Discovery Methodologies for *Extremely* Large Networks

Hi /r/networking,

To preface my questions, I am fairly new to the consulting space (although I have worked for MSPs for ~6 years now, almost entirely in networking).

I have just begun a network architecture assessment for a customer and to be frank, I'm totally overwhelmed by the scale of their environment.

To give you an example, one of their smaller data centers contains about 30 devices, which is a small hardware footprint; but the more one digs into the configuration of each device (going off of some minimal and sometimes out of date documentation) the more questions arise.

To get even more specific, one of their firewalls has ~75 static routes, with over 10 unique next-hops among those static routes for which I do not know the management IP of the device on the other end.

Obviously, it's kind of a mess, but that is why they brought us in.

My question is, to those of you who have been exposed to poorly documented networks of this scale; how did you manage to get a sense of traffic flows and architecture?

I'm looking for both tools, and methodologies/frameworks that would help me understand this large environment in a relatively short amount of time.

​

Thanks!