When a Domain is Blocked by Filtering Software
Can’t access your favorite websites because some stupid ISP or access point is using DNS-level filtering?
Set your DNS to use Google’s DNS:
8.8.8.8 and 8.8.4.4
Then flush the existing DNS cache and register the new DNS.
In Windows 7, you’ll need elevated privileges to changes to the DNS. Make sure you start cmd.exe as Administrator.
- Press the window Key
- Type “cmd”
- Right click the cmd.exe that’s found.
- Select “Run as administrator”
- Type
ipconfig /flushdns - Then type
ipconfig /registerdns
Now you’re free to roam the internet.
Static IP with DHCP-Assigned DNS on Ubuntu 9.10
There is a ton of bug reports regarding the Network-Manager’s nm-applet not properly configuring static ips. There are, and always have been, bugs in the nm-applet, in each of its versions. In short, getting a static ip with dhcp assigned DNS parameters requires editing the /etc/dhcp3/dhclient.conf file. Here we go.
sudo vi /etc/dhcp3/dhclient.conf>> alias { interface "eth0"; fixed-address 192.168.1.101; option subnet-mask 255.255.255.255; } <<sudo dhclient -rsudo dhclient
MySQL DNS Caching
On December 12, 2008, SCCOOS metadata system was broken. The error was cryptic, but the message was clear: Connection to [IP] denied.
Resolution
Using the MySQL command-line tool:
mysql -u admin -p [-h
mysql> flush hosts;
That’s it!
Chain of Events
- UCSD’s DNS was polluted, identifying 132.239.123.144 as ridge2000.org for the past few weeks.
- Sandbar was restarted last week, freeing up both the OS and MySQL DNS caches, which meant all new connections will need to query a DNS server to identify whether it’s an allowed machine or not (do you see a security vulnerability?).
- Both the OS and MySQL cached the hostname, but MySQL further rejected all connections from alfredo because MySQL thought that alfredo was ridge2000 instead.
- The mysql database, user table identifies user sccoos can connect to sandbar from alfredo.ucsd.edu.
- The OS cache probably cleared, but since so few machines access sandbar, the MySQL cache hadn’t filled up yet.
- Just last night (2008-12-22), the UCSD DNS purged the ridge2000.org name from its list, so UCSD’s DNS is clean, but any caches may still be polluted.
- Windows machines cycle their caches regularly, so the problem isn’t more wide-spread or commonly understood.
- The long-lasting MySQL DNS cache is disturbing, but alternatives would cripple the imperative nature of a database.
