Dell C1048P Port Extender Networking Configuration Guide for the C9000 Series - Page 977

• VLT peer device - One of a pair of devices that are connected with the special port channel known as the VLT interconnect (VLTi). VLT peer switches have independent management planes. A VLT interconnect between the VLT chassis maintains synchronization of L2/L3 control planes across the two VLT peer switches. The VLT interconnect uses either 10G or 40G user ports on the chassis. A separate backup link maintains heartbeat messages across an out-of-band (OOB) management network. The backup link ensures that node failure conditions are correctly detected and are not confused with failures of the VLT interconnect. VLT ensures that local traffic on a chassis does not traverse the VLTi and takes the shortest path to the destination via directly attached links. Important Points to Remember • VLT port channel interfaces must be switch ports. • If you include RSTP on the system, configure it before VLT. Refer to Configure Rapid Spanning Tree. • Dell Networking strongly recommends that the VLTi (VLT interconnect) be a static LAG and that you disable LACP on the VLTi. • Ensure that the spanning tree root bridge is at the Aggregation layer. If you enable RSTP on the VLT device, refer to RSTP and VLT for guidelines to avoid traffic loss. • If you reboot both VLT peers in BMP mode and the VLT LAGs are static, the DHCP server reply to the DHCP discover offer may not be forwarded by the ToR to the correct node. To avoid this scenario, configure the VLT LAGs to the ToR and the ToR port channel to the VLT peers with LACP. If supported by the ToR, enable the lacp-ungroup feature on the ToR using the lacp ungroup member-independent port-channel command. • If the lacp-ungroup feature is not supported on the ToR, reboot the VLT peers one at a time. After rebooting, verify that VLTi (ICL) is active before attempting DHCP connectivity. • When you enable IGMP snooping on the VLT peers, ensure the value of the delay-restore command is not less than the query interval. • When you enable Layer 3 routing protocols on VLT peers, make sure the delay-restore timer is set to a value that allows sufficient time for all routes to establish adjacency and exchange all the L3 routes between the VLT peers before you enable the VLT ports. • Only use the lacp ungroup member-independent command if the system connects to nodes using bare metal provisioning (BMP) to upgrade or boot from the network. • If the DHCP server is located on the ToR and the VLTi (ICL) is down due to a failed link when a VLT node is rebooted in BMP mode, it is not able to reach the DHCP server, resulting in BMP failure. • If the source is connected to an orphan (non-spanned, non-VLT) port in a VLT peer, the receiver is connected to a VLT (spanned) port-channel, and the VLT port-channel link between the VLT peer connected to the source and TOR is down, traffic is duplicated due to route inconsistency between peers. To avoid this scenario, Dell Networking recommends configuring both the source and the receiver on a spanned VLT VLAN. • Bulk synchronization happens only for global IPv6 Neighbors; link-local neighbor entries are not synced. • If all of the following conditions are true, MAC addresses may not be synced correctly: - VLT peers use VLT interconnect (VLTi) - Sticky MAC is enabled on an orphan port in the primary or secondary peer - MACs are currently inactive If this scenario occurs, use the clear mac-address-table sticky all command on the primary or secondary peer to correctly sync the MAC addresses. • If static ARP is enabled on only one VLT peer, entries may be overwritten during bulk sync. Configuration Notes VLT requires that you enable the feature and then configure the same VLT domain, backup link, and VLT interconnect on both peer switches. When you configure VLT, the following conditions apply. • VLT domain - A VLT domain supports two chassis members, which appear as a single logical device to network access devices connected to VLT ports through a port channel. Virtual Link Trunking (VLT) 977