Users Guide

• With peer routing, you need not use VRRP.
• You can use routing protocols in a VLT domain or between VLT domains (eVLT).
• VLT Proxy Gateway enables one VLT domain to act as the default gateway for its peer VLT domain in an eVLT topology.
Congure Virtual Link Trunking
VLT requires that you enable the feature and then congure the same VLT domain, backup link, and VLT interconnect on both peer
switches.
Important Points to Remember
• You cannot enable stacking simultaneously with VLT. If you enable both at the same time, unexpected behavior occurs.
• VLT port channel interfaces must be switch ports.
• If you include RSTP on the system, congure it before VLT. Refer to Congure Rapid Spanning Tree.
• If you include PVST on the system, congure it before VLT. Refer to PVST Conguration.
• 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. Refer to RSTP and VLT for guidelines to avoid trac loss, if you
enable RSTP on the VLT device.
• If you reboot both VLT peers in BMP mode and the VLT LAGs are static, the DHCP server reply to the DHCP discover oer may not be
forwarded by the ToR to the correct node. To avoid this scenario, congure 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 sucient 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.
• Ensure that you congure all port channels where LACP ungroup is applicable as hybrid ports and as untagged members of a VLAN.
BMP uses untagged dynamic host conguration protocol (DHCP) packets to communicate with the DHCP server.
• 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, trac is duplicated due to
route inconsistency between peers. To avoid this scenario, Dell Networking recommends conguring both the source and the receiver
on a spanned VLT VLAN.
• Bulk Sync 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 you enable static ARP on only one VLT peer, entries may be overwritten during bulk sync.
• For multiple VLT LAGs congured on the same VLAN, if a host is learned on one VLT LAG and there is a station move between LAGs,
the link local address redirects to the VLTi link on one of the peers. If this occurs, clear the link local address that is redirecting to the
VLTi link.
• VLT Heartbeat is supported only on default VRFs.
• In a scenario where one hundred hosts are connected to a Peer1 on a non-VLT domain and trac ows through Peer1 to Peer2; when
you move these hosts from a non-VLT domain to a VLT domain and send ARP requests to Peer1, only half of these ARP requests reach
Virtual Link Trunking (VLT)
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