Benefits of VSX
Control plane:
Dual control plane for better resiliency
Unified management (synchronized configuration and easy troubleshooting)
Live software upgrade with near zero downtime
In-chassis redundancy for the 8400 series switches and device level redundancy for all other platforms, such as for the 832x series switches.
Layer 2 distributed LAGs (aggregation switches to access switches):
Loop-free L2 multipathing (active-active)
Rapid failover
Simple configuration
No Spanning Tree Required
Layer 3 distributed LAGs (core switches to aggregate switches)
Distributed Layer 3 over VSX pair (various options: Routed Only Ports (ROPs), Switched Virtual Interfaces (SVIs), or LAG SVIs)
Unified datapath (active-active first hop gateway)
Layer 3 ECMP + Layer 2 VSX LAG (highly fault tolerant) with active-forwarding
Active Gateway:
Active-Active first hop gateway (VIP)
No VRRP/HSRP
Simple configuration (one command)
No gateway protocol overhead
DHCP relay redundancy