2.3 Checking for a well-configured DNS
NNMi uses Domain Name System (DNS) to determine relationships between host names and IP addresses. This can result in a large number of name service queries when auto-discovery is enabled.
Make sure that your DNS servers are well configured to prevent long delays when resolving name service queries. This means that the DNS server responding to NNMi name service queries has these characteristics:
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The DNS server is an authoritative server and does not forward DNS requests.
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The DNS server has consistent host name-to-IP address mappings and IP address-to-host name mappings.
If the network uses multiple DNS servers, all of them must respond consistently to all name service queries.
- Important note
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Round-robin DNS (used to do load balancing of Web application servers) is not appropriate because any given host name can map to different IP addresses over time.
- Reference note
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To improve the response time for nslookup, deploy a secondary DNS service on the NNMi management server or another system on the same subnet as the NNMi management server. Configure this secondary DNS service to mirror the information from the primary DNS service. Another option is to use the following files instead of DNS in small environments:
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Windows
%SystemRoot%\system32\drivers\etc\hosts
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UNIX
/etc/hosts
On the NNMi management server, make sure that the following are configured appropriately for your environment:
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The hosts file might take precedence with some OS configurations. Make sure that the hosts file contains a minimum of two entries:
127.0.0.1 localhost
NNMi-management-server-IP-address NNMi-management-server-name
NNMi-management-server-IP-address is the IP address of the fully qualified domain name (FQDN) of the NNMi management server. NNMi-management-server-name is the FQDN name for the NNMi management server set during installation.
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Windows
Make sure that all DNS servers used by the NNMi management server provide consistent host name-to-IP address mappings and IP address-to-host name mappings.
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UNIX
Make sure that nslookup discovery conforms to the nslookup command discovery sequence set in the nsswitch.conf file.
Make sure that all DNS servers that you are aware of provide consistent host name-to-IP address mappings and IP address-to-host name mappings.
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If you know that there are problems with the DNS configuration in your network domain (host names or addresses that do not resolve properly), instruct NNMi to avoid nslookup requests for unimportant devices. The benefits of doing this are as follows:
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Speed up spiral discovery
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Keep network traffic generated by NNMi to a minimum.
To identify problem devices to NNMi, create the two files listed below before configuring NNMi discovery. NNMi never issues a DNS request for host names or IP addresses identified in these files.
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hostnolookup.conf (enter fully qualified domain names or wildcards that identify groups of host names)
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ipnolookup.conf (enter IP addresses or wildcards that identify groups of IP addresses)
Use a text editor to populate the files. Place the files in the following locations on the NNMi management server:
- Windows
%NnmDataDir%shared\nnm\conf\
%NnmDataDir% is the data directory specified during installation.
- UNIX
/var/opt/OV/shared/nnm/conf/