The single-tier design is recommended for branch offices that do not require hardware redundancy and that have a small user base of up to 50 users. This profile consists of an access router providing WAN services and connections for the LAN services. The access router can connect the Layer 2 switch ports in one of three ways:
■ Using an ISR that has an optional EtherSwitch module that provides 16 to 48 Ethernet ports for client connections.
■ Trunking to an access switch that aggregates the Ethernet connections and can include support for PoE for IP phones and wireless APs.
■ Logical EtherChannel interface between the ISR and the access switches using the EtherSwitch module. The access switches can also provide PoE as needed.
The Layer 3 WAN services are based on the WAN and Internet deployment model. A T1 is used for the primary link, and an ADSL secondary link is used for backup. Other network fundamentals are supported, such as EIGRP, floating static routes, and QoS for bandwidth protection.
The ISR can support the default gateway function and other Layer 3 services such as DHCP, NAT, and IOS Firewall.
The Layer 2 services can be provided by the ISR or access switches such as the 35x0 or 3750 series switches. It is recommended that you use Rapid PVST+ for all Layer 2 branch offices where loops are present. Rapid PVST+ ensures a loop-free topology when multiple Layer 2 connections are used for redundancy purposes.
Figure 6-8 illustrates the single-tier branch design connecting back to the corporate office.
Figure 6-8 Single-Tier Profile (Small Branch)
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