Global System Configuration
Assign Global Configuration Information
35
Best Practice User Guide for the Catalyst 3850 and Catalyst 3650 Switch Series
Configure UDLD to Detect Link Failure
Step 5
Configure Unidirectional Link Detection (UDLD) in aggressive mode, not normal mode.
UDLD detects a unidirectional link, and then disables the affected interface and alerts you.
Unidirectional links can cause a variety of problems, including spanning-tree loops, black holes, and
nondeterministic 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.
In aggressive mode, if the link state of a port is determined to be bidirectional and the UDLD information
times out while the link on the port is still in UP state, UDLD tries to re-establish the state of the port.
If this not successful, the port is put into errdisable state. In normal mode, the port state for UDLD is
marked as undetermined, and operates according to its Spanning Tree Protocol state.
Do not change UDLD aggressive timers.
Note
UDLD in aggressive mode is not needed when the upstream device is a switch operating in VSS mode.
For more information about VSS-enabled campus design, see the
Campus 3.0 Virtual Switching System
.
Configure an Access List to Limit Switch Access
Step 6
If your network operation support is centralized, you can increase network security by using an access
list to limit the networks that can access your switch.
We recommend that you use an access list to permit IP addresses from known source management
locations.
In this example, only the hosts on the 192.168.128.0, 192.168.0.0, and 192.168.254.0 networks can
access your switch using SSH or SNMP. The following example shows an ACL that permits three
subnets. your network may have more subnets or fewer subnets. configure the ACL that best fits your
network. You can continue to add to the list, as required for your network deployment.
