Link: https://networkencyclopedia.com/mastering-internet-routing-with-bird-a-step-by-step-guide-to-building-your-own-routing-system/

As I was going through this link, l got curious about this "bird".

Could you please make it ELI5 ??

So in order for isp 1 and isp 2 to talk to each other they need to exchange IP addresses in the same way you exchange phone numbers so people can call you.

Doing that on an internet scale manually is not feasible, you need a dynamic routing system.

BIRD is software so any PC can engage in those exchanges between ISPs as opposed to buying a Cisco, Juniper(now HP), Huawei, Nokia device for several thousand dollars.

If you want to understand how routing happens between ISPs you should look up Border Gateway Protocol (BGP)

Bird is the word