DNS does not resolve on Expressway C

[Djeten]

Hello,

I'm setting up Expressway E & C for MRA.

My traversal zone fails and I see the error 'SIP Failed: DNS resolution failed'

When I use the DNS Lookup tool to resolve the fqdn of the expressway E, indeed it fails. 

When I add a 2nd server, like 8.8.8.8, and try to resolve using all dns servers, it fails:

However, with 2 DNS servers configured, but only selecting the initial DNS server, the DNS resolution works:

Why doesn't it work with only 1 DNS server configured? And why does it only work when I configure 2 servers, but only select the right one?

Kind regards

[b.winter]

Is the hostname of the EXP-E an external or an internal one?
If it's just an internal name, then a public DNS (like your google DNS 8.8.8.8) cannot resolve it.

And can the EXP-C also resolve the Reverse Pointer for the IP-address for the EXP-E FQDN? This is mandatory as stated in the deployment guide for MRA.

[Djeten]

I don't want it to resolve to 8.8.8.8. I want it to resolve to my dns server. But when I only configure my DNS server, the resolution fails. Only when I configure a second DNS server and select my DNS server, then the resolution works... but in the traversal zone configuration, I can not select a default dns server...

[b.winter]

Have you even configured the DNS server in the settings? Under "System" --> "DNS"
What you are trying to do is just testing the DNS lookup.

[Djeten]

Yes I have configured it in the DNS settings, otherwise I would not be able to select it in the DNS lookup tool...

[b.winter]

What about the question of the reverse pointer? Have you set it in the DNS?
What does the network log say?
In the worst case, take a logging and check the pcap-file with wireshark and check the DNS packets

[Djeten]

Yes, the PTR records are configured as well... I believe my DNS server is OK, because it can resolve when I manually select my DNS server...

I will take a pcap and check...

[Djeten · Accepted solution]

Solved it... I had also configured a 'per-domain DNS server' other than the defautl dns server and I had to add the DNS records there...

Thanks for the help

[Roger Kallberg]

As @b.winter replied the external DNS server does not have your internal DNS records that the C and E uses to form the traversal zone to E, so it cannot do name resolution for the name and therefor the setup of the zone fails. This is why the per-domain DNS server setting exists so that you can tell the E, and if needed C, that it should use these specific DNS servers for the domain(s) that you define in that configuration element.

[b.winter]

If you can resolve the FQDN with the test lookup, this shouldn't be a problem.
You can also test, if you can resolve the IP to FQDN.
And if the test is good, then you need to check the logs and wireshark file.