Secure Network Topologies

The foundation of a LAN is the topology, or network architecture. A topology is the physical and logical layout of a LAN in terms of resources provided, distance between nodes, and transmission medium. Depending upon the needs of the organization that the network services, there are several choices available for network implementation. Each topology has unique advantages and security issues that network architects should regard when designing their network layout.

Physical Topologies:

As defined by the Institute of Electrical and Electronics Engineers (IEEE), there are three common topologies for the physical connection of a LAN.
1. Ring Topology

The Ring topology connects each node using exactly two connections. This creates a ring structure where each node is accessible to the other, either directly by its two physically closest neighboring nodes or indirectly through the physical ring. Token Ring, FDDI, and SONET networks are connected in this fashion (with FDDI utilizing a dual-ring technique); however, there are no common Ethernet connections using this physical topology, so rings are not commonly deployed except in legacy or institutional settings with a large installed base of nodes (for example, a university).

2. Linear Bus Topology

The linear bus topology consists of nodes which connect to a terminated main linear cable (the backbone). The linear bus topology requires the least amount of cabling and networking equipment, making it the most cost-effective topology. However, the linear bus depends on the backbone being constantly available, making it a single point-of-failure if it has to be taken off-line or is severed. Linear bus topologies are commonly used in peer-to-peer LANs using co-axial (coax) cabling and 50-93 ohm terminators at both ends of the bus.

3. Star Topology

The Star topology incorporates a central point where nodes connect and through which communication is passed. This central point, called a hub can be either broadcasted or switched. This topology does introduce a single point of failure in the centralized networking hardware that connects the nodes. However, because of this centralization, networking issues that affect segments or the entire LAN itself are easily traceable to this one source.