1. ArubaOS-CX 10.11 Layer 2 Bridging Guide
Chapter: "Ethernet Ring Protection Switching (ERPS)"
Page 1.
Quote/Paraphrase: "ERPS provides sub-50 ms protection and recovery switching for Ethernet traffic in a ring topology and ensures that there are no loops formed at the Ethernet layer. ERPS is often used in carrier and metro Ethernet networks..." This document confirms ERPS is designed for the exact use case of interconnecting sites over a metro/carrier network with fast failover.
2. ArubaOS-CX 10.11 Virtual Switching Extension (VSX) Guide
Chapter: "VSX deployment considerations"
Section: "VSX split-brain detection".
Quote/Paraphrase: While not giving a hard number
the guide emphasizes the need for a low-latency
high-bandwidth ISL. Industry best practices for stretched clustering technologies like VSX typically recommend a round-trip time (RTT) of less than 10ms
which limits its geographical scope compared to carrier-grade protocols like ERPS.
3. Aruba Design Principles and Methodologies Guide
Chapter 2: "Aruba Campus for Midsize Networks"
Section: "Switching architecture".
Quote/Paraphrase: This guide differentiates VSF and VSX. It describes VSF as a technology for creating a single logical device from a stack of access switches
implying co-location. It positions VSX for the aggregation/core layer for high availability within a site. This context makes VSF clearly unsuitable for DCI between buildings.