Often, Microsoft Official Curriculum (MOC) courses breeze past the Browser Service. Yet, it is one of the more important elements of any Microsoft network.
In this three-part article, I've been offering information and tips about the nature and use of Browser Service. In part three, the finale of the series, I offer some insights into the uses of Master Browsers and Windows Internet Naming System (WINS).
WHAT THE MASTER BROWSER DOES
The Master Browser is responsible for keeping up the browse list and disseminating it to the backup browsers on the local network. It does very little talking to clients, except to tell them where they can find a backup browser. All systems running the Server service will announce themselves to the Master Browser at startup using a host announcement datagram, and then at 4, 8, and 12 minute intervals, and every 12 minutes thereafter. The Master Browser compiles all of these entries into the subnet's browse list.
If a domain consists of more than one TCP/IP subnet, each subnet will have its own Master Browser. The Master Browser updates the backup browser's browse lists, and also exchanges its browse list with the Domain Master Browser. It does this by sending an announcement over UDP port 138 to the Domain Master Browser, telling it to retrieve a copy of the Master Browser's browse list.
CHOOSING A MASTER BROWSER
An administrator may want one system on a subnet to be the subnet's Master Browser for a variety of reasons. This can be done by revisiting the HKEY_LOCAL_MACHINE\ SYSTEM\CurrentControlSet\Services\Browser\Parameters entry in the registry and setting an entry named IsDomainMasterBrowser to Yes. This entry will let the system in question win all browser elections by giving it priority over all other systems, unless there is a condition that prevents it (i.e. the system must be online during an election). I won't comment on the parallel to local politics, besides, I'm sure it's not true.
DOMAIN MASTER BROWSERS
Being the Domain Master Browser is one of the PDC's roles in an NT 4.0 domain. The Domain Master Browser will keep other Master Browsers on other TCP/IP subnets updated by collecting their browse lists, merging them all into one browse list and disseminating this browse list to all other Master Browsers in the domain on a regular basis. It does this every 12 minutes (just about everything around here happens every 12 minutes, did you notice?)
The Domain Naming Master also contacts WINS every 12 minutes for a list of all other domains registered with WINS. It does this by querying for all entries of DomainName<1b>, which are registered by all Domain Master Browsers. The Domain Master Browser will exchange its browse list with all other Domain Master Browsers, so every domain knows what is available in all other domains that are registered with the WINS service.
WHY THE BROWSER SERVICE NEEDS WINS
The Browser Service needs WINS or some type of NBNS (NetBIOS name service) because it must resolve the Master Browsers' names. Also, they must be able to resolve the Domain Master Browser's name, which the Domain Master Browser registered with WINS as the domain's name with a <1b> extension. Clients also use WINS to resolve server names in an NT 4.0 environment where NetBIOS names must be resolved. Even in a mixed Windows 2000 environment, you will probably need WINS for name resolution. Native mode Windows 2000 domains should not require WINS.
Browser elections were not covered in this article due to space limitations. Watch for my upcoming article on this topic.
About the author: Douglas Paddock is a CIW Security Analyst and MCSE, MCT, MCSA, A+, N+ qualified teacher at Louisville Technical Institute in Louisville, Ken.
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