© 2006 Cisco Systems, Inc. All rights reserved. BCMSN v Minimizing Service Loss and Data Theft in a Campus Network Preventing STP Forwarding Loops

© 2006 Cisco Systems, Inc. All rights reserved. BCMSN v Unidirectional Link Failure

© 2006 Cisco Systems, Inc. All rights reserved. BCMSN v Loop Guard Root

© 2006 Cisco Systems, Inc. All rights reserved. BCMSN v Before Loop Guard Root

© 2006 Cisco Systems, Inc. All rights reserved. BCMSN v With Loop Guard

© 2006 Cisco Systems, Inc. All rights reserved. BCMSN v UDLD and Loop Guard Configuration Commands Configuring and verifying UDLD udld enable show udld interface fa0/1 Configuring and verifying loop guard spantree global-default loopguard enable show spantree guard fa0/1

© 2006 Cisco Systems, Inc. All rights reserved. BCMSN v Configuring UDLD Switch(config)#udld enable Enables UDLD globally on all fiber-optic interfaces Switch(config-if)#udld enable Enables UDLD on an individual interface Switch(config-if)#no udld enable Disables UDLD on an individual nonfiber-optic interface Switch(config-if)#udld disable Disables UDLD on an individual fiber-optic interface

© 2006 Cisco Systems, Inc. All rights reserved. BCMSN v Resetting and Verifying UDLD Switch# udld reset Resets all interfaces that have been shut down by UDLD Switch#show udld interface Displays UDLD information for a specific interface

© 2006 Cisco Systems, Inc. All rights reserved. BCMSN v Configuring Loop Guard

© 2006 Cisco Systems, Inc. All rights reserved. BCMSN v Comparing Loop Guard and UDLD Loop GuardUDLD ConfigurationPer port Action granularityPer VLANPer Port AutorecoveryYes Yes, with errdisable timeout feature Protection against STP failures caused by unidirectional links Yes, when enabled on all root and alternative ports in redundant topology Yes, when enabled on all links in redundant topology Protection against STP failures caused by problem in software, resulting in designated switch not sending BPDU YesNo Protection against miswiringNoYes

© 2006 Cisco Systems, Inc. All rights reserved. BCMSN v Summary UDLD detects and disables an interface with unidirectional connectivity, protecting the network from anomalous STP conditions. Loop guard detects and disables an interface with Layer 2 unidirectional connectivity, protecting the network from anomalous STP conditions. UDLD and loop guard are configured and verified using specific commands. Implementation of UDLD and loop guard protects spanning tree operations from being disrupted due to unidirectional links.

© 2006 Cisco Systems, Inc. All rights reserved. BCMSN v