IBM 8271 Nways F12 User Manual page 87

What is the Switch Database?
The Switch Database is used by the stack to determine if a packet
should be forwarded, and which port should forward the packet if it is
to be forwarded. The database contains a list of entries, each
containing two items:
The MAC (Ethernet) address information from each endstation that
sends packets to the stack.
The port in the stack that receives packets from that endstation.
The number of addresses that the database can hold depends on the
number of Switch units in the stack. Each Model F12/F24 provides
support for 12,000 addresses, and each Model E12/E24 provides
support for 6,000 addresses.
Databases entries can have two states:
Learned — The stack has placed the entry into the Switch Database
when a packet was received. Learned entries are removed (aged
out) from the Switch Database if the stack does not receive packets
from that endstation for 30 minutes. This prevents the Switch
Database from becoming full with obsolete entries by ensuring that
when an endstation is removed from the network, its entry is also
removed from the database. Learned entries are also removed from
the Switch Database if the Switch that submitted the entry is reset
or powered-down.
Permanent — The entry has been placed into the Switch Database
using the Switch Database page. Permanent Entries are not removed
from the Switch Database unless they are deleted using the Switch
Database page.
Displaying the Switch Database
The Display Database Entries table of the Switch Database page
displays the Switch Database entries for the stack:
Unit 1 / 2 / 3 / 4
Displays the Switch unit in the stack that contains the port for the
entry.
Port
Displays the port for the entry.
Configuring the Stack 4-27