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 […]
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 […]
HSRP Vs VRRP Vs GLBP Redundancy Protocols
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 […]
Cisco Router Configuration Commands – CLI Cheat Sheet
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 […]
How to Configure Cisco Router 3G-4G Mobile Cellular Connection
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 […]
How to Configure Dynamic DDNS on Cisco Routers (DYNDNS)
The Internet uses IP addresses to refer to all resources but IP addresses are difficult to remember for humans. We instead use easy-to-remember domain names such as www.networkstraining.com to refer to Internet resources. Domain Name System (DNS) is the Internet directory service that automatically translates domain names to corresponding IP addresses. Dynamic Domain Name System […]
Configuring Static NAT on Cisco Routers
Network Address Translation (NAT) is an operation by which source and/or destination IP addresses within a packet are replaced with different IP addresses. NAT conserves available IP address space by allowing many private IP addresses to be represented by some smaller number of public IP addresses. Private IP addresses are defined in RFC 1918 and […]
Configuring EasyVPN Between Cisco Routers
Basically Cisco Easy VPN is usually used for Cisco easy VPN Client termination. In this post however, let’s consider the configuration of Cisco Easy VPN between two Cisco routers. Just keep in mind that an EasyVPN scenario involves a Server and Remote Clients. The basic configuration is performed on the Server and the configuration done […]
Using USB Flash Drives in Cisco routers
A few days ago I have written a post about Booting a Cisco Router from USB Flash. Related to that post and since I got some questions about the subject, it seems appropriate to add some more information about how USB Drives can be managed and used in Cisco IOS routers. Some things to consider: […]
Booting a Cisco IOS Router from a USB Flash Drive in Rommon Mode
Cisco routers typically store a copy of the device’s operating system (Cisco IOS) in their flash memory, and load this operating system image into RAM during the boot-up process. The flash memory of Cisco routers is usually internal or can be a removable flash card on higher end routers. However, it may happen that for […]
Configuring Cisco Router Interfaces
One of the main elements to configure on a Cisco router is its interfaces. The router is usually equipped with Ethernet interfaces (for LAN connectivity) or Serial/ATM/T1/E1 interfaces for WAN connectivity. Below you will find three typical router interface configuration scenarios to get an idea about this important setup. Configuring Ethernet or Fast Ethernet Interfaces […]
Using TCP Intercept to mitigate DoS SYN Attacks
The most common attack against Service Provider IP Networks is Denial of Service. Usually these attacks take the form of “Many-to-One Attacks” where multiple attacking sources send flooding traffic towards a single destination. These attacks are sometimes called Distributed Denial of Service. Usually the attacking hosts are “zombie” computers which are compromised by hackers and […]