<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:st1="urn:schemas-microsoft-com:office:smarttags" xmlns="http://www.w3.org/TR/REC-html40"> <head> <meta http-equiv=Content-Type content="text/html; charset=us-ascii"> <meta name=Generator content="Microsoft Word 11 (filtered medium)"> <o:SmartTagType namespaceuri="urn:schemas-microsoft-com:office:smarttags" name="country-region"/> <o:SmartTagType namespaceuri="urn:schemas-microsoft-com:office:smarttags" name="City"/> <o:SmartTagType namespaceuri="urn:schemas-microsoft-com:office:smarttags" name="place"/>  <style>  </style>  </head> <body lang=EN-US link=blue vlink=purple> <div class=Section1> My Configuration<o:p></o:p> I would like to use the check_dns plugin (that is included in nagios-plugins-1.4.12) to verify both forward and reverse DNS lookups for one of our domains. I am reliably informed that since we don’t actually own the IP space where our servers reside, we have only been given partial control over the DNS setup. As a result, we get somewhat unusual responses from a straightforward (reverse) nslookup on some of our IP addresses.<o:p></o:p> <o:p> </o:p> Let me elaborate: <o:p></o:p> <o:p> </o:p> # nslookup XXX.XXX.XXX.XXX<o:p></o:p> Server: AAA.BBB.CCC.DDD<o:p></o:p> <o:p> </o:p> Non-authoritative answer:<o:p></o:p> XXX.XXX.X.XXX.in-addr.arpa canonical name = XXX.XXX-XXX.XXX.X.XXX.in-addr.arpa.<o:p></o:p> XXX.XXX-XXX.XXX.X.XXX.in-addr.arpa name = host.mydomain.com.<o:p></o:p> <o:p> </o:p> Authoritative answers can be found from:<o:p></o:p> ....<o:p></o:p> ....<o:p></o:p> ....<o:p></o:p> #<o:p></o:p> <o:p> </o:p> The Problem<o:p></o:p> When I use the check_dns plugin to test this reverse lookup, it seems to return a list of 2 comma-separated matches for the hostname, and this makes it very messy to write a clean nagios command based around check_dns. Looking at the source (check_dns.c) I see that on line 135, it is matching any line of output from the nslookup response that contains the string “name = ” and appending this to a list of host names associated with this IP address. <o:p></o:p> <o:p> </o:p> Proposed Solution<o:p></o:p> I have worked around this problem by modifying check_dns.c as follows:<o:p></o:p> <o:p> </o:p> $ diff check_dns.old check_dns.c<o:p></o:p> 135c135<o:p></o:p> < if ((temp_buffer = strstr (chld_out.line[i], "name = ")))<o:p></o:p> ---<o:p></o:p> > if ((temp_buffer = strstr (chld_out.line[i], "name = ")) && (NULL == strstr (chld_out.line[i], "canonical name = ")))<o:p></o:p> <o:p> </o:p> This change tells the plugin to ignore any nslookup output containing the string “canonical name = ” but still matches those containing “name = “. And, for me, it does what I need.<o:p></o:p> <o:p> </o:p> Question<o:p></o:p> So, my question is this. Is the above change valid and should it be included in the next release, or perhaps a command-line option added to cater for such situations.<o:p></o:p> <o:p> </o:p> All comments welcome.<o:p></o:p> <o:p> </o:p> Many thanks,<o:p></o:p> <o:p> </o:p> -- James Mernin Senior Software Engineer,<o:p></o:p> Telecommunications Software & Systems Group,<o:p></o:p> Waterford Institute of Technology,<o:p></o:p> <st1:place w:st="on"><st1:City w:st="on">Waterford</st1:City>, <st1:country-region w:st="on">Ireland</st1:country-region></st1:place>.<o:p></o:p> <o:p> </o:p> +353 (0)51 845694 | <a href="mailto:jmernin@tssg.org">mailto:jmernin@tssg.org</a> | <a href="http://www.tssg.org/">http://www.tssg.org</a> | <a href="http://www.wit.ie/">http://www.wit.ie</a><o:p></o:p> <o:p> </o:p> </div> </body> </html>