Reference Guide

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Virtual IP
You can manage the stack using a single IP, known as a virtual IP, that is retained in the stack even after a
failover.
The virtual IP address is used to log in to the current master unit of the stack. Both IPv4 and IPv6
addresses are supported as virtual IPs.
Failover Roles
If the stack master fails (for example, is powered off), it is removed from the stack topology.
The standby unit detects the loss of peering communication and takes ownership of the stack
management, switching from the standby role to the master role. The distributed forwarding tables are
retained during the failover, as is the stack MAC address. The lack of a standby unit triggers an election
within the remaining units for a standby role.
After the former master switch recovers, despite having a higher priority or MAC address, it does not
recover its master role but instead takes the next available role.
To view failover details, use the show redundancy command.
MAC Addressing on S-Series Stacks
The S-Series has three MAC addresses: the chassis MAC, interface MAC, and null interface MAC.
All interfaces in the stack use the interface MAC address of the management unit, and the chassis MAC
for the stack is the master’s chassis MAC. The stack continues to use the master’s chassis MAC address
even after a failover. The MAC address is not refreshed until the stack is reloaded and a different unit
becomes the stack manager.
NOTE: If the removed management unit is brought up as a standalone unit or as part of a different
stack, there is a possibility of MAC address collisions.
A standalone is added to a stack. The standalone and the master unit have the same priority, but the
standalone has a lower MAC address, so the standalone reboots. In the second example, a standalone is
added to a stack. The standalone has a higher priority than the stack, so the stack (excluding the new
unit) reloads.
Example of Adding a Standalone with a Lower MAC Address to a Stack (S50 — Before)
Example of Adding a Standalone with a Lower MAC Address and Equal Priority to a Stack (S50 — After)
----------STANDALONE BEFORE CONNECTION---------------
Standalone#show system brief
Stack MAC : 00:01:e8:d5:ef:81
-- Stack Info --
Unit UnitType Status ReqTyp CurTyp Version Ports
Stacking
891