IGPs (IS-IS, OSPF, EIGRP) and BGP solve different problems and networks often need both. Some niche networks get away with using only BGP (massive datacenters), and some get away with using only an IGP (smaller networks), and some don't even need that (small networks).
IGPs (IS-IS, OSPF, EIGRP) and BGP solve different problems and networks often need both. Some niche networks get away with using only BGP (massive datacenters), and some get away with using only an IGP (smaller networks), and some don't even need that (small networks).