CSS: How does DNS Scripted Keepalive (ap-kal-dns) work?

Answered Question
Sep 29th, 2010
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Hello everyone,


I have a question about how does DNS Scripted Keepalive (ap-kal-dns) work on CSS 11503.


According to the "Using the CSS Scripting Language",

http://www.cisco.com/en/US/partner/docs/app_ntwk_services/data_center_app_services/css11500series/v7.50/configuration/administration/guide/Scripts.html


it says


Since we just want to see if the DNS server is alive we will send a simple DNS Query.  This query is hard coded in hexadecimal and sent raw to the DNS server.


and


Receive some unexplained response. We don't care what it is because an unstable DNS server or a non-existent one would probably not send ! us any data back at all.


but it also says


Failure Upon: 1. Not resolving the host's IP from the domain name


And according to the "How to Configure the CSS to Load Balance DNS Servers and Use the DNS Scripted Keepalives",


http://www.cisco.com/en/US/partner/products/hw/contnetw/ps789/products_configuration_example09186a00801d015a.shtml


it says


The script is hard-coded to resolve www.cisco.com.  It does not matter if the DNS server can resolve this address or not, as long as a DNS response comes back that the service is alive. This keepalive is only testing if a DNS server can respond to a query, not if it can resolve a specific name. The script queries from the CSS to DNS internal servers keep track of the availability of the DNS servers.


but it also says


Access to Internet Domain Name System Root Servers is required for successful implementation of DNS scripted keepalives.


So I am confused whether DNS server has to resolve the host's IP address correctly for DNS query received from CSS or just needs to reply any response but not need to resolve it.


I would like to recap about my question.


Q1: Does DNS Scripted Keepalive (ap-kal-dns) send DNS query with cisco.com as DNS name by default?

Q2: Does DNS server has to resolve IP address of  cisco.com or just need to respond for DNS query with any response but not need to resolve IP address of cisco.com?


I understand I should get capture data and see how DNS scripted keepalive works, but I can not prepare lab environment to do it at the present.


Your information would be appreciated.


Best regards,


Shinichi

Correct Answer by Gilles Dufour about 6 years 9 months ago

yes the query is for www.cisco.com and the script expect a reponse that contains the word cisco.


Gilles.

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Correct Answer
Gilles Dufour Thu, 09/30/2010 - 05:44
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yes the query is for www.cisco.com and the script expect a reponse that contains the word cisco.


Gilles.

snakayama Mon, 10/04/2010 - 18:21
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Hi Gilles,


Thank you very much for your reply!


Best regards,


Shinichi

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