When you set the link selection policy to Auto (the default setting), the BIG-IP®
system uses the lowest-numbered interface of the trunk as a reference link. (A
is a link that the BIG-IP system uses to make a link aggregation
decision.) The system then aggregates any links that have the same media properties and are
connected to the same peer as the reference link.
For example, suppose that you created a trunk to include interfaces 1.2 and 1.3, each with a
media speeds of 100 Mbps, and interface 1.4, with a different media speed of 1 Gbps. If you set
the link selection policy to Auto, the BIG-IP system uses the lowest-numbered interface, 1.2, as
a reference link. The reference link operates at a media speed of 100 Mbps, which means that the
system aggregates all links with that media speed (interfaces 1.2 and 1.3). The media speed of
interface 1.4 is different (1 Gbps), and therefore is not considered for link aggregation. Only
interfaces 1.2 and 1.3 become working member links and start carrying traffic.
If the media speed of interface 1.4 changes to 100 Mbps, the system adds that interface to the aggregation. Conversely, if the media speed of interface 1.4 remains at 1 Gbps, and the speed of the reference link changes to 1 Gbps, then interfaces 1.2 and 1.4 become working members, and 1.3 is now excluded from the aggregation and no longer carries traffic.