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* A dpif provider is usually easier to implement, but most
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appropriate for software switching. It "explodes" wildcard
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rules into exact-match entries. This allows fast hash lookups
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in software, but makes inefficient use of TCAMs in hardware
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that support wildcarding.
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rules into exact-match entries (with an optional wildcard mask).
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This allows fast hash lookups in software, but makes
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inefficient use of TCAMs in hardware that support wildcarding.
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The following sections describe how to implement each kind of port.
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Open vSwitch has a built-in ofproto provider named "ofproto-dpif",
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which is built on top of a library for manipulating datapaths, called
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"dpif". A "datapath" is a simple flow table, one that supports only
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exact-match flows, that is, flows without wildcards. When a packet
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arrives on a network device, the datapath looks for it in this
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exact-match table. If there is a match, then it performs the
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associated actions. If there is no match, the datapath passes the
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packet up to ofproto-dpif, which maintains an OpenFlow flow table
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(that supports wildcards). If the packet matches in this flow table,
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then ofproto-dpif executes its actions and inserts a new exact-match
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entry into the dpif flow table. (Otherwise, ofproto-dpif passes the
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"dpif". A "datapath" is a simple flow table, one that is only required
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to support exact-match flows, that is, flows without wildcards. When a
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packet arrives on a network device, the datapath looks for it in this
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table. If there is a match, then it performs the associated actions.
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If there is no match, the datapath passes the packet up to ofproto-dpif,
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which maintains the full OpenFlow flow table. If the packet matches in
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this flow table, then ofproto-dpif executes its actions and inserts a
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new entry into the dpif flow table. (Otherwise, ofproto-dpif passes the
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packet up to ofproto to send the packet to the OpenFlow controller, if
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one is configured.)
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When calculating the dpif flow, ofproto-dpif generates an exact-match
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flow that describes the missed packet. It makes an effort to figure out
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what fields can be wildcarded based on the switch's configuration and
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OpenFlow flow table. The dpif is free to ignore the suggested wildcards
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and only support the exact-match entry. However, if the dpif supports
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wildcarding, then it can use the masks to match multiple flows with
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fewer entries and potentially significantly reduce the number of flow
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misses handled by ofproto-dpif.
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The "dpif" library in turn delegates much of its functionality to a
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"dpif provider". The following diagram shows how dpif providers fit
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into the Open vSwitch architecture:
added
removed
PORTING
