One document matched: draft-zhou-li-vxlan-soe-00.txt
Network Working Group H. Zhou
Internet-Draft C. Li
Intended Status: Experimental eBay Inc.
Expires: September 14, 2014 March 13, 2014
Segmentation Offloading Extension for VxLAN
draft-zhou-li-vxlan-soe-00
Abstract
Segmentation offloading is nowadays common in network stack
implementation and well supported by para-virtualized network device
drivers for virtual machine (VM)s. This draft describes an extension
to Virtual eXtensible Local Area Network (VXLAN) so that segmentation
can be decoupled from physical/underlay networks and offloaded
further to the remote end-point thus improving data-plane performance
for VMs running on top of overlay networks.
Status of this Memo
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Copyright and License Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Requirements Notation . . . . . . . . . . . . . . . . . . . 4
1.2 Definition of Terms . . . . . . . . . . . . . . . . . . . . 4
2. Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1 VXLAN Header Extension . . . . . . . . . . . . . . . . . . 4
2.2 TX VTEP . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.3 RX VTEP - Hypervisors . . . . . . . . . . . . . . . . . . . 6
2.4 RX VTEP - Gateways . . . . . . . . . . . . . . . . . . . . . 6
3 Interoperability . . . . . . . . . . . . . . . . . . . . . . . 6
4 Security Considerations . . . . . . . . . . . . . . . . . . . . 6
5 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
6 References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6.1 Normative References . . . . . . . . . . . . . . . . . . . 7
6.2 Informative References . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7
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1 Introduction
Network virtualization over L3 transport is evolved along with server
virtualization in data-centers, and data plane performance is one of
the keys to the success of this combination. One of the most critical
improvements in OS kernel TCP/IP stack in recent years is
segmentation offloading, and now hypervisor providers support same
mechanism in para-virtualized Ethernet drivers so that virtual
servers can benefit from the same mechanism in virtualized world by
offloading segmentation tasks to the lowest layer on hypervisors or
NICs (if TSO is supported by the NICs equipped in the hypervisor).
Essentially, overlay networks has its own advantage comparing with
physical underlay networks in that it does not have a hard MTU
limitation. Therefore, segmentation offloading can be pushed to the
remote end-point of the transport tunnel, where segmentation can be
completely omitted if this remote end-point is on a hypervisor.
However, this advantage is not utilized when the transport of the
overlay is based on the Virtual eXtensible Local Area Network [I-
D.mahalingam-dutt-dcops-vxlan], which provides a transport mechanism
for logically isolated L2 overlay networks between hypervisors.
Lacking segmentation information in the VXLAN header, hypervisor
implementations have to make pessimistic decisions to always segment
the packet in the size specified by VMs before delivering to
hypervisors' IP stack, because it does not know whether the remote
end-point is bridged to a physical network with hard MTU limitations.
It is worth noting that the segmentation here is not the IP
fragmentation in terms of the physical network MTU, which may still
follow if the segment size resulting from the process above plus the
tunnel outer header is bigger than the physical network MTU.
To fulfill the potential of segmentation offloading on overlay, this
draft introduces segmentation metadata in VXLAN header. With the
capability of carrying segmentation metadata in packets, hypervisors
can offload the segmentation decision further to the remote tunnel
end-point, thus decoupling the segmentation for overlay from physical
limitations of underlay, providing higher flexibility to hyerpervisor
implementations to achieve significant performance gains in a major
part of VXLAN deployment scenarios.
Although the performance gains can be achieved is affected by the
physical network MTU, there is inherently no mandatory requirement to
physical layer:
1) When physical network MTU is far bigger than overlay MTU, the
offloading reduces the number of packets being transmitted by TX
hypervisors and received in RX hypervisors and RX VMs.
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2) When physical network MTU is close to overlay MTU, the number of
packets being transmitted in physical network (resulted in IP
fragmentation) may not be reduced significantly, but on RX side after
IP reassembling, the number of packets being delivered from the
hypervisor to the receiving VM is largely reduced, thus saving the
cost of hypervisor <-> VM interaction and protocol stack of the
receiving VM. Furthermore, a minor cost saving is that the bytes
being transmitted over physical network is slightly reduced because
only one copy of headers (inner L2-L4 header, VXLAN header and outer
UDP header) is transmitted for a large overlay packet.
In addition, offloading features support from NIC hardware is NOT a
requirement, either, to the performance gains discussed above.
1.1 Requirements Notation
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].
1.2 Definition of Terms
GSO: Generic Segmentation Offload.
TSO: TCP Segmentation Offload.
NIC: Network Interface Card.
VM: Virtual Machine.
TX: Sending side.
RX: Receiving side.
