|By Marten Terpstra||
|January 23, 2014 09:30 AM EST||
Last week I walked through the packet formats for VXLAN and NVGRE specifically focused on ways by which the overlay packets provide information to the physical network that help the physical network. Some of the initial extreme thoughts that the overlay and physical network can and should be completely ignorant of each other have softened more recently and more pragmatic thoughts of collaborating layers are being articulated. At Plexxi we have often mentioned that we believe the physical network and the overlay need to be closely orchestrated to get the most benefit out of the total network solution. And orchestration != ECMP.
In addition to VXLAN and NVGRE, Stateless Transport Tunneling (STT) is an encapsulation mechanism used by VMware, mostly for communication between server based vSwitches. It is a bit more involved and complicated than VXLAN and NVGRE, mostly because it was designed to carry large data packets, up to 64 Kbytes. Physical networks have limitations on the size of a packet that can be transferred. Ethernet standard maximum transmission unit (MTU) used to be 1500 bytes, but most ethernet devices these days can support jumbo packets allowing packets of 4, 9 or even 16 Kbytes in size. Even at those sizes, large data transfers are somewhat hampered by the work involved in taking a large chunk of data and then chopping them up into smaller portions to be transmitted. In a response to this, hardware vendors have taken some of this functionality and added it to the Network Interface Cards (NICs) on servers and have them do most of this segmentation and re-assembly work based on how TCP takes large portions of data and chops them into smaller segments. Doing his in hardware means it can be done faster, but more importantly, it removes this burden from the server CPUs, allowing them to do other (more useful) work.
STT was designed to make use of these TCP capabilities in NICs. STT can take ethernet packets up to 64 Kbytes from a VM on a server, and tunnel it to its destination as a 64 Kbyte entity. This STT frame has to be chopped into smaller pieces to match the MTU of the physical network, but an STT packet looks just like a TCP segment to the receiving NICs, allowing them to reconstruct the original 64 Kbyte packet without needing the CPU.
When the sending tunnel endpoint receives a large chunk of data to be transmitted at another VM at the other side of a tunnel, the vSwitch takes several steps to encapsulate this packet. First, it adds an STT Frame Header to the packet.
The STT Header is 18 bytes in length and has a variety of administrative fields, but the key field is the Context ID. This is a 64 bit field and its intended use is similar to the VXLAN Network Identifier (VNI) or the NVGRE Virtual Subnet ID (VSID). While the semantics of this field are somewhat defined, its value and how to use it is left open in the latest specifications. Its main purpose is to provide the receiving tunnel endpoint the information it needs to determine where this packet needs to be sent after decapsulation.
After the STT Frame Header has been added, this new packet (original packet + new STT header) is chopped into smaller pieces so that each piece is at least 62 bytes smaller than the MTU of the physical network. Each of these new segments receives 24 byte TCP like header, a normal 20 byte IP header, and of course the final 18 byte Ethernet header before transmission. The magic (or ugliness for those less enamored by STT) is in the TCP like header. These 24 bytes are formatted just like a normal TCP header to ensure the hardware in the NICs can re-assemble segments that belong together. The traditional Acknowledgement field in TCP is used as a fragment ID, essentially telling the NIC that all packets/segments that come in with the same fragment ID belong together and should be reassembled into the larger original ethernet frame. The traditional Sequence number is used as an offset indicator, to tell the NIC in what order the fragments need to be put together.
Similar to VXLAN and NVGRE described last week, STT has a mechanism to create entropy for the physical network to distinguish flows from each other and allow them to be balanced using ECMP (or link aggregation – LAG) based deployments. In STT, the TCP source port is used to create entropy. The originating tunnel end point will use some hash calculation on the original packets header information and use the result to populate the TCP source port. Switches in the physical network can now use the TCP port information from the tunneled packet in their hash calculation for ECMP or LAG packet distribution.
While STT is likely to be more efficient than either VXLAN or NVGRE for the transfer of large amount of information because it offloads the segmentation and re-assembly, it carries significantly more overhead than either VXLAN or NVGRE in additional header information for smaller packets. STT adds 80 bytes of new header to a VM originated ethernet packet for the first segment of this packet, 62 for each following segment. Compare that to a consistent 46 bytes for each NVGRE encapsulated packet, and 54 bytes for VXLAN. For traffic between VMs on the same server this may not matter, but it certainly does for traffic carried across the physical network. For the plentiful mice flows, we have likely doubled the size and bandwidth required for each.
A probably more significant drawback of STT comes from its strength. Designed for large packet transfers, once an original packet is encapsulated with STT header, chopped into parts, then encapsulated into individual ethernet, IP and TCP (like) headers, only the first packet provides any clue or context of the original source, destination, protocol, application and other content. The relevant pieces of that will only be found in the first segment, any follow up segments only provide enough information about the tunnel endpoints and no other original context without the first segment. And that makes debugging really hard. It also makes it hard to differentiate traffic on the physical network, even at a very high level Virtual Network identifier. And every existing network based service (realizing that one of the goals of overlay networks is to push this to the vSwitches themselves) will also have a hard time deciding what to do with these packets.
