Beta Draft Confidential
Redundancy
Redundancy Manager
D-6
4/5/03
CBX 500 Multiservice WAN Switch Hardware Installation Guide
Keep-Alive Monitoring
Redundant modules (active and standby) monitor each other's integrity through the
use of a keep-alive protocol. The Redundancy Manager in each module exchanges
keep-alive messages over the cell bus, and the redundant or standby module initiates
the poll.
The switch uses the following keep-alive timers and counters to determine the status
of an active module:
Keep-Alive Poll Timer — Triggers the transmission of keep-alive messages from the
redundant module to the active module. This value is set to expire every 0.5 seconds.
Keep-Alive Poll Counter — Dictates the number of consecutive keep-alive
responses from the active module that the redundant module can miss before it
“shoots” the active module. (“Shooting” the module reboots the active module and
enables the redundant module.) This value is set to 3.
Keep-Alive Poll Verification Timer — Verifies the active module’s receipt of
keep-alive messages from the redundant module. This value is set for 1 second and is
reset each time a keep-alive is received by the active module.
Keep-Alive Poll Verification Counter — Verifies the number of consecutive Keep
Alive Poll Timer time-outs received before “shooting” the redundant module and
reporting a problem. This value is set to 3.
In redundant configurations, keep-alive monitoring occurs as follows:
•
The redundant module initiates a “Hello” message to the active module, as set by
the expiration of the Keep-Alive Poll Timer.
•
For each keep-alive poll the active module receives, the active module sends a
response back to the redundant module.
•
If the redundant module does not receive responses according to the value set in
the Keep Alive Poll Counter, it assumes that the active module has failed and
shoots the active module using special redundancy hardware.
•
The redundant module performs a warm boot and takes over operation as the
active module.
