vNICs

A virtual Network Interface Card (vNIC) is a software-defined network interface presented to a virtual machine or container. It emulates the functionality of a physical NIC but is implemented in software by the virtualization layer, and is typically backed by a physical NIC (pNIC) and a virtual switch.

In most platforms, vNICs connect to a virtual switch (such as VMware's vSwitch, Open vSwitch, or a Linux bridge). Each vNIC exposes a MAC address and can be assigned an IP address within the guest OS. VLAN tagging and QoS policies can be applied at the virtual switch level to control traffic segmentation and priority.

Virtual NIC types vary by platform. Common examples include vmxnet3 or e1000 emulation in VMware, and virtio-net in KVM/QEMU. The guest operating system uses standard NIC drivers, while the host controls attachment to virtual networks. Some environments support SR-IOV, which enables synthetic network cards to expose multiple virtual functions directly to VMs for higher throughput and lower latency.

vNICs are not limited to virtual machines; container runtimes likewise assign virtual network interfaces via CNI plugins to connect containers to overlay or underlay networks. They may be bridged to a host network, attached to software-defined networks, or routed through virtual routers.

Management considerations include IP addressing, routing, MAC address visibility, NIC teaming or bonding for redundancy, and security groups that constrain traffic. Troubleshooting commonly involves host-level network commands and VM/container networking logs.