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.

About configuring DNS

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

If you configure DNS later, you need to

Create and edit the /etc/resolv.conf file in the filer's root volume.
Specify the domain name of the filer using the dns.domainname option.
Enable DNS on the filer using the dns.enable option.
Note
If you want to use DNS as your primary method of 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.

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, open and edit the /etc/resolv.conf file using a text editor.
		Edit the files to your needs.
		Save the file.

Specifying the DNS domain name

To specify the DNS domain name, complete the following step.

Note
You can also use this procedure to change the domain name of the filer.

Step	Action
1	Enter the following command: options dns.domainname domain domain is the new 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.

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

DNS is disabled by default.

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.

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

Example

>dns info

DNS is enabled

DNS caching is enabled

5 cache hits

8 cache misses

6 cache entries

0 expired entries

0 cache replacements

IP Address   State Last Polled                Avg RTT   Calls  Errs

------------------------------------------------------------------

172.19.2.2   UP  Fri Sep 13 19:15:10 GMT 2002     430   12     0

172.19.2.16  ??                                     0    0     0

172.19.3.11  ??                                     0    0     0

Default domain: lab.netapp.com

Search domains: lab.netapp.com netapp.com