Dell PowerSwitch S4820T Configuration Guide for the S4820T System 9.112.0P1 - Page 951

• If the DHCP server is located on the ToR and the VLTi (ICL) is down due to a failed link when a VLT node is rebooted in BMP mode, it is not able to reach the DHCP server, resulting in BMP failure. • If the source is connected to an orphan (non-spanned, non-VLT) port in a VLT peer, the receiver is connected to a VLT (spanned) portchannel, and the VLT port-channel link between the VLT peer connected to the source and ToR is down, traffic is duplicated due to route inconsistency between peers. To avoid this scenario, Dell Networking recommends configuring both the source and the receiver on a spanned VLT VLAN. • Bulk Sync happens only for Global IPv6 Neighbors; Link-local neighbor entries are not synced. • If all of the following conditions are true, MAC addresses may not be synced correctly: • VLT peers use VLT interconnect (VLTi) • Sticky MAC is enabled on an orphan port in the primary or secondary peer • MACs are currently inactive If this scenario occurs, use the clear mac-address-table sticky all command on the primary or secondary peer to correctly sync the MAC addresses. • If you enable static ARP on only one VLT peer, entries may be overwritten during bulk sync. • For multiple VLT LAGs configured on the same VLAN, if a host is learned on one VLT LAG and there is a station move between LAGs, the link local address redirects to the VLTi link on one of the peers. If this occurs, clear the link local address that is redirecting to the VLTi link. • VLT Heartbeat is supported only on default VRFs. • In a scenario where one hundred hosts are connected to a Peer1 on a non-VLT domain and traffic flows through Peer1 to Peer2; when you move these hosts from a non-VLT domain to a VLT domain and send ARP requests to Peer1, only half of these ARP requests reach Peer1, while the remaining half reach Peer2 (because of LAG hashing). The reason for this behavior is that Peer1 ignores the ARP requests that it receives on VLTi (ICL) and updates only the ARP requests that it receives on the local VLT. As a result, the remaining ARP requests still points to the Non-VLT links and traffic does not reach half of the hosts. To mitigate this issue, ensure that you configure the following settings on both the Peers (Peer1 and Peer2): arp learn-enable and mac-address-table stationmove refresh-arp. • In a topology in which two VLT peer nodes that are connected by a VLTi link and are connected to a ToR switch using a VLT LAG interface, if you configure an egress IP ACL and apply it on the VLT LAG of both peers using the deny ip any any command, the traffic is permitted on the VLT LAG instead of being denied. The correct behavior of dropping the traffic on the VLT LAG occurs when VLT is up on both the peer nodes. However, if VLT goes down on one of the peers, traffic traverses through VLTi and the other peer switches it to the VLT LAG. Although egress ACL is applied on the VLT nodes to deny all traffic, this egress ACL does not deny the traffic (switching traffic is not denied owing to the egress IP ACL). You cannot use egress ACLs to deny traffic properly in such a VLT scenario. • To support Q-in-Q over VLT, ICL is implicitly made as vlan-stack trunk port and the TPID of the ICL is set as 8100. • Layer 2 Protocol Tunneling is not supported in VLT. Configuration Notes When you configure VLT, the following conditions apply. • VLT domain • A VLT domain supports two chassis members, which appear as a single logical device to network access devices connected to VLT ports through a port channel. • A VLT domain consists of the two core chassis, the interconnect trunk, backup link, and the LAG members connected to attached devices. • Each VLT domain has a unique MAC address that you create or VLT creates automatically. • ARP tables are synchronized between the VLT peer nodes. • VLT peer switches operate as separate chassis with independent control and data planes for devices attached on non-VLT ports. • One device in the VLT domain is assigned a primary role; the other device takes the secondary role. The primary and secondary roles are required for scenarios when connectivity between the chassis is lost. VLT assigns the primary chassis role according to the lowest MAC address. You can configure the primary role manually. • In a VLT domain, the peer switches must run the same Dell Networking OS software version. Virtual Link Trunking (VLT) 951