the use of IGP is almost always recommended with or without route reflection and/or BGP confederations.
The reason is that iBGP sessions are usually configured using loopback addresses for better stability as session endpoints.
The IGP solves the problem of routing exchange of loopback addresses making them routable in the AS domain easily.
Both BGP route reflectors and BGP confederations are ways to achieve scalability in an iBGP deployment as they allow to minimize the total number of iBGP sessions in the domain.
In fact, without these two features each iBGP peer should have a direct iBGP session with every other iBGP device in the domain leading to N*(N-1)/2 BGP sessions that would overcome the capabilities of a single device (here N is the number of iBGP devices in the AS).
So the IGP provides IP reachability between endpoints and the other two features are scalability tools with route reflection far more used then BGP confederations.
In some specific environment like a bank network I have seen the case of use of BGP without an underlying IGP but I would say it is more an execption then the common rule
We are pleased to announce availability of Beta software for 16.6.3.
16.6.3 will be the second rebuild on the 16.6 release train targeted
towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are
looking for early feedback from customers befor...
Introduction Featured Speakers Luis Espejel is the Telecommunications
Manager of IENova, an Oil & Gas company. Currently he works with Cisco
IOS® and Cisco IOS XE platforms, and NX to some extent. He has also
worked as a Senior Engineer with the Routing P...
In this session you can learn more about Layer 3 multicast and the best
practices to identify possible threats and take security measures. It
provides an overview of basic multicast, the best security practices for
use of this technology, and recommendati...