Different factors can cause an interface to become unusable, such as an interface failure or interfaces being taken offline for maintenance. Without IPMP, the system can no longer be contacted by using any of the IP addresses that are associated with that unusable interface. Additionally, existing connections that use those IP addresses are disrupted.
With IPMP, multiple IP interfaces can be configured into an IPMP group. The group functions like an IP interface with data addresses to send or receive network traffic. If an underlying interface in the group fails, the data addresses are redistributed amongst the remaining underlying active interfaces in the group. Thus, the group maintains network connectivity despite an interface failure. With IPMP, network connectivity is always available, provided that a minimum of one interface is usable for the group.
IPMP also improves overall network performance by automatically spreading outbound network traffic across the set of interfaces within the IPMP group. This process is called outbound load spreading. The system also indirectly controls inbound load spreading by performing source address selection for packets whose IP source address was not specified by the application. However, if an application has explicitly chosen an IP source address, then the system does not vary that source address.
Note the following important information about the policies that IPMP enforces for inbound and outbound load spreading:
For on-link IP addresses, IPMP randomly selects a single active IP interface to reach that IP address. In the case where there are multiple, distinct connections for a given on-link IP address, all of those connections will use the same outbound IP interface. In addition, if the IP interface changes over time, the change affects all of the connections to that IP address.
For off-link IP addresses, IPMP randomly selects a single IP interface to reach the IP address of the on-link IP router through which the off-link IP address with be reached. This policy effectively means that all off-link IP addresses for a given IPMP group use a single IP interface.
Link aggregations perform functions that are similar to IPMP to improve network performance and availability. To compare these two technologies, see Appendix A, Link Aggregations and IPMP: Feature Comparison, in Managing Network Datalinks in Oracle Solaris 11.2 .