BGP Multipath
BGP on its own will not install multiple paths like OSPF or EIGRP to reach a destination.
To make BGP behave more like an IGP, and especially at scale with multiple ECMP links, this feature is needed.
Topology
R1 is connected to the ISP via two eBGP links.
eBGP on it’s own will install one best path.
┌─ eBGP ─┐
▼ ▼
┌────────┐ ┌────────┐
│ R1 ├────────┤ ISP │
│AS 64496├────────┤AS 64511│
└────────┘ └────────┘
R1(config-router)# maximum-paths ibgp maximum-number
References
Cisco Live - A Deep Dive into Basic and Design Best Practices for BGP and L3VPN