The most common scenario for big enterprise networks with multiple routers is to have a single IGP routing protocol (IGP = Interior Gateway Protocol) running between the routers in order to distribute all the routing information of the network. The most common IGP routing protocols used by today’s networks are OSPF, EIGRP (Cisco proprietary) and […]

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 setup a local username […]

Enhanced Interior Gateway Routing Protocol (EIGRP) is an enhanced version of the now obsolete IGRP. EIGRP is Cisco proprietary which means it is available only on Cisco routers and switches. EIGRP employs an algorithm referred to as the Diffusing Update Algorithm (DUAL) which guarantees fast convergence and loop-free operation at all times. It is an […]

This post is by no means an exhaustive tutorial about Cisco Routers and how to configure their numerous features. It is a step-by-step guide for the most basic configuration commands needed to make the router operational. When you first power up a new Cisco Router, you have the option of using the “setup” utility which […]

DHCP stands for Dynamic Host Configuration Protocol. Basically it’s a mechanism which assigns IP addresses to computers dynamically. Usually DHCP is a service running on a server machine in the network in order to assign dynamic IP addresses to hosts. However, Cisco Routers (and other devices such as ASA firewalls etc) can work also as […]

We have two types of IPSEC VPNs: Lan-to-Lan (or site-to-site) encrypted VPN and Remote Access VPN. The first one is extensively used to securely connect distant office networks and the second one for allowing remote users/teleworkers to access resources on a central site network. In this post we will describe briefly a Lan-to-Lan IPSEC VPN […]

The Cisco 800 series routers are part of the “Branch Office” category, used mainly for SOHO purposes or for connecting remote branch offices to a central location. They are “fixed hardware configuration” devices, meaning that they don’t have any plug-in hardware slots for inserting additional interfaces to the device (all the interfaces are fixed). All […]

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), […]

The depletion of the public IPv4 address space has forced the internet community to think about alternative ways of addressing networked hosts. Network Address Translation (NAT) therefore was introduced to overcome these addressing problems that occurred with the rapid expansion of the Internet. Even if NAT was suggested as a temporary solution, it has been […]

In this article we will discuss the similarities and differences between the 3 “First Hop Redundancy” protocols supported by Cisco devices. These are Hot Standby Router Protocol (HSRP), Virtual Router Redundancy Protocol (VRRP) and Gateway Load Balancing Protocol (GLBP). The main purpose of the above protocols is to provide redundancy to the default gateway (router […]

In a previous post, I have published a Cisco Switch Commands Cheat Sheet tutorial. Since these kinds of posts are useful as a reference for many people, I have decided to create also a Cisco Router Commands Cheat Sheet with the most useful and the most frequently used Command Line Interface (CLI) configuration commands for […]

The cellular mobile network has evolved so much the last decades with improved coverage, speed and reliability. Therefore it is now possible to use the 3G/4G cellular mobile network as a reliable backup-up connection of your main connection line. Cisco has several router devices that have either an embedded 3G/4G modem or a standalone HWIC […]

In today’s networks, WAN redundancy is very important even in small networks. To have a truly redundant WAN connectivity, you must use two different ISP connections. However, there is a catch here. You need to use BGP dynamic routing protocol (usually), which adds some complexity and extra requirements. In most cases, you will need two […]