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Ethernet Hot Standby Solution
840 USE 106 00 January 2003 171
Power-Up and
Ethernet
Services
The process of powering up affects the status of client/server services. To clarify
what happens during a power-up, the following section describes the power-up
effects on the Ethernet services.
The following table shows how the status of an NOE service is affected by the Hot
Standby state.
Hot Standby
Switchover
The following steps describe how NOEs coordinate the Hot Standby switchover.
HSBY State Status of NOE Services
Client Services Client/
Server
Services
Server Services
I/O Scanner Global Data Modbus
Messaging
FTP SNMP HTTP
Unassigned Run Run Run Run Run Run
Primary Run Run Run Run Run Run
Secondary Stop Stop Run Run Run Run
Offline Stop Stop Run Run Run Run
Step Action
1 NOE A (installed in a HSBY rack) detects that is local controller changed from
Primary to Offline.
2 NOE A changes its HSBY state from Primary to Offline with the same Ethernet
services running, starts its watch-dog timer (with 500 ms timeout setting), and
expects from its peer NOE an UDP request to swap the IP Address.
3 NOE B (installed in peer HSBY rack) detects that its local controller changed
state from Secondary to Primary.
4 NOE B stops all Ethernet services, sends an UDP request to its peer NOE (NOE
A) for the synchronization of the IP Address swap, starts its watch-dog timer
(with 500 ms timeout setting), and then waits for an UDP response from its peer
NOE.
5 Once NOE A receives the UDP request from NOE B (or after its watch-dog timer
times out), it stops all Ethernet services, sends an UDP response to NOE B (no
UDP response is sent to NOE B for watch-dog timeout case), swaps IP Address
as Secondary, and starts Secondary services.
6 As soon as NOE B receives the UDP response from NOE A (or after its watch-
dog timer times out), it swaps IP Addresses and starts Ethernet services as
Primary.
7 After NOE A senses that its local controller changes state from Offline to
Standby, it changes to Secondary accordingly.