156 Managing a Switch StackSwitch Stack MAC Addressing and Stack Design ConsiderationsThe switch stack uses the MAC addresses assigned to the stack master.If the backup unit assumes control due to a stack master failure or warmrestart, the backup unit continues to use the original stack master’s MACaddresses. This reduces the amount of disruption to the network becauseARP and other L2 entries in neighbor tables remain valid after the failover tothe backup unit.Stack units should always be connected with a ring topology (or otherbiconnected topology), so that the loss of a single stack link does not dividethe stack into multiple stacks. If a stack is partitioned such that some unitslose all connectivity to other units, then both parts of the stack start using thesame MAC addresses. This can cause severe problems in the network.If you move the stack master to a different place in the network, make sureyou power down the whole stack before you redeploy the stack master so thatthe stack members do not continue to use the MAC address of the redeployedswitch.NSF Network Design ConsiderationsYou can design your network to take maximum advantage of NSF. Forexample, by distributing a LAG's member ports across multiple units, thestack can quickly switch traffic from a port on a failed unit to a port on asurviving unit. When a unit fails, the forwarding plane of surviving unitsremoves LAG members on the failed unit so that it only forwards traffic ontoSIM The system's MAC addresses. System up time. IP address,network mask, default gateway on each managementinterface, DHCPv6 acquired IPv6 address.Voice VLAN VoIP phones identified by CDP or DHCP (not LLDP)NOTE: Each switch is assigned three consecutive MAC addresses. The switchuses the MAC addresses for the service port, network port, and routinginterfaces. A stack of switches uses the MAC addresses assigned to the stackmaster.Table 8-1. Applications that Checkpoint DataApplication Checkpointed Data
