Archive for Virtual LAN

CCNA Lab Projects

Posted in Cisco Certification with tags , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , on June 2, 2011 by jjrinehart

I normally do not post more than once a day but wanted to get these documents back out there, I have created another CCNA Lab Project that was an absolute blast to come up with.  It’s amazing what you can create with just a pen and paper while taking off in an airplane!

Here are the highlights:

  1. Simulated Metro-Ethernet Primary Network
  2. Internet Access at Remote Sites
  3. VPN/GRE Backup Network
  4. Multiple Routing Protocols
  5. A Few Mind Bending Twists Thrown In

Here are the links to the documents, I deployed this in my own lab and will be compiling an answer key for #2.  Enjoy!

Project 1:

CCNA Lab Project Document 12-18-2010

Project 2:

** Just Added Project #3 **

– Joe

Invisible Networks (No Kidding), the World of Virtual LANs (VLANS), Part II

Posted in Cisco Certification with tags , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , on June 2, 2011 by jjrinehart


Words are funny things, and if you start using the word trunk at a cocktail party, people will probably look at you strangely, as it evokes images of luggage, large animals, or the back of an automobile (pictured above).  As I mentioned previously, this term comes from the telephony world, and it is worthy of a bit of explanation.  The analog line between a residential home is typically referred to as a local loop or subscriber loop and is designed to carry a single phone conversation.  These lines all terminate at the central office, and if the call is destined for someone else served by that office, a connection is made locally.  If the call is destined to another location, it is bundled together with other calls and sent over a single connection to another central office–multiple calls on a single line…this is essential the definition of a trunk.  In the LAN switching world the principle is the same–if the destination is local, the switch passes the traffic out the correct port, otherwise, it is sent across a single connection to another switch or switches, and a trunk link carries multiple VLANs across a single line.

As you would see in looking at a compact car next to an SUV, all trunks are not created equal, and there are actually two types in the Cisco networking world. These two types are Cisco’s InterSwitch Link (ISL) and the IEEE’s 802.1Q (dot1q), and each have their own distinctive characteristics.  Understanding the differences is a critical factor to both passing the CCNA exam and surviving in the real world of networking.

  1. ISL

To begin with, ISL is a Cisco-proprietary trunking protocol, meaning it will only work on Cisco switches.  If you operate a mixed environment, then ISL will not be your friend.  ISL (like some tunneling protocols) operates by taking the existing frame and wrapping it in a completely new frame and header.  This makes things simple when the header is stripped off at the destination switch/VLAN because the original frame is left intact (no FCS recalculations).  The VLAN id is carried in the ISL header, and there is no concept of a native VLAN.  Pretty straightforward, right?

        2. 802.1Q

802.1Q (referred to as dot1q in command-line syntax) is an industry-standard trunking protocol, so all switches are able to use it.  Unlike ISL, 802.1Q inserts a VLAN tag into the existing frame, which requires that the FCS be recalculated when altering the frame.  The only exception to this is the native VLAN, which in plain English just means that the frame is left untouched, or more properly, untagged.

Next, we will talk about a protocol that seems like a good idea on the surface, but can have disastrous consequences.  Just remember it’s not a bug, it’s a feature!

– Joe

Invisible Networks (No Kidding), the World of Virtual LANs (VLANS), Part I

Posted in Cisco Certification with tags , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , on May 31, 2011 by jjrinehart

As mentioned previously, LANs became the victims of their own success when more and more users became added, creating congestion, collisions, and such.  While the advent of Layer 2 switches solved most of those problems, there were still some issues just due to the nature of layer two devices, namely broadcasts.  If you recall our earlier discussions, a switch floods (sends out all ports except the originating one) unknown unicast, multicast, and broadcast traffic, which can still create congestion issues.  Only Layer 3 devices (e.g., L3 switches and routers) block broadcasts, giving use of the term broadcast domain.

To segment up networks, you can certainly build physically separate LAN segments, but it doesn’t take a math genius to see how pricey that option would quickly become.  This is essentially the thought process behind Virtual Local Area Networks, or VLANs., which are created logically rather than physically.  VLANs create logically separate (“invisible”) network segments on a switch, and even across switches, and thus contain broadcasts in that particular segment.  Aside from broadcast containment, they also have other advantages, as follows:

  1. Design Flexibility: Grouping users by location, function, departments, and such.
  2. Spanning Tree Simplicity: Limiting the use of STP (covered later)
  3. Security: Isolation of servers or sensitive network segments.
  4. IP Telephony: Separation of Voice and Data Traffic.

So if VLANs are so amazing, what are the drawbacks?  I have what I call three immutable laws of life, namely, it will always cost more than you think, it will always cost more than you think, and if it’s too good to be true, it probably is!  VLANs isolate networks at Layer 2, so the challenge is allowing them to communicate with one another, so if there is a catch, this is it.  A smart way to look at it is to consider the Hawaiian islands.

Why is living in Hawaii more expensive?  The simple answer is that it has to do with living on islands, namely that everything has to be shipped in from the mainland, and that traveling between islands requires more expensive transportation.  Someone wanting to travel from Oahu to Maui has to get on a plane or boat, it’s not simply a matter of jumping in a car and driving a few hours.  In the Florida Keys, this is accomplished through a series of very long bridges.

Think of VLANs as islands…isolated segments of the network that are self-contained and stand on their own.  For this to be communicated across multiple switches, a set of virtual connections (analogous to traveling between islands, whether by plane or bridge) has to be built, referred to as Trunks.  The term trunk comes from old world telephony, where specialized lines between central offices carried multiple conversations at once.  Next time, we will delve into the different types of trunks used on Cisco switches.

– Joe