Cisco Load Balancing with Failover setup example

There is Cisco router of 7200 series with 4 FastEthernet interfaces (FE) and 2 serial ports. It should act as load balancer and failover for LAN connected to it via one FE 1/0 interface while two identical Internet connections are going to FE 0/0 and FE 0/1 (let’s name these connections as ISP_1 and ISP_2). No dynamic routing protocols are used by ISPs but only static routing. The primary task […]

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Install nfdump and nfsen netflow tools in Linux

Using nfsen it is possible to view IP traffic statistics on Linux interfaces including the graphs showing data sent and received (see the screenshot to the right) as well as historical information about all data transfers. So after you’ve configured nfsen and nfdump to monitor traffic on certain Linux server or router you’ll be able to answer the following example questions: What IP was downloading data through 48161 last Wednesday? […]

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Quick Tip: Increase port range available for applications

By default an average Linux distribution allows applications to use the following TCP port range for outgoing connections: 32,786-65,536. That’s why your system can handle up to 28,232 TCP sessions at time. Notice, this is more than enough if your Linux system is installed on the laptop or desktop and you just use it for occasional visits to facebook.com, gmail.com and linuxscrew.com (yeah!). But if you run proxy/webcache like squid […]

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Sendmail for virtual users with procmail, spamassassin and dovecot

Today I’d like to describe setup of sendmail that allows to establish receiving of e-mails for certain domain and sort incoming messages between virtual users. Those users must be able to fetch received e-mails via POP3 or IMAP protocols with or without TLS encryption. The key aspect of this kind of setup is that we will make sendmail working with virtual users which aren’t present in /etc/passwd so once it’s […]

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Namebench: cross-platform DNS benchmarking tool

It was long time ago when I wrote here last time but today I’d like to share the link to an application that would be appreciated by everyone starting from Linux starter wishing to speed up his/her Internet connection and ending with system administrators who may want to run benchmarks and run stress tests against certain DNS service(s). I am talking about Namebench. This is cross platform tool written in […]

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