I recently read a must-read blog post by Russ White in which he argued that you need to understand both theory and practice (see also Knowledge or Recipes and my other certification rants) and got a painful flashback of a discussion I had with a corner-cutting SE (fortunately he was an exception) almost two decades ago when I was teaching my Advanced OSPF course at Cisco.
Him: How many OSPF routers can you have in an area? (asked during the first morning of a 3-day course)
Me: As you’ll see in these three days, OSPF is a pretty complex protocol, so there’s no right answer. It depends on the area topology, the frequency of topology changes, the type of routers… For example, areas with low-end routers have to be smaller due to their limited CPU power, for example.
Him: You don’t understand. I need a simple answer that I can use in my desings.
Me: How about 50?
Him: And how many OSPF areas can you have on a router?
Me: Obviously that depends on the area size (and all other things I already mentioned), the CPU power of the router, what other things that same router is doing, the desired convergence speed…
Him: That’s too complex. I need a simpler answer.
Me: Well, the official answer is three. Is that good enough for you?