Users Guide

Peer1, while the remaining half reach Peer2 (because of LAG hashing). The reason for this behavior is that Peer1 ignores the ARP
requests that it receives on VLTi (ICL) and updates only the ARP requests that it receives on the local VLT. As a result, the remaining
ARP requests still points to the Non-VLT links and trac does not reach half of the hosts. To mitigate this issue, ensure that you
congure the following settings on both the Peers (Peer1 and Peer2): arp learn-enable and mac-address-table station-
move refresh-arp.
• 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 device in the VLT domain is assigned a primary role; the other device 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 manually.
• In a VLT domain, the peer switches must run the same Dell Networking 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 can consist of 10G or 40G ports. A maximum of eight ports are supported. A combination of 10G and 40G
ports is not supported.
• The port channel must be in Default mode (not Switchport mode) to have VLTi recognize it.
• The system automatically includes the required VLANs in VLTi. You do not need to manually select VLANs.
• VLT peer switches operate as separate chassis with independent control and data planes for devices attached to non-VLT ports.
• Port-channel link aggregation (LAG) across the ports in the VLT interconnect is required; individual ports are not supported. Dell
Networking strongly recommends conguring a static LAG for VLTi.
• The VLT interconnect synchronizes L2 and L3 control-plane information across the two chassis.
• The VLT interconnect is used for data trac only when there is a link failure that requires using VLTi in order for data packets to
reach their nal destination.
• Unknown, multicast, and broadcast trac can be ooded across the VLT interconnect.
• MAC addresses for VLANs congured across VLT peer chassis are synchronized over the VLT interconnect on an egress port such
as a VLT LAG. MAC addresses are the same on both VLT peer nodes.
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Virtual Link Trunking (VLT)