Dell Force10 S4820T S4820T Configuration Guide - Page 806

www.dell.com | support.dell.com • Configure an EdgePort on page 813 • Preventing Network Disruptions with BPDU Guard on page 953 • Influence RSTP Root Selection on page 814 • Configuring Spanning Trees as Hitless on page 959 • SNMP Traps for Root Elections and Topology Changes on page 815 • Fast Hellos for Link State Detection on page 815 • Flush MAC Addresses after a Topology Change on page 667 Important Points to Remember • RSTP is disabled by default. • FTOS supports only one Rapid Spanning Tree (RST) instance. • All interfaces in VLANs and all enabled interfaces in Layer 2 mode are automatically added to the RST topology. • Avoid using the range command to add a large group of ports to a large group of VLANs; adding a group of ports to a range of VLANs sends multiple messages to the RSTP task. When using the range command, Dell Force10 recommends limiting the range to 5 ports and 40 VLANs. RSTP and VLT VLT provides loop-free redundant topologies and does not require rapid spanning tree protocol (RSTP). RSTP can cause temporary port state blocking and may cause topology changes after link or node failures. Spanning tree topology changes are distributed to the entire layer 2 network, which can cause a network-wide flush of learned MAC and ARP addresses, requiring these addresses to be re-learned. However, enabling RSTP can detect potential loops caused by non-system issues such as cabling errors or incorrect configurations. RSTP is useful for potential loop detection but should be configured using the specifications below to minimize possible topology changes after link or node failure. The following recommendations will help you avoid these issues and the associated traffic loss caused by using rapid spanning trees when VLT is enabled on both VLT peers: • Any ports at the edge of the spanning tree's operating domain should be configured as edge ports, which are directly connected to end stations or server racks. Ports connected directly to layer 3-only routers not running STP should have RSTP disabled or be configured as edge ports. • Ensure the primary VLT node is the root bridge and the secondary VLT peer node has the second-best bridge ID in the network. If the primary VLT peer node fails, the secondary VLT peer node becomes the root bridge, avoiding problems with spanning tree port state changes that occur when a VLT node fails or recovers. • Even with this configuration, if the node has non-VLT ports using RSTP that are not configured as edge ports and are connected to other layer 2 switches, spanning tree topology changes can still be detected after VLT node recovery. To avoid this scenario, ensure that any non-VLT ports are configured as edge ports or have RSTP disabled. 806 | Rapid Spanning Tree Protocol (RSTP)