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Old 22nd September 2011, 04:55
cly cly is offline
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Question Firewall/DNS issue?

I have installed ISPConfig3 and used it for a couple of months successfully on 2 seperate VPS servers at the same ISP - one as a web/mysql/ftp/dns server, and the other as a mail/dns server. Just recently, for some reason, the web server has, what I believe, a firewall issue, but I can't figure out what is going on:

Configuration:
Server A (with the problem): Web/mysql/ftp/dns
Firewall configuration: TCP 20,21,22,25,53,80,443,3306,8080,8081 UDP 53,161,3306
Debian 6 64bit on OpenVZ

Server B (works fine): mail/dns
Firewall configuration: TCP 22,25,53,110,143,3306 UDP 53,161,3306
Debian 6 64bit on OpenVZ

What happens:
1) Server A has login delays of 15 seconds between entering username and password
2) Cannot ping/resolve any name from Server A (no name resolution)
3) Can ping IP addresses fine
4) If I telnet to a DNS server on port 53, it fails unless the firewall is disabled, even though both TCP and UDP 53 are configured on the firewall.
4) If the firewall is disabled, everything works fine - name resolution and fast logins

The first time I built Server A it worked fine the whole time. I installed SNMPD and it stopped working, so thought it might have been that, but it appears that it may have been a coincidence. So I rebuilt the server, and as soon as the firewall is turned on, the problem comes back. There is no such problem with Server B. I have deleted the firewall rules and recreated them (and even rebuilt the whole server).

Both servers have the same resolv.conf, and Server A works fine with the firewall disabled and Sever B works fine all the time.

Any help would be appreciated
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