CIDR Table – Basic Reference (From Wikipedia)

Address Format Difference to last address Mask Addresses Relative to class Typical use Decimal 2n A, B, C a.b.c.d / 32 + 1 20 ​1⁄256 C Host route a.b.c.d / 31 + 2 21 ​1⁄128 C Point to point links (RFC 3021) a.b.c.d / 30 + 4 22 ​1⁄64 C Point to point links (glue network) a.b.c.d / 29 + 8 23 ​1⁄32 C Smallest multi-host network a.b.c.d / 28 + 16 24 ​1⁄16 C Small LAN a.b.c.d / 27 + 32 25 ⅛ C a.b.c.d / 26 + 64 26 ¼ C a.b.c.d / 25 + 128 27 ½ C Large LAN a.b.c.0 / 24 + 256 28 1 C a.b.c.0 / 23 + 512 29 2 C a.b.c.0 / 22 + 1,024 210 4 C a.b.c.0 / 21 + 2,048 211 8 C Small ISP / large business a.b.c.0 / 20 + 4,096 212 16 C a.b.c.0 / 19 + 8,192 213 32 C ISP / large business a.b.c.0 / 18 +

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Interrupt Coalescence (also called Interrupt Moderation, Interrupt Blanking, or Interrupt Throttling)

A common bottleneck for high-speed data transfers is the high rate of interrupts that the receiving system has to process – traditionally, a network adapter generates an interrupt for each frame that it receives. These interrupts consume signaling resources on the system’s bus(es), and introduce significant CPU overhead as the system transitions back and forth between “productive” work and interrupt handling many thousand times a second. To alleviate this load, some high-speed network adapters support interrupt coalescence. When multiple frames are received in a short timeframe (“back-to-back”), these adapters buffer those frames locally and only interrupt the system once. Interrupt coalescence together with large-receive offload can roughly be seen as doing on the “receive” side what transmit chaining and large-send offload (LSO) do for the “transmit” side. Issues with interrupt coalescence While this scheme lowers interrupt-related system load significantly, it can have adverse effects on timing, and make TCP traffic more bursty or “clumpy”. Therefore it would make sense to

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SAN Switch basic concepts – Fabric Switch

SAN Switch basic concepts SAN Switch basic concepts – SAN environment provides block-oriented I/O between the computer systems and the target disk systems. The SAN may use Fiber Channel or Ethernet (iSCSI) to provide connectivity between hosts and storage. In either case, the storage is physically decoupled from the hosts. The storage devices and the hosts now become peers attached to a common SAN fabric that provides high bandwidth, longer reach distance, the ability to share resources, enhanced availability, and other benefits of consolidated storage. SAN is created by using the Fiber Channel to link peripheral devices such as disk storage and tape libraries A SAN (Storage Area Network) Switch is device that connects the sever and shared pools of the storage devices and is dedicated to moving storage Traffic. It is shown as below Picture: SAN Switch Basic Connectivity Diagram between Servers, SAN Storage, SAN Switch and Tape Library. Picture: Basic Connectivity Diagram SAN Switch will contain below physical

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Linux Command – Using Netstat the Proper Way !!

How to install netstat netstat is a useful tool for checking your network configuration and activity. It is in fact a collection of several tools lumped together. Install “net-tools” package using yum [root@livedvd ~]$ sudo yum install net-tools Loaded plugins: fastestmirror Loading mirror speeds from cached hostfile * base: * extras: * updates: Resolving Dependencies –> Running transaction check —> Package net-tools.x86_64 0:2.0-0.17.20131004git.el7 will be installed –> Finished Dependency Resolution Dependencies Resolved =============================================================================== Package         Arch         Version                          Repository  Size ================================================================================ Installing: net-tools       x86_64       2.0-0.17.20131004git.el7         base       304 k Transaction Summary ================================================================================ Install  1 Package Total download size: 304 k Installed size: 917 k Is this ok [y/d/N]: y Downloading packages: net-tools-2.0-0.17.20131004git.el7.x86_64.rpm              | 304 kB   00:00 Running transaction check Running transaction test Transaction test succeeded Running transaction Installing : net-tools-2.0-0.17.20131004git.el7.x86_64                    1/1 Verifying  : net-tools-2.0-0.17.20131004git.el7.x86_64                    1/1 Installed: net-tools.x86_64 0:2.0-0.17.20131004git.el7   Complete!   The netstat Command Displaying the Routing Table When you invoke netstat with the –r flag, it displays the kernel routing table in the way

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Knockd – Detailed And Simpler (Silent Assassin….)

As I could see there are lot of articles about knockd and it’s implementation. So, what are my efforts to make this unique? I made it simple, but detail oriented  and have commented on controversies and criticism that exist. Here is an outline on what I’ve discussed. What is port knocking? What is knockd? How it works? Installation What we are trying to achieve Pre-requisite before implementation of knockd: Implementation scenario Testing Disclaimer So, here we go. What is port knocking? Wikipedia Definition: Port knocking is a method of externally opening ports on a firewall by generating a connection attempt on a set of pre-specified closed ports (in this case, telnet). Once a correct sequence of connection attempts is received, the firewall rules are dynamically modified to allow the host which sent the connection attempts to connect over specific port(s) /* in this article point of view, it’s ssh port 22 */ It’s basically like, every request would knock the

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