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Chapter 4

IP Multicast in a Data Center

Data Center Logical Topology

The best way to accommodate IP Multicast in the data center is to place multicast sources on a separate VLAN that is located in the aggregation layer. Placing the multicast sources on a dedicated VLAN will bypass the difficulties of using firewalls and multicast, as well as other issues like multicast on router-less subnets.

Back-End Layer

The back-end layer consists of the infrastructure, security, and management devices supporting the interaction with the database systems that hold the business data. The back-end layer features are almost identical to those needed at the application layer, yet the security considerations are more stringent and aimed at protecting the data, critical or not.

The back-end layer is primarily for the relational database systems that provide the mechanisms to access the Enterprise information, which makes them highly critical. The hardware supporting the relational database systems range from medium sized servers to mainframes, some with locally attached disks and others with separate storage.

Multicast requirements are not common at the back-end layer. The synchronization of database contents requires an acknowledgement-based method of synchronization and multicast does not provide a mechanism to support an acknowledgement-based service, unless a vendor has written a proprietary extension.

Storage Layer

The storage layer consists of the storage infrastructure such as Fibre-Channel switches or iSCSI routers that connect server to storage devices, as well as the storage devices to where the data resides. At the data center, storage devices, such as tape and disk subsystems, need a high-speed connection to provide block level access to information from the database servers. This implies the disk subsystems are used to consolidate information from dedicated local disks to a centralized repository supporting the database systems. Multicast is not typically used at this layer.

Data Center Logical Topology

The logical architecture, presented in Figure 4-1, shows the relationship between the data center layers and the traditional campus layers. From a logical viewpoint, the front-end servers are separated from the applications servers, which are separated from the database servers. The traffic flow is then client-to-front-end servers, front-end servers-to-application servers, and finally application servers-to-database servers. The logical separation just implies each layer is a distinct functional area. Regardless of the logical separation, the Layer 2 switches providing connectivity within each layer can be though of as comparable to access switches and the aggregation switches equivalent to distribution switches.

Cisco AVVID Network Infrastructure IP Multicast Design



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