Dell S4048-ON, Руководство по настройке

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Primary and Secondary VLT Peers
To prevent issues when connectivity between peers is lost, you can designate Primary and Secondary roles for VLT peers . You can
elect or configure the Primary Peer. By default, the peer with the lowest MAC address is selected as the Primary Peer. You can
configure another peer as the Primary Peer using the VLT
domain domain-id role priority priority-value
command.
If the VLTi link fails, the status of the remote VLT Primary Peer is checked using the backup link. If the remote VLT Primary Peer is
available, the Secondary Peer disables all VLT ports to prevent loops.
If all ports in the VLTi link fail or if the communication between VLTi links fails, VLT checks the backup link to determine the cause of
the failure. If the failed peer can still transmit heartbeat messages, the Secondary Peer disables all VLT member ports and any Layer
3 interfaces attached to the VLAN associated with the VLT domain. If heartbeat messages are not received, the Secondary Peer
forwards traffic assumes the role of the Primary Peer. If the original Primary Peer is restored, the VLT peer reassigned as the Primary
Peer retains this role and the other peer must be reassigned as a Secondary Peer. Peer role changes are reported as SNMP traps.
RSTP and VLT
VLT provides loop-free redundant topologies and does not require RSTP.
RSTP can cause temporary port state blocking and may cause topology changes after link or node failures. Spanning tree topology
changes are distributed to the entire layer 2 network, which can cause a network-wide flush of learned MAC and ARP addresses,
requiring these addresses to be re-learned. However, enabling RSTP can detect potential loops caused by non-system issues such as
cabling errors or incorrect configurations. To minimize possible topology changes after link or node failure, RSTP is useful for potential
loop detection. Configure RSTP using the following specifications.
The following recommendations help you avoid these issues and the associated traffic loss caused by using RSTP when you enable
VLT on both VLT peers:
• Configure any ports at the edge of the spanning tree’s operating domain as edge ports, which are directly connected to end
stations or server racks. Disable RSTP on ports connected directly to Layer 3-only routers not running STP or configure them as
edge ports.
• Ensure that the primary VLT node is the root bridge and the secondary VLT peer node has the second-best bridge ID in the
network. If the primary VLT peer node fails, the secondary VLT peer node becomes the root bridge, avoiding problems with
spanning tree port state changes that occur when a VLT node fails or recovers.
• Even with this configuration, if the node has non-VLT ports using RSTP that you did not configure as edge ports and are
connected to other Layer 2 switches, spanning tree topology changes are still detected after VLT node recovery. To avoid this
scenario, ensure that you configure any non-VLT ports as edge ports or disable RSTP.
VLT Bandwidth Monitoring
When bandwidth usage of the VLTi (ICL) exceeds 80%, a syslog error message (shown in the following message) and an SNMP trap
are generated.
%STKUNIT0-M:CP %VLTMGR-6-VLT-LAG-ICL: Overall Bandwidth utilization of VLT-ICL-LAG (port-
channel 25)
crosses threshold. Bandwidth usage (80 )
When the bandwidth usage drops below the 80% threshold, the system generates another syslog message (shown in the following
message) and an SNMP trap.
%STKUNIT0-M:CP %VLTMGR-6-VLT-LAG-ICL: Overall Bandwidth utilization of VLT-ICL-LAG (port-
channel 25)
reaches below threshold. Bandwidth usage (74 )VLT show remote port channel status
VLT and Stacking
You cannot enable stacking on S4048–ON units with VLT.
If you enable stacking on a unit on which you want to enable VLT, you must first remove the unit from the existing stack. For
information about how to remove a unit from a stack, refer to
Removing a Unit from an S-Series Stack . After you remove the unit,
you can configure VLT on the unit.
Virtual Link Trunking (VLT)
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