DNS Maintenance, Updates, and Scavenging


DNS RRs often become stale, or no longer relevant, as computers are disconnected from the network or IP addresses are changed without first notifying the DNS server. The process of scavenging those records removes them from a database after their original owners do not update them. Scavenging is not turned on, by default, but you can enable this feature in Windows Server 2003 by following these steps:

  1. Open the DNS MMC snap-in by Start, Administrative Tools, DNS.

  2. Right-click the server name and choose Properties.

  3. Select the Advanced tab.

  4. Check the Enable Automatic Scavenging of Stale Records box.

  5. Select a scavenging period, as shown in Figure 13.18, and click OK to save your changes.

    Figure 13.18. Turning on scavenging.

    graphics/13fig18.jpg

Scavenging makes a DNS database cleaner, but aggressive scavenging can also remove valid entries. It is therefore wise, if you're using scavenging, to strike a balance between a clean database and a valid one.

Root Hints

By default, a DNS installation includes a listing of Internet-level name servers that can be used for name resolution of the .com , .net , .uk , and like domain names on the Internet. When a DNS server cannot resolve a query locally in its cache or in local zones, it consults the Root Hints list, which indicates which servers to begin iterative queries with.

The Hints file should be updated on a regular basis to ensure that the servers listed are still relevant. This file is located in \%systemroot%\system32\DNS\cache.dns and can be updated on the Internet at the following address:

ftp://ftp.rs.internic.net/domain/named.cache

Forwarders

Forwarders are name servers that handle all iterative queries for a name server. In other words, if a server cannot answer a query from a client resolver, servers that have forwarders simply forward the request to an upstream forwarder that will do the iterative queries to the Internet root name servers. Forwarders are used often in situations in which an organization uses the DNS servers of an ISP to handle all name-resolution traffic. Another common situation occurs when Active Directory's DNS servers handle all internal AD DNS resolution but forward outbound DNS requests to another DNS environment within an organization, such as a legacy Unix BIND server.

In conditional forwarding, queries that are made to a specific domain or set of domains are sent to a specifically defined forwarder DNS server. This type of scenario is normally used to define routes that internal domain resolution traffic will follow. For example, if an organization controls the companyabc.com domain namespace and the companyxyz.com namespace, it might want queries between domains to be resolved on local DNS servers, as opposed to being sent out to the Internet just to be sent back again so that they are resolved internally.

Forward-only servers are never meant to do iterative queries, but rather to forward all requests that cannot be answered locally to a forwarder or set of forwarders. If those forwarders do not respond, a failure message is generated.

If you plan to use forwarders in a Windows Server 2003 DNS environment, you can establish them by following these steps:

  1. Open the DNS MMC snap-in by choosing Start, Administrative Tools, DNS.

  2. Right-click the server name and choose Properties.

  3. Select the Forwarders tab.

  4. In the DNS Domain box, determine whether conditional forwarders will be established. If so, add them by clicking the New button.

  5. Add the IP address of the forwarders into the Selected Domain's Forwarder IP Address List box, as shown in Figure 13.19.

    Figure 13.19. Setting up forwarders.

    graphics/13fig19.jpg

  6. If this server will be configured only to forward, and to otherwise fail if forwarding does not work, check the Do Not Use Recursion for This Domain box.

  7. Click OK to save the changes.

Using WINS for Lookups

In environments with a significant investment in WINS lookups, the WINS database can be used in conjunction with DNS to provide DNS name resolution. If a DNS query has exhausted all DNS methods of resolving a name, a WINS server can be queried to provide for resolution. This method creates several WINS RRs in DNS that are established to support this approach.

To enable WINS to assist with DNS lookups, follow these steps:

  1. Open the DNS MMC snap-in by choosing Start, Administrative Tools, DNS.

  2. Navigate to DNS\< Servername >\Forward Lookup Zones.

  3. Right-click the zone in question and choose Properties.

  4. Choose the WINS tab.

  5. Check the Use WINS Forward Lookup box.

  6. Enter the IP address of the WINS Server(s), click Add, and then click OK to save the changes.



Microsoft Windows Server 2003 Insider Solutions
Microsoft Windows Server 2003 Insider Solutions
ISBN: 0672326094
EAN: 2147483647
Year: 2003
Pages: 325

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