Replication

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Replication

Because WINS clients are configured to communicate only with specified WINS servers, the database on each WINS server may not have entries for all the WINS clients in the network. In fact, many TCP/IP implementations divide WINS clients among different WINS servers to balance the load. Unfortunately, WINS clients cannot resolve addresses registered with another WINS server unless the registrations from that server are somehow copied to the client’s WINS server. WINS replication is the process used to copy one WINS server’s database to another WINS server.

You can configure a WINS server so it replicates its database with another WINS server. This way, clients registered with one WINS server can be added to the database of another server. Static mappings entered on one server are also replicated to replication partners. In fact, you can enter static entries on only one WINS server and yet these entries can be propagated to any number of WINS servers through replication.

After you enable replication, clients seeking name resolution can see not only entries from their server but entries of the replication partners. Remember that clients register their names with the WINS server for which the clients are configured. WINS registrations are not done through broadcasts (in fact, one of main benefits of WINS is the reduction of broadcast traffic). Because one WINS server is collecting registrations just for its clients, the only way for its clients to resolve names registered with another WINS server is for replication to be configured between the servers.

To set up replication, you must configure a WINS server as a push partner or a pull partner. A push partner sends its entries to another server, such as if you want to send a copy of the database from this WINS server to the other WINS server. A pull partner receives entries from another server, such as if you want this server to receive a copy of the database from another WINS server. You must always configure WINS servers in pairs; otherwise, replication won’t work. Figure 9.3 shows a WINS server that is configured to be a push and a pull partner.

At the very least, one WINS server must be a push partner to send its entries out, while the other WINS server must be a pull partner to receive the entries. Replication does not occur unless both WINS servers are properly configured. If both WINS servers are configured as push and pull partners, then each server ends up with entries from the other server. In theory, the combined database on each WINS server should be the same. However, due to the lag time in replication, this doesn’t always happen. Exercise 9.7 at the end of the chapter shows how to configure a WINS server as a replication partner.

Deciding which WINS server will be a push partner and which will be a pull partner is often driven by performance considerations. You often use a pull partner across slow WAN links because you can configure a pull partner to replicate only at certain times, such as at night when the WAN link is not as heavily utilized. In this case, you could make the WINS server on each side of the WAN link a pull partner with the other WINS server. This is known as pull-pull replication.

On faster links, you can use push partners. Push partners replicate when a specified number of changes are made to the database. These updates can happen fairly frequently, but are not too large because you are not waiting to replicate a whole day’s worth of changes. If you want two WINS servers to have identical databases, you must configure each WINS server to be a push and a pull partner for the other server.

You can configure a replication partner to start replication in several ways:

1.	When the WINS server starts, you can configure this startup replication for either a push or a pull partner.
2.	At a specified interval, such as every 24 hours. This applies to pull replication.
3.	When a push partner reaches a specified number of changes to the database. These changes include name registrations and name releases. When this threshold is reached, the push partner notifies all its pull partners that it has changes for replications.
4.	You can manually force replication from the WINS Manager.

WINS can automatically replicate with other WINS servers if your network supports multicasting. By default, every 40 minutes, each WINS server sends a multicast to the address 224.0.1.24. Any servers found through this multicast are automatically configured as push and pull partners, with replication set to occur every two hours. If the routers on your network do not support multicasting, the WINS servers only see other servers on the same subnet.

You can turn off this multicasting feature by editing the registry in the following location:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\NetBT\Parameters

Change the value of UseSelfFndPnrs to 0. Change the value of McastIntvl to a large number.

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