Posts

Fixing ip_conntrack Bottlenecks: The Tale Of The DNS Server With Many Tiny Connections

/
I manage a server which has a sole purpose: serving DNS requests. We use PowerDNS, which has been great. It is a DNS server whose backend is SQL, making administration of large numbers of records very easy. It is also fast, easy to use, open source and did I mention it is free? The server has been humming along for years now. The traffic graphs don't show a lot of data moving through it because it only serves DNS requests (plus MySQL replication) in the form of tiny UDP packets. Read on to follow my story of how I fixed this tricky problem. No kittens were harmed in the writing of this post.

Linux Command Line, Generating a Random File

/
It is very easy to create a random file using the linux command…

Tweaking TCP for Fast (100mbps+) Connections and Transfers on Linux

/
We recently did some speed testing on a few of the servers on our network, and we were not receiving the speeds expected considering they were sitting on a physical 100mbps ethernet port. The servers were indeed on physical 100mbps connection, however wget (TCP/IP, HTTP Port 80) download tests showed only a max of about 1.5MB/sec (note the 8bit/byte conversion, so this translates to about 12mbits).

A Poor Man's VPN: Proxy Web Connection to Remote Server (via SSH and Tunnel)

/
Did you ever have a situation where you needed to access a website…

Command Line Packet Sniff Existing Running Process in Linux

Have you ever come across a server that is doing a lot of traffic?…

Easy Search and Replace in Multiple Files on Linux Command Line

/
I recently came across a typo that existed in a bunch of html…