I noticed something really really strange I can't figure out, while wiresharking both my 2 Ubuntus 14.04 LTS : somehow randomly, Ubuntu seems to drop some incomming DNS replies. This happens both for IPv4 and IPv6, with ip(6)tables -P INPUT ACCEPT / ip(6)tables -P OUTPUT ACCEPT. Here are the Wireshark records ( obfuscated ) :
Internet Control Message Protocol / Type: 3 (Destination unreachable) / Code: 3 (Port unreachable) Internet Protocol Version 4, Src: 126.96.36.199 (188.8.131.52), Dst: 192.168.1.140 (192.168.1.140) User Datagram Protocol, Src Port: domain (53), Dst Port: 26305 (26305)
ICMPv6 / Type: Destination Unreachable (1) / Code: 4 (Port unreachable) Internet Protocol Version 6, Src: 2620:0:ccc::2 (2620:0:ccc::2), Dst: 2001:db8:0:2::200 (2001:db8:0:2::200) User Datagram Protocol, Src Port: domain (53), Dst Port: 60285 (60285)
This happens at random times, only a few replies dropped while a big DNS benchmark. I does happen when not benchmarking of course. It happens the same on two, distinct, fresh installed and perfectly working Ubuntu 14.04 LTS install.
I've researched the web, found a few hints ( related to dnsmasq / new Ubuntu way to handle DNS requests / 127.0.0.1 local nameserver ), but nothing that allowed me to get rid of those ennoying DNS replies drop.
Any clues about this ?