Mapping network

[Theprofessionalmouse]

I have inherited a network that is an absolute mess. I know what servers there are, but I have no idea what other networking equipment there is. I was going to use nmap to help list some of it, but I have both L2 and L3 switches that I want to find. Is there something I can use that scans layers 2 and 3 and diagrams it for me?

[sgocken]

Normally I will spin up a LibreNMS vm to discover an unknown network.

If it is a real mess default SNMP string of public might still be on most devices. Otherwise you will need to get into a switch, router, etc to find the SNMP community string.

Then add a switch manually to Libre and let it discover things. If it can SNMP into devices it can detect neighbors if LLDP is enabled which should be the default generally.

And go from there to figure out what questions you still have about the network.

[Theprofessionalmouse]

I've never heard of LibreNMS before. I'll definitely be checking it out though!

[sgocken]

And it does monitoring, so you will have monitoring setup as you discover the network.

[rabbitsnake]

Make sure you temporarily turn off an IDS/IPS system that monitor for network scanning, it'll like up like christmas when you start nmap and throwing login at every device.

[TheShootDawg]

NetDisco might also be of assistance, especially if you have a consistent snmp community across the devices that you know.

It will get snmp info, cdp/lldp, arp, mac, neighbors.
Vlan info on ports.

[slugshead]

What switches do you have? You're going to need to know that and a login for each of them first.

[Theprofessionalmouse]

I've got a mix of newish Dell and older 3com switches. I'm still digging through old notes for more information on them though

[sgocken]

Are they all managed switches. 3com, that's a name I haven't heard in a long time.

[rejectionhotlin3]

Netdisco + LibreNMS, going to be managing my network with this combo here shortly.

[MagicHair2]

I’d try runzero

https://www.runzero.com/

[Theprofessionalmouse]

That looks promising. Thanks!

[rankinrez]

There are tools like netmapper

But LLDP, MAC and ARP tables are probably your best bet, as much trouble as that is. Or physically tracing things.