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VALE(4) FreeBSD Kernel Interfaces Manual VALE(4)

a very fast Virtual Local Ethernet using the netmap API

device netmap

vale is a feature of the netmap(4) module that implements multiple Virtual switches that can be used to interconnect netmap clients, including traffic sources and sinks, packet forwarders, userspace firewalls, and so on.
vale is implemented completely in software, and is extremely fast. On a modern machine it can move almost 20 Million packets per second (Mpps) per core with small frames, and about 70 Gbit/s with 1500 byte frames.

vale dynamically creates switches and ports as clients connect to it using the netmap(4) API.
vale ports are named valeSSS:PPP where vale is the prefix indicating a VALE switch rather than a standard interface, SSS indicates a specific switch (the colon is a separator), and PPP indicates a port within the switch. Both SSS and PPP have the form [0-9a-zA-Z_]+ , the string cannot exceed IFNAMSIZ characters, and PPP cannot be the name of any existing OS network interface.
See netmap(4) for details on the API.

vale currently supports up to 4 switches, 16 ports per switch, with 1024 buffers per port. These hard limits will be changed to sysctl variables in future releases.

vale uses the following sysctl variables to control operation:
The maximum number of packets processed internally in each iteration. Defaults to 1024, use lower values to trade latency with throughput.
Set to non-zero values to enable in-kernel diagnostics.

Create one switch, with a traffic generator connected to one port, and a netmap-enabled tcpdump instance on another port:
tcpdump -ni valea:1 & 
pkt-gen  -i valea:0 -f tx &
Create two switches, each connected to two qemu machines on different ports.
qemu -net nic -net netmap,ifname=vale1:a ... & 
qemu -net nic -net netmap,ifname=vale1:b ... & 
qemu -net nic -net netmap,ifname=vale2:c ... & 
qemu -net nic -net netmap,ifname=vale2:d ... &

Luigi Rizzo, Giuseppe Lettieri: VALE, a switched ethernet for virtual machines, June 2012,

The vale switch was designed and implemented in 2012 by Luigi Rizzo and Giuseppe Lettieri at the Universita` di Pisa.
vale was funded by the European Commission within FP7 Projects CHANGE (257422) and OPENLAB (287581).
July 27, 2012 FreeBSD 12.0-RELEASE

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