Content

| 6.3 |  | Troubleshooting Transport Layer Issues on Network Hosts |
| 6.3.4 |  | Common issues with NetBIOS networks |

There are four common NetBIOS-related issues:

- NetBIOS node type misconfiguration
- NetBIOS workgroup mismatch
- NetBIOS scope mismatch
- Duplicate NetBIOS names

These issues are usually a result of misconfiguration by a user or network engineer. Note that several of these problems can be caused by DHCP server misconfiguration.

One of the most common misconfigurations on a small NetBIOS network is the NetBIOS node type. Recall from previous content that there are four possible settings for the NetBIOS node type:

- B-node (Broadcast node)
- P-node (Peer-to-peer node)
- M-node (Mixed node)
- H-node (Hybrid node)

Obviously, configuring the NetBIOS node type as peer-to-peer in a network that does not have a NetBIOS name server stops the network from functioning. Conversely, using broadcast-mode in a routed network stops the hosts from accessing resources across the router.

The NetBIOS node type is usually set using a DHCP server. Recall that DHCP can be used to configure more than just a client IP address. DHCP can be used to set a number of optional settings on the client. The settings are referred to as DHCP options. DHCP options commonly used are shown in Figure . Because Cisco routers can be configured as DHCP servers, NetBIOS DHCP options need to be taken into account. Use the commands netbios-name-server name-server-address and netbios-node-type type from DHCP-configuration mode to implement NetBIOS DHCP options from a Cisco router-based DHCP server.

DHCP options 44 and 46 are commonly used in NetBIOS networks with NetBIOS name servers.

The NetBIOS node type can also be set manually on Windows hosts. The registry of the Windows machine must be edited in order to do this. Further information on this can be found in knowledge-base article 160177 at http://support.microsoft.com/.

When two NetBIOS computers have different values defined for the workgroup name, these computers are unable to communicate. The workgroup name is usually configured during the initial installation of the computer operating system or when networking is being added to the computer. The workgroup name is not case-sensitive.

The NetBIOS Scope ID is a left-over piece of NetBIOS technology rarely used in modern networking. A NetBIOS Scope is a group of computers that can only communicate with each other. Because the NetBIOS Scope ID is blank by default, a single computer misconfigured with a NetBIOS Scope ID is not able to communicate with other hosts on the network.

Because this is a setting that is not often used, it can be quite difficult to troubleshoot. Note that like the NetBIOS node type, the NetBIOS Scope ID can also be controlled centrally from the DHCP server, using DHCP option 47. Unlike the node type however, the Scope ID can also be easily altered on the local machine through the network interface GUI.

When duplicate NetBIOS names exist in a network, the duplicate hosts are unable to connect to the network until they are configured with a unique NetBIOS name. Duplicate NetBIOS names occur most often when there is no structure to the naming scheme in a NetBIOS network.

In small networks, the lack of a structure poses no real issue. In larger networks however, a system for ensuring unique NetBIOS naming is strongly recommended.

Note that the host name can be set using DHCP option 12. This option is intended for use when using DHCP reservations (where an IP address is specifically reserved for a given MAC address), as it allows for full host-specific network information to be controlled from a single administrative interface. Obviously, using DHCP option 12 with dynamic DHCP clients would cause significant problems on the network.