36 VLANs, Spanning Tree, and Static Link AggregationAdvantages of SMLTSMLT improves the reliability of Layer 2 networks that operate betweenedge switches and the network center aggregation switches by providingthe following:• load sharing among all links• fast failover in case of link failures• elimination of single point of failure• fast recovery, in case of nodal failure• transparent and interoperable solution• elimination of STP convergence issuesThese advantages are described in more detail in the sections that follow.Single point of failure eliminationSMLT helps eliminate all single points of failure and create multiple pathsfrom all edge switches to the core of the network. In case of failure, SMLTrecovers as quickly as possible so that no unused capacity is created.Finally, SMLT provides a transparent and interoperable solution that requiresno modification on the part of the majority of existing edge devices.SMLT compared to Spanning Tree ProtocolNetworks that are designed to have edge switches dual-homed to twoaggregation switches, and that have VLANs spanning two or more edgeswitches, experience the following design constraints:• spanning tree must be used to detect loops• no load sharing exists over redundant links• slow network convergence exists in case of failure (30–45 seconds)Figure 8 "Resilient networks with Spanning Tree Protocol" (page 37) showsa typical aggregator switch configuration dependent upon STP for loopdetection.Nortel Ethernet Routing Switch 8300Configuration — VLANs, Spanning Tree, and Static Link Aggregation using Device ManagerNN46200-510 03.01 Standard4.0 27 August 2007Copyright © 2005-2007, Nortel Networks.
