When enabled, the Network Discovery method gathers information about devices on your network, like the other discovery methods that are available in SMS do. However, the Network Discovery method is unique because, besides computers, it also finds network devices such as printers, routers, and bridges. Basically, the Network Discovery method finds any device on the network that has an IP address.
You can configure Network Discovery to discover resources in subnets, domains, and Simple Network Management Protocol (SNMP) devices. If the site is configured with standard security, you can also configure Network Discovery to discover resources in Microsoft Dynamic Host Configuration Protocol (DHCP) servers. You can configure Network Discovery to find routers in an ordered list of community names and specify the maximum number of hops within which to find routers.
The Network Discovery method can be used to:
Discover potential SMS clients.
Collect resource discovery data so that the Client Push Installation method can later install client components on those resources.
Gather data so that Network Trace can display a detailed map that includes SMS sites and the connections between SMS primary site servers and other site systems.
Collect resource information that you can later use for collections, reports, and queries.
When you enable the Network Discovery method, you can specify the level of detail and the scope of the discovery information that Network Discovery gathers. These are described in the following sections.
You can set the level of details for Network Discovery by selecting one of the following discovery types: topology; topology and client; or topology, client, and client operation system.
Network Discovery uses SNMP to discover routers and subnets. SMS Network Trace uses this data to provide information about the health of network links between SMS site systems. For more information about Network Trace, see Chapter 10, "Maintaining and Monitoring the Network," in the MicrosoftSystems Management Server 2003 Operations Guide.
When you select the topology discovery type, Network Discovery discovers subnets and creates DDRs for network devices that have an SNMP agent. DDRs contain information about each identified resource.
With the topology discovery type, Network Discovery first connects to the local router (default gateway) to collect IP addresses from its ipRouteNextHop routing table. Network Discovery uses this information to find other network devices that are connected to the router.
Network Discovery attempts to query the specified DHCP servers to retrieve the active leases and defined subnet lists that are configured on that server. Network Discovery then attempts to resolve the IP address to a name for each network device and subnet that it discovers.
Figure 4.1 illustrates topology discovery.
Figure 4.1 Topology discovery
Topology and Client
Network Discovery uses SNMP, DHCP, and domain browsing to identify routers, subnets, potential clients, and any other resource, such as printers or gateways, within the specified area of the network.
With the topology and client discovery type, Network Discovery performs topology discovery and attempts to discover as many other IP devices as possible within the subnets and domains that you specify. Network Discovery retrieves the ipNetToMediaTable value from any device that responds to SNMP. This value returns arrays of IP addresses that are client computers or other resources such as printers, UNIX workstations, hubs, and bridges.
To establish what the device is, Network Discovery pings the IP address of the device to determine if it is active. Based on its findings, Network Discovery does one of the following:
If the device is not active, Network Discovery does not use SNMP to contact the device.
If the device is active, Network Discovery attempts to use SNMP to determine if it is a router. If it is a router, Network Discovery retrieves its routing table and gathers any additional IP addresses in the table. If the device is not a router, but it can still respond to SNMP, Network Discovery also tries to get any IP addresses that the device has in its table.
Network Discovery then tries to resolve the NetBIOS name. If the name cannot be resolved, the IP address of the device is used for its name. When the device is displayed under Collections in the SMS Administrator console, the IP address appears in the Name column.
Network Discovery enumerates the local domain and any other specified domains. Network Discovery can discover any computer that you can view from your site server when browsing My Network Places on your Windows desktop. Network Discovery retrieves the IP address and then pings (using an Internet Control Message Protocol echo request) each device that it finds to determine which computers are currently active. Network Discovery must find the subnet mask for the device to create a DDR for it. As a result, domain discovery is not a good source for the information that is needed to report a device. Figure 4.2 illustrates topology and client discovery.
Figure 4.2 Topology and client discovery
Topology, Client, and Client Operating System
Network Discovery uses SNMP, DHCP, domain browsing, and Windows Networking calls to identify the same items as in the topology and client discovery type and the operating systems of potential clients within the specified area of the network. This level increases the scope of your collections by populating collections that are based on operating systems related queries. However, the extra time that is required to retrieve the operating system information increases the discovery time and the network traffic.
