Occasional Contributor II

RAP5 Redundancy DNS issue

I need a help on a DNS issue for RAP5 and I would like to know if anyone had had this situation before (and found a solution :) )

In a project the RAP5 is being used for WAN redundancy (over 3G). The problem is that in this case the controller has an internal IP address in the WAN ( and an "real" IP address for 3G (

We configured the RAP5 controller parameter as being the name, and we setup two DNS servers: internal that resolve to and an external DNS server that resolve to Of course RAP5 was configured with both DNS server addresses (and it can only access internal DNS when over WAN and can only reach external DNS when over 3G, so it should properly get the right IP address dependin on the situation)

The issue is that when WAN link gets down, the RAP5 does not re-resolve automatically. When WAN link goes down, the 3G link goes up, but RAP5 keep trying to access controller over IP address (it is clearly cached). If RAP5 is rebooted it works fine (as it resolves to, but when WAN link gets back to up, same problem (it keep trying to access IP).

Is there any way to configure RAP5 or the DNS servers to allow this to work? To setup a short DNS TTL (5 seconds) is not a good option, as this would create too much traffic over normal use.

Any suggestion are welcome...
Guru Elite

Re: RAP5 Redundancy DNS issue

You cannot do this the way it is setup right now. The RAP will always try to contact the controller via 3G on the internal private DNS address that you have configured, using the DNS address it got in the first place.

You might want to just try putting a DNS a-record that ONLY resolves to the public ip address. This will ONLY work if the firewall that you are doing the 1:1 NAT for the controller's public address is separate from the one you use to reach the internet via your wired connection. This should always work over 3g.

*Answers and views expressed by me on this forum are my own and not necessarily the position of Aruba Networks or Hewlett Packard Enterprise.*
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Re: RAP5 Redundancy DNS issue


This is a show stopper for 1500 RAP5s, do you think it is possible to make a RFE for this, a FLUSH DNS when the link flip?, or it is just not the way the RAPs work?

Renato Cinini
Mobility Category Manager
Aruba, an HPE Company
Latin America Region
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