Specifications

Chapter 5. Planning 131
Layer 2 failover
Depending on the configuration, each compute node can have one IP address
per each Ethernet port, or it can have one virtual NIC consisting of two or more
physical interfaces with one IP address. This configuration is known as NIC
teaming technology. From an IBM Flex System perspective, NIC Teaming is
useful when you plan to implement high availability configurations with automatic
failover if there are internal or external uplink failures.
We can use only two ports on a compute node per virtual NIC for high availability
configurations. One port is active, and the other is standby. One port (for
example, the active port) is connected to the switch in I/O bay 1, and the other
port (for example, the standby port) is to be connected to the switch in I/O bay 2.
If you plan to use an Ethernet expansion card for high availability configurations,
then the same rules apply. Active and standby ports need to be connected to a
switch on separate bays.
If there is an internal port or link failure of the active NIC, the teaming driver
switches the port roles. The standby port becomes active and the active port
becomes standby. This action is done quickly, within a few seconds. After
restoring the failed link, the teaming driver can perform a failback or can do
nothing, depending on the configuration.
Look at topology 1 in Figure 5-1 on page 129. Assume that NIC Teaming is on,
the compute node NIC port connected to switch 1 is active, and the other node is
on standby. If something goes wrong with the internal link to switch 1, then the
teaming driver detects the status of NIC port failure and performs a failover. But
what happens if external connections are lost (the connection from chassis
switch 1 to Enterprise Switch 1 is lost)? The answer is that nothing happens
because the internal link is still on and the teaming driver does not detect any
failure. So the network service becomes unavailable.
To address this issue, the Layer 2 Failover technique is used. Layer 2 Failover
can disable all internal ports on the switch module if there is an upstream links
failure. A disabled port means no link, so the NIC Teaming driver performs a
failover. This special feature is supported on the IBM Flex System and
BladeCenter switch modules. Thus, if Layer 2 Failover is enabled and you lose
connectivity with Enterprise Switch 1, then the NIC Teaming driver performs a
failover and the service is available through Enterprise Switch 2 and chassis
switch 2.
Layer 2 Failover is used with NIC active or standby teaming. Before using NIC
Teaming, verify whether it is supported by the operating system and applications.