1. What is a wireless local loop? In a telephone network, a wireless local loop (WLL) is a generic term for an access system that uses a wireless link to connect subscribers to their local exchange in place of conventional copper cable. Using a wireless link shortens the construction period and also reduces installation and … Continue reading

Ethernet Private Line

Ethernet Private Line (EPL) and Ethernet Virtual Private Line (EVPL) are Carrier Ethernet data services defined by the Metro Ethernet Forum. EPL provides a point-to-point Ethernet virtual connection (EVC) between a pair of dedicated user–network interfaces (UNIs), with a high degree of transparency. EVPL provides a point-to-point or Point-to-Multipoint connection between a pair of UNIs. The services are categorized as an E-Line service type, with an expectation … Continue reading


AMS-IX is a distributed exchange, currently present at multiple independent colocation facilities in Amsterdam. Each site is equipped with one or more access devices to enable connections to the AMS-IX infrastructure. Colocation services for connected networks are available at all data centre facilities, these are not part of the AMS-IX services. The current implementation of the AMS-IX … Continue reading

Network traffic measurement

In computer networks, network traffic measurement is the process of measuring the amount and type of traffic on a particular network. This is especially important with regard to effective bandwidth management. Network performance could be measured using either active or passive techniques. Active techniques (e.g. Iperf) are more intrusive but are arguably more accurate. Passive techniques are of less network … Continue reading

Layer 2 Vs. Layer 3 Networks

LAYER 2 NETWORKS A switch works with MAC addresses at layer 2 of the OSI 7 layer model. Devices used on a Layer 2 Ethernet network include network interface cards, hubs, bridges and switches. Ethernet devices use ‘burned in’ MAC addresses to identify each host. These addresses are attached to network interface cards and cannot … Continue reading

What’s VPLS

Cisco says it as: Virtual Private LAN Services (VPLS) is a class of VPN that supports the connection of multiple sites in a single bridged domain over a managed IP/MPLS network. VPLS presents an Ethernet interface to customers, simplifying the LAN/WAN boundary for Service Providers and customers, and enabling rapid and flexible service provisioning, because … Continue reading

How To Remove Old Kernels In CentOS

Ever had the the “no space left” message after trying to install a new kernel ? The thing is that by default the system will keep the old kernels there, so the best option is to set it to delete the old ones automatically. Starting from the beginning: For one self information, check how many … Continue reading

What does “arp who-has tell” means?

05:47:34.050566 arp who-has xxx.xxx.xxx.xxx tell yyy.yyy.yyy.yyy Basically this means that yyy.yyy.yyy.yyy has data to send to xxx.xxx.xxx.xxx but don’t know the MAC address associated to it, so it’s trying to update the ARP table cache. For geeks who want to understand thoroughly, check links below: RFC826 ARP by Wireshark ARP

SFP module (Small form-factor pluggable transceiver )

The small form-factor pluggable (SFP) is a compact, hot-pluggable transceiver used for both telecommunication and data communications applications. The form factor and electrical interface are specified by a multi-source agreement (MSA). It interfaces a network device motherboard (for a switch, router, media converter or similar device) to a fiber optic or copper networking cable. It … Continue reading

WCCP (Web Cache Communication Protocol)

Web Cache Communication Protocol (WCCP) is a content-routing protocol that provides a mechanism to redirect traffic flows in real-time. It has built-in load balancing, scaling, fault tolerance, and service-assurance (failsafe) mechanisms. The Web Cache Communication Protocol (WCCP) is a Cisco-developed protocol that allows certain Cisco routers and switches to transparently redirect traffic to a cache … Continue reading

How to Check for Dropped Packets

Open the “Start” menu and type “Command prompt” into the search bar. If you are on Windows Vista or newer, simply wait for the “Command prompt” menu item to appear or, if you are on Windows XP or older, click the “Search” button and allow the computer to seek out the file. Run the “Command … Continue reading

What’s ISAKMP (Internet Security Association and Key Management Protocol)

ISAKMP is a protocol for establishing Security Associations (SA) and cryptographic keys in an Internet environment. ISAKMP defines the procedures for authenticating a communicating peer, creation and management of Security Associations, key generation techniques, and threat mitigation (e.g. denial of service and replay attacks). As a framework,[1] ISAKMP is typically utilized by IKE for key … Continue reading

Simple way to leverage browser caching in WordPress using .htaccess

Not much to tell, you can use the code bellow and paste to the top of your .htaccess ## EXPIRES CACHING ## ExpiresActive On ExpiresByType image/jpg “access 1 year” ExpiresByType image/jpeg “access 1 year” ExpiresByType image/gif “access 1 year” ExpiresByType image/png “access 1 year” ExpiresByType text/css “access 1 month” ExpiresByType application/pdf “access 1 month” ExpiresByType … Continue reading

BVI Interface

BVI stands for Bridge-Group Virtual Interface. A BVI (Bridge Group Virtual Interface) is a routed interface that represents a set of interfaces that gets bridged. So lets say for example that in your router you have two interfaces that needs to get bridged (one wireless and one wired for example) and you want them to … Continue reading

How to encrypt Pre-Shared Keys in Your Cisco VPN

I guess you have already noticed that the VPN pre-shared keys stay in plain text even after applying password encryption. Below you can find a short explanation on how to encrypt it and keep it all safe: This is the VPN config before encryption: ****************************************************************** crypto isakmp policy 1 encr 3des authentication pre-share group 2 … Continue reading

Stateful firewall (SPI)

In computing, a stateful firewall (any firewall that performs stateful packet inspection (SPI) or stateful inspection) is a firewall that keeps track of the state of network connections (such as TCP streams, UDP communication) traveling across it. The firewall is programmed to distinguish legitimate packets for different types of connections. Only packets matching a known active connection will be allowed by the firewall; others will be rejected. … Continue reading

Virtual Routing and Forwarding (VRF)

Virtual routing and forwarding (VRF) is a technology included in IP (Internet Protocol) network routers that allows multiple instances of a routing table to exist in a router and work simultaneously. This increases functionality by allowing network paths to be segmented without using multiple devices. Because traffic is automatically segregated, VRF also increases network security and can eliminate … Continue reading


The NTU , abbreviation of Nephelometric Turbidity Unit , is a measure of the turbidity (turbidity) of a liquid . The method of measurement of the NTU is based on the reflecting power of the settleable difficult or completely colloidal particles in the liquid. During the measurement, a beam of light shone on the fluid and perpendicular to this the light volume measured. The more light the more it is measured … Continue reading