I have decided to write this tutorial (only for test purpose) to show how it is simple decode a G.729 stream using SPAN port, Wireshark, VoiceAge G.729 decoder and Audacity software. What is G.729? G.729 is an audio data compression algorithm for voice that compresses digital voice in packets of 10 milliseconds duration. It is officially described as Coding of speech at 8 kbit/s using conjugate-structure algebraic-code-excited linear prediction.

An access list is a sequential list consisting of at least one permit statement and possibly one or more deny statements that apply to IP addresses and possibly upper-layer IP protocols. Time-based ACLs is a Cisco feature introduced in the Release 12.0.1.T to allow access control based on time. The time range, identified by a name, can be ‘absolute‘ or ‘periodic‘. Use time-based access list is easy and can be useful in some situations. To implement it, you need: Define time-range Define ACL, where the time-range is applied to Apply ACL; for istance: to the interface, to the vty, to [...]

Traceroute is a tool for measuring the route path and transit times of packets across an Internet Protocol (IP) network. Traceroute sends a sequence of Internet Control Message Protocol (ICMP) packets addressed to a destination host. Tracing the intermediate routers traversed involves control of the time-to-live (TTL) Internet Protocol parameter. Routers decrement this parameter and discard a packet when the TTL value has reached zero, returning an ICMP error message (ICMP Time Exceeded) to the sender. In a Data Center, it is often required to find a host and the layer2 path. To do it, Cisco has implemented a good [...]

Cisco IOS Embedded Event Manager (EEM) is a powerful and flexible subsystem that provides real-time network event detection and onboard automation. It gives you the ability to adapt the behavior of your network devices to align with your business needs. Customers can use EEM to create and run programs or scripts directly on a router or switch. The scripts are referred to as EEM Policies and can be programmed using a simpleCLI-based interface or using a scripting language called Tool Command Language (TCL). EEM allows customers to harness the significant intelligence within Cisco IOS Softwareto respond to real-time events, automate [...]

Often in a network environment, it is needed to manage a router/switch via console, but what can you do if you don’t have a computer with a serial interface? You can use another router! It is easy to do it. 1) Connect the console interface of the router/switch to the router aux interface using a rollover cable. Rollover cables essentially have one end of the cable wired exactly opposite from the other. As you can see below, this essentially “rolls over” the wires.

Cron is a time-based job scheduler in Unix-like computer operating systems. The name cron comes from the word “chronos”, Greek for “time”. Cron enables users to schedule jobs (commands or shell scripts) to run periodically at certain times or dates. It is commonly used to automate system maintenance or administration, though its general-purpose nature means that it can be used for other purposes, such as connecting to the Internet and downloading email. What can I use to schedule a script or a command in Cisco? The kron feature Kron provides the ability to schedule some EXEC command-line interface (CLI) commands [...]

What can I do if I forgot the password in my router? The fastest solution is replace it with the ‘password recovery‘ (you can try to find the password with bruteforce attack but I think it is not the better solution..). During the password recovery procedure, it is fundamental sent the correct ‘Break’ key sequence to enable ROMMON, but, as you know, the ‘break’ sequence depends by the software that you use! Below the standard break key sequence combinations for the most common operating systems.

Do you remember the “Cisco regular expressions” tutorial? A regular expression is entered as part of a command and is a pattern made up of symbols, letters, and numbers that represent an input string for matching (or sometimes not matching). Matching the string to the specified pattern is called pattern matching. Pattern matching either succeeds or fails. If a regular expression can match two different parts of an input string, it will match the earliest part first. In this tutorial, I will explain how to use the ‘show’ command with the regular expression.

The origins of regular expressions lie in automata theory and formal language theory, both of which are part of theoretical computer science. These fields study models of computation (automata) and ways to describe and classify formal languages. In the 1950s, mathematician Stephen Cole Kleene described these models using his mathematical notation called regular sets. The SNOBOL language was an early implementation of pattern matching, but not identical to regular expressions. Ken Thompson built Kleene’s notation into the editor QED as a means to match patterns in text files. A regular expression is entered as part of a command and is [...]

A number of shortcuts exist within the IOS command line interface. The most famous shortcut is the ‘TAB’ command, that completes a partially typed CLI command. For istance, if you type “sh ru” and press TAB, it will complete the command as “show running-config“. Below the complete list of the IOS shortcuts: Ctrl+T: Swap the current character with the one before it Ctrl+K: Erase all characters from the current cursor position to the end of the line Ctrl+X: Erase all characters from the current cursor position to the beginning of the line Ctrl+L: Reprint the line Ctrl+C: Exit configuration mode