Posts Tagged ‘loop’

Configuring PVST+ on Cisco Switches

Wednesday, February 1st, 2012

Per VLAN Spanning Tree Plus (PVST+) is a flavor of Spanning Tree Protocol (see prior blog, Default STP Behavior on Cisco Switches) which maintains a spanning tree instance for each VLAN in the network. This means certain VLAN trunks (using 802.1q) can be forwarded for some VLANs while being blocked for others. Further, changes in one STP domain will not effect other spanning tree instances on other VLANs. Additionally, since each VLAN is treated as a separate network, layer 2 load balancing can be accomplished by forwarding some VLANs on one trunk and other VLANs on another trunk. (more…)


Default STP Behavior on Cisco Switches

Tuesday, January 31st, 2012

In a prior blog, Functionality of Layer 2 Switches/Bridges, I discussed the core functionality of layer 2 switches. In this blog, I hit upon the Spanning Tree Protocol (STP) used on layer 2 switches to prevent loops. As mentioned before, loops can be created via layer 2 switches by using more than one link to connect to the same switches. This is often done for redundancy purposes but is not possible without STP. (more…)