pastebin - Untitled - post number 678550

DNS Resolving issues over ipv4(?)

 

Ubuntu feisty, 2.6.20-16-generic #2 SMP x86_64 GNU/Linux.

 

After briefly playing with OpenDNS DNS servers as a secondary DNS (208.67.222.222) and subsequently removing it (leaving the router gateway 10.13.37.76 as primary DNS) I began to notice some abnormalities on my system; I mention this only because of the tight correlation in time and subject. I have no idea if it was causative with respect to my to-be-explained probem.

 

Quite suddenly after restarting Opera for arbitrary reasons I found I was no longer able to load websites which rely on DNS resolution. When I manually substituted the IP of the domains in question (resolved via ping and/or host in a terminal) I had no issues (besides images and such not on the same http server failing to load). I tried restarting and waited more than 10 minutes with Opera open to see if it was caching issues. It was not. I should note that firefox worked fine at this point. I thought to try disabling ipv6, thinking opera might have been having a problem with seeing ipv6 routes that weren't there or something equally outlandish.

 

terminal with ipv6 enabled, initial system state:

$ ip -6 route

fe80::/64 dev eth0  metric 256  expires 21333570sec mtu 1500 advmss 1440 hoplimit 4294967295

ff00::/8 dev eth0  metric 256  expires 21333570sec mtu 1500 advmss 1440 hoplimit 4294967295

$ ip a | grep inet6

    inet6 ::1/128 scope host

    inet6 fe80::250:8dff:feef:3220/64 scope link

$ lsmod | grep v6

ipv6                  307456  12

$ host www.google.com

www.google.com is an alias for www.l.google.com.

www.l.google.com has address 64.233.167.104

www.l.google.com has address 64.233.167.99

www.l.google.com has address 64.233.167.147

(network connectivity)

 

I then created 'bad_list' in modprobe.d/ containing the line "alias net-pf-10 off", restarted, and did the above again and also tried out a variety of applications using DNS resolution (not limited to opera and firefox as shown here).

 

terminal with ipv6 disabled:

$ ip -6 route

10.13.37.0/24 dev eth0  proto kernel  scope link  src 10.13.37.192

169.254.0.0/16 dev eth0  scope link  metric 1000

default via 10.13.37.76 dev eth0

$ ip -a | grep inet6

(null)

$ lsmod | grep v6

(null)

$ host www.google.com

www.google.com is an alias for www.l.google.com.

www.l.google.com has address 64.233.167.99

www.l.google.com has address 64.233.167.104

www.l.google.com has address 64.233.167.147

$ firefox &

[1] 5666

$ opera &

[1] 5668

 

With ipv6 disabled both opera and firefox failed to resolve any domain. So it is likely not an opera problem. I was thrown off track because I had ipv6 resolution disabled in firefox (about:config, filter: network.dns.disableIPv6 < true) *with ipv6 up* and that didn't stop firefox, or other applications using icmp and/or dns resolution for that matter, from working fine. I wouldn't have suspected this behavior was possible initially if something related to ipv4 was broken (on my system).

 

Regardless, I turned ipv6 back on by commenting out the line in modprobe.d/bad_list and restarted.

 

In this configuration opera still fails to resolve any domains but firefox, xchat, standalone java apps like the KGS Go server client, and most other applications I try work fine with DNS resolving. It seems to me this indicates a system/ipv4 related problem and isn't opera caused (again). If anyone has any ideas on how to narrow down the problem further I'd love to hear it.