UNC Path Name Resolution???

Technowiz

I was on another forum helping someone with a technical issue where they could ping a server by name but couldn't get to the UNC path \\servername. Someone else who was trying to help them was pointing them toward DNS. I told them they need to look at netbios as UNC paths used netbios for name resolution. They responded that DNS was used first and then netbios. Well I didn't argue with them because I could very well be wrong. It has happened once or twice on rare occasion. But I tried to google the right answer to confirm what I was being told and still have yet to figure it out. Does anyone know how exactly UNC paths are resolved and if DNS is involved at all? Any relevant links would be great. Thanks!

undomiel

If you do some packet sniffing and watch what happens when you submit a UNC request as I recall it first attempts to use netbios unless you specify to disable netbios. Then it is supposed to fall back to DNS. Don't forget that the TCP/IP Netbios Helper Service needs to be enabled for proper resolution to occur even if you aren't using WINS & Netbios.

doom969

Actually, this correct for os'S prior to windows 2000.
(NT3.5 - Nt4,95 - 98 - ME )

In windows 2000 xp 2003 vista and 2008, the system will first try to resolve the name using dns by appending the default dns suffix. If that fail, it will then attempt to resolve using wins or a netbios bradcast.

Technowiz

Well I just tried it with wireshark and the first request for the name was made by DNS followed immediately by a NBNS name request by broadcast followed by the negative response from the DNS server. So it appears that it does indeed use DNS first. I would still like to find some official documentation on this name resolution process if anyone happens to come across it. I learn something new every day!

undomiel

Thanks for the correction doom.

Here's some documentation to help you technowiz: http://www.microsoft.com/technet/prodtechnol/windows2000serv/reskit/prork/prcc_tcp_gclb.mspx?mfr=true

It also mentions some RFCs to look at if you want to take a nap as well!

doom969

undomiel wrote:

Thanks for the correction doom.

Here's some documentation to help you technowiz: http://www.microsoft.com/technet/prodtechnol/windows2000serv/reskit/prork/prcc_tcp_gclb.mspx?mfr=true

It also mentions some RFCs to look at if you want to take a nap as well!

No prob undomiel.

Documentation on this is hard to find, I dont know why. Its one of those things you have to play with, to know it.
Since win2000, microsoft made dns the primary method of resolution for everything but the network neighborhood, wich still rely on a netbios broadcast to populate itself.
(There might be another exception that I'm not aware of.)