• In case of dual RPM, configure the virtual IP address as backup link. This is needed so that thebackup link wont flap duirng RPM failover scenarios. See Configuring a Virtual IP Address.• Virtual link trunks (VLTs) between access devices and VLT peer switches• To connect servers and access switches with VLT peer switches, you use a VLT port channel, asshown in Overview. Up to 48 port-channels are supported; up to eight member links aresupported in each port channel between the VLT domain and an access device.• VLT provides a loop-free topology for port channels with endpoints on different chassis in the VLTdomain.• VLT uses shortest path routing so that traffic destined to hosts via directly attached links on achassis does not traverse the chassis-interconnect link.• VLT allows multiple active parallel paths from access switches to VLT chassis.• VLT supports port-channel links with LACP between access switches and VLT peer switches. DellNetworking recommends using static port channels on VLTi.• If VLTi connectivity with a peer is lost but the VLT backup connectivity indicates that the peer is stillalive, the VLT ports on the Secondary peer are orphaned and are shut down.• In one possible topology, a switch uses the BMP feature to receive its IP address,configuration files, and boot image from a DHCP server that connects to the switch throughthe VLT domain. In the port-channel used by the switch to connect to the VLT domain,configure the port interfaces on each VLT peer as hybrid ports before adding them to theport channel (refer toConnecting a VLT Domain to an Attached Access Device (Switch or Server)). To configure aport in Hybrid mode so that it can carry untagged, single-tagged, and double-tagged traffic,use the portmode hybrid command in Interface Configuration mode as described inConfiguring Native VLANs.• For example, if the DHCP server is on the ToR and VLTi (ICL) is down (due to either anunavailable peer or a link failure), whether you configured the VLT LAG as static or LACP,when a single VLT peer is rebooted in BMP mode, it cannot reach the DHCP server, resultingin BMP failure.• 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, ingressand egress ACLs, and Layer 2 control protocols RSTP only).NOTE: PVST+ passthrough is supported in a VLT domain. PVST+ BPDUs does not resultin an interface shutdown. PVST+ BPDUs for a nondefault VLAN is flooded out as anyother L2 multicast packet. On a default VLAN, RTSP is part of the PVST+ topology in thatspecific VLAN (default VLAN).• For detailed information about how to use VRRP in a VLT domain, see the following VLT and VRRPinteroperability 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 sameVLAN 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, IPv6 dynamic routing, flow control, port monitoring, and jumbo frames.• In a VLT domain, ingress and egress QoS policies are supported on physical VLT ports, which canbe members of VLT port channels in the domain.Virtual Link Trunking (VLT) 1170
