Dell C1048P Port Extender Networking Configuration Guide for the C9000 Series - Page 981

RSTP and VLT VLT provides loop-free redundant topologies and does not require 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 nonsystem issues such as cabling errors or incorrect configurations. To minimize possible topology changes after link or node failure, RSTP is useful for potential loop detection. Configure RSTP using the following specifications. The following recommendations help you avoid these issues and the associated traffic loss caused by using RSTP when you enable VLT on both VLT peers: • Configure any ports at the edge of the spanning tree's operating domain as edge ports, which are directly connected to end stations or server racks. Disable RSTP on ports connected directly to Layer 3-only routers not running STP or configure them as edge ports. • Ensure that 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 you did not configure as edge ports and are connected to other Layer 2 switches, spanning tree topology changes are still detected after VLT node recovery. To avoid this scenario, ensure that you configure any non-VLT ports as edge ports or disable RSTP. VLT Bandwidth Monitoring When bandwidth usage of the VLTi (ICL) exceeds 80%, a syslog error message (shown in the following message) and an SNMP trap are generated. %STKUNIT0-M:CP %VLTMGR-6-VLT-LAG-ICL: Overall Bandwidth utilization of VLT-ICL-LAG (portchannel 25) crosses threshold. Bandwidth usage (80 ) When the bandwidth usage drops below the 80% threshold, the system generates another syslog message (shown in the following message) and an SNMP trap. %STKUNIT0-M:CP %VLTMGR-6-VLT-LAG-ICL: Overall Bandwidth utilization of VLT-ICL-LAG (portchannel 25) reaches below threshold. Bandwidth usage (74 )VLT show remote port channel status VLT and High Availability High availability (HA) support on VLT ensures seamless and uninterrupted flow of VLT features during RPM failure (failover). When RPM failover happens, the new active RPM triggers a new VLT registration to its VLT peer. It ensures that the VLT node with new active RPM receives all the VLT information from its VLT peer. When the standby RPM performs the check-in and registration function (with the active RPM), the latter performs a bulk synchronization of all the peer VLT information. The existing CLI configuration synchronized to the standby RPM ensures that the local VLT configurations are always available at standby RPM as well. The VLT backup link functionality is also modified to manage the two management interfaces in a dual RPM. A virtual management IP must be configured on the dual RPM VLT node to maintain uninterrupted VLT backup functionality. For more information, refer to "VLT backup link" section in the Configuration Notes VLT and IGMP Snooping When configuring IGMP Snooping with VLT, ensure the configurations on both sides of the VLT trunk are identical to get the same behavior on both sides of the trunk. When you configure IGMP snooping on a VLT node, the dynamically learned groups and multicast router ports are automatically learned on the VLT peer node. Virtual Link Trunking (VLT) 981