Chapter 1. IntroductionGFK-2224Q January 2017 15Web Server Operation in a Redundancy SystemOnly the active unit processes Web server requests at the Redundant IP address and responds to Web pagerequests. The backup unit does not respond to the Redundant IP address. When the active Ethernet interfacechanges to backup, it takes down all Web server connections and their underlying TCP connections. The Webserver maintains its underlying TCP connection only long enough to process each web page request; a new TCPconnection is opened, used, and closed for each subsequent Web page display or update. So unless a Web pagechange or update is requested during the redundancy role switch, the operation of the Redundant IP address istransparent to the Web remote browser. Any Web page request in process over the Redundant IP when a roleswitch occurs is terminated.Although not recommended, the remote browser may issue Web server requests to the direct IP address. Boththe active and backup units respond to Web server requests received at the direct IP address. Remote Webbrowsers are expected to use the Redundant IP address when communicating to a redundant system.FTP Operation in a Redundancy SystemFTP operations are used to transfer setup and configuration data to the Ethernet interface, not forcommunication with the actual PLC application. Therefore, FTP operations should only be performed using thedirect IP address.SNTP Operation in a Redundancy SystemA PACSystems Ethernet Interface can operate as an SNTP client only, so it only receives broadcast timemessages from an SNTP Server on the network. SNTP operation is unaffected by the current Ethernetredundancy state or by redundancy role switches.Remote Station Manager Operation in a Redundancy SystemThe remote Station Manager should respond to the direct IP address regardless of whether the unit is active orbackup, or whether or not Redundant IP is configured.Only the active unit responds to remote Station Manager commands at the Redundant IP address. The backupunit does not respond to the Redundant IP address. (Station Manager responses from the Redundant IP addresscan be misleading because it is difficult to determine which Ethernet interface is actually responding.)IP Address Configuration in a Redundancy SystemRedundancy systems should explicitly configure both the direct IP address and the Redundant IP address. Donot set up the direct IP address via BOOTP.The Redundant IP address must be configured on the same local sub-network as the direct IP address andgateway IP address (if used).
