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=== Design principles === <span id="stateless"></span> ==== Stateless ==== Where possible, offloads SHOULD be implemented in a stateless manner. That is, all information associated consumed or produced for a packet is communicated along with the packet. A stateful implementation may store per-flow state on the device, requiring additional communication to keep host and device state in sync. At the scale of modern servers and hyperscale deployments, this adds complexity and additional performance limitations. It should be avoided where possible. See the performance section for a summary of the canonical workloads and their scale. <span id="protocol-independence"></span> ==== Protocol Independence ==== Where possible, offloads SHOULD be implemented in a protocol independent manner. Protocol dependent offloads are fragile, in that they break when protocols are revised or replaced. Tunneling and transport layer encapsulation are common in hyperscale systems. Protocols used may be standard, such as Generic Routing Encapsulation (GRE) as defined in IETF RFCs 2784 and 2890. But even standard protocols can be extended, for example GRE key and sequence number extensions of RFC 2890. Hyperscale providers operate in a closed world, and as such are not limited to standardized protocols. They may extend standard headers with proprietary fields or entirely replace standard protocols with custom ones. They may stacks protocols in arbitrary ways to encapsulate multiple layers of information, e.g., for routing, traffic shaping and sharing application metadata out-of-band (OOB). <span id="programmable-parsers"></span> ===== Programmable Parsers ===== Devices with a programmable hardware parser allow the administrator to push firmware updates to support custom protocols. A programmable parser is still strictly less desirable than protocol independent offloads, as programmable parsers introduce correlated roll-outs between software and firmware. At hyperscale, correlated roll-outs and potential roll-backs add significant complexity and risk. This target of protocol independence is in conflict with some features defined in this spec (RSS, header-split, etcetera). That is why the prescriptive opening sentence of this section starts with “where possible”. Where features can be implemented without parsing, that design MUST be taken. <span id="checksum-offload"></span>
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