Dell Force10 S4820T S4820T Configuration Guide - Page 1013

• Layer 3 VLAN connectivity VLT peers is enabled by configuring a VLAN network interface for the same VLAN on both switches. • Software features supported on VLT port-channels: • In a VLT domain, the following software features are supported on VLT port-channels: 802.1p, LLDP, flow control, port monitoring, jumbo frames. • Software features supported on non-VLT ports: • In a VLT domain, the following software features are supported on non-VLT ports: OSPF, BGP, IS-IS, DHCP relay, sFlow, ingress and egress QOS, ingress and egress ACLs, 802.1x, and all protocols currently supported in FTOS. • VLT and VRRP interoperability: • In a VLT domain, VRRP interoperates with virtual link trunks that carry traffic to and from access devices (see Figure 53-1). The VLT peers belong to the same VRRP group and are assigned master and backup roles. Each peer actively forwards L3 traffic, reducing the traffic flow over the VLT interconnect. • VRRP elects the router with the highest priority as the master in the VRRP group. To ensure VRRP operation in a VLT domain, you must configure VRRP group priority on each VLT peer so that a peer is either the master or backup for all VRRP groups configured on its interfaces. See Set VRRP Group (Virtual Router) Priority for more information. • To verify that a VLT peer is consistently configured for either the master or backup role in all VRRP groups, enter the show vrrp command on each peer. • You must also configure the same L3 routing (static and dynamic) on each peer so that L3 reachability and routing tables are identical on both VLT peers. Both the VRRP master and backup peers should be 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 master or backup router, the show vrrp command output displays one peer as master and the other peer as backup. • Failure scenarios: • On a link failover, when a VLT port channel fails, the traffic destined for that VLT port channel is re-directed 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 in fact 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, upon 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. Virtual Link Trunking (VLT) | 1013