Cabletron Systems 9A426-01, Руководство пользователя

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Introduction
Redundancy
To ensure the transmission of data from a 9A426-01 Module to an ATM backbone,
the module offers an additional “redundant” front panel port. Redundancy can be
achieved by inserting a second APIM in the module’s front panel APIM port,
connecting cables to that APIM, and enabling the redundancy feature via SNMP
(network management) of the module (you can also disable redundancy via
network management). Only one APIM port on the module can be active at one
time. The inactive port, if occupied, serves as the “redundant APIM”.
The 9A426-01 Module also provides users with a variety of options to monitor
and control redundancy. First, a user can select which port is the “primary” port
and which port is the “redundant” port. This feature allows the user to select a
port with more (or less) bandwidth according to the importance of the network
uplink and the cost of the connection.
A second feature of redundancy on the 9A426-01 Module is the ability to test both
APIM links at any time. This test reassures the user that if one port fails, the other
redundant port (and associated connections) will function properly. This feature
allows the user to correct any cabling errors or deficiencies while in a test status as
opposed to real-time status.
A third feature of redundancy on the 9A426-01 Module is evident when an actual
switch (failover) to the redundant link occurs. At that time, the module will audit
the primary link (at a user-selectable time of day) to determine if that link is once
again able to function. If the primary link is able to function, the module will
switch back to the primary link. The “time of day” option provides users with the
ability to check the primary port’s condition during “off peak hours” to minimize
network disruption.
The process of switching to a redundant link is a multiple step procedure. First,
the module severs its connections to all ELANs. The module then proceeds to find
a redundant link. During the re-establishment of connections, all communications
to ELAN services cease. Once the redundant link is established as the new link, all
of the primary link’s ELAN configuration information and PVC data is “carried
over” to the active link.
For example, if the module’s primary link was connected to ELAN1, and the
primary link became unusable, the module will sever its connection to ELAN1,
immediately switch to the module’s redundant link, and then begin to re-
establish communications with ELAN1 (by making a request to join ELAN1).
Once the join process is completed (connecting to the LES and BUS), data
communications will commence. All connections that map MAC to ATM
information will be flushed. This MAC to ATM table will be re-established the
first time the legacy LAN systems attempts to communicate across the ATM.