Which of the following technologies are Layer 4 load balancing technologies? (Select All that Apply)

Layer 4 load balancing makes routing decisions based on information from the transport layer (Layer 4) of the OSI model, primarily using source/destination IP addresses and TCP/UDP port numbers. Nginx (via its stream module), LVS (Linux Virtual Server), and HAProxy (in mode tcp) are all widely-used technologies that can operate at Layer 4 to distribute TCP and UDP traffic among a pool of backend servers without inspecting the application-layer content.

B. PPP (Point-to-Point Protocol) is a Data Link Layer (Layer 2) protocol used to establish a direct connection between two network nodes. It is not a load balancing technology.

- NGINX Official Documentation, "Module ngxstreamcoremodule". This document details the configuration for TCP/UDP (Layer 4) load balancing.

- The Linux Virtual Server Project (www.linuxvirtualserver.org) documentation. The project's core function is providing high-performance Layer 4 switching (load balancing).

- HAProxy Documentation, "Configuration Manual". The manual describes the use of mode tcp for Layer 4 load balancing.

- Kurose, J. F., & Ross, K. W. (2017). Computer Networking: A Top-Down Approach (7th ed.). Pearson. Chapter 3 (Transport Layer) and Chapter 5 (Link Layer) provide the foundational knowledge to distinguish between Layer 4 functions and Layer 2 protocols like PPP.