In order to control what machines are plugged into your network, Cisco introduced the “switchport port-security” command.   In this tutorial I’m going to explain how to use this command, and different options available using it.   Below is the breakdown of the commands I used in the live demo, and an explanation of each. [...]

Once VLANS have been defined on a switch and you have placed ports into their corresponding VLANS, traffic is limited to remain inside it’s Virtual LAN. The only way for traffic to leave the switch, is to have it sent on a port that is in the same VLAN as its source, or sent over [...]

Almost 100% of Cisco switches will have a 50 second delay on a port before it goes live. What this means, is that when you plug a new device into a switch such as a PC, there will be a 50 second delay before the port will become active and the PC will be able [...]

The configuration of an IP address on a switch is slightly different from a router. On a router we configure the IP address on the physical interface, however on a switch the physical interfaces are running at Layer 2 and hence don’t have IP addresses configured on them.   Even though a switch does not [...]

Cisco offers a password recovery technique for almost every device they have available. In this post, I’m going to cover how to complete a password recovery on a Cisco router. There are 2 things that have to be in place before a password recovery can be done. 1/ Physical access to the router 2/ A [...]

DHCP (Dynamic Host Configuration Protocol) allows a server (in this scenario a Cisco router) to issue IP addresses to computers on the network dynamically. This is not a great solution for servers, which should have static IP addresses, but for client computers needing access to the network quickly and easily, this is certainly a great [...]

Cisco routers use HDLC (High-Level Data Link Control protocol )as their default encapsulation protocol on serial lines. This works fine and there are no major problems with running HDLC however it lacks the troubleshooting commands that PPP (Point-to-Point Protocol) provides us. I learnt the value of PPP about 10 years back when I was installing [...]

Two commands which are often confused or misunderstood, are the clock rate and bandwidth commands. In order to understand clock rate we first need to understand how the cabling works on routers. When connecting two routers together with a serial cable, one of the routers needs to host the DCE (Data Communications Equipment) side of [...]

If you find yourself often connecting to the same devices and are looking a quicker way to telnet to them rather than constantly typing the entire IP address for each one. Or if you have a very large network and find it hard to remember every devices IP address, but you can remember the host [...]

Often when typing commands in a hurry, or just typing incorrect commands, Cisco routers will try to do a lookup to find out if the invalid command is the name of another device you are trying to connect to. This results in the router displaying ‘Translating “the command”…domain server (255.255.255.255)’ three times and not accepting [...]