One of the advantages of the Cisco ASA firewall is that you can configure multiple virtual interfaces (subinterfaces) on the same physical interface, thus extending the number of security zones (firewall “legs”) on your network. Each subinterface must belong to a different Layer2 VLAN, with a separate Layer3 subnet. There are limits on the number of […]
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NMAP (Network Mapper) is the de facto open source network scanner used by almost all security professionals to enumerate open ports and find live hosts in a network (and much more really). One of my responsibilities in my job is to perform white hat penetration testing and security assessments in corporate systems to evaluate their […]
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HSRP (Hot Standby Router Protocol) is the Cisco proprietary protocol for providing redundancy in router networks. The standard router redundancy protocol which is used by other vendors is VRRP (Virtual Router Redundancy Protocol), however Cisco has created its own proprietary protocol (HSRP) which works very well on Cisco routers. In a Local Area Network (LAN), […]
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Network infrastructure devices (routers, switches, load balancers, firewalls etc) are among the assets of an enterprise that play an important role in security and thus need to be protected and configured accordingly. Many enterprises focus on protecting their data, servers, applications, databases etc but they forget about security of network devices which are sometimes installed […]
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For a CCNA certification exam you must be prepared to answer questions about three important networking concepts, Unicast, Broadcast and Multicast. Even if these terms can be pretty confusing at the beginning, they are actually not that complicated. Learn how to keep them straight, along with other vital CCNA exam information. At the beginning of […]
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Usually, in the world of network security, when we talk about Firewalls we mean the devices that help protect your computer systems and networks from attacks and provide a “wall” in front of servers and IT resources. The above concept of a “Firewall” refers to the classic network hardware firewall such as the Cisco ASA, […]
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The Cisco “reload” command is used on almost all IOS Cisco networking devices (routers, switches etc) to restart (or reboot) the appliance. This command might seem very basic but it has some interesting practical applications that we will see later in this article. Basic Command Usage As we have said above, the basic usage of this […]
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Computer networks keep changing the way we live and do things in the 21st century. This is because virtually every computing activity or information sharing we do today depends on one form of network or another. The Internet is a very good example of a computer network that allows users to get information from any […]
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We know that a Layer 2 VLAN is an isolated Broadcast Domain and for communicating between VLANs a Layer 3 Device is required (either router or Layer3 switch) for inter-VLAN Routing. A Private VLAN gives us the opportunity to divide a VLAN into Sub VLANs. In the case of PVLAN, a normal Layer 2 VLAN […]
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The ASA 5500 and 5500-X series firewall can work as DHCP relay agent which means that it receives DHCP requests from clients on one interface and forwards the requests to a DHCP server on another interface. Usually the DHCP server is located in the same layer 3 subnet with its clients. There are situations however […]
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There are mainly two ways to authenticate to a Cisco router device (and also to other networking devices in general). Using an external authentication service (such as AAA server, Radius, TACACS etc) or by having local usernames and passwords on the device itself. In this article we will discuss how to configure a local username […]
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Computer networking has been around for several decades, which is the backbone of what we all know as the Internet today. The Internet is simply a network of networks, which means there is no such thing as a standalone computer on a network. For a user or host computer to participate in data and resource […]
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Routing and Switching form the foundation of computer networks and the Internet in general. A network engineer must know routing principles like the back of his/her hand!! The core functionality of Layer 3 in the OSI model (Network Layer) is to forward (route) packets received on an interface of a routing device to the best […]
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