Installation and Reference Guide HP AdvanceStack 100Base-THub-12TX, Hub-12TXM, and Switch Modules 1997-06

HP Hub-12TX/Hub-12TXM Installation and Reference Guide
Setting Up Network Connections 3-3
Using Management Agents
The Hub-12TXM includes an SNMP management agent. To add
SNMP functionality to an entire stack, a Hub-12TXM must be
included in the stack. You may include multiple agents in a
stack to provide a fail-safe backup management agent.
SNMP Backup Agent
The AdvanceStack Hub-12TX/Hub-12TXM system supports a
backup function for the management agent. This special
function allows the stack to have two or more SNMP network
management agents, wherein one agent is configured as the
Master agent and others as Backup agents.
The agent in backup mode behaves as a Hub-12TX. But if the
Master agent fails, the Backup agent takes over its functions
using the latest data mirrored from the Master, including its IP
address. Note that to manage the stack out-of-band after the
Backup has assumed control, you must plug your PC or modem
into the serial port of the Backup agent. If you are using HP
AdvanceStack Assistant, just ensure that your network
management station can access the new control agent via its
current network connection.
Note: Placing redundant agents in a stack will cause the system to
set the agent at the top of the Stacking Cable chain as the Master, and
the others as Backups. If more than one backup exists in a stack, the
backup agent higher up the Stacking Cable chain will be chosen to
function as the Master if it fails. Moreover, if a new agent is added to the
top of the Stacking Cable chain, the system will set this as the Master
and mirror the latest data from the agent with the longest up-time.