Internet DRAFT - draft-sridharan-virtualization-nvgre
draft-sridharan-virtualization-nvgre
Network Working Group P. Garg Ed.
Internet Draft Y. Wang Ed.
Intended Category: Informational Microsoft
Expires: October 12, 2015 April 13, 2015
NVGRE: Network Virtualization using Generic Routing Encapsulation
draft-sridharan-virtualization-nvgre-08.txt
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Abstract
This document describes the usage of Generic Routing Encapsulation
(GRE) header for Network Virtualization (NVGRE) in multi-tenant
datacenters. Network Virtualization decouples virtual networks and
addresses from physical network infrastructure, providing isolation
and concurrency between multiple virtual networks on the same
physical network infrastructure. This document also introduces a
Network Virtualization framework to illustrate the use cases, but
the focus is on specifying the data plane aspect of NVGRE.
Table of Contents
1. Introduction...................................................2
1.1. Terminology...............................................4
2. Conventions used in this document..............................4
3. NVGRE: Network Virtualization using GRE........................5
3.1. NVGRE Endpoint............................................5
3.2. NVGRE frame format........................................6
3.3. Inner 802.1Q Tag..........................................9
3.4. Reserved VSID.............................................9
4. NVGRE Deployment Consideration................................10
4.1. ECMP Support.............................................10
4.2. Broadcast and Multicast Traffic..........................10
4.3. Unicast Traffic..........................................10
4.4. IP Fragmentation.........................................11
4.5. Address/Policy Management & Routing......................11
4.6. Cross-subnet, Cross-premise Communication................11
4.7. Internet Connectivity....................................13
4.8. Management and Control Planes............................13
4.9. NVGRE-Aware Devices......................................13
4.10. Network Scalability with NVGRE..........................14
5. Security Considerations.......................................15
6. IANA Considerations...........................................15
7. References....................................................15
7.1. Normative References.....................................15
7.2. Informative References...................................16
8. Authors and Contributors......................................16
9. Acknowledgments...............................................17
1. Introduction
Conventional data center network designs cater to largely static
workloads and cause fragmentation of network and server capacity
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[6][7]. There are several issues that limit dynamic allocation and
consolidation of capacity. Layer 2 networks use Rapid Spanning Tree
Protocol (RSTP) which is designed to eliminate loops by blocking
redundant paths. These eliminated paths translate to wasted capacity
and a highly oversubscribed network. There are alternative
approaches such as TRILL that address this problem [13].
The network utilization inefficiencies are exacerbated by network
fragmentation due to the use of VLANs for broadcast isolation. VLANs
are used for traffic management and also as the mechanism for
providing security and performance isolation among services
belonging to different tenants. The Layer 2 network is carved into
smaller sized subnets typically one subnet per VLAN, with VLAN tags
configured on all the Layer 2 switches connected to server racks
that host a given tenant's services. The current VLAN limits
theoretically allow for 4K such subnets to be created. The size of
the broadcast domain is typically restricted due to the overhead of
broadcast traffic. The 4K VLAN limit is no longer sufficient in a
shared infrastructure servicing multiple tenants.
Data center operators must be able to achieve high utilization of
server and network capacity. In order to achieve efficiency it
should be possible to assign workloads that operate in a single
Layer 2 network to any server in any rack in the network. It should
also be possible to migrate workloads to any server anywhere in the
network while retaining the workloads' addresses. This can be
achieved today by stretching VLANs, however when workloads migrate
the network needs to be reconfigured which is typically error prone.
By decoupling the workload's location on the LAN from its network
address, the network administrator configures the network once and
not every time a service migrates. This decoupling enables any
server to become part of any server resource pool.
The following are key design objectives for next generation data
centers:
a) location independent addressing
b) the ability to a scale the number of logical Layer 2/Layer 3
networks irrespective of the underlying physical topology or
the number of VLANs
c) preserving Layer 2 semantics for services and allowing them to
retain their addresses as they move within and across data
centers
d) providing broadcast isolation as workloads move around without
burdening the network control plane
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This document describes use of the Generic Routing Encapsulation
(GRE, [3][4]) header for network virtualization. Network
virtualization decouples a virtual network from the underlying
physical network infrastructure by virtualizing network addresses.
Combined with a management and control plane for the virtual-to-
physical mapping, network virtualization can enable flexible virtual
machine placement and movement, and provide network isolation for a
multi-tenant datacenter.
