Users Guide

• Software features supported on VLT port-channels
• In a VLT domain, the following software features are supported on VLT port-channels: 802.1p,
ingress and egress ACLs, BGP, DHCP relay, IS-IS, OSPF, active-active PIM-SM, PIM-SSM, VRRP,
Layer 3 VLANs, LLDP, flow control, port monitoring, jumbo frames, IGMP snooping, sFlow, ingress
and egress ACLs, and Layer 2 control protocols RSTP and PVST only.
NOTE: Peer VLAN spanning tree plus (PVST+) passthrough is supported in a VLT domain.
PVST+ BPDUs does not result in an interface shutdown. PVST+ BPDUs for a nondefault
VLAN is flooded out as any other L2 multicast packet. On a default VLAN, RTSP is part of
the PVST+ topology in that specific VLAN (default VLAN).
• In a VLT domain, ingress and egress QoS policies are supported on physical VLT ports, which can
be members of VLT port channels in the domain.
• Ingress and egress QoS policies applied on VLT ports must be the same on both VLT peers.
• Apply the same ingress and egress QoS policies on VLTi (ICL) member ports to handle failed
links.
• For detailed information about how to use VRRP in a VLT domain, see the following VLT and VRRP
interoperability section.
• For information about configuring IGMP Snooping in a VLT domain, see VLT and IGMP Snooping.
• 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, IPv6 dynamic routing, port monitoring, and jumbo frames.
• Software features not supported with VLT
• In a VLT domain, the following software features are not supported on VLT ports: 802.1x, DHCP
snooping, FRRP, GVRP, ERSPAN, RSPAN, VXLAN, ingress and egress QOS.
• VLT and VRRP interoperability
• In a VLT domain, VRRP interoperates with virtual link trunks that carry traffic to and from access
devices (see Overview). 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, 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. For more information, see
Setting VRRP Group (Virtual Router) Priority.
• To verify that a VLT peer is consistently configured for either the master or backup role in all VRRP
groups, use the show vrrp command on each peer.
• Configure the same L3 routing (static and dynamic) on each peer so that the L3 reachability and
routing tables are identical on both VLT peers. Both the VRRP master and backup peers must 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
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
Virtual Link Trunking (VLT) 1034