When I don't have a DNS

It just happened to me that the DNS of my ISP was down. Under a Ubuntu Intrepid Ibex (8.10) in a place where I damn needed the web.
In this case, you just have to ensure that you have a replacement DNS server, for instance, the public 4.2.2.4, which works very well so far. Edit the config file /etc/resolv.conf.auto and add the following lines:

nameserver my.usual.dns.ip
nameserver 4.2.2.4

After that, restart the networking service by:

# /etc/init.d/networking restart

and the web works again.