Network Management Strategies for the CIO
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Good question!
VLANs are a hot topic these days and will continue to be for a long time, as more people understand the potential they have.
As you correctly noted, assignment to a VLAN must be done at the switch level since the switch is the "backbone" to all available VLANs within the network. The switch can be configured to work in either 'Trunk' mode or 'normal' mode, each one designed to deliver maximum flexibility and functionality of your network's backbone.
When a port is configured to "trunk" mode, it will carry information belonging to all VLANs. These ports are then called "trunk ports" and the packets passed through them are tagged so they can be identified to which VLAN they belong. The other type of port, that is, 'normal' ports are assigned to a specific VLAN, and all packets exiting the interface contain no VLAN tags whatsoever.
Creating multiple VLANs in a network is quite cool, but what if you need hosts between these VLANs to communication between each other? In this case, let me show you two of the most popular methods used:
1) A PC/Host acting as a router
Port1(vlan1)----------PC Port2(vlan2)-----------^
In this situation, the PC has two network interface cards, each one connecting to one port of either VLANs. The PC would also require internal routing to be enabled, so it may pass packets from one network (or VLAN) to another.
2) Layer 3 switch!
The second, and most expensive, method is using a Layer 3 switch. These switches have the ability
to route between networks/VLANs and are quite impressive and expensive!
With Layer 3 switches, you have the ability to also introduce access lists and configure your switch with an IP address in every VLAN, which is used as gateway by all hosts within that VLAN.
This was first published in March 2004
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