Deployment options for upstream connectivity with active-active forwarding

Aggregate core links can be configured in one of the following ways:

  • Layer 3-LAG/routed ports: Simple VLAN-free configuration best suited when the network runs on a single VRF domain. With multiple VRFs in the network, one would need multiple routed ports, one per VRF.

  • P2P SVI links: Each aggregate-core link is on its own VLAN. The layer 2 links can carry traffic for multiple SVIs and therefore multiple VRFs can be carried over the same link.

  • VSX multichassis LAGs: The aggregate-core links can be multichassis layer 2 links carrying traffic for multiple SVIs and VRFs. This configuration provides for layer 2 LAG and layer 3 ECMP-based active-active forwarding for traffic from core to access.

In these configurations, the two VSX switches run as independent control planes (OSPF/BGP) and present themselves as different routers in the network. In the datapath however, they function as a single router and support active-active forwarding.