• 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, , DHCPsnooping, FRRP, IPv6 dynamic routing, ingress and egress QOS.• VLT and VRRP interoperability– In a VLT domain, VRRP interoperates with virtual link trunks that carry traffic to and from accessdevices (refer to Overview). The VLT peers belong to the same VRRP group and are assignedmaster and backup roles. Each peer actively forwards L3 traffic, reducing the traffic flow over theVLT interconnect.– VRRP elects the router with the highest priority as the master in the VRRP group. To ensure VRRPoperation in a VLT domain, configure VRRP group priority on each VLT peer so that a peer is eitherthe master or backup for all VRRP groups configured on its interfaces. For more information, referto Setting VRRP Group (Virtual Router) Priority.– To verify that a VLT peer is consistently configured for either the master or backup role in all VRRPgroups, use the show vrrp command on each peer.– Also configure the same L3 routing (static and dynamic) on each peer so that the L3 reachabilityand routing tables are identical on both VLT peers. Both the VRRP master and backup peers mustbe able to locally forward L3 traffic in the same way.– In a VLT domain, although both VLT peers actively participate in L3 forwarding as the VRRP masteror backup router, the show vrrp command output displays one peer as master and the otherpeer as backup.• Failure scenarios– On a link failover, when a VLT port channel fails, the traffic destined for that VLT port channel isredirected to the VLTi to avoid flooding.– When a VLT switch determines that a VLT port channel has failed (and that no other local portchannels are available), the peer with the failed port channel notifies the remote peer that it nolonger has an active port channel for a link. The remote peer then enables data forwarding acrossthe interconnect trunk for packets that would otherwise have been forwarded over the failed portchannel. This mechanism ensures reachability and provides loop management. If the VLTinterconnect fails, the VLT software on the primary switch checks the status of the remote peerusing the backup link. If the remote peer is up, the secondary switch disables all VLT ports on itsdevice to prevent loops.– If all ports in the VLT interconnect fail, or if the messaging infrastructure fails to communicateacross the interconnect trunk, the VLT management system uses the backup link interface todetermine 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 secondaryswitch 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. Ineither case, after recovery of the peer link or reestablishment of message forwarding across theinterconnect trunk, the two VLT peers resynchronize any MAC addresses learned whilecommunication 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 PeersPrimary and Secondary VLT Peers are supported on the Z9000 platform.To prevent issues when connectivity between peers is lost, you can designate Primary and Secondaryroles for VLT peers . You can elect or configure the Primary Peer. By default, the peer with the lowest828 Virtual Link Trunking (VLT)
