How can you discover network topology?

Network Mapping and Network Topology DiscoveryTo create a network map using LANState software, you need to add network devices (you can scan your network for saving your time), draw lines for linking devices, and draw areas for grouping devices. The ability of using lines and areas, a quantity of different icons for representing different types of network equipment significantly raise the visual perception of the created network map.The program supports the automatic network topology discovery using the SNMP protocol. If you have managed switches with SNMP enabled on them, the program will download the topology information from the switches and draw a network map automatically.

or  if you have Cisco you can use Cisco discovery Protocol CDP and Link Layer Discovery Protocol (LLDP)

 

By using CDP ..(Cisco Discovery Protocol)

-Cisco discovery Protocol CDP

-Link Layer Discovery Protocol (LLDP)

-Traceroute

 

I think the best way is to use CDP which is Cisco Discovery Protocol but this will success only if the routers are from Cisco.

Depends on the environment  however :

 

Windows : ( with)   System Center Configuration Manager 2007

1. In the Configuration Manager console, navigate to System CenterConfiguration Manager / Site Database / Site Management /<site name>/ Site Settings / Discovery Methods.

2. Configure Network Discovery as discussed in How to Configure Network Discovery with the following specifics:

   • On the General tab, select Topology from the Type of Discovery options. 
   • On the Subnets tab, ensure that the Search local subnets check box is selected. This is normally done by default.

There are also many free tools, but most "true" network enviroments will provide a set to tools to discover topology. OR you can getr "gritty" and use command tools 

You can find network topology by mapping it. First of all you need access to the switches or routers in the environment. They can be cisco or non-cisco. If you start from any one switch and use the two commands "show cdp neighbors" and "show ldp neighbors" you will see the cisco and non-cisco devices connected to the switch, write down the port connected. Once done, telnet to one of the switches and check its neighbors. Keep doing this until you have seen all the switches and you have a full-topology.

 

Another method is to use the cmd on a computer and check trace path of the route. Use "tracert x.x.x.x" to ping the core or distribution layer switches, or the router and you will see in between different subnets the packet moves from.

 

or download ip scanner software, it will scan most of the ip address and subnets. You need to be good in subnetting to know how many networks are there but it does not give a full topology only the subnets you have in your network.

 

Hope this helps.

To determine your network topology

1. In the Configuration Manager console, navigate to System CenterConfiguration Manager / Site Database / Site Management /<site name>/ Site Settings / Discovery Methods.

2. Configure Network Discovery as discussed in How to Configure Network Discovery with the following specifics:

• On the General tab, select Topology from the Type of Discovery options. 
• On the Subnets tab, ensure that the Search local subnets check box is selected. This is normally done by default.

On the Domains tab, ensure that the Search local domain check box is selected. This is normally done by default. Using the Maximum hops drop-down list, specify how many router hops Network Discovery should make in mapping your topology. If you are unsure, use a small number, as you can increase it later. For more information on how the number of hops will affect the mapping of your network topology.

I have little experience with SolarWinds Network Topology Mapper, installed it in the lab and scanned my test network.

CDP protocol or PRTG S.W or System Center Configuration Manager