The HUB monitoring function issues the ping command to adjacent HUB at regular intervals and switches the interface to be used when a line failure is detected. Up to two HUBs can be registered per virtual interface. This function is available exclusively for NIC switching mode.
This function can also monitor a transfer path between two HUBs (this is called HUB-to-HUB monitoring function). HUB-to-HUB monitoring function detects a failure between two HUBs. This function can thus prevent a communication error from occurring due to NIC switching when a HUB-to-HUB failure occurs.
Information
If the standby patrol function is used, the HUB-to-HUB monitoring is not required because the standby patrol function is comprised with HUB-to-HUB monitoring function. (See section "2.4.2 Standby patrol function")
Figure 2.34 HUB monitoring function shows an outline of the HUB monitoring function
Figure 2.34 HUB monitoring function
Point
If a hub cannot have an IP address, IP address of a host or a router that is connected to the hub can be monitored. However, if the monitored host or router stops, polling the host or router fails and a NIC switching event might occur. In order to prevent an unnecessary switching process, it is recommended to set up two monitoring targets, as well as enabling HUB-to-HUB monitoring function in case one of the monitoring targets stops.
Note
Refer to "7.7 hanetpoll Command" for configuration of HUB-to-HUB monitoring feature.
It is not recommended to operate with a single HUB. It is possible to have only one configuration for a remote end when using a single HUB. However, it defeats the purpose of multiplexing transfer paths if the HUB breaks.
If the operation starts without HUB-to-HUB monitoring function, the primary HUB (Switch/HUB1 in the Figure 2.35 HUB-to-HUB monitoring disabled) is monitored using the ping command. When a failure is detected in the primary HUB, the NIC of the currently active system is inactivated and then the standby NIC is activated. After the standby NIC is activated, the secondary HUB (Switch/HUB2 in the Figure 2.35 HUB-to-HUB monitoring disabled) is monitored using the ping command.
Figure 2.35 HUB-to-HUB monitoring disabled
If the operation starts using the HUB-to-HUB monitoring function, the secondary HUB (Switch/HUB2 in the Figure 2.36 HUB-to-HUB monitoring enabled (failure on the secondary monitoring)) is monitored using the ping command.
When a failure is detected on the secondary hub, HUB-to-HUB monitoring function starts polling the primary hub, as well as polling the secondary hub (Switch/HUB1 in Figure 2.36 HUB-to-HUB monitoring enabled (failure on the secondary monitoring)).
(During this occasion, a monitoring failure message (No.872) regarding the secondary HUB will be output. Use this message to investigate the cause of the failure)
Once the polling process on the primary HUB starts, this function then monitors both secondary and primary HUBs interchangeably. Monitoring process against the secondary HUB is recovery monitoring and it will stop monitoring the primary HUB when HUB-to-HUB monitoring function detects recovery of the secondary HUB. HUB-to-HUB monitoring function determines transfer path failure by checking the number of monitoring failures (the default is 5 times). If failures were detected repeatedly on both primary and secondary HUBs, then it determines there was transfer path failure. Note that a message (No.872) will be reported regarding the failure on the secondary HUB, therefore it is possible to recover the secondary HUB before the primary HUB switches to secondary HUB.
Also, when a failure is detected in the primary HUB after switching to the secondary interface with transfer path failure, a message (No.873) will be output.
Figure 2.36 HUB-to-HUB monitoring enabled (failure on the secondary monitoring)
Figure 2.37 HUB-to-HUB monitoring enabled (failure on the primary monitoring)
