Design Guide

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LAN Baseline Architecture Overview—Branch Office Network
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Branch LAN Design Considerations
Branch LAN Design Considerations
Branch LAN infrastructure provides connectivity to the end devices to access the corporate network. In
a small office and even a medium-sized branch office, the resources are typically located at the corporate
headquarters and accessed through a wide area network (WAN) of varying bandwidth. For certain branch
offices, a limited amount of end user connectivity is desired, and these end users access the
computational resources at the corporate headquarters. However, it is also desired that the computational
resources be deployed in certain branch offices. In such a case, in addition to providing connectivity to
the corporate headquarters, the branch LAN must meet additional requirements. Based on these
computational and connectivity requirements, branch offices can be categorized into the following
categories:
• Small branch (up to 50 users)
• Medium branch (up to 100 users)
• Large branch (up to 200 users)
The small branch office is typically characterized by small number of users, usually less than 50 users.
The medium branch office is up to 100 users. The large branch office should accommodate up to 200
users. Typically, secure connectivity to the corporate headquarters is the main focus for small- and
medium-sized branch offices. In a small- and medium-sized office, the following issues must be
considered when deploying the LAN:
• Coverage considerations for wireless LAN (WLAN) users in a branch office
• Distance considerations from the closet to the desk for wired clients
• Inline power requirements for all IP phone users in the branch office
• Security, and manageability considerations
For the large branch office, several services and computational resources must be provided as well as
end user connectivity to the corporate office. These services are typically handled by well-defined
entities in campus environments. These entities have their own LAN design and tie into the campus core.
The following services are expected to be provided in large branch office designs in addition to the
services mentioned above for small and medium sized branch offices.:
• DMZ and small server farm
• Wide area file services
• Local authentication (survivability) for users
• Security services such as intrusion detection/prevention
• High availability and scalability
Deployment of the above features/services means increased switching capabilities for the LAN. The
network must not only be designed to meet current requirements, but should scale and be able to
accommodate value-added services without having to redesign the entire network.
These additional requirements for a large branch office LAN are met by a multilayer LAN architecture.
The following section provides more details about the considerations and capabilities of a multilayer
branch LAN architecture.