With the topology, client, and client operating system discovery type, Network Discovery attempts to find devices and IP addresses by using the mechanisms described in the "Topology and Client" section earlier in this chapter. Network Discovery then performs a LAN Manager call to each computer to identify the operating system. As a result, Network Discovery successfully identifies the operating system of any computer supporting LAN Manager calls. The following platforms support LAN Manager calls:
Windows NT 4.0
Windows Server 2003 family
Windows for Workgroups
Some UNIX workstations
Some MS-DOS® computers
During network discovery, the operating systems for all computers running Windows 95, Windows 98, and Windows Millennium Edition are displayed as Windows 9x in the SMS Administrator console because they all report the same operating system version through LAN Manager. However, when you deploy computers running Windows 98 as SMS clients, SMS displays their operating system correctly.
Figure 4.3 illustrates topology, client, and client operating system discovery.
Figure 4.3 Topology, client, and client operating system discovery
Network Discovery can use various methods to gather information about resources on your network. You can configure Network Discovery with a discovery scope to control the methods that are used. Discovery scope can include subnets, domains, SNMP devices, and, if the site is configured with standard security, DHCP servers. Depending on the specified discovery scope, Network Discovery can discover resources such as computers, gateways, routers, IP addresses, subnet masks, and media access control (MAC) addresses. When Network Discovery searches for system resources, it processes these combined options to gather the required information and to generate a single DDR for each discovered resource.
By default, Network Discovery attempts to enumerate the computers in the local domain by using the Windows Computer Network Browser service (that is, browsing). You can also specify additional domains to discover. Network Discovery can discover computers in the same domains that can be discovered by using the site server to browse My Network Places.
Although Network Discovery can gather data about resources in domains, a DDR is created only for devices that have an IP address within the discovery scope.
To gather data from SNMP devices, Network Discovery uses specified SNMP community names to access the SNMP devices. Each community name must have Read access to at least some of the devices to gather information. By default, Network Discovery uses the SNMP default community name public. If your SMS site server has multiple network interface cards, then Network Discovery attempts to connect to all of the local SNMP devices.
To discover routers on the local network, Network Discovery uses the Router Information Protocol and SNMP and listens for Open Shortest Path First (OSPF) multicast addresses. Network cards typically support the filtering of multicast addresses, and the operating system registers with them when an application registers with Winsock. If an application fails to register because the network card cannot support any more multicast filters, the operating system typically clears out the filters, registers for all multicast addresses, and performs the filtering itself. In cases where no more slots exist on a network card, Network Discovery cannot use OSPF. As a result, the router is only discovered if it has SNMP enabled.
You can specify a hop count to limit the number of routers from the default gateway that Network Discovery tries to discover. If the hop count is set to zero, Network Discovery searches only the default gateway. If the hop count value is greater than zero, Network Discovery contacts each of the devices within the range of the specified hop count, establishes whether they are routers by using the ipForwarding scalar on the router, and then retrieves data from their routing tables. Network Trace uses this information to build diagrams of SMS site systems.
Figure 4.4 illustrates the router hop count process. Each time that you increment the hop count, you extend the discovery to another set of gateways. Incrementing the hop count is an effective method of enabling discovery for your entire network.
Figure 4.4 Router hop count
If your site server is also a DHCP client, DHCP discovery is automatically enabled for its DHCP server. The DHCP server managing this process stores:
A database of the MAC addresses belonging to computers requesting IP addresses.
The IP address of each computer.
The name of each computer.
The configuration information for the DHCP server.
The DHCP server uses its configuration information to determine which networks it is managing. Network Discovery retrieves information from the DHCP server in the form of remote procedure calls made directly to the database on the DHCP server.
Static IP addresses are not always discovered when Network Discovery enumerates the DHCP server. Network Discovery neither finds IP addresses that are configured as part of an excluded range of IP addresses on the DHCP server nor discovers IP addresses that are reserved for manual assignment. If your network devices use SNMP, Network Discovery can use SNMP to find their static addresses.
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