Specifications
Core Layer April 2014
95
Procedure 2 Configure LAN switch universal settings
In this design, there are features and services that are common across all LAN switches, regardless of the type
of platform or role in the network. These are system settings that simplify and secure the management of the
solution.
This procedure provides examples for some of these settings. The actual settings and values depend on your
current network configuration.
Table 8 - Common network services used in the design examples
Setting Value
Domain Name cisco.local
Active Directory, DNS, DHCP Server 10.4.48.10
Authentication Control System 10.4.48.15
Network Time Protocol Server 10.4.48.17
EIGRP Named Mode Configuration Name CAMPUS
EIGRP AS or OSPF AS 100
Multicast Range 239.1.0.0/16
Step 1: Configure the device hostname to make it easy to identify the device.
hostname [hostname]
Step 2: If the switch VTP mode has been changed from the default, configure VTP transparent mode. This
design uses VTP transparent mode because the benefits of dynamic propagation of VLAN information across the
network are not worth the potential for unexpected behavior resulting from operational error.
VLAN Trunking Protocol (VTP) allows network managers to configure a VLAN in one location of the network and
have that configuration dynamically propagate out to other network devices. However, in most cases, VLANs are
defined once during switch setup with few, if any, additional modifications.
vtp mode transparent
Step 3: Enable Rapid Per-VLAN Spanning-Tree (PVST+). Rapid PVST+ provides an instance of RSTP (802.1w) per
VLAN. Rapid PVST+ greatly improves the detection of indirect failures or linkup restoration events over classic
spanning tree (802.1D).
Although this architecture is built without any Layer 2 loops, you should still enable spanning tree with the most
up-to-date network safeguards. By enabling spanning tree, you ensure that if any physical or logical loops are
accidentally configured, no actual layer 2 loops occur.
spanning-tree mode rapid-pvst
Step 4: Enable Unidirectional Link Detection (UDLD) as the default for fiber ports.
UDLD is a Layer 2 protocol that enables devices connected through fiber-optic or twisted-pair Ethernet cables to
monitor the physical configuration of the cables and detect when a unidirectional link exists. When UDLD detects
a unidirectional link, it disables the affected interface and alerts you. Unidirectional links can cause a variety
of problems, including spanning-tree loops, black holes, and non-deterministic forwarding. In addition, UDLD
enables faster link failure detection and quick reconvergence of interface trunks, especially with fiber, which can
be susceptible to unidirectional failures.
udld enable