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VTNET(4) Kernel Interfaces Manual VTNET(4) NAME vtnet -- VirtIO Ethernet driver SYNOPSIS To compile this driver into the kernel, place the following lines in your kernel configuration file: device vtnet Alternatively, to load the driver as a module at boot time, place the following line in loader.conf(5): if_vtnet_load="YES" DESCRIPTION The vtnet device driver provides support for VirtIO Ethernet devices. If the hypervisor advertises the appropriate features, the vtnet 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 in- terface MTU setting. Two flavors of TCP LRO are supported: Hardware TCP LRO, which is per- formed by the host providing TCP segments larger than the MTU to the guest, and Software TCP LRO, which is performed by the network stack of the guest processing TCP segments in an optimized way. Only one flavour of TCP LRO should be used. Since hardware TCP LRO can have bad interactions with IP forwarding and software TCP LRO mitigates several drawbacks of hardware TCP LRO, the default setting is to disable hard- ware TCP LRO. See the loader tunable hw.vtnet.X.lro_disable. TCP/UDP receive checksum offload cannot be configured independently for IPv4 and IPv6. Selecting an MTU larger than 1500 bytes with the ifconfig(8) utility configures the adapter to receive and transmit Jumbo Frames. For more information on configuring this device, see ifconfig(8). LOADER TUNABLES Tunables can be set at the loader(8) prompt before booting the kernel or stored in loader.conf(5). hw.vtnet.csum_disable hw.vtnet.X.csum_disable This tunable disables receive and transmit checksum offloading for TCP and UDP. This also implies that TCP segmentation of- floading and large receive offload are disabled. The default value is 0. hw.vtnet.fixup_needs_csum hw.vtnet.X.fixup_needs_csum This tunable enforces the calculation of a valid TCP or UDP checksum for packets received with VIRTIO_NET_HDR_F_NEEDS_CSUM being set in the flags field of the structure struct virtio_net_hdr. It also marks the checksum as being correct in the mbuf packet header. The default value is 0. This tunable is deprecated and will be removed in FreeBSD 16. hw.vtnet.tso_disable hw.vtnet.X.tso_disable This tunable disables TCP segmentation offloading. The default value is 0. hw.vtnet.lro_disable hw.vtnet.X.lro_disable This tunable disables hardware TCP LRO. The default value is 1. hw.vtnet.mq_disable hw.vtnet.X.mq_disable This tunable disables multiqueue. The default value is 0. hw.vtnet.mq_max_pairs hw.vtnet.X.mq_max_pairs This tunable sets the maximum number of transmit and receive queue pairs. Multiple queues are only supported when the Mul- tiqueue 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. hw.vtnet.tso_maxlen hw.vtnet.X.tso_maxlen This tunable sets the TSO burst limit. The default value is 65535. hw.vtnet.rx_process_limit hw.vtnet.X.rx_process_limit This tunable sets the number of RX segments processed in one pass. The default value is 1024. hw.vtnet.lro_entry_count hw.vtnet.X.lro_entry_count This tunable sets the software TCP LRO entry count. The de- fault value is 128, the minimum value is 8. hw.vtnet.lro_mbufq_depth hw.vtnet.X.lro_mbufq_depth This tunable sets the depth of the software TCP LRO mbuf queue. The default value is 0. hw.vtnet.altq_disable This tunable disables ALTQ support, allowing the use of multi- queue instead. This option applies to all interfaces. The de- fault value is 0. TRANSMIT QUEUE STATISTICS For each transmit queue of each interface the following read-only sta- tistics are provided: dev.vtnet.X.txqY.rescheduled The number of times the transmit interrupt handler was resched- uled. dev.vtnet.X.txqY.tso The number of times TCP segment offloading was performed. dev.vtnet.X.txqY.csum The number of times transmit checksum offloading for UDP or TCP was performed. dev.vtnet.X.txqY.omcasts The number of multicast packets that were transmitted. dev.vtnet.X.txqY.obytes The number of bytes that were transmitted (based on Ethernet frames). dev.vtnet.X.txqY.opackets The number of packets that were transmitted (Ethernet frames). RECEIVE QUEUE STATISTICS For each receive queue of each interface the following read-only sta- tistics are provided: dev.vtnet.X.rxqY.rescheduled The number of times the receive interrupt handler was resched- uled. dev.vtnet.X.rxqY.host_lro The number of times TCP large receive offload was performed. dev.vtnet.X.rxqY.csum_failed The number of times a packet with a request for receive or transmit checksum offloading was