When would we want to do traffic steering?

Question

After going over EIGRP, I ran into offset lists which allow the modification of the metric of routes advertised by EIGRP and provide the option of traffic engineering.

I am not very experienced with traffic steering/engineering yet. May I know, is there an example where we would want to steer traffic/modify the path a packet is taking throughout the routing domain? After all, if we are running dynamic routing protocols, shouldn't they automatically determine the best path for the traffic for every destination?

Thank you in advance for your help.

Answer 1

One example would be when the 'best path' is not actually desirable for the traffic in question. The selected path might be the most efficient (shortest in terms of routed hops etc.) but might traverse a slower link, or a link that is billed differently than other links that have a longer path but incur no additional cost or provide higher performance, etc.

Additional concerns might be security of one path vs. another, the ability to monitor traffic on one link vs. another, etc. There can also be temporary needs such as maintenance work or troubleshooting/testing where diverting certain traffic from the best path might be desirable.