VLSM and Subnetting Practice.

On the last article, we mostly talked about Subnetting theory, however, subnetting is one of those topics which you don’t really understand until you practice, practice and… practice. I mean, you still need the theory of course, but you need just enough theory to get you started with the practice. While practicing, you are going to hear “click!” in your head… many times.

1.2 Select the components required to meet a given network specification.

As you can imagine, there are many aspects you will need to take into consideration when putting together a network, specially if dealing with a large corporate network. It’s simply not the same, configuring a network for a small office with 5 employees than configuring a network for a corporate branch with 5000 employees.
Some of the concepts we need to consider when designing a LAN are very straight forward like physical space, cabling, power source, static IP addressing, etc. and some are more complex like flexibility, expandability, security, routing protocol implementation, dynamic IP addressing, IP sub-netting, etc. Basically, the complexity of a network is directly proportional to the size of the network itself.
Luckily, we are getting ready for the CCNA, and its scope states; “…skills required to install, operate, and troubleshoot small to medium-size enterprise branch networks”, so let’s keep this in mind.

1.1 Purpose and functions of network devices: routers, switches, bridges and hubs.

We are going to start, slowly but surely, building a theoretical network in our minds. In order to do this, we are going to start from the beginning; recognizing all the components of a modern network as well as some not so modern devices. For now, it is going to be a basic description of each device’s function, but we will elaborate on each concept as we move forward. Let’s begin.

Broadcast and Collision Domains.

Terms you need to understand.

Broadcast: In this case, a Data-Link layer (Layer 2) message sent to ALL devices attached to the same network segment.

Collision: When more then one device transmit data at the same time on shared media, the packets collide, data becomes corrupted and after a random period of time, devices have to re-transmit the data.

Broadcast Domain: All devices that a Broadcast message reaches at the Data -Link layer within a network is called a Broadcast domain. A network can have more then one Broadcast domain and a Broadcast domain is delimited by devices that stop Broadcast messages.

Collision Domain: Anywhere within a network where a Collision can occur. The limits of a Collision domain are marked by those devices that break up Collision Domains.

IPv6 for future CCNAs (+), Final Part.

Unicast Addresses: Unique-Local.
Before we talk about Unique-Local Addresses (ULA), let me tell you about Site-Local addresses; it was deprecated in favor of the ULA back in 2004 because the term “site” was too ambiguous, no body agreed upon a clear definition of the term “site”; what was considered a “Site”?
Also, the provability of Site-Local address being globally unique were no that high, as opposed to ULAs.
ULAs are meant to be routed within an organization’s LAN or even WAN, but they are not routable over the public network (Internet), hence, you can think of ULAs very much as IPv4’s Private addresses.

Spanning Tree Protocol, from a future CCNA`s perspective.

Hi guys, this post got awarded “Best Publication” at the Cisco Support Community”!  Thanks a lot.

A little bit of history:
Before we talk about Spanning Tree Protocol, let’s organize the different variants of STP. The original STP was developed by Radia Perlman while working for DCE back in 1990. At this time there were no switches yet, only bridges, but because bridges and switches technically do the same job -only switches do it more efficiently and have more features- they suffer from the same issues. Also, because STP was developed during a time when therewere only bridges, the terminology used in STP, even today, makes reference to bridges a lot (Root Bridge, Bridge-ID, etc.). So, when you read about STP from different sources, remember that the terms Switch and Bridge might be used interchangeably.