1.1.b Identify Cisco express forwarding concepts

1.1.b [ii] Load balancing Hash

In a router, act of distributing packets across multiple links based on layer 3 routing information is known as load balancing. If a router discovers multiple paths to a destination, the routing table is updated with multiple entries for that destination.

Usually the paths have the same metric, however there are routing protocols that allow unequal cost (or metric) load balancing. A router learns about the existence of parallel paths through the routing protocols and builds its routing table accordingly.

The number of paths used is limited by the number of entries the given IP routing protocol puts in the routing table, the default in IOS is 4 entries for most routing protocols with the exception of BGP, where it is one entry (only the best path). The maximum number of paths that can be configured are 6.

Cisco IOS supports two primary modes of load balancing, i.e. per-destination and per-packet basis.

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 905-911).  . Kindle Edition.