Dell Force10 S4820T S4820T Configuration Guide - Page 1009

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 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. Configuring Virtual Link Trunking VLT requires that you enable the feature and then configure the same VLT domain, backup link, and VLT interconnect on both peer switches. Important Points to Remember • Stacking cannot be enabled simultaneously with VLT. If both are enabled at the same time, unexpected behavior will occur. See VLT and Stacking. • VLT port channel interfaces must be switch ports. • If RSTP is included on the system, it must be configured before VLT. See RSTP Configuration. • Dell Force10 strongly recommends that the VLTi (VLT interconnect) must be a static LAG and that LACP should be disabled on the VLTi. • The spanning tree root bridge should be at the Aggregation layer. If RSTP is enabled on the VLT device, refer to RSTP and VLT for guidelines to avoid traffic loss. • If both VLT peers are rebooted in JumpStart mode and 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 command lacp ungroup member-independent port-channel. • If the lacp-ungroup feature is not supported on the ToR, VLT peers should be rebooted one at a time. After rebooting, verify that VLTi (ICL) is active before attempting DHCP connectivity. • When IGMP snooping is enabled on the VLT peers, ensure the value of the delay-restore command is not less than the query interval. • When Layer 3 routing protocols are enabled 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 sr before the VLT ports are enabled. • The lacp ungroup member-independent command should only be used if the system connects to nodes using BMP to upgrade or boot from the network. • Ensure all port channels where LACP ungroup is applicable are configured as hybrid ports and as untagged members of a VLAN. BMP uses untagged DHCP packets to communicate with the DHCP server. Virtual Link Trunking (VLT) | 1009