received and this request failed. The different reasons for the failure are counted by dev.vtnet.X.rx_csum_inaccessible_ipproto, dev.vtnet.X.rx_csum_bad_ipproto, dev.vtnet.X.rx_csum_bad_ethtype, and dev.vtnet.X.rx_csum_bad_offset. dev.vtnet.X.rxqY.csum The number of times receive checksum offloading for UDP or TCP was performed. dev.vtnet.X.rxqY.ierrors The number of times an error occurred during input processing. dev.vtnet.X.rxqY.iqdrops The number of times a packet was dropped during input process- ing. dev.vtnet.X.rxqY.ibytes The number of bytes that were received (based on Ethernet frames). dev.vtnet.X.rxqY.ipackets The number of packets that were received (Ethernet frames). INTERFACE TRANSMIT STATISTICS For each interface the following read-only transmit statistics are pro- vided: dev.vtnet.X.tx_task_rescheduled The sum of dev.vtnet.X.txqY.rescheduled over all transmit queues of the interface. dev.vtnet.X.tx_tso_offloaded The sum of dev.vtnet.X.txqY.tso over all transmit queues of the interface. dev.vtnet.X.tx_csum_offloaded The sum of dev.vtnet.X.txqY.csum over all transmit queues of the interface. dev.vtnet.X.tx_defrag_failed The number of times an attempt to defragment an mbuf chain failed during a transmit operation. dev.vtnet.X.tx_defragged The number of times an mbuf chain was defragmented during a transmit operation. dev.vtnet.X.tx_tso_without_csum The number of times TCP segment offloading was attempted with- out transmit checksum offloading. dev.vtnet.X.tx_tso_not_tcp The number of times TCP segment offloading was attempted for a non-TCP packet. dev.vtnet.X.tx_csum_proto_mismatch The number of times the IP protocol version of the transmit checksum offloading request did not match the IP protocol ver- sion of the packet. dev.vtnet.X.tx_csum_unknown_ethtype The number of times a transmit offload operation was requested for an ethernet frame for which the EtherType was neither IPv4 nor IPv6 (considering simple VLAN tagging). INTERFACE RECEIVE STATISTICS For each interface the following read-only receive statistics are pro- vided: dev.vtnet.X.rx_task_rescheduled The sum of dev.vtnet.X.rxqY.rescheduled over all receive queues of the interface. dev.vtnet.X.rx_csum_offloaded The sum of dev.vtnet.X.rxqY.csum over all receive queues of the interface. dev.vtnet.X.rx_csum_failed The sum of dev.vtnet.X.rxqY.csum_failed over all receive queues of the interface. dev.vtnet.X.rx_csum_inaccessible_ipproto The number of times a packet with a request for receive or transmit checksum offloading was received where the IP protocol was not accessible. dev.vtnet.X.rx_csum_bad_offset The number of times fixing the checksum required by hw.vtnet.fixup_needs_csum or hw.vtnet.X.fixup_needs_csum was attempted for a packet where the csum is not located in the first mbuf. dev.vtnet.X.rx_csum_bad_ipproto The number of times a packet with a request for receive or transmit checksum offloading was received where the IP protocol was neither TCP nor UDP. dev.vtnet.X.rx_csum_bad_ethtype The number of times a packet with a request for receive or transmit checksum offloading was received where the EtherType was neither IPv4 nor IPv6. dev.vtnet.X.rx_mergeable_failed The number of times receiving a mergable buffer failed. dev.vtnet.X.rx_enq_replacement_failed The number of times the enqueuing the replacement receive mbuf chain failed. dev.vtnet.X.rx_frame_too_large The number of times the frame was loger than the mbuf chain during large receive offload without mergeable buffers. dev.vtnet.X.mbuf_alloc_failed The number of times an mbuf cluster allocation for the receive buffer failed. INTERFACE CONFIGURATION PARAMETER For each interface the following read-only configuration parameters are provided: dev.vtnet.X.act_vq_pairs The number of active virtqueue pairs. dev.vtnet.X.req_vq_pairs The number of requested virtqueue pairs. dev.vtnet.X.max_vq_pairs The maximum number of supported virtqueue pairs. SEE ALSO arp(4), netintro(4), ng_ether(4), virtio(4), vlan(4), ifconfig(8) HISTORY The vtnet driver was written by Bryan Venteicher <bryanv@FreeBSD.org>. It first appeared in FreeBSD 9.0. CAVEATS The vtnet driver only supports LRO when the hypervisor advertises the mergeable buffer feature. FreeBSD 15.0 September 30, 2025 VTNET(4)
NAME | SYNOPSIS | DESCRIPTION | LOADER TUNABLES | TRANSMIT QUEUE STATISTICS | RECEIVE QUEUE STATISTICS | INTERFACE TRANSMIT STATISTICS | INTERFACE RECEIVE STATISTICS | INTERFACE CONFIGURATION PARAMETER | SEE ALSO | HISTORY | CAVEATS
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