After upgrading my Kubuntu to 14.04 from 12.04, I got extremely slow DNS lookup in Firefox and Thunderbird.
I have checked the communications with Wireshark. Launching e.g. http://vs.hu in Firefox (28), I got the following packets:
No. Time Source Destination Protocol Length Info
1 0.000000000 192.168.1.13 192.168.1.1 DNS 65 Standard query 0xb406 A vs.hu
No. Time Source Destination Protocol Length Info
2 0.013074000 192.168.1.1 192.168.1.13 DNS 82 Standard query response 0xb406 A 91.120.239.162
No. Time Source Destination Protocol Length Info
3 0.013363000 192.168.1.13 192.168.1.1 DNS 65 Standard query 0x7f30 AAAA vs.hu
No. Time Source Destination Protocol Length Info
4 0.014928000 192.168.1.1 192.168.1.13 DNS 110 Standard query response 0x7f30 PTR vs.hu
No. Time Source Destination Protocol Length Info
5 5.003951000 192.168.1.13 192.168.1.1 DNS 65 Standard query 0x1ff5 A vs.hu
No. Time Source Destination Protocol Length Info
6 5.019617000 192.168.1.1 192.168.1.13 DNS 82 Standard query response 0x1ff5 A 91.120.239.162
No. Time Source Destination Protocol Length Info
7 5.020167000 192.168.1.13 192.168.1.1 DNS 65 Standard query 0xc659 AAAA vs.hu
No. Time Source Destination Protocol Length Info
8 5.021866000 192.168.1.1 192.168.1.13 DNS 110 Standard query response 0xc659 PTR vs.hu
No. Time Source Destination Protocol Length Info
9 10.008493000 192.168.1.13 91.120.239.162 TCP 74 45348 > http [SYN] Seq=0 Win=29200 Len=0 MSS=1460 SACK_PERM=1 TSval=267003 TSecr=0 WS=128
It starts 1-1 query, IPV4 and IPV6, both servers reply. Then it starts this process again at 5th second. Finally only at 10th seconds starts reading data from server using TCP protocol. Using Chrome browser, there is no problem, however it uses MDNS protocol in the beginning of the communication. It cannot be a hardware (driver) problem. Same problem exists both with wired and wireless LAN. Moreover I started my 2nd computer (contains Kubuntu 12.04) with 14.04 LiveCD, and this problem also emerged there immediately.
I have run a similar test on my 2nd computer with Kubuntu 12.04, where there is no problem with DNS lookups in Firefox (28). Strange, but I do not see the IPV6 query there among the packets, no repeated queries, and no delays. Checking IPV6, it is not disabled there.
By the way, ping and dig reply almost immediately on 14.04.
Does anybody know what is going on? Where are these 5 seconds delays from? Perhaps my router or the Mozilla products hate 14.04? :)
