Specifications

Chapter 2. IBM System Networking Switch 10Gb Ethernet switch features 81
Monitoring trunk links
Layer 2 Failover can be enabled on any trunk group in IBM System Networking switches,
including LACP trunks. Trunks can be added to failover trigger groups. Then, if some
specified number of monitor links fail, the switch disables all the control ports in the switch.
When the control ports are disabled, it causes the NIC team on the affected servers to fail
over from the primary to the backup NIC. This process is called a failover event.
When the appropriate number of links in a monitor group return to service, the switch enables
the control ports. This configuration causes the NIC team on the affected servers to fail back
to the primary switch (unless Auto-Fallback is disabled on the NIC team). The backup switch
processes traffic until the primary switch’s control links come up, which can take up to
5 seconds.
Figure 2-14 is a simple example of Layer 2 Failover. One switch is the primary, and the other
is used as a backup. In this example, all ports on the primary switch belong to a single trunk
group, with Layer 2 Failover enabled, and Failover Limit set to 2. If two or fewer links in trigger
1 remain active, the switch temporarily disables all control ports. This action causes a failover
event on Server 1 and Server 2.
This feature is also referred to as
Uplink Failure Detection. The switch constantly monitors
the port or port trunk group to the Core Network. When a failure is detected, the switch
disables the pre-configured ports connected to the servers.
Figure 2-14 Basic Layer 2 Failover
Setting the failover limit
You can use the failover limit to specify the minimum number of operational links required
within each trigger before the trigger initiates a failover event. For example, if the limit is two,
a failover event occurs when the number of operational links in the trigger is two or fewer.
When you set the limit to zero, the switch triggers a failover event only when no links in the
trigger are operational.
Manually monitoring port links
You can use the Manual Monitor to configure a set of ports or trunks to monitor for link
failures (a monitor list), and another set of ports or trunks to disable when the trigger limit is
reached (a control list). When the switch detects a link failure on the monitor list, it
automatically disables the items in control list. When server ports are disabled, the
corresponding server’s network adapter can detect the disabled link, and trigger a
network-adapter failover to another port or trunk on the switch, or another switch.
The switch automatically enables the control list items when the monitor list items return
to service.
Layer 2 Failover with other features
Layer 2 Failover works together with static trunks, LACP, and STP.