At a high level the concepts of larger packets, hardware offload, reduced CPU load and interrupts all make sense. But most data center ethernet networks can easily support 9k or even 16k packets, so perhaps the gap between 16k packet based transfer and 64k semi-stream based communication is really not that much considering that the bulk of packets are small to begin with (remember those mice and elephants?). Perhaps aligning the MTU of the virtual port with that of the network may be worthwhile to have the STT and original header in each and every packet on the wire. Regardless of whether that is a real wire, or a virtual one.
[Today's fun fact: One of the primary reasons the Mayflower pilgrims ended their voyage at Plymouth Rock was pretty much the same reason people today suspend their journeys: they ran out of beer. No need for a funny punch line on that one]
The post Stateless Transport Tunneling (STT) meets the Network appeared first on Plexxi.
DevOps Summit at Cloud Expo New York is offering a limited time FREE "Expo Plus" registration option in New York. On site registration price of $1,95 will be set to 'free' for delegates who register during special offer. To take advantage of this opportunity, attendees can use the coupon code, and secure their registration to attend all keynotes, @DevOpsSummit sessions at Cloud Expo, expo floor, and SYS-CON.tv power panels. Special FREE registration givess access to all Containers and Microservices sessions. Registration page is located at the DevOps Summit site. Your DevOps Summit registratio...
Jun. 2, 2015 07:30 PM EDT Reads: 1,982
Jun. 2, 2015 06:15 PM EDT Reads: 1,750
ThingsExpo New York is offering a limited time FREE "Expo Plus" registration option in New York. On site registration price of $1,95 will be set to 'free' for delegates who register during special offer. To take advantage of this opportunity, attendees can use the coupon code, and secure their registration to attend all keynotes, ThingsExpo sessions, expo floor, and SYS-CON.tv power panels. Special FREE registration givess access to all DevOps, Containers and Microservices sessions as well. Registration page is located at the ThingsExpo site.
Jun. 2, 2015 06:00 PM EDT Reads: 1,998
With major technology companies and startups seriously embracing IoT strategies, now is the perfect time to attend @ThingsExpo in Silicon Valley. Learn what is going on, contribute to the discussions, and ensure that your enterprise is as "IoT-Ready" as it can be! Internet of @ThingsExpo, taking place Nov 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with 17th Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. The Internet of Things (IoT) is the most profound change in personal an...
Jun. 2, 2015 06:00 PM EDT Reads: 3,770
Jun. 2, 2015 05:30 PM EDT Reads: 3,047
Health care systems across the globe are under enormous strain, as facilities reach capacity and costs continue to rise. M2M and the Internet of Things have the potential to transform the industry through connected health solutions that can make care more efficient while reducing costs. In fact, Vodafone's annual M2M Barometer Report forecasts M2M applications rising to 57 percent in health care and life sciences by 2016. Lively is one of Vodafone's health care partners, whose solutions enable older adults to live independent lives while staying connected to loved ones. M2M will continue to gr...
Jun. 2, 2015 05:30 PM EDT Reads: 3,427
Akana, a leading provider of API Management, API Security and Cloud Integration solutions, announced that it is introducing DevOps automation to the API lifecycle. New capabilities in Akana's API Management platform significantly reduce the time required to update API definitions and versions. DevOps teams will be able to work faster in designing and developing APIs, as well as managing them at runtime and publishing them to a portal.
Jun. 2, 2015 05:15 PM EDT Reads: 1,396
Growth hacking is common for startups to make unheard-of progress in building their business. Career Hacks can help Geek Girls and those who support them (yes, that's you too, Dad!) to excel in this typically male-dominated world. Get ready to learn the facts: Is there a bias against women in the tech / developer communities? Why are women 50% of the workforce, but hold only 24% of the STEM or IT positions? Some beginnings of what to do about it!
Jun. 2, 2015 05:00 PM EDT Reads: 1,688
17th Cloud Expo, taking place Nov 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA, will feature technical sessions from a rock star conference faculty and the leading industry players in the world. Cloud computing is now being embraced by a majority of enterprises of all sizes. Yesterday's debate about public vs. private has transformed into the reality of hybrid cloud: a recent survey shows that 74% of enterprises have a hybrid cloud strategy. Meanwhile, 94% of enterprises are using some form of XaaS – software, platform, and infrastructure as a service.
Jun. 2, 2015 04:00 PM EDT Reads: 3,189
Imagine a world where targeting, attribution, and analytics are just as intrinsic to the physical world as they currently are to display advertising. Advances in technologies and changes in consumer behavior have opened the door to a whole new category of personalized marketing experience based on direct interactions with products. The products themselves now have a voice. What will they say? Who will control it? And what does it take for brands to win in this new world? In his session at @ThingsExpo, Zack Bennett, Vice President of Customer Success at EVRYTHNG, will answer these questions a...
