NetBIOS over TCP/IP

NetBIOS over TCP/IP (NBT) is the session-layer network service that performs name-to-IP address mapping for name resolution.

NetBIOS Name Types

NetBIOS computer names are always 16 byte strings. Computer names can be up to 15 characters long, the last byte is reserved for a suffix that is the resource or service code. Below is a table of resource and service codes. When naming a computer it is best to use characters that are compatible with the DNS naming convention for WINS-DNS integration.

Common NetBIOS Names Service That Registers the Name
<computer name>[00h] Workstation (your NetBIOS Redirector)
<computer name>[03h] Messenger(listens for messages sent to your computer)
<computer name>[20h] Server (Shares your resources to the network)
<user name>[03h] Messenger (listens for messages sent to your logon ID)
<domain name>[1Dh] Master Browser
<domain name>[1Bh] Domain Master Browser

Methods of Resolution

Name Cache

The NetBIOS name cache is checked first no matter what node type is configured on the machine. The cache is always local. Names resolved in the last 600 seconds (10 minutes) remain in the cache.

Names can permanently be loaded in the cache. Machines defined with the #PRE tag in the LMHOSTS file .

To check the name cache nbtstat -c will show all resolved names.

Netbios Name Server

B-Node (Broadcast Node)
Broadcast mode uses broadcasts only.

  1. NetBIOS Name Cache
  2. Broadcast a NetBIOS Name Query
  3. Checking the LMHOSTS file
  4. Checking a HOSTS file
  5. Checking with a DNS server

Configuration - Leave the WINS address empty
Use- Broadcasts are typically blocked by routers so a b-node configuration will only be effective on a single subnet.

P-Node(Peer-to-Peer Node)

  1. NetBIOS Name Cache
  2. Asking a NetBIOS Name Server
  3. HOSTS file
  4. DNS

Configuration - Configure though DHCP lease offering

M-Node(Mixed Node)

  1. NetBIOS Name Cache
  2. Broadcast a NetBIOS Name Query
  3. Checking the LMHOSTS file
  4. Asking a NetBIOS Name Server
  5. Checking a HOSTS file
  6. Checking with a DNS server

Configuration - Configure though DHCP lease offering

H-Node(Hybrid Node)

  1. NetBIOS Name Cache
  2. Asking a NetBIOS Name Server
  3. Broadcast a NetBIOS Name Query
  4. Checking the LMHOSTS file
  5. Checking a HOSTS file
  6. Checking with a DNS server

Configuration - Enter the WINS server address

LMHOSTS file Local text file that maps IP addresses to the NetBIOS computer names of Windows networking computers on remote networks
HOSTS file Local text file that hosts names to IP addresses.Typically used to resolve host names for TCP/IP utilities.
Domain Name System (DNS) Maintains a database of IP address/computer name (host name) mappings.