Allied Telesis AT-2700FX Installation Manual page 41

Fail-over Protection
Another feature of the LBFO driver is fail-over protection. This feature is
useful in situations where a network device could benefit from link
redundancy, but not necessarily load balancing. The fail-over feature
protects against a loss of network connectivity should an adapter lose its
link to a remote device or the remote device loses power or is taken out of
service, such as for maintenance. When the link is lost on the primary
adapter, the redundant adapter automatically takes over the task of
sending and receiving network traffic.
There are two possible configurations for this feature. In the first
configuration both the primary link and the redundant link are connected to
the same remote node. This is illustrated in Figure 1 where the links from a
server containing two network adapter cards both go to the same Ethernet
switch. If the primary link should fail, the redundant link automatically takes
over, preventing a loss of network connectivity to the server.
Redundant
Figure 1. Fail-over Protection - Configuration #1
The drawback to this configuration is that it does not protect against a loss
of network access to the server should the switch lose power or be
removed from service. Fortunately, with fail-over protection the links can
go to different remote nodes. An example is illustrated in Figure 2 where
the primary and redundant links of the two adapters in the server go to
different Ethernet switches. Now, if the switch where the primary link is
connected loses power or is removed from service, network connectivity to
the server continues uninterrupted through the other Ethernet switch.
Redundant
Figure 2. Fail-over Protection - Configuration #2
Primary
Link
Link
Primary
Link
Link
Network Adapter Card Installation Guide
41