Ever wonder why BGP seems to be such a complicated protocol to administer? It seems pretty straightforward to set up. Some commands, and you have a BGP session. Easy huh? BGP is one of those things where the more BGP feeds you bring in, the more complex traffic management becomes. Why? Take a look at the following graphic.
What you are looking at is a small visualization of some of the AS connections to Hurricane Electric (AS6939) in North America. This is not all of them, just what I could fit on the screen for this article. Some of these are “transit ASes” which means they sit between Hurricane and another network or networks. This is important to understand because they can influence how your traffic reaches customers or resources on Hurricane electric if they are between you and them. The same thing goes for Hurricane Electric. They are a transit AS between companies and resources. Their policies in terms of BGP traffic can influence your traffic. This is just one AS. There are thousands and thousands of others.
Now imagine you have 4 upstream providers with various peerings and upstream peers. Each one of them can do various manipulations to the same destination. Your routers will pick the best path, but that path may have Congestion or a host of other influences on your traffic.
For myself, as a network engineer, being able to diagnose and troubleshoot path issues is an art, just as it is a science.j2networks family of sites