In this mode, multiple physical NICs (LAN cards) connected on the same network are connected and switching control of lines is performed based on the exclusive use. Also, a virtual interface is generated so that multiple NICs can be seen as one logical NIC. A TCP/IP application can conduct communication with the remote system, irrespective of the physical network redundant configuration, by using an IP address set in this virtual interface as its own IP address of the local system.
Figure 2.12 Example of duplicated operation in Virtual NIC mode
Duplicated NICs are connected to the same network. The remote system with which communication is to be carried out can be connected to either the same network or a different network via routers.
If each network device (such as the HUB and routers) has the duplicating function in a multi-vendor environment, this mode is effective when improving overall reliability in combination with these devices. In this case, the range of duplication is defined for each vendor.
This mode is appropriate, for example, to communications in a multi-vendor environment in which UNIX servers and PC servers of other companies are mixed.
Figure 2.13 System configuration in Virtual NIC mode shows a system configuration for Virtual NIC mode:
Figure 2.13 System configuration in Virtual NIC mode
The following explains each component and its meaning:
Indicates, of the duplicated NICs, the physical interface to be used first by activating it. An IP address is not set.
Indicates the physical interface to be used after switching when a line failure is detected in the Primary physical interface. An IP address is not set.
Indicates a local IP address for communication with the remote device. In Virtual NIC mode, it is possible to use both IPv4 and IPv6 addresses as an address form. This IP is set for a virtual interface.
Indicates the IP address of a monitored device (HUB) obtained when the Primary physical interface is used. In Virtual NIC mode, it is possible to use both IPv4 and IPv6 addresses as an address form.
Indicates the IP address of a monitored device (HUB) obtained when the Secondary physical interface is used. In Virtual NIC mode, it is possible to use both IPv4 and IPv6 addresses as an address form.
In Virtual NIC mode, link statuses of LAN cards and network communication statuses are both monitored.
Link status monitoring function
This function monitors the Ethernet link statuses of all duplicated LAN cards. When a link down occurred with a LAN card on the active side, a failover to a LAN card on the standby side is performed.
Network monitoring function
This function uses two methods listed below to monitor the network status to which a virtual interface is connected.
Type | Monitoring method |
|---|---|
HUB monitoring | A ping is sent periodically from active NICs to the switch/HUB to check whether the switch/HUB is operating normally. |
Standby patrol | A monitoring frame (proprietary Ethernet frame) is sent periodically from standby NICs to active NICs. This function checks that there is no error in active NICs and standby NICs, as well as in network devices on the transfer path between NICs. |
When a failure without link down has occurred in a network device and an error is detected by both monitoring methods, a failover to a standby NIC is performed. Likewise, failbacks can be effected automatically after detecting that the network has recovered.
Figure 2.14 Monitoring method in Virtual NIC mode
Switching operation changes the status of an active NIC into "inactive" state and then changes the status of standby NIC to "active" so that standby NIC can run as a new active device. At this point, the MAC address and IP addresses are taken over and then broadcast packet, in which the MAC address of the local node is set as the source, is sent. This operation notifies switch of a transfer path to HUB.
In addition, when a failure is detected, a message is output to notify an error to the system log.
Figure 2.15 Outline of switching operation performed when a failure occurs in Virtual NIC mode
If a relevant NIC recovers after NIC switching occurs due to failure detection, you must switch it back manually via hanetnic change command.
This command recovers the system and NIC to operate as an active NIC. In addition, if you setup a Standby Patrol Function, it automatically fails back the defective NIC without manually executing hanetnic change command.
Any system can be connected.
The requirement for user applications that can be operated in this mode is as follows:
Application using the TCP or UDP.
