Unexpected behaviour of 'attempts' option in /etc/resolv.conf

Question

I'd like Linux to make only one request to DNS server, wait for 5 sec timeout and then abort the lookup if no answer.

To do this I set the following options in /etc/resolv.conf assuming that attempts element in options means the exact number of DNS requests:

nameserver 'DNS Server IP address'
domain     'Domain Name'
options     attempts:1 timeout:5

But the system behaves unexpectedly. In fact for these settings I observe:

DNS request
Wait for a 5 sec timeout
DNS request repeat
Wait for a 5 sec timeout

If I set attempts:2, there will be 4 requests.

Do I correctly understand that '1 attempt' in fact means 'make a request and then re-request after timeout'?
Is there a way to change this behaviour so the system would send only one DNS request in scope of 1 attempt?

Thanks

score 1 · Answer 1 · answered Nov 24 '17 at 21:41

1

Your interpretation looks correct to me.

Did you check what these two queries are? Maybe the first one is for AAAA record and second one is for A record, which is the normal behavior. If so, try adding inet6:off in options Also, probably trivial, but verify the number of nameserver items you have. The timeout is for each of them sequentially.

answered Nov 24 '17 at 21:41

Patrick Mevzek

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`inet6:off` terrible advice – Jacob Evans Nov 25 '17 at 07:16
Yes, this is only to debug the reason for the two queries. – Patrick Mevzek Nov 25 '17 at 09:23
1

Or run tcpdump? – Jacob Evans Nov 25 '17 at 15:12
Hello guys, thanks for the answers. By 'DNS request' I mean both A and AAAA type of queries. So in fact I observe in traces 'A request, AAA reguest, timeout, A request, AAAA request, timeout'. So both types of queries are duplicated. – Maxim Nov 27 '17 at 09:30

Unexpected behaviour of 'attempts' option in /etc/resolv.conf

1 Answers1