Physical and virtual networking
The key virtual networking components in virtual architecture are virtual Ethernet adapters and virtual switches. A virtual machine can be configured with one or more virtual Ethernet adapters. A virtual switch enables virtual machines on the same ESXi host to communicate with each other using the same protocols used over physical switches, without the need for additional hardware.
VMware technology lets you link local virtual machines to each other and to the external network through a virtual switch. A virtual switch, just like any physical Ethernet switch, forwards frames at the data link layer. An ESXi host can contain multiple virtual switches. The virtual switch connects to the external network through physical Ethernet adapters. The virtual switch is capable of binding multiple virtual network cards together, offering greater availability and bandwidth to the virtual machines.
Virtual switches are similar to modern physical Ethernet switches in many ways. Like a physical switch each virtual switch is isolated and has its own forwarding table, so every destination the switch looks up can match only ports on the same virtual switch where the frame originated. This feature improves security, making it difficult for hackers to break virtual switch isolation.
Virtual switches also support VLAN segmentation at the port level, so that each port can be configured as an access or trunk port, providing access to either single or multiple VLANs.