Attention Network Detectives !!!

[tufer0001]

Imagine you are hired by a business that needs assistance with their LAN/WAN. There is no documentation and all you have is a laptop and telnet/ssh. How would you go about discovering the network(s) and how things interconnect ? Also, what would you do to baseline performance ?

[Georg Pauwen]

Hello,

there are numerous (SNMP-based) tools which you can download from the Internet, and that allow you to do some sort of network discovery. You would need to know the SNMP (read) community of the devices you are trying to discover though...

If you have access to Visio or CiscoWorks Campus Manager, these applications have an autodiscovery feature as well.

Check the link below for a listing of SNMP-based tools:

SNMPLINK.org

http://www.snmplink.org

HTH,

GP

[paddyxdoyle]

I've been in the same situation myself.

Use CDP on your core devices to discover other connected devices and build your topology map.

"show cdp neighbour" will give you a list of which devices are connected to which interfaces

"show cdp neighbour detail" will show you more information about a specific device including IP so you can move around the network.

I've heard this method being called a CDP sniff.

Normally i would start with a layer3 diagram showing all the main sites and interconnections with addressing. You can then delve down into each site looking at all the switches and how they are connected into the core.

For baseling MRTG could help which is an open source network monitoring tool, this relies on your having SNMP enabled on all your device (www.mrtg.org)

Also get youself a copy of MS Visio which is an essential app for creating digrams of a network topology.

HTH

Paddy