Cisco Data Center Fundamentals

Chapter 4

Port Channels and vPCs

In early Layer 2 Ethernet network environments, Spanning Tree Protocol (STP) was the primary solution to limit the disastrous effects of a topology loop in the network. STP has one suboptimal principle: to break loops in a network, only one active path is allowed from one device to another, regardless of how many actual connections might exist in the network. The single logical link creates two problems: one problem is that half (or more) of the available system bandwidth is off limits to data traffic, and the other problem is that a failure of the active link tends to cause multiple seconds of systemwide data loss while the network re-evaluates the new “best” solution for network forwarding in the Layer 2 network. ...