Resolves hostnames using reverse DNS lookups.
If a lookup fails, it will keep the event but not add the given field.
The number of resulting events from this function is limited by the
configuration parameter MAX_STATE_LIMIT, whose default
limit is 20000. If the number of events exceeds this limit, the result
will be truncated with a warning.
To prevent the rdns function from blocking query execution for an
indeterminate amount of time, a timeout is applied to all RDNS requests.
If an RDNS request doesn't return a result within the timeout, the lookup
is considered to have failed for the associated event. However, if the
request eventually returns, its result is added to an internal cache
within LogScale for a period of time. Therefore, a static query using the
rdns function may fail a lookup for an event on its
first execution, but succeed in a subsequent execution. In live queries
this behaviour is less of a problem, as the rdns
function will be evaluated continually. Thus, it is preferable to mainly
use the rdns function in live queries.
Note
Note that reverse DNS can generally not be considered authoritative and should only be considered informational. The owner of an IP address can change it to point to an arbitrary hostname.
For an authoritative alternative without the above limitations, consider
using asn() instead.
If no RDNS server is specified then a system default is used. This can be
overwritten via server to select a different default
server.
The allowed IP addresses and servers that can be queried can be restricted by setting:
IP_FILTER_RDNS– for filtering which IP addresses one may do reverse dns queries against.IP_FILTER_RDNS_SERVER– for filtering which DNS servers may be specified in the function.
| Parameter | Type | Required | Default | Description |
|---|---|---|---|---|
as | string | false | hostname | Specifies the field into which the resolved value is stored. |
field | string | true | Specifies the field to run the RDNS lookup against. [a] | |
server | string | false | Specifies a DNS server address. | |
rdns() Examples
Resolve ipAddress (if present) using the server 8.8.8.8, and store the resulting DNS name in dnsName
rdns(ipAddress, server="8.8.8.8", as=dnsName)Resolve ipAddress (if present) and store the resulting DNS name in hostname
rdns(ipAddress)