Using DNS to maintain host information

Advantage of using DNS

DNS enables you to maintain host information centrally. As a result, you do not have to update the /etc/hosts file every time you add a new host to the network. If you have several filers on your network, maintaining host information centrally saves you from updating the /etc/hosts file on each filer every time you add or delete a host.

A conventional filer policy for efficient host name resolution is to do both of the following:

Maintain a short /etc/hosts file containing local interfaces, as described in Ways to add entries to the /etc/hosts file.
Enable DNS with DNS caching, as described in About configuring DNS and What DNS name caching does.

About configuring DNS

You can configure the filer to use one or more DNS servers either during the setup procedure or later using the command line or FilerView.

If you configure DNS during the setup procedure, the filer's DNS domain name and name server addresses are configured

Automatically if you use DHCP to configure onboard interfaces
Manually if you do not use DHCP--you must enter the values when prompted

If you configure DNS later, you need to take these actions:

Specify DNS name servers.
Specify the DNS domain name of the filer.
Enable DNS on the filer.

You can enable DNS and set DNS configuration values in either of these ways:

Using FilerView
See Configuring DNS with FilerView.
At the command line
See the appropriate instructions:

If you want to use primarily DNS for host-name resolution, specify it ahead of other methods in the hosts map in the /etc/nsswitch.conf file. For information about how to edit the nsswitch.conf file, see Changing the host name search order.

Correct host-name resolution depends on the correct configuration of the DNS server. If you experience problems with host-name resolution or data availability, check the DNS server in addition to local networking.

For more information about filer DNS resolution of host names, see the NetApp dns(8) manual page.

Configuring DNS with FilerView

To set or modify DNS configuration values with FilerView, complete the following steps.

Step	Action
1	In FilerView, click Network in the list on the left.
2	In the list under Network, click Manage DNS and NIS Name Service.
3	If you want to....	Then...
	Enable DNS	Select Yes in the DNS Enabled field.
	Set or modify the DNS domain name	Enter a name in the DNS Domain Name field. Examples of configuration values are listed in Specifying the DNS domain name.
	Specify or modify DNS servers	Enter up to three IP addresses in the DNS Servers fields. Examples of configuration values are listed in Creating or editing /etc/resolv.conf.
	Specify or modify the search list for host name lookup	Enter a name in the DNS Domain Search field.

Creating or editing /etc/resolv.conf

To create or edit the /etc/resolv.conf file, complete the following step.

Step	Action
1	If...	Then...
	You are creating the /etc/resolv.conf file	Using a text editor, create the /etc/resolv.conf file in the root volume. The file can consist of up to three lines, each specifying a name server host in the following format: nameserver ip_address Example: nameserver 192.9.200.10 nameserver 192.9.200.20 nameserver 192.9.200.30
	You are editing the /etc/resolv.conf file	From a workstation that has access to the filer's root volume, edit the /etc/resolv.conf file using a text editor.

You can optionally set or modify the domain search list for DNS host name lookup. For more information, see the NetApp resolv.conf(5) manual page.

Specifying the DNS domain name

To specify or change the DNS domain name, complete the following step at the filer command line.

Step	Action
1	Enter the following command: options dns.domainname domain domain is the new domain name, which follows the filer host name in the fully qualified domain name. For example, the domain name of a filer toaster.netapp.com is netapp.com.

Disabling or enabling DNS

To disable or enable DNS, complete the following step at the filer command line.

Step	Action
1	Enter the following command: options dns.enable {off\|on} Use `off` to disable DNS or `on` to enable DNS.

If you did not configure DNS during the Data ONTAP setup procedure, DNS is disabled by default.

Once enabled, DNS should be disabled only when you change host-name resolution procedures or when you troubleshoot problems with the DNS name server or Windows Active Directory server.

Note
The filer CIFS implementation depends on DNS to provide the Windows Active Directory service. Therefore, disabling DNS might interrupt CIFS services.

What DNS name caching does

DNS name caching enables the DNS name resolver to speed up the process by which it converts host names into IP addresses. DNS name caching stores DNS requests by caching them so that they are easy to find the next time. Name caching improves DNS performance in the case of name server failure as well as reducing the time it takes for cluster takeover and giveback.

Disabling or enabling DNS name caching

To disable or enable DNS name caching, complete the following step at the filer command line.

Caution
Disabling DNS name caching clears the DNS name cache.

Step	Action
1	Enter the following command: options dns.cache.enable {on\|off} Use `on` to enable DNS name caching or `off` to disable DNS name caching.

DNS name caching is enabled by default.

Flushing the DNS cache

Entries in the DNS cache have a set expiration. If an entry that has expired is needed again, the filer contacts the DNS server to get an updated entry. However, if a DNS entry changes before it has expired, you must flush the DNS cache to force the filer to get the new DNS record.

If some of your DNS records change often, you should make sure that your DNS server transmits them with a low Time to Live (TTL). (You set this in the DNS server.) You can also disable DNS caching on the filer via the dns.cache.enable option, but this may have an adverse performance impact.

To flush the DNS cache, complete the following step.

Step	Action
1	Enter the following command: dns flush

Displaying DNS information

You can display the following types of DNS information:

Status of the DNS resolver
List of DNS servers configured in the /etc/resolv.conf
State of each DNS server
Timestamp when the DNS server was last polled
Average round-trip time of a DNS query
Total number of DNS queries made
Number of failed DNS queries
Default domain configured on the filer
List of other domains that will be used with unqualified names for name lookup

To display DNS information, complete the following step.

Step	Action
1	Enter the following command: dns info

For more information about the dns info display, see the NetApp dns(1) manual page.