Network virtualization enables customers to bring their own address
spaces into a multi-tenant datacenter while the datacenter
administrators can place the customer virtual machines anywhere in
the datacenter without reconfiguring their network switches or
routers, irrespective of the customer address spaces.
1.1. Terminology
Please refer to [9][11] for more formal definition of terminology.
The following terms were used in this document.
Customer Address (CA): These are the virtual IP addresses assigned
and configured on the virtual NIC within each VM. These are the only
addresses visible to VMs and applications running within VMs.
Network Virtualization Edge (NVE): An entity that performs the
network virtualization encapsulation and decapsulation.
Provider Address (PA): These are the IP addresses used in the
physical network. PA's are associated with VM CA's through the
network virtualization mapping policy.
Virtual Machine (VM): These are instances of OS's running on top of
hypervisor over a physical machine or server. Multiple VMs can share
the same physical server via the hypervisor, yet are completely
isolated from each other in terms of compute, storage, and other OS
resources.
Virtual Subnet Identifier (VSID): a 24-bit ID that uniquely
identifies a virtual subnet or virtual layer 2 broadcast domain.
2. 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].
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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. Network Virtualization using GRE (NVGRE)
This section describes Network Virtualization using GRE, NVGRE.
Network virtualization involves creating virtual Layer 2 topologies
on top of a physical Layer 3 network. Connectivity in the virtual
topology is provided by tunneling Ethernet frames in GRE over IP
over the physical network.
In NVGRE, every virtual Layer 2 network is associated with a 24-bit
identifier, called a Virtual Subnet Identifier (VSID). A VSID is
carried in an outer header as defined in Section 3.2. , allowing
unique identification of a tenant's virtual subnet to various
devices in the network. A 24-bit VSID supports up to 16 million
virtual subnets in the same management domain, in contrast to only
4K achievable with VLANs. Each VSID represents a virtual Layer 2
broadcast domain, which can be used to identify a virtual subnet of
a given tenant. To support multi-subnet virtual topology, datacenter
administrators can configure routes to facilitate communication
between virtual subnets of the same tenant.
GRE is a proposed IETF standard [3][4] and provides a way for
encapsulating an arbitrary protocol over IP. NVGRE leverages the GRE
header to carry VSID information in each packet. The VSID
information in each packet can be used to build multi-tenant-aware
tools for traffic analysis, traffic inspection, and monitoring.
The following sections detail the packet format for NVGRE, describe
the functions of a NVGRE endpoint, illustrate typical traffic flow
both within and across data centers, and discuss address, policy
management and deployment considerations.
3.1. NVGRE Endpoint
NVGRE endpoints are the ingress/egress points between the virtual
and the physical networks. The NVGRE endpoints are the NVEs as
defined in the NVO Framework document [9]. Any physical server or
network device can be an NVGRE endpoint. One common deployment is
for the endpoint to be part of a hypervisor. The primary function of
this endpoint is to encapsulate/decapsulate Ethernet data frames to
and from the GRE tunnel, ensure Layer 2 semantics, and apply
isolation policy scoped on VSID. The endpoint can optionally
participate in routing and function as a gateway in the virtual
topology. To encapsulate an Ethernet frame, the endpoint needs to
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know the location information for the destination address in the
frame. This information can be provisioned via a management plane,
or obtained via a combination of control plane distribution or data
plane learning approaches. This document assumes that the location
information, including VSID, is available to the NVGRE endpoint.
3.2. NVGRE frame format
The GRE header format as specified in RFC 2784 and RFC 2890 [3][4]
is used for communication between NVGRE endpoints. NVGRE leverages
the Key extension specified in RFC 2890 [4] to carry the VSID. The
packet format for Layer 2 encapsulation in GRE is shown in Figure 1.
