Network topology

Ian Mason nanog at
Wed Oct 15 21:05:14 UTC 2008

On 15 Oct 2008, at 17:52, Colin Alston wrote:

> On 2008/10/15 06:29 PM Bill Woodcock wrote:
>> InterMapper. 
>> intermapper/index.html
>>                                 -Bill
> Whoa, quite a serious looking piece of software. Will check it out.
> Was kinda hoping to write my own software though, but perhaps I can  
> craftily learn something from it :)

If you have SNMP access pull:-

	1) Is it a bridge or a router?
	2) ARP Table
	3) MAC forwarding table
	4) Interfaces with MAC and IP addresses
	5) Netmasks

from each such router or bridge in the network. Use the information  
from one to help you discover the
others recursively. Have a termination condition that stops this  
process walking off your network and
attempting to discover the whole Internet.

That's enough to figure out both logical and physical topology.

Without SNMP (or similar) access it's nigh impossible to figure out.  
If you only have access to a subset
of the routers and bridges in the network you MAY have enough to  
figure out the topology - 50% is enough
if it's the right 50%.


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