Jun. 2, 2015 04:00 PM EDT Reads: 1,603
"People are a lot more knowledgeable about APIs now. There are two types of people who work with APIs - IT people who want to use APIs for something internal and the product managers who want to do something outside APIs for people to connect to them," explained Roberto Medrano, Executive Vice President at SOA Software, in this SYS-CON.tv interview at Cloud Expo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
Jun. 2, 2015 03:00 PM EDT Reads: 5,333
“Connect2Me is basically a game changer in the IoT industry. We have created IoT connecter middleware that can enable a connection to any kind of device," explained Yasser Khan, CTO of Connect2Me, in this SYS-CON.tv interview at @ThingsExpo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
Jun. 2, 2015 02:15 PM EDT Reads: 3,382
2015 predictions circa 1970: houses anticipate our needs and adapt, city infrastructure is citizen and situation aware, office buildings identify and preprocess you. Today smart buildings have no such collective conscience, no shared set of fundamental services to identify, predict and synchronize around us. LiveSpace and M2Mi are changing that. LiveSpace Smart Environment devices deliver over the M2Mi IoT Platform real time presence, awareness and intent analytics as a service to local connected devices. In her session at @ThingsExpo, Sarah Cooper, VP Business of Development at M2Mi, will d...
Jun. 2, 2015 01:00 PM EDT Reads: 1,834
"Matrix is an ambitious open standard and implementation that's set up to break down the fragmentation problems that exist in IP messaging and VoIP communication," explained John Woolf, Technical Evangelist at Matrix, in this SYS-CON.tv interview at @ThingsExpo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
Jun. 2, 2015 01:00 PM EDT Reads: 4,732
The basic integration architecture, as defined by ESBs, hasn’t changed for more than a decade. Most cloud integration providers still rely on an ESB architecture and their proprietary connectors. As a result, enterprise integration projects suffer from constraints of availability and reliability of these connectors that are not re-usable across other integration vendors. However, the rapid adoption of APIs and almost ubiquitous availability of APIs amongst most SaaS and Cloud applications are rapidly redefining traditional integration approaches and their reliance on proprietary connectors. ...
Jun. 2, 2015 12:45 PM EDT Reads: 1,259
The world is at a tipping point where the technology, the device and global adoption are converging to such a point that we will see an explosion of a world where smartphone devices not only allow us to talk to each other, but allow for communication between everything – serving as a central hub from which we control our world – MediaTek is at the heart of both driving this and allowing the markets to drive this reality forward themselves. The next wave of consumer gadgets is here – smart, connected, and small. If your ambitions are big, so are ours. In his session at @ThingsExpo, Jack Hu, D...
Jun. 2, 2015 12:45 PM EDT Reads: 1,937
The only place to be Nov 3-5 is Cloud Expo | @ThingsExpo | DevOps Summit 2015 West at the Santa Clara Convention Center in Santa Clara, CA. Join us there as delegates from all over the world come to listen to and engage with speakers & sponsors from the leading Cloud Computing, IoT, Big Data and DevOps companies. Cloud Expo & @ThingsExpo are the leading events covering the booming market of Cloud Computing, IoT & Big Data for the enterprise. Speakers from all over the world will be hand-picked for their ability to explore the economic strategies that utility/cloud computing provides. Whether...
Jun. 2, 2015 12:45 PM EDT Reads: 2,422
The enterprise market will drive IoT device adoption over the next five years. In his session at @ThingsExpo, John Greenough, an analyst at BI Intelligence, division of Business Insider, will analyze how companies will adopt IoT products and the associated cost of adopting those products. John Greenough is the lead analyst covering the Internet of Things for BI Intelligence- Business Insider’s paid research service. Numerous IoT companies have cited his analysis of the IoT. Prior to joining BI Intelligence, he worked analyzing bank technology for Corporate Insight and The Clearing House Pay...
Jun. 2, 2015 12:30 PM EDT Reads: 1,575
Explosive growth in connected devices. Enormous amounts of data for collection and analysis. Critical use of data for split-second decision making and actionable information. All three are factors in making the Internet of Things a reality. Yet, any one factor would have an IT organization pondering its infrastructure strategy. How should your organization enhance its IT framework to enable an Internet of Things implementation? In this session, James Kirkland, Red Hat's Chief Architect for the Internet of Things and Intelligent Systems, will describe how to revolutionize your architecture and...
Jun. 2, 2015 12:00 PM EDT Reads: 1,972
All major researchers estimate there will be tens of billions devices - computers, smartphones, tablets, and sensors - connected to the Internet by 2020. This number will continue to grow at a rapid pace for the next several decades. With major technology companies and startups seriously embracing IoT strategies, now is the perfect time to attend @ThingsExpo, June 9-11, 2015, at the Javits Center in New York City. Learn what is going on, contribute to the discussions, and ensure that your enterprise is as "IoT-Ready" as it can be
Jun. 2, 2015 12:00 PM EDT Reads: 3,522