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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
Outer Ethernet Header: |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (Outer) Destination MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|(Outer)Destination MAC Address | (Outer)Source MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (Outer) Source MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Optional Ethertype=C-Tag 802.1Q| Outer VLAN Tag Information |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ethertype 0x0800 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Outer IPv4 Header:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| IHL |Type of Service| Total Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification |Flags| Fragment Offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time to Live | Protocol 0x2F | Header Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (Outer) Source Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (Outer) Destination Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
GRE Header:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| |1|0| Reserved0 | Ver | Protocol Type 0x6558 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Virtual Subnet ID (VSID) | FlowID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Inner Ethernet Header
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (Inner) Destination MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|(Inner)Destination MAC Address | (Inner)Source MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (Inner) Source MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ethertype 0x0800 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(Continued on the next page)
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Inner IPv4 Header:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| IHL |Type of Service| Total Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification |Flags| Fragment Offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time to Live | Protocol | Header Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Original IP Payload |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1 GRE Encapsulation Frame Format
The outer/delivery headers include the outer Ethernet header and the
outer IP header:
o The outer Ethernet header: The source Ethernet address in the
outer frame is set to the MAC address associated with the NVGRE
endpoint. The destination endpoint may or may not be on the same
physical subnet. The destination Ethernet address is set to the MAC
address of the nexthop IP address for the destination NVE. The outer
VLAN tag information is optional and can be used for traffic
management and broadcast scalability on the physical network.
o The outer IP header: Both IPv4 and IPv6 can be used as the
delivery protocol for GRE. The IPv4 header is shown for illustrative
purposes. Henceforth the IP address in the outer frame is referred
to as the Provider Address (PA). There can be one or more PA address
associated with an NVGRE endpoint, with policy controlling the
choice of PA to use for a given Customer Address (CA) for a customer
VM.
The GRE header:
o The C (Checksum Present) and S (Sequence Number Present) bits in
the GRE header MUST be zero.
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o The K bit (Key Present) in the GRE header MUST be set to one. The
32-bit Key field in the GRE header is used to carry the Virtual
Subnet ID (VSID), and the FlowId:
- Virtual Subnet ID (VSID): This is a 24-bit value that is used
to identify the NVGRE based Virtual Layer 2 Network.
- FlowID: This is an 8-bit value that is used to provide per-
flow entropy for flows in the same VSID. The FlowID MUST NOT
be modified by transit devices. The encapsulating NVE SHOULD
provide as much entropy as possible in the FlowId. If a FlowID
is not generated, it MUST be set to all zero.
o The protocol type field in the GRE header is set to 0x6558
(transparent Ethernet bridging)[2].
The inner headers (headers of the GRE payload):
o The inner Ethernet frame comprises of an inner Ethernet header
followed by optional inner IP header, followed by the IP payload.
The inner frame could be any Ethernet data frame not just IP. Note
that the inner Ethernet frame's FCS is not encapsulated.
o For illustrative purposes IPv4 headers are shown as the inner IP
headers but IPv6 headers may be used. Henceforth the IP address
contained in the inner frame is referred to as the Customer Address
(CA).
3.3. Inner 802.1Q Tag
The inner Ethernet header of NVGRE MUST NOT contain 802.1Q tag. The
encapsulating NVE MUST remove any existing 802.1Q Tag before
encapsulation of the frame in NVGRE. A decapsulating NVE MUST drop
the frame if the inner Ethernet frame contains an 802.1Q tag.
3.4. Reserved VSID
The VSID range from 0-0xFFF is reserved for future use.
The VSID 0xFFFFFF is reserved for vendor specific NVE-NVE
communication. The sender NVE SHOULD verify receiver NVE's vendor
before sending a packet using this VSID, however such verification
mechanism is out of scope of this document. Implementations SHOULD
choose a mechanism that meets their requirements.
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4. NVGRE Deployment Considerations
4.1. ECMP Support
ECMP may be used to provide load balancing. If ECMP is used, it is
RECOMMENDED that ECMP hash is calculated either using the outer IP
frame fields and entire Key field (32-bit) or inner IP and transport
frame fields.
4.2. Broadcast and Multicast Traffic
To support broadcast and multicast traffic inside a virtual subnet,
one or more administratively scoped multicast addresses [8][10] can
be assigned for the VSID. All multicast or broadcast traffic
originating from within a VSID is encapsulated and sent to the
assigned multicast address. From an administrative standpoint it is
possible for network operators to configure a PA multicast address
for each multicast address that is used inside a VSID, to facilitate
optimal multicast handling. Depending on the hardware capabilities
of the physical network devices and the physical network
architecture, multiple virtual subnet may re-use the same physical
IP multicast address.
Alternatively, based upon the configuration at NVE, the broadcast
and multicast in the virtual subnet can be supported using N-Way
unicast. In N-Way unicast, the sender NVE would send one
encapsulated packet to every NVE in the virtual subnet. The sender
NVE can encapsulate and send the packet as described in the Unicast
Traffic Section 4.3. This alleviates the need for multicast support
in the physical network.
