HP Cisco Catalyst Blade Switch 3020 Cisco Catalyst Blade Switch 3020 for HP So - Page 427

Chapter 21 Configuring UDLD Configuring UDLD If the detection window ends and no valid reply message is received, the link might shut down, depending on the UDLD mode. When UDLD is in normal mode, the link might be considered undetermined and might not be shut down. When UDLD is in aggressive mode, the link is considered unidirectional, and the port is disabled. If UDLD in normal mode is in the advertisement or in the detection phase and all the neighbor cache entries are aged out, UDLD restarts the link-up sequence to resynchronize with any potentially out-of-sync neighbors. If you enable aggressive mode when all the neighbors of a port have aged out either in the advertisement or in the detection phase, UDLD restarts the link-up sequence to resynchronize with any potentially out-of-sync neighbor. UDLD shuts down the port if, after the fast train of messages, the link state is still undetermined. Figure 21-1 shows an example of a unidirectional link condition. Figure 21-1 UDLD Detection of a Unidirectional Link Switch A TX RX Switch B successfully receives traffic from Switch A on this port. TX RX However, Switch A does not receive traffic from Switch B on the same port. If UDLD is in aggressive mode, it detects the problem and disables the port. If UDLD is in normal mode, the logical link is considered undetermined, and UDLD does not disable the interface. Switch B 98648 Configuring UDLD These sections contain this configuration information: • Default UDLD Configuration, page 21-4 • Configuration Guidelines, page 21-4 • Enabling UDLD Globally, page 21-5 • Enabling UDLD on an Interface, page 21-5 • Resetting an Interface Disabled by UDLD, page 21-6 OL-8915-01 Cisco Catalyst Blade Switch 3020 for HP Software Configuration Guide 21-3