VLANs

C

The Layer 2 mechanism that logically groups network nodes into separate broadcast domains is VLAN (Virtual Local Area Network).

VLAN is a technology used to divide a single physical network into multiple logical networks. Each VLAN operates as a separate broadcast domain, which means that broadcast traffic sent by a device on one VLAN will not be received by devices on other VLANs.

A VLAN is created by assigning ports on a network switch to a specific VLAN ID. Devices connected to ports in the same VLAN can communicate with each other as if they were connected to the same physical LAN. Devices in different VLANs must communicate through a router or Layer 3 switch.

IS-IS levels and OSPF areas are both Layer 3 mechanisms used to logically group network nodes into separate routing domains. They are used to improve network scalability and reduce the size of routing tables.

IS-IS is a link-state routing protocol that uses levels to partition a network into separate routing domains. Each level is identified by a level number, and routers within the same level share routing information.

OSPF (Open Shortest Path First) is another link-state routing protocol that uses areas to divide a network into separate routing domains. Each area has its own link-state database and shares summarized routing information with other areas.

IP subnets, on the other hand, are used to divide a network into smaller address spaces. Subnetting allows for more efficient use of IP address space and provides a way to organize devices into logical groups. However, it does not logically group network nodes into separate broadcast domains.

Therefore, the correct answer is C, VLAN.