4.3. Unicast Traffic
The NVGRE endpoint encapsulates a Layer 2 packet in GRE using the
source PA associated with the endpoint with the destination PA
corresponding to the location of the destination endpoint. As
outlined earlier, there can be one or more PAs associated with an
endpoint and policy will control which ones get used for
communication. The encapsulated GRE packet is bridged and routed
normally by the physical network to the destination PA. Bridging
uses the outer Ethernet encapsulation for scope on the LAN. The only
requirement is bi-directional IP connectivity from the underlying
physical network. On the destination, the NVGRE endpoint
decapsulates the GRE packet to recover the original Layer 2 frame.
Traffic flows similarly on the reverse path.
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4.4. IP Fragmentation
RFC 2003 [12] Section 5.1 specifies mechanisms for handling
fragmentation when encapsulating IP within IP. The subset of
mechanisms NVGRE selects are intended to ensure that NVGRE
encapsulated frames are not fragmented after encapsulation en-route
to the destination NVGRE endpoint, and that traffic sources can
leverage Path MTU discovery.
A sender NVE MUST NOT fragment NVGRE packets. A receiver NVE MAY
discard fragmented NVGRE packets. It is RECOMMENDED that MTU of
physical network accommodates the larger frame size due to
encapsulation. Path MTU or configuration via control plane can be
used to meet this requirement.
4.5. Address/Policy Management & Routing
Address acquisition is beyond the scope of this document and can be
obtained statically, dynamically or using stateless address auto-
configuration. CA and PA space can be either IPv4 or IPv6. In fact
the address families don't have to match, for example, a CA can be
IPv4 while the PA is IPv6 and vice versa.
4.6. Cross-subnet, Cross-premise Communication
One application of this framework is that it provides a seamless
path for enterprises looking to expand their virtual machine hosting
capabilities into public clouds. Enterprises can bring their entire
IP subnet(s) and isolation policies, thus making the transition to
or from the cloud simpler. It is possible to move portions of a IP
subnet to the cloud however that requires additional configuration
on the enterprise network and is not discussed in this document.
Enterprises can continue to use existing communications models like
site-to-site VPN to secure their traffic.
A VPN gateway is used to establish a secure site-to-site tunnel over
the Internet and all the enterprise services running in virtual
machines in the cloud use the VPN gateway to communicate back to the
enterprise. For simplicity we use a VPN GW configured as a VM shown
in Figure 2 to illustrate cross-subnet, cross-premise communication.
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+-----------------------+ +-----------------------+
| Server 1 | | Server 2 |
| +--------+ +--------+ | | +-------------------+ |
| | VM1 | | VM2 | | | | VPN Gateway | |
| | IP=CA1 | | IP=CA2 | | | | Internal External| |
| | | | | | | | IP=CAg IP=GAdc | |
| +--------+ +--------+ | | +-------------------+ |
| Hypervisor | | | Hypervisor| ^ |
+-----------------------+ +-------------------:---+
| IP=PA1 | IP=PA4 | :
| | | :
| +-------------------------+ | : VPN
+-----| Layer 3 Network |------+ : Tunnel
+-------------------------+ :
| :
+-----------------------------------------------:--+
| : |
| Internet : |
| : |
+-----------------------------------------------:--+
| v
| +-------------------+
| | VPN Gateway |
|---| |
IP=GAcorp| External IP=GAcorp|
+-------------------+
|
+-----------------------+
| Corp Layer 3 Network |
| (In CA Space) |
+-----------------------+
|
+---------------------------+
| Server X |
| +----------+ +----------+ |
| | Corp VMe1| | Corp VMe2| |
| | IP=CAe1 | | IP=CAe2 | |
| +----------+ +----------+ |
| Hypervisor |
+---------------------------+
Figure 2 Cross-Subnet, Cross-Premise Communication
The packet flow is similar to the unicast traffic flow between VMs,
the key difference in this case the packet needs to be sent to a VPN
gateway before it gets forwarded to the destination. As part of
routing configuration in the CA space, a per-tenant VPN gateway is
provisioned for communication back to the enterprise. The example
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illustrates an outbound connection between VM1 inside the datacenter
and VMe1 inside the enterprise network. When the outbound packet
from CA1 to CAe1 reaches the hypervisor on Server 1, the NVE in
Server 1 can perform an equivalent of a route lookup on the packet.
