How XRN Interacts with other Features 683STP/RSTP STP/RSTP should be used for multihomed links if you are not able to useaggregated links. Figure 184 shows how STP will prevent a loop occurring on amultihomed link.STP/RSTP should always be enabled if your multihomed links are aggregated links.Figure 182 shows how, on interconnect failure, STP/RSTP will detect the potentialloop caused by the aggregated links splitting and block a path to prevent the loopoccurring.Figure 184 How XRN interacts with STP/RSTPResilient Links In Figure 185, if Switch A within the Distributed Fabric fails, the Switch 3300 willdetect that a link has gone down and will make the standby link to Switch B activeand pass all traffic down the link to Switch B.When using resilient links in a Distributed Fabric network the resilient links must beconfigured at the remote end rather than at the Distributed Fabric. In a unit failurescenario as described above it would not matter if the resilient links wereconfigured at the Distributed Fabric end. However, on an interconnect failure itwould matter.For example, if the resilient links were configured on Switches A and B, if theinterconnect fails, both Switches will detect a failed link to Switch 3300 and bothA and B will activate their links to Switch 3300. So both links in the resilient linkwill be passing traffic, potentially causing a loop in the network.Figure 185 How XRN interacts with Resilient LinksSwitch 5500XRN Distributed FabricResilient LinkStandby LinkActive LinkSwitch A Switch B
