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by spooks
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Exam Hints: WINS & WINS Proxy |
8/18/03 |
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By Orion IV
For the 70-216 test, a lot of focus will be on how well you understand WINS and different scenarios where WINS, WINS Proxy, NetBIOS and broadcasts are used.
First, you must have a thorough understanding of how to install and configure a WINS server and what hostname and NetBIOS name resolution is as opposed to DNS name resolution.
Second, this paper is to guide you through some of the more advanced topics and tricky question types you might see in one form or another at the test.
Let’s examine a sample network:
We have 2 subnets – A and B. We have a mixed environment with Windows and UNIX. There is no DNS service on the network, only NetBIOS is used for hostname resolution.
So let’s look at the kinds of problems we might be presented with.
- The first types of questions could relate to understanding NetBIOS, broadcasts and the “LMHosts” file.
- What hosts can communicate? If we look at the figure we will see both segments have both UNIX and Windows clients. Using NetBIOS they can communicate by broadcasts to discover who is on the subnet. Broadcasts will not be allowed across the routers, so all hosts on Subnet A can communicate amongst themselves and so can the hosts on Subnet B. So in order for hosts on Subnet A to be able to access files or web-pages on the servers located on Subnet B, they must know the IP address up front by using either the LMHost file or have a WINS infrastructure implemented.
Note that even though no DNS infrastructure has been implemented it is not impossible for clients to access the Web-Server; the name resolution is just different than usual on the Internet by using NetBIOS to find the IP address of the server. One could type in “http://NETBIOS-name” in the browser and the client will use any IP resolution it has available – DNS, WINS, Broadcasts, Host file or LMHosts file.
- A tricky question might relate to a host on Subnet A that used to be able to communicate with a server on Subnet B, but after the server was renamed it cannot anymore – Why? The point here is to identify how they once communicated. If WINS is implemented the problem could be an incorrect static entry now that the server name is changed, a crashed WINS or WINS Proxy server, or an outdated entry to the local LMHosts file of the client. Often the available solutions in the test will give you a hint.
- Next the WINS infrastructure is implemented, so there might be some questions on who can use this service.
- After WINS has been implemented the first simple types of questions might ask you who can use WINS. Only Microsoft clients can use WINS for host-name lookup and must be WINS clients that register their hostname in the WINS database automatically. So for any Windows client to resolve a UNIX server on the “other” subnet across the router, manual entries with host-name to IP must be added to the WINS database. Now all hosts can be resolved by using WINS - if the client is capable of using WINS.
- Next it would be interesting to make the UNIX servers able to use NetBIOS host-name resolution across the network subnets. To do this, a WINS Proxy is used to intercept the UNIX host’s NetBIOS broadcasts on each subnet (segment). The WINS Proxy server will then forward the lookup to the WINS server and return the answer as if the target host had answered itself with “host-name abc, this is me! – my IP is w.x.y.z”. It doesn't matter which subnet the WINS server is on, each subnet requires a WINS Proxy to do perform this service for non-WINS clients on that particular subnet. Also, make sure the WINS Proxy points to the WINS server.
- Finally, the topics Tombstoning, Hub-and-spoke and replication will be important topics to prepare for.
- Tombstoning is marking WINS records as obsolete and ready for deletion. This is necessary you have more than 1 WINS server in order to avoid situations where we delete a host on one WINS server only to have it replicated back from the other WINS server.
- Hub-and-spoke is a topology where the WINS servers replicate with one central “hub” WINS server that all others connect and replicate with. This makes it possible for all WINS records to be replicated to all servers in two steps, from a WINS server to the Hub WINS server and them to all other WINS servers. There may be more than two steps in some cases. Relating to the Hub-and-spoke, one might be asked about the convergence time of the replication. In the typical 2 step scenario the convergence time is the maximum time that will occur before a replication is completed to all WINS servers in the Hub-and-spoke topology. The convergence time is equal to the sum of the two longest replication intervals.
- One should also be sure to know what Burst Handling is and how it is used. It is used when multiple hosts try to register their host-names at a WINS server and the server simply can’t keep up with all the requests. The server then grants a temporary registration to the clients and asks them to come back for proper registration in the WINS database within a short period of time. Each host is given a random time so the problem is not just postponed a little. If a lot of hosts can’t register in WINS, one might have to enable Burst Handling or decrease the threshold for Burst Handling. This situation will typically happen after a general power down of all clients because of a power outage.
- Replication happens between WINS servers by using either Push replication to notify other WINS servers after a preset number of changes so they then ask for a replication or after regular timed intervals using Pull replication. Often both are used so replication happens after a certain number of changes or after a specific time interval. Be sure not to confuse the two!
Enjoy!
Additional reading:
Windows 2000 Server Windows Internet Naming Service Overview
WINS Best practices
Deleting and tombstoning records
Deploying WINS
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