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Cisco WAN Manager User’s Guide
Version 10.5, Part Number 78-12945-01 Rev. D0, August 2003
Chapter11 CWM to CWM Communications
Degrade Mode
Degrade Mode
The user is able to continue the provisioning of network data, even when communications between a
Primary CWM and Secondary CWM have been interrupted. If for any reason the communications
between CWM servers are interrupted, user data provisioning will be suspended on the Secondary
CWM, but user data provisioning will continue on the Primary CWM. During that time, the provisioning
of user data and monitoring of the network are not impacted. This is called the Degraded Mode of
Operation.
In order to provide CWM to CWM communications, a CWM workstation must be able to determine,
transparently to the network, if another CWM workstation is currently running in the network. This
requires IP connectivity between all CWM workstations. If all Secondary CWMs have lost IP
connectivity with the Primary CWM, then all Secondary CWMs will function in the degraded mode of
operation.
Degrade mode is defined by a loss of connectivity between the Primary CWM and any Secondary
CWMs, in which all Secondary CWMs are unable to provision user data, including the adding, deleting,
or modifying of user data, while waiting for a connection with the Primary CWM to be restored. In the
degrade mode a Secondary CWM can still manage the network data (not user data), and provisioning of
network data can still proceed.
Interruption in communications between CWMs may be due to some of the following failures:
• Failure Detection
• Unexpected Exit of the Primary CWMGateway
• Unexpected Exit of the Secondary CWMGateway
• Primary CWM has lost IP or physical connectivity to all Secondary CWMs
• One Secondary CWM has lost IP connectivity with the Primary CWM
• The CWMGateway process dies on the Primary CWM and is not re-started by watchdog.
• The CWM workstation crashed or was powered off
• Primary CWM has lost IP or physical connectivity with the only Secondary CWM in a domain
• Loss of Heartbeat from Primary CWMGateway
Recovering From Degrade Mode
Failure Detection
The failure recovery scenario involves handling the unexpected death of either the Primary
CWMGateway or a Secondary CWMGateway as well as handling the loss of IP connectivity between
the Primary and Secondary CWMGateways. Note, that the CWMGateway process will be launched by
watchdog, so that it can be automatically restarted if it dies unexpectedly. Also, an Orbix-specific
callback mechanism (CORBA::IT_IOCallback) would be used to indicate any break in connection
between the Primary CWMGateway and the Secondary CWMGateway processes. This will enable all
Secondary CWMGateway processes to detect whenever the Primary CWMGateway dies unexpectedly
and vice versa. Loss of a heartbeat message from the Primary CWMGateway in two consecutive
heartbeat intervals will indicate a loss of IP connectivity.