Tag Archives: L2

Per-VLAN Spanning Tree Plus (PVST+)

Spanning-tree protocol is one of the oldest ways to ensure loop-free topology of an ethernet network. Why we need it, where we need it and how it works is the subject of today’s recap post.

Etherchannel, LAG, portchannel and friends

An EtherChannel is a way to use multiple physical interfaces as a single logical one. That logical one appears as a single interface to MAC table, STP and management plane. That solves two main concerns: it adds bandwidth and it prevents STP from considering several parallel links a loop, thus preventing it from being blocked.

Recap: VLAN Trunking Protocol

Cisco VTP – the VLAN Trunking Protocol is a management tool for large L2 deployments. It provides a simple way to synchronize VLAN names and numbers across Cisco switching infrastructure, also automates some traffic optimizations (the VLAN pruning).

VLAN allocation

Speaking of L2 design, there are several aspects to the VLAN allocation on the switches: standard and extended VLAN ID ranges, reserved IDs, internal usage, protocol limitations and design best practices.