through the use of equal
cost multiple path (ECMP) and ECMP traffic load-balancing, and the
use of traffic engineering tools based on BGP and/or MPLS-TE as
applicable. In the Layer2 case, SPB or TRILL based protocols provide
for load-balancing across parallel paths or equal cost paths between
two nodes. Traffic follows the shortest path. For multicast, data
plane replication at layer2 or layer3 happens in the data plane
albeit with different attributes after multicast trees are built via
a control plane and/or snooping. In the presence of VM mobility,
optimal forwarding relates to avoiding triangulation and providing
for optimum forwarding between any two VMs.
8.3. VM Mobility
IP VPN technology may be used to support DC Interconnect for
different functions like VM Mobility and Cloud Management. A
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description of VM Mobility between server blades located in different
IP subnets using extensions to existing BGP-MP and IP VPN procedure
is described in [VM-Mobility]. Other solutions can exist as well.
What is needed is a solution that provides for fast convergence
toward the steady state whereby communication among any two VMs can
take place on the shortest path or most optimum path, transit
triangulation time is minimized, traffic black-holing is avoided, and
impact on routing scale for both IPv4 and IPv6 is controllable or
minimized.
9. Security Considerations
No new security issues are introduced beyond those described already
in the related L2VPN drafts.
10. IANA Considerations
IANA does not need to take any action for this draft.
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.
[RFC4761] Kompella, K. and Rekhter, Y. (Editors), "Virtual Private
LAN Service (VPLS) Using BGP for Auto-Discovery and
Signaling", RFC 4761, January 2007.
[RFC4762] Lasserre, M. and Kompella, V. (Editors), "Virtual Private
LAN Service (VPLS) Using Label Distribution Protocol (LDP)
Signaling", RFC 4762, January 2007.
[PBB-VPLS] Balus, F. et al. "Extensions to VPLS PE model for Provider
Backbone Bridging", draft-ietf-l2vpn-pbb-vpls-pe-model-
04.txt (work in progress), October 2011.
[PBB-Interop] Sajassi, A. et al. "VPLS Interoperability with Provider
Backbone Bridging", draft-ietf-l2vpn-pbb-vpls-interop-
02.txt (work in progress), July 2011.
[802.1ah] IEEE 802.1ah "Virtual Bridged Local Area Networks,
Amendment 6: Provider Backbone Bridges", Approved Standard
June 12th, 2008
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[802.1aq] IEEE Draft P802.1aq/D4.3 "Virtual Bridged Local Area
Networks, Amendment: Shortest Path Bridging", Work in
Progress, September 21, 2011
[RFC6325] Perlman, et al., "Routing Bridges (Rbridges): Base Protocol
Specification", RFC 6325, July 2011.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, February 2006.
[RFC4797] Rosen, E. and Y. Rekhter, " Use of Provider Edge to
Provider Edge (PE-PE) Generic Routing encapsulation (GRE)
or IP in BGP/MPLS IP Virtual Private Networks ", RFC 4797,
January 2007.
11.2. Informative References
[RFC4026] Andersson, L. et Al., "Provider Provisioned Virtual Private
Network (VPN) Terminology", RFC 4026, May 2005.
[802.1Qbp] IEEE Draft P802.1Qbp/D0.1 "Virtual Bridged Local Area
Networks, Amendment: Equal Cost Multiple Paths (ECMP)",
Work in Progress, October 13, 2011
[802.1Qbg] IEEE Draft P802.1Qbg/D1.8 "Virtual Bridged Local Area
Networks, Amendment: Edge Virtual Bridging", Work in
Progress, October 17, 2011
[EVPN] Raggarwa, R. et al. "BGP MPLS based Ethernet VPN", draft-
raggarwa-sajassi-l2vpn-evpn-04.txt (work in progress),
September 2011.
[PBB-EVPN] Sajassi, A. et al. "PBB-EVPN", draft-sajassi-l2vpn-pbb-
evpn-02.txt (work in progress), July 2011.
[VM-Mobility] Raggarwa, R. et al. "Data Center Mobility based on
BGP/MPLS, IP Routing and NHRP", draft-raggarwa-data-center-
mobility-01.txt (work in progress), September 2011.
[RFC4719] Aggarwal, R. et al., "Transport of Ethernet over Layer 2
Tunneling Protocol Version 3 (L2TPv3)", RFC 4719, November
2006.
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[MVPN] Rosen, E. and Raggarwa, R. "Multicast in MPLS/BGP IP VPN",
draft-ietf-l3vpn-2547bis-mcast-10.txt (work in progress),
January 2010.
[ARPproxy] Carl-Mitchell, S. and Quarterman, S., "Using ARP to
implement transparent subnet gateways", RFC 1027, October
1987.
[MYERS] Myers, A., Ng, E. and Zhang, H., "Rethinking the Service
Model: Scaling Ethernet to a Million Nodes"
http://www.cs.cmu.edu/~acm/papers/myers-hotnetsIII.pdf
[Fine-Grained] Eastlake, D. et Al., "RBridges: Fine-Grained
Labeling", draft-eastlake-trill-rbridge-fine-labeling-
01.txt (work in progress), October 2011.
12. Acknowledgments
In addition to the authors the following people have contributed to
this document:
Javier Benitez, Colt
Dimitrios Stiliadis, Alcatel-Lucent
Samer Salam, Cisco
This document was prepared using 2-Word-v2.0.template.dot.
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Authors' Addresses
Nabil Bitar
Verizon
40 Sylvan Road
Waltham, MA 02145
Email: nabil.bitar@verizon.com
Florin Balus
Alcatel-Lucent
777 E. Middlefield Road
Mountain View, CA, USA 94043
Email: florin.balus@alcatel-lucent.com
Marc Lasserre
Alcatel-Lucent
Email: marc.lasserre@alcatel-lucent.com
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Wim Henderickx
Alcatel-Lucent
Email: wim.henderickx@alcatel-lucent.com
Ali Sajassi
Cisco
170 West Tasman Drive
San Jose, CA 95134, USA
Email: sajassi@cisco.com
Luyuan Fang
Cisco
111 Wood Avenue South
Iselin, NJ 08830
Email: lufang@cisco.com
Yuichi Ikejiri
NTT Communications
1-1-6, Uchisaiwai-cho, Chiyoda-ku
Tokyo, 100-8019 Japan
Email: y.ikejiri@ntt.com
Mircea Pisica
BT
Telecomlaan 9
Brussels 1831, Belgium
Email: mircea.pisica@bt.com
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