DnsMonitor
This monitor tests the availability of the DNS service on remote IP interfaces. A DNS query is sent to check for a response of either an A or AAAA resource record.
The monitor is marked as up if it receives a valid response from the DNS Server. For hostnames that have multiple resource records, it is possible to test if the number of responses are within a given boundary.
The monitor can be simulated with the command line tool host:
~ % host -v -t a www.google.com 8.8.8.8
Trying "www.google.com"
Using domain server:
Name: 8.8.8.8
Address: 8.8.8.8#53
Aliases:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 9324
;; flags: qr rd ra; QUERY: 1, ANSWER: 5, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;www.google.com. IN A
;; ANSWER SECTION:
www.google.com. 283 IN A 74.125.232.17
www.google.com. 283 IN A 74.125.232.20
www.google.com. 283 IN A 74.125.232.19
www.google.com. 283 IN A 74.125.232.16
www.google.com. 283 IN A 74.125.232.18
Received 112 bytes from 8.8.8.8#53 in 41 ms| This monitor is intended for testing the availability of a DNS service. To monitor the DNS resolution of some of your nodes from a client’s perspective, use the DNSResolutionMonitor. |
DnsMonitor versus DNSResolutionMonitor
The DnsMonitor is a test against a specific DNS server. Use this service to determine if the monitored node provides DNS resolution of requests sent to it. In Meridian, the DNS server is the node and the DnsMonitor sends a lookup request for a given A record to the DNS server IP address. The service goes down if the DNS server doesn’t have a valid A record in its zone database or has other issues resolving A records.
The DNSResolutionMonitor measures the availability and record outages of hostname resolution from a client perspective. Use this service to determine if the monitored node can be resolved by DNS hosted somewhere else in your network.
Configuration and use
| Parameter | Description | Default |
|---|---|---|
retry |
Number of retries before the service is marked as down. |
0 |
timeout |
Time in milliseconds to wait for the A Record response from the server. |
5000 |
port |
UDP port for the DNS server |
53 |
lookup |
DNS A Record for lookup test |
localhost |
fatal-response-codes |
A comma-separated list of numeric DNS response codes considered fatal if present in the server’s response.
Default value is 2 and corresponds to |
2 |
min-answers |
Minimum number of records in the DNS server response for the given lookup. |
n/a |
max-answers |
Maximum number of records in the DNS server response for the given lookup. |
n/a |
This monitor implements the Common Configuration Parameters.
Example
This example shows how to monitor whether the IP interface from a given DNS server resolves a DNS request. This service should be bound to a DNS server which should be able to give a valid DNS response for DNS request www.google.com. The service is up if the DNS server gives between one and 10 A record responses.
<service name="DNS-www.google.com" interval="300000" user-defined="false" status="on">
<parameter key="lookup" value="www.google.com" />
<parameter key="fatal-response-code" value="2" />
<parameter key="min-answers" value="1" />
<parameter key="max-answers" value="10" />
</service>
<monitor service="DNS-www.google.com" class-name="org.opennms.netmgt.poller.monitors.DnsMonitor" />To have response time graphs for the name resolution you have to configure RRD graphs for the given ds-names (dns-res-v4, dns-res-v6, dns-res-both, dns-res-either, dns-res-cname-mx) in $OPENNMS_HOME/etc/response-graph.properties.