Configuration manual

• If you reboot both VLT peers in BMP mode and the VLT LAGs are static, the DHCP server reply to the
DHCP discover offer may not be forwarded by the ToR to the correct node. To avoid this scenario,
configure the VLT LAGs to the ToR and the ToR port channel to the VLT peers with LACP. If supported
by the ToR, enable the lacp-ungroup feature on the ToR using the lacp ungroup member-
independent port-channel command.
• If the lacp-ungroup feature is not supported on the ToR, reboot the VLT peers one at a time. After
rebooting, verify that VLTi (ICL) is active before attempting DHCP connectivity.
• When you enable IGMP snooping on the VLT peers, ensure the value of the delay-restore
command is not less than the query interval.
• When you enable Layer 3 routing protocols on VLT peers, make sure the delay-restore timer is set to a
value that allows sufficient time for all routes to establish adjacency and exchange all the L3 routes
between the VLT peers before you enable the VLT ports.
• Only use the lacp ungroup member-independent command if the system connects to nodes
using bare metal provisioning (BMP) to upgrade or boot from the network.
• Ensure that you configure all port channels where LACP ungroup is applicable as hybrid ports and as
untagged members of a VLAN. BMP uses untagged dynamic host configuration protocol (DHCP)
packets to communicate with the DHCP server.
• 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) port-channel, 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.
• 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.
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 chassis in the VLT domain is assigned a primary role; the other chassis 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.
– In a VLT domain, the peer switches must run the same Dell Networking operating system (OS)
software version.
– Separately configure each VLT peer switch with the same VLT domain ID and the VLT version. If
the system detects mismatches between VLT peer switches in the VLT domain ID or VLT version,
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Virtual Link Trunking (VLT)