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Understanding GSLB Resiliency when DNS Views are used


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I have inherited a deployment and I am trying to understand what will happen to some of our GSLB'd services in the event of an outage of a HA pair, or loss of connectivity between HA pairs in a GSLB site. I'm new to ADC's implementation of GSLB so please bear with me.


An example of the setup is:


  • 2 * GSLB Sites: Site A and Site B
  • Site A subnet: 192.168.1.X
  • Site B subnet: 192.168.2.X
  • Domain: service.example.com
  • A local GSLB service in each site:
    • Site A returns a public IP of
    • Site B returns a public IP of
  • A remote service in each site corresponding to the other sites local service
  • DNS Views configured on the services as follows:
    • Site A Local Service: If a connection comes from 192.168.1.X then the view returns the VIP
    • Site A Remote service: If a connection comes from 192.168.2.X then the view returns the VIP
    • Site B Local Service: If a connection comes from 192.168.2.X then the view returns the VIP
    • Site B Remote service: If a connection comes from 192.168.1.X then the view returns the VIP
  • Monitoring is configured on the load-balanced virtual server at the end of the VIP, not on any GSLB component.
  • ADC version:


In normal operations, external queries are given or depending on location. Internal clients always get the IP in their subnet. My questions are:


  1. If I disable the Site A Remote service then force a client with IP 192.168.2.X to query Site A for service.example.com the client is returned an IP of This is the correct IP but I don't understand how the Site A ADC is able to respond with the correct IP when I have disabled the remote service. Is this MEP at work because the service is still up on the Site B ADC?
  2. If the MEP connection between ADCs is unavailable I assume each ADC will mark the "remote" service as DOWN. Is that correct? If "yes" then am I also correct in understanding that any queries originating from a client in the other site will either fail to resolve, or will be given the public IP of the service? Basically, if the MEP link is down and a client in Site A sends a query to the Site B ADC, what IP would the client be returned?
  3. If both the Local and Remote Service in each site had the same DNS views applied, how do the ADCs determine which one to respond with? (I appreciate that it doesn't really matter for the result but I would like to understand the logic behind the ADC's decision-making)


My main concern is point 2. I don't want to find ourselves in a situation where we have a site unavailable and half the internal clients are resolving the wrong address or none at all.


Any guidance or advice would be greatly appreciated. Thanks

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