The cross premise packet will match the default gateway rule as CAe1
is not part of the tenant virtual network in the datacenter. The
virtualization policy will indicate the packet to be encapsulated
and sent to the PA of tenant VPN gateway (PA4) running as a VM on
Server 2. The packet is decapsulated on Server 2 and delivered to
the VM gateway. The gateway in turn validates and sends the packet
on the site-to-site VPN tunnel back to the enterprise network. As
the communication here is external to the datacenter the PA address
for the VPN tunnel is globally routable. The outer header of this
packet is sourced from GAdc destined to GAcorp. This packet is
routed through the Internet to the enterprise VPN gateway which is
the other end of the site-to-site tunnel, at which point the VPN
gateway decapsulates the packet and sends it inside the enterprise
where the CAe1 is routable on the network. The reverse path is
similar once the packet reaches the enterprise VPN gateway.
4.7. Internet Connectivity
To enable connectivity to the Internet, an Internet gateway is
needed that bridges the virtualized CA space to the public Internet
address space. The gateway need to perform translation between the
virtualized world and the Internet. For example, the NVGRE endpoint
can be part of a load balancer or a NAT, which replaces the VPN
Gateway on Server 2 shown in Figure 2.
4.8. Management and Control Planes
There are several protocols that can manage and distribute policy;
however, it is out of scope of this document. Implementations SHOULD
choose a mechanism that meets their scale requirements.
4.9. NVGRE-Aware Devices
One example of a typical deployment consists of virtualized servers
deployed across multiple racks connected by one or more layers of
Layer 2 switches which in turn may be connected to a layer 3 routing
domain. Even though routing in the physical infrastructure will work
without any modification with NVGRE, devices that perform
specialized processing in the network need to be able to parse GRE
to get access to tenant specific information. Devices that
understand and parse the VSID can provide rich multi-tenancy aware
services inside the data center. As outlined earlier it is
imperative to exploit multiple paths inside the network through
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techniques such as Equal Cost Multipath (ECMP). The Key field (32-
bit field, including both VSID and the optional FlowID) can provide
additional entropy to the switches to exploit path diversity inside
the network. A diverse ecosystem is expected to emerge as more and
more devices become multi-tenant aware. In the interim, without
requiring any hardware upgrades, there are alternatives to exploit
path diversity with GRE by associating multiple PAs with NVGRE
endpoints with policy controlling the choice of PA to be used.
It is expected that communication can span multiple data centers and
also cross the virtual to physical boundary. Typical scenarios that
require virtual-to-physical communication includes access to storage
and databases. Scenarios demanding lossless Ethernet functionality
may not be amenable to NVGRE as traffic is carried over an IP
network. NVGRE endpoints mediate between the network virtualized and
non-network virtualized environments. This functionality can be
incorporated into Top of Rack switches, storage appliances, load
balancers, routers etc. or built as a stand-alone appliance.
It is imperative to consider the impact of any solution on host
performance. Today's server operating systems employ sophisticated
acceleration techniques such as checksum offload, Large Send Offload
(LSO), Receive Segment Coalescing (RSC), Receive Side Scaling (RSS),
Virtual Machine Queue (VMQ) etc. These technologies should become
NVGRE aware. IPsec Security Associations (SA) can be offloaded to
the NIC so that computationally expensive cryptographic operations
are performed at line rate in the NIC hardware. These SAs are based
on the IP addresses of the endpoints. As each packet on the wire
gets translated, the NVGRE endpoint SHOULD intercept the offload
requests and do the appropriate address translation. This will
ensure that IPsec continues to be usable with network virtualization
while taking advantage of hardware offload capabilities for improved
performance.
4.10. Network Scalability with NVGRE
One of the key benefits of using NVGRE is the IP address scalability
and in turn MAC address table scalability that can be achieved.
NVGRE endpoint can use one PA to represent multiple CAs. This lowers
the burden on the MAC address table sizes at the Top of Rack
switches. One obvious benefit is in the context of server
virtualization which has increased the demands on the network
infrastructure. By embedding a NVGRE endpoint in a hypervisor it is
possible to scale significantly. This framework allows for location
information to be preconfigured inside a NVGRE endpoint allowing
broadcast ARP traffic to be proxied locally. This approach can scale
to large sized virtual subnets. These virtual subnets can be spread
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across multiple layer 3 physical subnets. It allows workloads to be
moved around without imposing a huge burden on the network control
plane. By eliminating most broadcast traffic and converting others
to multicast the routers and switches can function more efficiently
by building efficient multicast trees. By using server and network
capacity efficiently it is possible to drive down the cost of
building and managing data centers.
