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I have found that the Azure DNS service does not return an IP address on the CNAME record lookup. For example Google or AWS Route 53 DNS servers kindly return IP addresses of corresponding A record on the same query. For test purposes I created www1 CNAME record pointing to the www.myzone.com:

AWS Route 53 test

$ dig www.myzone.com @ns-560.awsdns-06.net
;; ANSWER SECTION:
www.myzone.com.        7200    IN      A       MY.IP.ADD.RESS

$ dig www1.myzone.com @ns-560.awsdns-06.net
;; ANSWER SECTION:
www1.myzone.com.       3600    IN      CNAME   www.myzone.com.
www.myzone.com.        7200    IN      A       MY.IP.ADD.RESS

Google DNS servers shows same result:

$ dig www1.myzone.com @8.8.8.8
;; ANSWER SECTION:
www1.myzone.com.       3599    IN      CNAME   www.myzone.com.
www.myzone.com.        7199    IN      A       MY.IP.ADD.RESS

MS Azure test

$ dig www.myzone.com @ns1-02.azure-dns.com
;; ANSWER SECTION:
www.myzone.com.        7200    IN      A       MY.IP.ADD.RESS

$ dig www1.myzone.com @ns1-02.azure-dns.com
;; ANSWER SECTION:
www1.myzone.com.       3600    IN      CNAME   www.myzone.com.

Note that the Azure DNS returns no IP address on the 2nd query.

My question: is it an expected behavior and can I configure Azure DNS to return corresponding A record on the CNAME request like AWS or Google do?

I've found couple of the similar but unanswered topics on the MS forums (1, 2).

2

Yes, name server should return both CNAME and A in your specific scenario. RFC1034 says "Both of these RRs would be returned in the response to the type A query".

3

What you have observed is the current by-design behaviour of Azure DNS. Azure DNS does not currently 'chase' domain names in CNAME (and similar record type) RDATA. Instead, it relies on the recursive DNS service to re-query--which it does, so the scenario works end to end. There is a slight additional latency caused by the re-query, but in practice this is negligible due to DNS caching.

The reason for this design is to prevent chasing across domain names. For example, if you have foo.com on an Azure DNS name server, it may be shared with bar.com on the same name server belonging to someone else. We don't chase from foo.com to bar.com, since you might prefer to use a different bar.com on a different server.

We are tracking a backlog item to enable chasing within a domain name in future.

Jonathan Tuliani, Program Manager, Azure DNS

  • Can we get a status update on this? It seems to me that following RFC would be the best way. – S. Walker Sep 14 '18 at 17:21

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