Switch Stack Mac Addressing And Stack Design Considerations; Nsf Network Design Considerations - Dell PowerConnect 8024 User Configuration Manual

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Switch Stack MAC Addressing and Stack Design Considerations

The switch stack uses the MAC addresses assigned to the stack master.

Each switch is assigned three consecutive MAC addresses. The switch

uses the MAC addresses for the service port, network port, and routing

interfaces. A stack of switches uses the MAC addresses assigned to the stack

If the backup unit assumes control due to a stack master failure or warm

restart, the backup unit continues to use the original stack master's MAC

addresses. This reduces the amount of disruption to the network because

ARP and other L2 entries in neighbor tables remain valid after the failover to

the backup unit.

Stack units should always be connected with a ring topology (or other

biconnected topology), so that the loss of a single stack link does not divide

the stack into multiple stacks. If a stack is partitioned such that some units

lose all connectivity to other units, then both parts of the stack start using the

same MAC addresses. This can cause severe problems in the network.

If you move the stack master to a different place in the network, make sure

you power down the whole stack before you redeploy the stack master so that

the stack members do not continue to use the MAC address of the redeployed

You can design your network to take maximum advantage of NSF. For

example, by distributing a LAG's member ports across multiple units, the

stack can quickly switch traffic from a port on a failed unit to a port on a

surviving unit. When a unit fails, the forwarding plane of surviving units

removes LAG members on the failed unit so that it only forwards traffic onto

LAG members that remain up. If a LAG is left with no active members, the

LAG goes down. To prevent a LAG from going down, configure LAGs with

members on multiple units within the stack, when possible. If a stack unit

fails, the system can continue to forward on the remaining members of the

Managing a Switch Stack

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