VTEP: Virtual Tunnel End Point
2. Approach
2.1 VXLAN Header Extension
The new VXLAN Segmentation Offloading Extension (VXLAN-soe) header is
defined as:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S|C|R|R|I|R|R|R| Reserved | Overlay MTU |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| VXLAN Network Identifier (VNI) | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The changes to VXLAN are:
S Bit: Flag bit 0 is defined as the S (Segmentation Offloading
Extension) bit.
S = 1 indicates that VXLAN-soe is applied to the encapsulated
overlay packet, and the C Bit and Overlay MTU field (see below)
are valid.
S = 0 indicates that VXLAN-soe is NOT applied, and the C Bit and
Segment Size field MUST be set to 0 in accordance with VXLAN.
C Bit: Flag bit 1 is defined as the C (Checksum) bit. This bit is
valid only if the S bit is set to 1.
C = 1 indicates that the checksum to the encapsulated packet is
required, and SHALL be re-calculated when the segmentation is
being performed.
C = 0 indicates that the checksum to the encapsulated packet is
NOT needed.
Overlay MTU: bit 16 - 31 is defined as the MTU desired by TX VM for
the segmentation being offloaded.
Its value indicates the max size of an overlay segment including
its L3 header, but NOT including Ethernet header. This field is
valid only if the S bit is set.
2.2 TX VTEP
VTEP at TX side MUST set the S bit to 1 if the packet to be
encapsulated is NOT segmented and it decides to offload the
segmentation to the remote end-point. In such case the C bit and
Overlay MTU field MUST be set accordingly. This is the typical use
case when the TX VTEP is a hypervisor transmitting TCP stream of
VMs with large sliding windows.
VTEP at TX side MUST clear the S bit if the packet to be
encapsulated is segmented already or does NOT need to be segmented
in terms of the overlay MTU. In such case, the encapsulation is in
the same format as specified in VXLAN. This is the typical use
case when the TX VTEP is a hypervisor transmitting small size
overlay packets, or a gateway forwarding overlay packets without
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offloading requirements.
2.3 RX VTEP - Hypervisors
When a VTEP at RX side is on a hypervisor, checking of the S bit
is OPTIONAL.
2.4 RX VTEP - Gateways
When a VTEP at RX side is on a gateway node that connects overlay
networks and physical networks, the S bit MUST be checked and the
VTEP MUST ensure the segmentation specified by the header fields
is performed by the VTEP itself or offloaded further - it MAY
offload the segmentation again to the subsequent transmission
mechanisms: such as GSO and TSO, or, if the link to the next hop
is also an overlay based on VXLAN-soe (or other tunneling
protocols that supports segmentation offloading), pass the
segmentation metadata to the next hop.
3 Interoperability
In addition to offload segmentation requests from VMs, VXLAN-soe
enabled VTEP is able to offload segmentation requests from STT [I-
D.davie-stt] overlay, because the metadata required in VXLAN-soe
header is a subset of STT metadata. The additional segmentation
offloading information carried in STT metadata such as L4 offset
can be obtained by examine inner headers of the packets.
VXLAN-soe defines Overlay MTU at the same position of Protocol
Type field in VXLAN-gpe [I-D.quinn-vxlan-gpe], another extension
of VXLAN. This is not a problem because VXLAN-soe is introduced
for segmentation offloading use cases where Ethernet header is
always encapsulated, and it uses different flag bits to be
distinguished from VXLAN-gpe.
4 Security Considerations
There is no special security issues introduced by this extension
to VXLAN.
5 IANA Considerations
This document creates no new requirements on IANA namespaces
[RFC5226].
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6 References
6.1 Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
6.2 Informative References
[I-D.mahalingam-dutt-dcops-vxlan]
Mahalingam, M., Dutt, D., Duda, K., Agarwal, P., Kreeger,
L., Sridhar, T., Bursell, M., and C. Wright, "VXLAN: A
Framework for Overlaying Virtualized Layer 2 Networks over
Layer 3 Networks", draft-mahalingam-dutt-dcops-vxlan-08
(work in progress), February 2014.
[I-D.davie-stt]
Davie, B. and J. Gross, "A Stateless Transport Tunneling
Protocol for Network Virtualization (STT)", draft-davie-
stt-05(work in progress), March 2014.
[I-D.quinn-vxlan-gpe]
Agarwal, P., Fernando, R., Kreeger, L., Lewis, D., Maino,
F., Quinn, P., Yong, L., Xu, X., Smith, M., Yadav, N., and
U. Elzur, "Generic Protocol Extension for VXLAN", draft-
quinn-vxlan-gpe-02 (work in progress), December 2013.
Authors' Addresses
Han Zhou
eBay, Inc.
EMail: hzhou8@ebay.com
Chengyuan Li
eBay, Inc.
Email: chengyli@ebay.com
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