In order for 2 VLANS to be able to communicate, the traffic must be routed. This can be done either by a multi-layer switch which will have routing capabilities, or the packets can be routed by a router (Router on a Stick) As an example, I have 2 VLANS, VLAN 10 and VLAN 20 which […]
VTP (VLAN Trunking protocol) is a protocol used to replicate the VLAN information across switches, however there are a few things that must be made clear… VLAN information will only be sent on trunk ports Only the VLAN identity is replicated, NOT which ports are configured to use that VLAN! Maintains database consistency through a […]
A VLAN is a Virtual LAN which allows us to logically separate computers on our network. In previous years, an office would have a physical switch or hub in each office, and offices were structured around the job function. In other words, all sales people would be in the same office and would all be […]
SPAN (Switched Port Analyser) is a requirement whenever you have a system that wishes to log and monitor traffic that is passing through a switch. Since a switch only sends traffic to the machine requiring the packets, adding a sniffer to the switch would result in you only seeing traffic to your sniffer, from your […]
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. Physical access to the router A console connection […]
Additional configuration to further lockdown Cisco router security.
In most smaller networks, or networks that have a few network administrators, when you log into a Cisco device you are only prompted for a password. This will take you to the Router> prompt where more than likely you will immediately type ‘enable’ to enter into privileged exec mode, and you will be prompted with […]
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 […]
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 […]
It is important to understand that any TCP packet that is routed over a network requires bi-directional support. This means that even though I may have a route on my router to your network, if you don’t have a route back to me, the transmission of packets will fail. TCP uses acknowledgments to confirm the […]