20 Cisco LAN Switching Configuration Handbook
■ Remote access: This is called a WAN block.
■ Telephony servers and gateways: This is called a PSTN block.
■ Legacy networks (Token Ring, FDDI, and so on): This is similar to the WAN
block, using a router to provide connectivity to various network media types.
■ Common workgroups of users: End users located in the same building, on the
same floor, or in the same area of a floor are called switch blocks. A switch
block typically groups access layer switches and the distribution switches to
which they connect.
a. Core
■ If Layer 2 switches are used, don’t create a spanning-tree loop by connecting
the two core switches.
■ Be sure to identify and configure both primary and secondary root bridge
switches for each VLAN. Typically, the root bridge should be placed close
to the core layer. Refer to section “7-2: STP Configuration,” in Chapter 7,
“Spanning Tree Protocol (STP).”
■ If Layer 3 switches are used, connect the core switches with multiple links.
See section “4-4: EtherChannel,” in Chapter 4, “Layer 2 Interface
Configuration.”
■ In a Layer 3 core, make use of Layer 3 routing protocol to provide redun-
dant routing paths, as possible leverage Equal Cost Multi Pathing (ECMP).
See section “8-3: Router Redundancy with HSRP,” in Chapter 8,
“Configuring High Availability Features.”
■ Each core switch should connect to each distribution switch for full redun-
dancy. If Layer 3 is not used in the core or distribution layers, use STP
BackboneFast to reduce STP convergence time. See section “7-2: STP
Configuration,” in Chapter 7.
b. Server block
■ Use redundant uplinks into the distribution or core layer. Utilize STP
UplinkFast (section “7-2: STP Configuration” in Chapter 7) or HSRP (section
“8-6: Router Redundancy with HSRP” in Chapter 8) for fast failover.
■ Consider using dual network interface cards (NIC) in servers for redundancy.
Connect the NICs into different switch cards or modules.
c. Internet block
■ Use Server Load Balancing to distribute traffic across multiple servers in a
server farm. See section “10-1: SLB,” in Chapter 10, “Server Load
Balancing (SLB).”
■ Use Firewall Load Balancing to distribute traffic across multiple firewalls in a
firewall farm. See section “10-2: SLB Firewall Load Balancing,” in Chapter 10.
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