Growing the Spanning Tree

When a company’s lifeblood involve electronic transactions and instant access to storage and databases, network downtime is unacceptable.

In the WAN and LAN technology exists that help prevent or reroute around problems to avoid downtime.

In the LAN world at least there is a well-known technology called the Spanning Tree Protocol. SPT basically defines redundant paths for data to take and eliminate looping whereby packets continue to look for a destination. Loops create problems by adding overhead and denigrating network performance.

According to Cisco the current STP standard (802.1d) was designed at a time where recovering connectivity after an outage within a minute or so was considered adequate performance. The knock against STP is that it takes too long to recover from failures.

Our Tech Update author (jeff.hayes@ind.alcatel.com) writes about an enhancement to the 801.2d standard that helps eliminate STP problems: 802.1w Rapid Reconfiguration of Spanning Tree and the Rapid Spanning-Tree Protocol (RSTP).

In a nutshell RSTP ensures rapid recovery of connectivity following the failure of a bridge/switch, bridge port or LAN. A new root port can transition rapidly to the forwarding port state. Experts claim RSTP lets a Layer 2 link failover to a redundant link in less than a second, compared with STP which can take up to 30 seconds to reroute around a bad link.

There plenty more information on RSTP at : https://www.nwfusion.com/tech/2003/0210techupdate.html