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Problem using DNS TCP query on service does not support IPv6

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.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty margin-bottom:0;

0

• Symptom
  
  After adding "options use-vc" in /etc/resolv.conf, tools like wget/curl cannot resolve hostname any more. Dig/nslookup works. And if change the nameserver to 1.1.1.1, or 8.8.8.8, all work.


• Research
  
  After TCPDump with the cross matrix of wget/nslookup/myDNS/1.1.1.1. I found that:
  
  
  1. wget makes both IPv4 and IPv6 queries in one request; nslookup only makes IPv4.
  
  
  2. 1.1.1.1 returns both IPv4 and IPv6 (resolve to CNAME, not IPv6 address) answer in one response; My DNS returns only IPv4.
  
  
  3. A testing code calling getaddrinfo works the same way as wget.
  
  


• Conclusion
  
  With TCP DNS, glibc keeps asking in both IPv4 and IPv6, if the answer contains no IPv6, it fails.

Question: Is this by design? Why?

OS: Newly installed Ubuntu bionic LTS.

networking dns bind glibc

share|improve this question

edited Apr 16 at 3:56

Magicloud

asked Apr 15 at 3:54

MagicloudMagicloud

26833 silver badges1616 bronze badges

add a comment | 

0

• Symptom
  
  After adding "options use-vc" in /etc/resolv.conf, tools like wget/curl cannot resolve hostname any more. Dig/nslookup works. And if change the nameserver to 1.1.1.1, or 8.8.8.8, all work.


• Research
  
  After TCPDump with the cross matrix of wget/nslookup/myDNS/1.1.1.1. I found that:
  
  
  1. wget makes both IPv4 and IPv6 queries in one request; nslookup only makes IPv4.
  
  
  2. 1.1.1.1 returns both IPv4 and IPv6 (resolve to CNAME, not IPv6 address) answer in one response; My DNS returns only IPv4.
  
  
  3. A testing code calling getaddrinfo works the same way as wget.
  
  


• Conclusion
  
  With TCP DNS, glibc keeps asking in both IPv4 and IPv6, if the answer contains no IPv6, it fails.

Question: Is this by design? Why?

OS: Newly installed Ubuntu bionic LTS.

networking dns bind glibc

share|improve this question

edited Apr 16 at 3:56

Magicloud

asked Apr 15 at 3:54

MagicloudMagicloud

26833 silver badges1616 bronze badges

add a comment | 

• Symptom
  
  After adding "options use-vc" in /etc/resolv.conf, tools like wget/curl cannot resolve hostname any more. Dig/nslookup works. And if change the nameserver to 1.1.1.1, or 8.8.8.8, all work.


• Research
  
  After TCPDump with the cross matrix of wget/nslookup/myDNS/1.1.1.1. I found that:
  
  
  1. wget makes both IPv4 and IPv6 queries in one request; nslookup only makes IPv4.
  
  
  2. 1.1.1.1 returns both IPv4 and IPv6 (resolve to CNAME, not IPv6 address) answer in one response; My DNS returns only IPv4.
  
  
  3. A testing code calling getaddrinfo works the same way as wget.
  
  


• Conclusion
  
  With TCP DNS, glibc keeps asking in both IPv4 and IPv6, if the answer contains no IPv6, it fails.

Question: Is this by design? Why?

OS: Newly installed Ubuntu bionic LTS.

networking dns bind glibc

share|improve this question

edited Apr 16 at 3:56

Magicloud

asked Apr 15 at 3:54

MagicloudMagicloud

26833 silver badges1616 bronze badges

share|improve this question

edited Apr 16 at 3:56

Magicloud

asked Apr 15 at 3:54

MagicloudMagicloud

26833 silver badges1616 bronze badges

share|improve this question

edited Apr 16 at 3:56

Magicloud

asked Apr 15 at 3:54

MagicloudMagicloud

26833 silver badges1616 bronze badges

asked Apr 15 at 3:54

MagicloudMagicloud

26833 silver badges1616 bronze badges

asked Apr 15 at 3:54

MagicloudMagicloud

26833 silver badges1616 bronze badges