Which of the following is NOT a capability of Open vSwitch?

Open vSwitch (OVS) is a multilayer virtual switch that provides advanced networking functions within a virtualized environment. It supports Layer 2 switching, Layer 3 forwarding through OpenFlow rules, Quality of Service (QoS) for traffic management, and various encapsulation protocols like VLAN, VXLAN, and GRE for creating overlay networks.
Option D, "Direct pass-through from VM to the NIC," describes Single Root I/O Virtualization (SR-IOV). SR-IOV is a hardware-based virtualization technology that allows a physical NIC to be partitioned into multiple Virtual Functions (VFs), which are then directly assigned to VMs. This process bypasses the hypervisor's virtual switch (like OVS) entirely, providing near-native performance. Therefore, direct pass-through is a feature of SR-IOV, not OVS; in fact, it is an alternative to using OVS for packet processing.

A. OVS is designed for network virtualization and extensively uses encapsulation protocols like VLAN (802.1Q), VXLAN, and GRE to create tunnels and overlay networks.
B. While primarily a Layer 2 switch, OVS can perform Layer 3 forwarding by programming its flow tables with rules that match on IP addresses and forward packets accordingly.
C. OVS includes robust Quality of Service (QoS) capabilities, allowing for the configuration of policing (rate-limiting) and queuing disciplines to manage bandwidth and prioritize traffic.

1. Nokia Nuage Networks VSP Fundamentals, Student Guide (Course Number: TTP35003-1-1), Module 2: VSP Components.

Section: Virtual Routing and Switching (VRS): This section details that the Nuage VRS is an enhanced version of Open vSwitch. It explicitly states that VRS (OVS) is responsible for L2/L3 forwarding, QoS policy enforcement, and VXLAN/GRE encapsulation for traffic within the data center. It also contrasts this with SR-IOV as a separate high-performance option that bypasses the VRS.

2. Open vSwitch Official Documentation, ovs-vswitchd.conf.db(5) man page.

Section: Port Table, trunks column: "A list of VLANs that this port trunks. When this is configured, only packets with a 802.1Q header with a VLAN in this list are forwarded..." (Confirms VLAN capability).

Section: Interface Table, type column: Describes interface types including gre, vxlan, confirming encapsulation capabilities.

Section: QoS Table: "Quality of Service (QoS) configuration for each Port." (Confirms QoS capability).

3. Sallam, A., & Li, T. (2018). Performance Analysis of Open vSwitch with DPDK and SR-IOV in NFV Environment. 2018 21st Conference on Innovation in Clouds, Internet and Networks and Workshops (ICIN).

Abstract & Section I (Introduction): This peer-reviewed paper explicitly compares OVS and SR-IOV. It states, "SR-IOV allows a VM to directly access the NIC, bypassing the hypervisor vSwitch which results in a high throughput and low latency." This confirms that SR-IOV's direct pass-through mechanism is distinct from and bypasses OVS.

DOI: https://doi.org/10.1109/ICIN.2018.8401614