One not so bright day I connected my laptop to the home network and discovered that I lost name resolution. I.e., I could ping other computers by IP address, but not by name. I.e. ping 192.168.0.100 would work, while ping mymachine would not. It used to be fine before! What happened?

It was working fine for years. I read numerous articles on the Internet, but it took a while until I found what the problem was. After hours of investigation I found that something turned my laptop from B-node to P-node. But I am jumping ahead.

Name resolution in Windows network is done via ages old NetBIOS protocol. Simple networks (no routers between computers) use broadcast mode: each computer just shouts into space something like “my name is Vasya and my IP is 192.168.1.24!”. All other computers take note of it and this is how name resolution is done. Computer shouting its name into space is called “B-node” where B stands for “broadcast”.

Broadcast approach works fine for small networks, but not for bigger ones. As the number of computers grows, name broadcasts start creating significant traffic. Also, broadcasts normally do not travel through routers. For bigger networks, Microsoft invented a concept of WINS server. A particular computer is designated as a book-keeper, and everyone sends name information just to it. Computer sending name information only to the WINS server is called “P-node”, where P stands for “peer-to-peer”.

Of course, for a P-node to work properly there must be a WINS server, and everyone else on the network must go to the same server. Since my home network does not have a WINS server, when my laptop switched to P-node mode, it lost all name resolution.

The type of NETBIOS node is stored in registry, under HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Netbt\Parameters\NodeType key. This Technet article describes possible values and their meaning.

It’s been several years since I had to deal with this stuff. For the most part, name resolution just works. Silently changing my laptop from B-node to P-node was just sneaky. It probably happened when I connected it to the office network, but I am not sure exactly when.