Using Auto-Discover

You can use Auto-Discover to create a new map. If your network contains Layer 2-enabled switches, you can also use Layer 2 information to increase the accuracy of a map's representation of your network topology. For more information, see Mapping With Layer 2(Pg 1).

For existing maps, you will need to use the manual technique(Pg 1) for converting the map. For new maps you create with Auto-Discovery, use the automatic technique(Pg 1).

To Auto-Discover to create an initial network map:

1. From the File menu, choose New... The New Map Con-structor window appears.
2. Enter a map name and click Next.

 

3. Click to choose Auto-discovery, then click Create. The Automatic Device Discovery window appears, as shown below.

 

 

4. Enter a host name or IP address you want to use as the starting point for auto-discovery.
   A name is suggested for you. It is the DNS name or IP address of a router, or if there's no router, the computer InterMapper is running on. Use the default value, or enter any of the following:
   • A DNS name
   • An IP address (if you want to create a map of another part of a network.)
     If you enter the name or address of an SNMP-speaking router, InterMapper draws interconnections to other routers in the network more quickly.
5. If you have SNMP-speaking devices in your network, specify an SNMP Community string.
6. Select your Discovery Options, as explained in The Auto-Discovery Window below.
7. Click the Filter button to set a filter for the discovery.
8. Click OK to start the Auto-discovery process. A Discovery Status bar appears as shown. The status bar shows progress statistics for subnets, queued routers, and addresses remaining to be scanned:
   
9. As the network is scanned, discovered devices appear in the current map (or in a list if you have cleared the Automatically Layout check box.) When InterMapper has found all the devices within the specified subnet, the Discovery Status bar disappears.

• Click the Map View button near the upper left corner of the Map window to view your network as a map, showing devices and networks as icons, with the interconnections between them.

To stop the Auto-discover process:

• Click the Cancel button. The discovery process is stopped, and no new devices or networks are added. All devices added before you stopped the process remain in the list.

The Automatic Device Discovery Window

You control the starting point, the SNMP Community string, the breadth of the network search, and the kinds of devices that are automatically added to the map using this window.

• Starting host name - The DNS name, IP address, or WINS name of a device to use as a starting point for the auto-discovery.
• Specify an SNMP community -The SNMP Read-only community string to be used to interrogate all devices. (InterMapper attempts to read SNMP information using the specified community string. It is set to 'public' by default.)
• Stay within NN hops of starting device - Stops autodiscovery after InterMapper has searched the specified number of hops from the starting device.
• Scan for devices on all networks - Specify which kinds of devices should be automatically added to the map. Click to check this box, or click Edit Filters... to open the Network Scanning window.
• Click Automatically layout to let InterMapper layout the map automatically.
• Click Start Discovery to initiate a scan of the specified host.

The Network Filter Dialog

Check the filters you want to use to add devices to the map:

• Active - InterMapper performs a complete IP address scan for each network. A device is added for each IP address that responds.
• Named - Each IP address in the subnet is looked up in the DNS. If a corresponding name is present, the device is added to the map.
• SNMP - InterMapper sends an SNMP GetRequest to each address in the range. Any device that responds is added to the map and uses the SNMP Basic Traffic probe. If the device does not respond to SNMP, the probe is set to Ping/Echo.
• HTTP - If the device responds to an HTTP request, an HTTP probe is added to the device (along with SNMP Basic Traffic or Ping/Echo probe), and the device becomes a probe group.

What Happens During Autodiscovery?

During autodiscovery, InterMapper attempts to discover all devices on a network, based on the IP address and SNMP string provided. It does this by querying the router and ARP tables. Then, using any scan filters specified in the Network Scanning window, it scans all attached subnets, mapping all devices it finds, until it reaches the hop count specified in the Discovery Options section of the Automatic Device Discovery window. It then performs the following processes concurrently and iteratively until the specified limits are reached:

• If InterMapper discovers an SNMP-speaking router, it attempts to discover what interfaces the router has, and what other routers are connected to those interfaces. InterMapper then queries each of the discovered routers for their connected networks, and begins autodiscovery on each network.
• For each network or subnet discovered, InterMapper pings every address on that subnet to find more active or named devices.
• When InterMapper finds a device, it uses several techniques to characterize it. For example, it sends SNMP queries (with the specified SNMP community strings) to determine what kind of device is present.

Warning: In autodiscovery mode, InterMapper may ping or query every device address on a subnet. If your network has an intrusion detection system, autodiscovery may trigger your intrusion alarms. Be sure to check with the network manager before using this feature.

Note: It may take a long time to do autodiscovery on a large subnet (a Class A or B subnet). InterMapper limits its autodiscovery queries to two per second so that it doesn't overload any networks and thus it takes about 32,000 seconds (a shade under 10 hours) to scan that class B subnet (with 65,535 addresses) completely.

To create your maps more quickly, you can type or paste one or more host DNS names, IP addresses, or WINS names into the Add Devices... window (Insert menu). (WINS names must be preceded by "\\".) InterMapper immediately adds them to the map and connects them to the proper network.

You can also import a list of devices from a text file. For more information, see Importing Data Into Maps .

Below is a typical map after autodiscovery has finished.

Autodiscovered devices and networks. Routers
are interconnected by links to networks.