Resilient/Consistent Hashing ECMP support for LAG

Resilient hashing is now supported by link aggregation groups (LAGs) and equal cost multipath (ECMP) sets. A LAG combines Ethernet interfaces (members) to form a logical point-to-point link that increases bandwidth, provides reliability, and allows load balancing. Resilient hashing enhances LAGs by minimizing destination remapping when a new member is added to or deleted from the LAG. Resilient hashing works in conjunction with the default static hashing algorithm. It distributes traffic across all members of a LAG by tracking the flow's LAG member utilization. When a flow is affected by a LAG member change, the packet forwarding engine (PFE) rebalances the flow by reprogramming the flow set table. Destination paths are remapped when a new member is added to or existing members are deleted from a LAG. Resilient hashing applies only to unicast traffic and supports a maximum of 1024 LAGs, with each group having a maximum of 256 members. An ECMP group for a route contains multiple next-hop equal cost addresses for the same destination in the routing table. (Routes of equal cost have the same preference and metric values.) Junos OS uses a hash algorithm to choose one of the next-hop addresses in the ECMP group to install in the forwarding table. Flows to the destination are rebalanced using resilient hashing. Resilient hashing enhances ECMPs by minimizing destination remapping when a new member is added to or deleted from the ECMP group.