One of the most useful and popular commands used on Cisco devices is the “show interface” command. It can be very useful at troubleshooting connectivity issues and physical port issues, check the status of physical ports, watch how much traffic is passing through the interface, which IP address is assigned to the interface (for Layer3 […]
Configuring GRE Tunnel Through a Cisco ASA Firewall
In this configuration tutorial I will show you how to configure a GRE tunnel between two Cisco IOS routers. One of the routers is located behind a Cisco ASA 5500 Firewall, so I will show you also how to pass GRE traffic through a Cisco ASA as well. As you might know already, GRE tunnel […]
The Protocol of the Internet – eBGP and iBGP Tutorial and Configuration
The Border Gateway Protocol (BGP) is considered to be the routing protocol of the Internet because it runs between Internet Service Providers (ISPs) to interconnect all Autonomous Systems (AS) comprising the whole internet. Of course the above refers to External BGP (eBGP) which runs between different Autonomous Systems. There is also another “flavor” of BGP […]
How to Configure Static Routing on Cisco IOS Routers (Examples)
Cisco IOS Routers support both static and dynamic routes. In small networks (2 to 5 routers) I would suggest to configure only static routes, especially if the network is not going to change much over time. Of course dynamic routing (using dynamic routing protocols such as RIP, OSPF, EIGRP) is much more flexible and scalable […]
Redistribution Between Cisco EIGRP into OSPF and Vice Versa (Example)
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 […]
Configuring Local Username and Password on a Cisco IOS Router
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 […]
How to Configure EIGRP on Cisco Routers (With Example)
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 […]
Basic Cisco Router Configuration Step-By-Step Commands
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 […]
How to Configure DHCP on Cisco Routers (With Command Examples)
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 […]
Lan-to-Lan IPSEC VPN Between Cisco Routers – Configuration Example
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 […]
How to Configure Cisco 800 Series Router Configuration for Internet Access
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 […]
Cisco Router HSRP Configuration – Two Examples
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), […]
Configuring NAT on Cisco Routers Step-by-Step (PAT, Static NAT, Port Redirection)
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 […]