Information Technology Reference
In-Depth Information
Small Branch Design
The small branch design is recommended for branch offices that do not require hardware
redundancy and that have a small user base supporting up to 50 users. This profile con-
sists 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:
Integrated Layer 2 switching using an optional EtherSwitch module that provides 16
to 48 Ethernet ports for client connections. Some modules support PoE.
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External Layer 2 switching using a trunk connection to an access switch that aggre-
gates the Ethernet connections. The access switch can also include PoE to support IP
phones and wireless APs.
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Logical EtherChannel interface between the ISR and the access switches using the
EtherSwitch module. The access switches can also provide PoE as needed.
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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, IPsec VPN, and IOS Firewall.
Layer 2 services can be provided by the Cisco ISR using switch modules or the Cisco Cat-
alyst 2960, 3560 or 3750 series-based access switches. It is recommended that you use
Rapid Per VLAN Spanning Tree Plus (PVST+) for all Layer 2 branch offices where loops
are present. Rapid PVST+ ensures a loop-free topology when multiple Layer 2 connec-
tions are used for redundancy purposes.
Both the Cisco 2921 and the 2951 ISRs support three integrated 10/100/1000 Ethernet in-
terfaces, which support Layer 3 routing, and one slot for a network module. There are 16,
24, and 48 port Cisco EtherSwitch network modules available.
Figure 7-8 illustrates the small branch design connecting back to the corporate office
where the corporate resources are located.
Medium Branch Design
The medium branch design is recommended for branch offices of 50 to 100 users, which is
similar to the small branch but with an additional access router in the WA N edge (slightly
larger) allowing for redundancy services. Ty pic ally, two 2921 or 2951 routers are used to
support the WA N , and separate access switches are used to provide LAN connectivity.
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