Managing IP-Tbales

Overview Iptables is a rule-based firewall, which will process each rule in order until it finds one that matches. Todo: include example here Usage The iptables utility is typically pre-installed on your linux distribution, but isn’t actually running any rules. You’ll find the utility here on most distributions: /sbin/iptables Blocking a Single IP Address You…


TCP Segment Retransmission Timers and the Retransmission Queue 

TCP Transaction Example with Retransmission Let’s use an example to clarify how acknowledgments and retransmissions work in TCP (illustrated in Figure 223, to which you may wish to refer as you read on). Suppose the server in a connection sends out four contiguous segments (numbered starting with 1 for clarity): Segment #1:Sequence Number field is 1 and…


IP address classes and structure

IP address classes and structure When the IEEE committee sat down to sort out the range of numbers that were going to be used by all computers, they came up with five different ranges or, as we call them, “classes” of IP addresses. When someone applies for IP addresses they are given a certain range…


General Overview of Layer 2

General Overview of Layer 2 Layer 2 is Data Link Layer (DLL) as per OSI Model. As we know function of each layer is to provide services to above layer, so DLL provide various services to Layer 3: Network Layer. Various services which DLL provides are: Framing network layer data packets. Flow Control Multiple Access…


$df and $du

With these two commands, not only can you discover details about the free space on the mounted file systems, but you can also see the amount of space used by individual directories. df The df command shows the disk space usage on all the currently mounted file systems. Here is what the output from running…


$ps aux

Symptoms The ps command, for Process Status, displays a header line followed by lines containing information about the processes that are running on the IPSO platform. For example: [admin]# ps -aux USER PID %CPU %MEM VSZ RSS TT STAT STARTED TIME COMMAND root 6372 0.0 0.1 432 220 p0 R+ 3:15PM 0:00.02 ps -aux root…



Know what is happening in “real time” on your systems is in my opinion the basis to use and optimize your OS. On ArchLinux or better on GNU/Linux in general the top command can help us, this is a very useful system monitor that is really easy to use, and that can also allows us…


Linux troubleshooting commands explained

As you all know, there’s quite a number of commands available in linux which could become a bit confusing at times. When to use which command and what important information the command use will display. Hence I came up with a list, hope this proves helpful.

hqdefault (1)

What’s an initial RAM disk?

The initial RAM disk (initrd) is an initial root file system that is mounted prior to when the real root file system is available. The initrd is bound to the kernel and loaded as part of the kernel boot procedure. The kernel then mounts this initrd as part of the two-stage boot process to load…