Public bug reported:
This bug is reproducable on precise and trusty, but not on xenial,
neither on EL6/EL7.
Steps to reproduce:
1) Ensure /etc/resolv.conf contains both IPv6 and IPv4 entries, starting
with an IPv6 entry:
# echo -e "nameserver 2001:4860:4860::\nnameserver
2001:4860:4860::8844\nnameserver 8.8.8.8\nnameserver 4.4.4.4\n" >
/etc/resolv.conf
2) Block the traffic from the (first) name server
# ip6tables -A INPUT -j DROP -p udp --sport 53
3) Fire up tcpdump on port 53 (preferably in a different window)
# tcpdump -n port 53 &
4) Try to resolve some DNS entry
# ping google.com
Expected behaviour: the resolver will try all name servers in
/etc/resolv.conf and will succeed when trying the IPv4 servers.
Observed behaviour: the resolver will only try the IPv6 servers.
5) Change the ordering in the resolv.conf file like this:
# echo -e "nameserver 2001:4860:4860::\nnameserver
8.8.8.8\nnameserver 2001:4860:4860::8844\nnameserver 4.4.4.4\n" >
/etc/resolv.conf
6) Retry step #4
Notice that now the resolver will only try the first entry in
/etc/resolv.conf and not the other one.
Our setup is like #5, and one single dropped package would cause
resolving to fail.
** Affects: bind (Ubuntu)
Importance: Undecided
Status: New
** Tags: bind dns resolving
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https://bugs.launchpad.net/bugs/1688549
Title:
Problems with mix of IPv4 and IPv6 entries in /etc/resolv.conf causing
occationally failed resolving
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