In the collapsed core design, each access layer switch has a redundant link to each distribution layer switch. All Layer 3 subnets present in the access layer terminate at the distribution switches’ Layer 3 ports, as in the basic switch block design. The distribution switches connect to each other with redundant links, completing a path to use during a failure.
The two-node redundant core has been expanded to include four core switches. This is known as a multinode core. Each of the four core switches is connected to the other core switches to form a fully meshed core layer.
Even though the multinode core is fully meshed, the campus network is still divided across the two pairs of core switches. Each switch block has redundant connections to only one core pair—not to all of the core switches.