Based on the number of users in the branch, three design models can be used, each of
which offers a certain amount of scalability. The choice of models is affected by requirements such as high availability, because some of the interfaces on the edge router do not support Ether Channels. If a server farm must be supported in the branch, the design must support the required port density to connect the small server farms and to meet the additional DMZ requirements. High availability, scalability, and advanced services add to the cost of the infrastructure. Layer 2 and Layer 3 switches do provide some alternatives to which software images can be used to keep the cost low while still providing high availability and scalability. Also, the infrastructure can be reused to migrate to advanced services if required without having to redesign.

The requirement are different for different-sized branch offices. Based on the discussions above, the following lists the basis for LAN design at the branches:

• Number of users
• Cost
• High availability
• Scalability
• Security
• Server farms and DMZ requirements
• Management