Dell PowerEdge FX2/FX2s User Manual
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• Software features supported on VLT port-channels
– For information about configuring IGMP Snooping in a VLT domain, refer to
– All system management protocols are supported on VLT ports, including SNMP, RMON, AAA, ACL,
DNS, FTP, SSH, Syslog, NTP, RADIUS, SCP, TACACS+, Telnet, and LLDP.
– Enable Layer 3 VLAN connectivity VLT peers by configuring a VLAN network interface for the same
VLAN on both switches.
– Dell Networking does not recommend enabling peer-routing if the CAM is full. To enable peer-
routing, a minimum of two local DA spaces for wild card functionality are required.
• Software features supported on VLT physical ports
– In a VLT domain, the following software features are supported on VLT physical ports: 802.1p,
LLDP, flow control, port monitoring, and jumbo frames.
• Software features not supported with VLT
– In a VLT domain, the following software features are supported on non-VLT ports: 802.1x, , DHCP
snooping, FRRP, IPv6 dynamic routing, ingress and egress QOS.
• Failure scenarios
– On a link failover, when a VLT port channel fails, the traffic destined for that VLT port channel is
redirected to the VLTi to avoid flooding.
– When a VLT switch determines that a VLT port channel has failed (and that no other local port
channels are available), the peer with the failed port channel notifies the remote peer that it no
longer has an active port channel for a link. The remote peer then enables data forwarding across
the interconnect trunk for packets that would otherwise have been forwarded over the failed port
channel. This mechanism ensures reachability and provides loop management. If the VLT
interconnect fails, the VLT software on the primary switch checks the status of the remote peer
using the backup link. If the remote peer is up, the secondary switch disables all VLT ports on its
device to prevent loops.
– If all ports in the VLT interconnect fail, or if the messaging infrastructure fails to communicate
across the interconnect trunk, the VLT management system uses the backup link interface to
determine whether the failure is a link-level failure or whether the remote peer has failed entirely.
If the remote peer is still alive (heartbeat messages are still being received), the VLT secondary
switch disables its VLT port channels. If keepalive messages from the peer are not being received,
the peer continues to forward traffic, assuming that it is the last device available in the network. In
either case, after recovery of the peer link or reestablishment of message forwarding across the
interconnect trunk, the two VLT peers resynchronize any MAC addresses learned while
communication was interrupted and the VLT system continues normal data forwarding.
– If the primary chassis fails, the secondary chassis takes on the operational role of the primary.
• The SNMP MIB reports VLT statistics.
Primary and Secondary VLT Peers
Primary and Secondary VLT Peers are supported on the Aggregator.
To prevent issues when connectivity between peers is lost, you can designate Primary and Secondary
roles for VLT peers . You can elect or configure the Primary Peer. By default, the peer with the lowest
MAC address is selected as the Primary Peer.
If the VLTi link fails, the status of the remote VLT Primary Peer is checked using the backup link. If the
remote VLT Primary Peer is available, the Secondary Peer disables all VLT ports to prevent loops.
If all ports in the VLTi link fail or if the communication between VLTi links fails, VLT checks the backup link
to determine the cause of the failure. If the failed peer can still transmit heartbeat messages, the
Secondary Peer disables all VLT member ports and any Layer 3 interfaces attached to the VLAN
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PMUX Mode of the IO Aggregator