Border Gateway Protocol or BGP, to be precise, does not load balance, since (by default) it selects only a solo best path, while the reason that it does not load balance since it is an application and not a routing protocol. As for the sake of arguments, routing protocols such as RIP, EIGRP, IGRP, OSPF are capable of distributing the outgoing/ incoming traffic among multiple path.

Also, BGP is an attribute of the routing table negative to the interface, based on what you assign to your IGP is what could be promoted into BGP. True, BGP uses port 179 for transport, while OPSF uses port 89 and EIGRP 88 etc., but who does the routing lookup for the next hop destination – that is IGP not BGP. IGP will manage most load balance automatically but in the BGP scenario, it is done manually in order to allow multipath eBGP with the number of paths to install using the maximum-path which means that the next hop address for each path must also be different in order for that path to be taken into account. Therefore, unless you have your own “AS” on the internet BGP load balance is not suited for your network as because what happens when you have two different ISP?

However, mid-sized ISPs that have tried to implement BGP load balancing as a means to multi-home two or more gateways will concur about the technical difficulties involved in setting up BGP. Configuring the optimum route announcements to other BGP peers to achieve a balanced traffic flow is equally difficult. Especially load balancing inbound traffic to a multi-homed network over several inbound paths becomes positively challenging because of the limitations of the BGP route selection process. Fundamentally, BGP load balancing requires the network administrator to divide a large IP address block into smaller blocks and tweak the route announcement to spread the blocks so that they look optimal on the different routes, as otherwise the external networks may all pick a specific route and create congestion on that one specific route, creating chaos.