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Creating a fully ‘safe’ and trusted e-mail domain for Hotmail/Gmail

We recently encountered a lot of issues when trying to e-mail to Hotmail, Live.com or Gmail users – all email messages turned up in the Junk folder. This was odd since we didn’t alter anything on our side and we know for a fact that our clients don’t send any spam out. The past few ...

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Tuning Apache2 & MySQL

I’ve spent a lot of time on tweaking our Apache2 and MySQL-Cluster setup to gain more performance without assigning more resources to it. I ended up with a very good configuration for several thousand visitors per day. Hardware Configuration – Make sure you have enough processing power on the webservers. Mysql-cluster uses relatively low CPU, ...

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Linux security – Server Hardening

Since i have to manage a lot of linux boxes in our network i was looking for a way to secure all of these boxes against the ‘basics’ and i made noted (yea, really!) of this. Here you will find some of the basic security tips. Audit your server In my search i found that ...

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Postfix – Greyfix file not found

After updating Postfix on our mailservers we encountered a problem with our greylisting. Our logs showed an error message like this: warning: problem talking to server private/greyfix: No such file or directory The solution was very simple, simply add the following to the ‘master.cf’ file in /etc/postfix: greyfix unix – n n – – spawn user=nobody argv=/usr/local/sbin/greyfix ...

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Jumbo Frames

Every data unit on a network has to be assembled by the sender, and its headers have to be read by the network  components between the sender and the receiver. The receiver then reads the frame and TCP/IP headers before processing the data. This activity, plus the headers added to frames and packets to get ...

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Zabbix – Monitoring Windows Server 2008

Download zabbix agent file from http://www.zabbix.com/download.php and extract the file. Open command prompt from Start > Run and  then type cmd then click ok Create new folder for zabbix agent mkdir c:\Program Files\zabbix Now copy zabbix_agentd.exe, zabbix_get.exe and zabbix_sender.exe from win32 (or win64 for 64-bit windows)  folder to this new directory. Now create a new configuration file for zabbix using command prompt or notepad (as you please). ...

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DDOS – ISP’s worst nightmare

I was looking on the website of arbor, they keep nice statistics on DDOS attacks around the globe. Arbor makes a DDOS appliance that is used by many large carriers to detect DDOS attacks and protect them. These appliances send information and statistics back to Arbor and end up in a report. Many people think ...

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Monitoring: Spanning Tree state through SNMP

Within our network all switches use Spanning-Tree in orde to provide failover would a switch failure occur. Although we monitor each switch separately i always had the need to monitor the STP port states and see if one of the ports/trunks did a failover (and then, why). After searching for a while i tried using SNMP to find ...

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XenServer iScsi on HP Procurve 2810/2910

My objective is to try and eliminate performance bottlenecks on our iscsi setup. Our current situation is several Xenserver hosts running virtual machines from our iScsi storage as well as Hyper-V virtual machines on separate LUN’s. The last months we see more delay on our iScsi network. You can check the delay of iScsi traffic several ways ...

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mod_geoip for Apache2 On Debian

This guide explains how to set up mod_geoip with Apache2 on a Debian Squeeze system. mod_geoip looks up the IP address of the client end user. This allows you to redirect or block users based on their country. You can also use this for advertising purposes To install mod_geoip, we simply run: apt-get install libapache2-mod-geoip ...

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