5. Security Considerations
This proposal extends the Layer 2 subnet across the data center and
increases the scope for spoofing attacks. Mitigations of such
attacks are possible with authentication/encryption using IPsec or
any other IP based mechanism. The control plane for policy
distribution is expected to be secured by using any of the existing
security protocols. Further management traffic can be isolated in a
separate subnet/VLAN.
The checksum in the GRE header is not supported. The mitigation of
this is to deploy NVGRE based solution in a network that provides
error detection along the NVGRE packet path, for example, using
Ethernet CRC or IPsec or any other error detection mechanism.
6. IANA Considerations
This document has no IANA actions.
7. References
7.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[2] Ethertypes, ftp://ftp.isi.edu/in-
notes/iana/assignments/ethernet-numbers
[3] D. Farinacci et al, "Generic Routing Encapsulation (GRE)", RFC
2784, March, 2000.
[4] G. Dommety, "Key and Sequence Number Extensions to GRE", RFC
2890, September 2000.
[5] Institute of Electrical and Electronics Engineers, "Virtual
Bridged Local Area Networks", IEEE Standard 802.1Q, 2005
Edition, May 2006.
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7.2. Informative References
[6] A. Greenberg et al, "VL2: A Scalable and Flexible Data Center
Network", Proc. SIGCOMM 2009.
[7] A. Greenberg et al, "The Cost of a Cloud: Research Problems in
the Data Center", ACM SIGCOMM Computer Communication Review.
[8] B. Hinden, S. Deering, "IP Version 6 Addressing Architecture",
RFC 4291, February 2006.
[9] M. Lasserre et al, "Framework for DC Network Virtualization",
RFC 7365, October 2014.
[10] D. Meyer, "Administratively Scoped IP Multicast", BCP 23, RFC
2365, July 1998.
[11] T. Narten et al, "Problem Statement: Overlays for Network
Virtualization", RFC 7364, October 2014.
[12] C. Perkins, "IP Encapsulation within IP", RFC 2003, October
1996.
[13] J. Touch, R. Perlman, "Transparent Interconnection of Lots of
Links (TRILL): Problem and Applicability Statement", RFC 5556,
May 2009.
8. Authors and Contributors
M. Sridharan
A. Greenberg
Y. Wang
P. Garg
N. Venkataramiah
Microsoft
K. Duda
Arista Networks
I. Ganga
Intel
G. Lin
Google
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M. Pearson
Hewlett-Packard
P. Thaler
Broadcom
C. Tumuluri
Emulex
9. Acknowledgments
This document was prepared using 2-Word-v2.0.template.dot.
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Authors' Addresses
Murari Sridharan
Microsoft Corporation
1 Microsoft Way
Redmond, WA 98052
Email: muraris@microsoft.com
Yu-Shun Wang
Microsoft Corporation
1 Microsoft Way
Redmond, WA 98052
Email: yushwang@microsoft.com
Albert Greenberg
Microsoft Corporation
1 Microsoft Way
Redmond, WA 98052
Email: albert@microsoft.com
Pankaj Garg
Microsoft Corporation
1 Microsoft Way
Redmond, WA 98052
Email: pankajg@microsoft.com
Narasimhan Venkataramiah
Facebook Inc
1730 Minor Ave.
Seattle, WA 98101
Email: navenkat@microsoft.com
Kenneth Duda
Arista Networks, Inc.
5470 Great America Pkwy
Santa Clara, CA 95054
kduda@aristanetworks.com
Ilango Ganga
Intel Corporation
2200 Mission College Blvd.
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M/S: SC12-325
Santa Clara, CA - 95054
Email: ilango.s.ganga@intel.com
Geng Lin
Google
1600 Amphitheatre Parkway
Mountain View, California 94043
Email: genglin@google.com
Mark Pearson
Hewlett-Packard Co.
8000 Foothills Blvd.
Roseville, CA 95747
Email: mark.pearson@hp.com
Patricia Thaler
Broadcom Corporation
3151 Zanker Road
San Jose, CA 95134
Email: pthaler@broadcom.com
Chait Tumuluri
Emulex Corporation
3333 Susan Street
Costa Mesa, CA 92626
Email: chait@emulex.com
Sridharan et al Informational [Page 19]
