If you cannot ping or access anything outside of the 127.0.0.1 address space run this command.

This must be in place to allow communication. But due to the code using iptables for traffic management and their refusal to add this rule you must do it your self. Debian by default (at least on my etch box) had a default deny rule that killed any communication not allowed by a rule. This is to fix issues with the isp_network daemon.

Did you installed the Debian your self or was this just an Image ??
Never had such a problem per default on Debian Sarge/Etch.

Greez BeNe

Yes I installed it myself. Opened a bug report 2 times and it was closed by rats with a wontfix notation. I could access the system perfectly before installing ispcp and when I installed it (followed directions to the letter) it locked all traffic out and i had to go to console. Traced it down to the iptables blocking all traffic that was related or established because it did not have that rule in its rule file. As soon as i added it, it worked as designed. I recomended on the bug report to add just one rule and it was closed very promptly. This problem has been seen on this forum under the name of cant ping cant resolve ip/dns, dns not found, at least 6 posts i found had this same issue but no fix. Just my 2c so others won't have the same issue due to coding flaw/debian policy.