HP StorageWorks Storage Mirroring application notes Guidelines for networking and failover (T2558-96063, February 2008)

Storage Mirroring Guidelines for networking and failover application notes 5
File and print sharing with SMB and NetBT
Windows file and print sharing uses the SMB protocol, which has historically relied on NetBIOS. NetBIOS,
in turn, required NetBIOS over TCP/IP (NetBT) to function on IP networks. NetBT uses Transmission Control
Protocol (TCP) port 139 and has a limitation of binding only to the primary IP address of each Network
Interface Card (NIC). This is explained in Microsoft Knowledge Base article 131641 and can be seen by
using a port scanner to probe TCP port 139 (the “nbsession” port) on an adapter with multiple addresses.
This will show that NetBT is listening on TCP port 139 only on the primary address.
Windows 2000 and later versions do not require the NetBT layer and use SMB directly on top of TCP/IP
using port 445 (TCP and User Datagram Protocol (UDP)). This implementation does not have the
aforementioned binding limitation and allows clients to establish SMB sessions to any IP address on the
server using port 445. In order to be backward compatible with legacy clients and servers, Windows
2000 also supports SMB on NetBT using port 139, which inherits the primary IP address limitation. If
NetBT is disabled, a Windows 2000 system will use only port 445 for SMB session. See the following
three diagrams.
The command
netstat -a -n will show a Windows 2000 system listening on UDP 0.0.0.0:445 and TCP
0.0.0.0:445. An IP address of 0.0.0.0 indicates a global binding, so it is listening on TCP and UDP port
445 on all IP addresses for SMB communications. The NetBT binding will be shown as TCP
172.16.137.5:139 for the primary IP address on each NIC, indicating that it is listening only on those IP
addresses.
Within Microsoft there is not a standardized way to refer to the implementation of SMB on port 445.
Knowledge Base article 150543 refers to it as “Direct Hosting of SMB Over TCP/IP.” Article 204279 refers
Primary IP 192.168.15.4
Secondary IP 192.168.15.5
Primary IP 10.10.10.4
Secondary IP 10.10.10.5
Windows NT 4.0 and Earlier
NetBT bound only to the Primary IP Addresses:
Primary IP 192.168.15.4
Secondary IP 192.168.15.5
Primary IP 10.10.10.4
Secondary IP 10.10.10.5
Windows 2000 and Later with NetBT Enabled
NetBT bound to the Primary IP Addresses:
SMB/IP bound to all
IP Addresses
Primary IP 192.168.15.4
Secondary IP 192.168.15.5
Primary IP 10.10.10.4
Secondary IP 10.10.10.5
Windows 2000 and Later with NetBT Disabled
NetBT bound to no IP Addresses:
SMB/IP bound to all
IP Addresses