Administrator Guide

• 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.
• In a topology in which two VLT peer nodes that are connected by a VLTi link and are connected to a ToR switch using a VLT LAG
interface, if you congure an egress IP ACL and apply it on the VLT LAG of both peers using the deny ip any any
command, the trac is permitted on the VLT LAG instead of being denied. The correct behavior of dropping the trac on the
VLT LAG occurs when VLT is up on both the peer nodes. However, if VLT goes down on one of the peers, trac traverses
through VLTi and the other peer switches it to the VLT LAG. Although egress ACL is applied on the VLT nodes to deny all trac,
this egress ACL does not deny the trac (switching trac is not denied owing to the egress IP ACL). You cannot use egress
ACLs to deny trac properly in such a VLT scenario.
• To support Q-in-Q over VLT, ICL is implicitly made as vlan-stack trunk port and the TPID of the ICL is set as 8100.
• Layer 2 Protocol Tunneling is not supported in VLT.
Conguration Notes
When you congure 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.
– A VLT domain consists of the two core chassis, the interconnect trunk, backup link, and the LAG members connected to
attached devices.
– Each VLT domain has a unique MAC address that you create or VLT creates automatically.
– ARP tables are synchronized between the VLT peer nodes.
– VLT peer switches operate as separate chassis with independent control and data planes for devices attached on non-VLT
ports.
– One chassis in the VLT domain is assigned a primary role; the other chassis takes the secondary role. The primary and
secondary roles are required for scenarios when connectivity between the chassis is lost. VLT assigns the primary chassis
role according to the lowest MAC address. You can congure the primary role.
– In a VLT domain, the peer switches must run the same Dell Networking operating system (OS) software version.
– Separately congure each VLT peer switch with the same VLT domain ID and the VLT version. If the system detects
mismatches between VLT peer switches in the VLT domain ID or VLT version, the VLT Interconnect (VLTi) does not activate.
To nd the reason for the VLTi being down, use the show vlt statistics command to verify that there are mismatch
errors, then use the
show vlt brief command on each VLT peer to view the VLT version on the peer switch. If the VLT
version is more than one release dierent from the current version in use, the VLTi does not activate.
– The chassis members in a VLT domain support connection to orphan hosts and switches that are not connected to both
switches in the VLT core.
• VLT interconnect (VLTi)
– The VLT interconnect must consist of either 10G or 40G ports. A maximum of sixteen 10G or 40G ports are supported. A
combination of 10G and 40G ports are not supported.
– A VLT interconnect over 1G ports is not supported.
– The port channel must be in Default mode (not Switchport mode) to have VLTi recognize it.
Virtual Link Trunking (VLT)
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