.\" Copyright (c) 2011 Bryan Venteicher
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.Dd January 22, 2012
.Dt VTNET 4
.Os
.Sh NAME
.Nm vtnet
.Nd VirtIO Ethernet driver
.Sh SYNOPSIS
To compile this driver into the kernel,
place the following lines in your
kernel configuration file:
.Bd -ragged -offset indent
.Cd "device vtnet"
.Ed
.Pp
Alternatively, to load the driver as a
module at boot time, place the following line in
.Xr loader.conf 5 :
.Bd -literal -offset indent
if_vtnet_load="YES"
.Ed
.Sh DESCRIPTION
The
.Nm
device driver provides support for VirtIO Ethernet devices.
.Pp
If the hypervisor advertises the appropriate features, the
.Nm
driver supports TCP/UDP checksum offload for both transmit and receive,
TCP segmentation offload (TSO), TCP large receive offload (LRO),
hardware VLAN tag stripping/insertion features, a multicast hash filter,
as well as Jumbo Frames (up to 9216 bytes), which can be
configured via the interface MTU setting.
Selecting an MTU larger than 1500 bytes with the
.Xr ifconfig 8
utility configures the adapter to receive and transmit Jumbo Frames.
.Pp
For more information on configuring this device, see
.Xr ifconfig 8 .
.Sh LOADER TUNABLES
Tunables can be set at the
.Xr loader 8
prompt before booting the kernel or stored in
.Xr loader.conf 5 .
.Bl -tag -width "xxxxxx"
.It Va hw.vtnet.csum_disable
.It Va hw.vtnet. Ns Ar X Ns Va .csum_disable
This tunable disables receive and send checksum offload.
The default value is 0.
.It Va hw.vtnet.tso_disable
.It Va hw.vtnet. Ns Ar X Ns Va .tso_disable
This tunable disables TSO.
The default value is 0.
.It Va hw.vtnet.lro_disable
.It Va hw.vtnet. Ns Ar X Ns Va .lro_disable
This tunable disables LRO.
The default value is 0.
.It Va hw.vtnet.mq_disable
.It Va hw.vtnet. Ns Ar X Ns Va .mq_disable
This tunable disables multiqueue.
The default value is 0.
.It Va hw.vtnet.mq_max_pairs
.It Va hw.vtnet. Ns Ar X Ns Va .mq_max_pairs
This tunable sets the maximum number of transmit and receive queue pairs.
Multiple queues are only supported when the Multiqueue feature is negotiated.
This driver supports a maximum of 8 queue pairs.
The number of queue pairs used is the lesser of the maximum supported by the
driver and the hypervisor, the number of CPUs present in the guest, and this
tunable if not zero.
The default value is 0.
.El
.Sh SEE ALSO
.Xr arp 4 ,
.Xr netintro 4 ,
.Xr ng_ether 4 ,
.Xr virtio 4 ,
.Xr vlan 4 ,
.Xr ifconfig 8
.Sh HISTORY
The
.Nm
driver was written by
.An Bryan Venteicher Aq Mt bryanv@FreeBSD.org .
It first appeared in
.Fx 9.0 .
.Sh CAVEATS
The
.Nm
driver only supports LRO when the hypervisor advertises the
mergeable buffer feature.