Building Blocks

Building Blocks

When designing a switched network, following a modular approach is a good practice. These modules can be thought of as the building blocks of an overall network. After the design and configuration of the basic building blocks are well understood inside an organization, additional building blocks can be added as the network grows, without greatly increasing the complexity of troubleshooting and operating the network. Following this approach, Figure 11-2 illustrates a simple building block that could be used to handle switching in a single location. In this figure, each access layer switch services a single floor of users in a facility, with each access switch having dual connections to the distribution switches. In the smallest of networks, this may be the only infrastructure that exists, and in this case, the distribution switches also function as core switches in what is termed a collapsed backbone. In this situation, a trunk carrying the two access layer VLANs connects the core/distribution switches and forms simple loops for VLANs 101 and 102 that spanning tree will block. In this connection, users connected to either switch have connections to both distribution layer switches, and the distribution switches provide Layer 3 routing via switched virtual interfaces (SVIs) for each VLAN. In addition, Hot Standby Router Protocol (HSRP) can be configured so that SW-D1 is the active router for VLAN 101, while SW-D2 is the active router for VLAN 102. Administrators then point workstation default gateways to the appropriate HSRP IP address for their respective VLANs.