If you've read our previous article The VLAN Concept - Introduction to VLANs then you should feel comfortable with terms such as 'VLAN', 'Static & Dynamic VLANs', however this is just the beginning in this complex world. This article will start to slowly expand on these terms to help understand how VLANs are implemented inside an enterprise network.
To begin with, we will take a closer look at the port interfaces on these smart switches and then start moving towards the interfaces connecting to the network backbone where things become slightly more complicated, though do not be alarmed since our detailed and easy to read diagrams are here to ensure the learning process is as enjoyable as possible.
VLAN Links - Interfaces
When inside the world of VLANs there are two types of interfaces, or if you like, links. These links allow us to connect multiple switches together or just simple network devices e.g PC, that will access the VLAN network. Depending on their configuration, they are called Access Links, or Trunk Links.
VLAN Configuration, InterVLAN routing,Trunk Link configuration for Cisco Layer 3 switches (3550, 3560 series, 3750 series, 4500 series and 6500 series switches) is covered extensively at the following article: Basic & Advanced Catalyst Layer 3 Switch Configuration: Creating VLANs, InterVLAN Routing (SVI), VLAN Security – VLAN Hopping, VTP Configuration, Trunk Links, NTP. IOS License Requirements for SVI Routing.
Access Links are the most common type of links on any VLAN switch. All network hosts connect to the switch's Access Links in order to gain access to the local network. These links are your ordinary ports found on every switch, but configured in a special way, so you are able to plug a computer into them and access your network.
Here's a picture of a Cisco Catalyst 3550 series switch, with it's Access Links (ports) marked in the Green circle:
We must note that the 'Access Link' term describes a configured port - this means that the ports above can be configured as the second type of VLAN links - Trunk Links. What we are showing here is what's usually configured as an Access Link port in 95% of all switches. Depending on your needs, you might require to configure the first port (top left corner) as a Trunk Link, in which case, it is obviously not called a Access Link port anymore, but a Trunk Link!