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Windows Server



    

NetBIOS    

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NetBIOS



Jan
11

NetBIOS

In Windows, Microsoft has developed a proprietary protocol for name resolution.

Windows Internet Name Server WINS for short.

WINS stores names of computers in a format called NetBIOS and for communication it uses a proprietary protocol called NetBUI. It uses the ports 137, 138, 139 to work.

In NBT, the name service operates on UDP port 137 (TCP port 137 can also be used, but rarely is).

·          NBT is NetBIOS Over TCP/IP for short

Datagram mode is connectionless; the application is responsible for error detection and recovery. In NBT, the datagram service runs on UDP port 138.

Session mode lets two computers establish a connection, allows messages to span multiple packets, and provides error detection and recovery. In NBT, the session service runs on TCP port 139.

 

The name of the computer that you provide in the Computer Properties tab, (sysdm.cpl) is the NetBIOS name of the computer. The WINS Server uses this name and maps it to an IP address which is then used for name resolution process to work properly. The protocol under the scene for communication is NetBUI.

NetBIOS is an acronym for Network Basic System.

 

NetBIOS over TCP/IP [NetBT / NBT]

NetBIOS can also work over the TCP/IP Protocol.

 

http://technet.microsoft.com/en-us/library/bb727013.aspx

Enabling NetBIOS over TCP/IP

You can enable NetBT for computers running Windows Server 2003 or Windows XP by opening Network Connections, right-clicking a connection, clicking the Internet Protocol (TCP/IP) component, clicking Properties, clicking Advanced, clicking the WINS tab, and clicking the appropriate option in NetBIOS setting. Figure 11-2 shows the WINS tab.

clip_image001

Figure 11-2 The WINS tab

For the NetBIOS setting, you can choose any of the following options:

·         Default Enables NetBT if the network connection has a static IPv4 address configuration. If the network connection uses the Dynamic Host Configuration Protocol (DHCP), it uses the DHCP options in the received DHCPOffer message to either disable NetBT or enable and configure NetBT. To disable NetBT using DHCP, configure the Disable NetBIOS over TCP/IP (NetBT) Microsoft vendor-specific option for the value of 2. This is the default setting for LAN connections.

·         Enable NetBIOS over TCP/IP Enables NetBT, regardless of the DHCP options received. This is the default setting for remote connections (dial-up or virtual private network).

·         Disable NetBIOS over NetBIOS Disables NetBT, regardless of the DHCP options received.

NetBT is not required for computers running Windows 2000, Windows XP, or Windows Server 2003 unless you use NetBIOS applications on your network, such as the Computer Browser service. The Computer Browser service maintains the list of computers in the Microsoft Windows Networkwindow of My Network Places. Unlike versions of Windows prior to Windows 2000, file and printer sharing with Windows 2000, Windows XP, or Windows Server 2003 can operate without the use of NetBT.

 

http://technet.microsoft.com/en-us/library/bb727013.aspx

 

 

Commands to follow:

            To flush the NetBIOS cache:

            nbtstat –rR

 

Services

NetBIOS provides three distinct services:

·         Name service (NetBIOS-NS) for name registration and resolution.

·         Datagram distribution service (NetBIOS-DGM) for connectionless communication.

·         Session service (NetBIOS-SSN) for connection-oriented communication.

(Note: SMB, an upper layer, is a service that runs on top of the Session Service and the Datagram service, and is not to be confused as a necessary and integral part of NetBIOS itself. It can now run atop TCP with a small adaptation layer that adds a packet length to each SMB message; this is necessary because TCP only provides a byte-stream service with no notion of packet boundaries.)

 

Name service

In order to start sessions or distribute datagrams, an application must register its NetBIOS name using the name service. NetBIOS names are 16 octets in length and vary based on the particular implementation. Frequently, the 16th octet, called the NetBIOS Suffix, designates the type of resource, and can be used to tell other applications what type of services the system offers. In NBT, the name service operates on UDP port 137 (TCP port 137 can also be used, but rarely is).

The name service primitives offered by NetBIOS are:

·         Add name – registers a NetBIOS name.

·         Add group name – registers a NetBIOS "group" name.

·         Delete name – un-registers a NetBIOS name or group name.

·         Find name – looks up a NetBIOS name on the network.

NetBIOS name resolution is not supported by Microsoft for Internet Protocol Version 6 (IPv6).

 

Datagram distribution service

Datagram mode is connectionless; the application is responsible for error detection and recovery. In NBT, the datagram service runs on UDP port 138.

The datagram service primitives offered by NetBIOS are:

·         Send Datagram – send a datagram to a remote NetBIOS name.

·         Send Broadcast Datagram – send a datagram to all NetBIOS names on the network.

·         Receive Datagram – wait for a packet to arrive from a Send Datagram operation.

·         Receive Broadcast Datagram – wait for a packet to arrive from a Send Broadcast Datagram operation.

 

Session service

Session mode lets two computers establish a connection, allows messages to span multiple packets, and provides error detection and recovery. In NBT, the session service runs on TCP port 139.

The session service primitives offered by NetBIOS are:

·         Call – opens a session to a remote NetBIOS name.

·         Listen – listen for attempts to open a session to a NetBIOS name.

·         Hang Up – close a session.

·         Send – sends a packet to the computer on the other end of a session.

·         Send No Ack – like Send, but doesn't require an acknowledgment.

·         Receive – wait for a packet to arrive from a Send on the other end of a session.

In the original protocol used to implement NetworkBIOS services on PC-Network, to establish a session, the initiating computer sends an Open request which is answered by an Open acknowledgment. The computer that started the session will then send a Session Request packet which will prompt either a Session Accept or Session Reject packet.

During an established session, each transmitted packet is answered by either a positive-acknowledgment (ACK) or negative-acknowledgment (NAK) response. A NAK will prompt retransmission of the data. Sessions are closed by the non-initiating computer by sending a close request. The computer that started the session will reply with a close response which prompts the final session closed packet.

 

 



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