Understanding Link Aggregation
You can combine multiple physical Ethernet ports to form a logical point-to-point link, known as a link aggregation group (LAG) or bundle. A LAG provides more bandwidth than a single Ethernet link can provide. Additionally, link aggregation provides network redundancy by load-balancing traffic across all available links. If one of the links fails, the system automatically load-balances traffic across all remaining links. In a Virtual Chassis, LAGs can be used to load-balance network traffic between member routers.
The maximum number of interfaces that can be grouped into a LAG and the maximum number of LAGs supported on a router varies according to the router model and the version of and the version of Juniper Networks Junos operating system (Junos OS) that is running on that router.