A fabric connects VLANs. If you understand a VLAN, you know that they permit network connections only between specific switch ports or specifically identified ports (“tagged” ports). Consequently, it would be impossible for two VLANs to communicate with each other. A fabric makes these VLAN-to-VLAN connections possible.
We can illustrate a network fabric more easily by rewinding the term to one of its earliest uses: the early phone system. In a telephone switchboard, subscriber lines (customer phone numbers) ran in a grid pattern in the back of the switchboard, but they didn’t touch each other until the operator inserted the plugs of a patch cable to join them. With some “plugboards” (what a switchboard was actually called), an operator could conference multiple lines by adding more patch cords.
These patch cords essentially acted like a VLAN, allowing only the subscribers whose lines were “patched in” to join the conversation.
But the switchboard only covered one exchange, that is, one three-digit phone number prefix. If a subscriber wanted to conference someone from another exchange, there had to be patch from one exchange to another. This was handled by a long-distance operator. Each exchange had a more robust outgoing line, called a “trunk line,” that connected exchanges in some central place. The long-distance operators could bridge trunks in a specific way, involving a local operator in each of the “bridged” exchanges.
By now, you’re probably starting to recognise a lot of network terms, which is completely appropriate. Almost all modern networking technology originated in the telephone system.
Now imagine that you want to conference in six people, two in each of three distant exchanges. Each exchange operator had to patch two numbers and a trunk line. The long-distance operator had to patch three trunks in a specific way that prevented the conversation from going out to all numbers attached to the trunk.
The details of the method aren’t particularly relevant here, but it usually involved a pair of “bridge clips” that connected non-adjacent wire-crossings, with an insulated portion that laid across wires that weren’t meant to be connected. It looked a lot like a little bridge when properly placed.
Think of each of the local exchange conferences as a VLAN; the long-distance operator’s patch cables created what was called a “fabric.” Our use of fabric is exactly the same idea: some number of private “conversations” (connections) connected to each other so that specific people in each “group” can all talk to each other.
You could describe a fabric as a VLAN namespace. It’s a switch or a combination of switches that use trunking to provide access to specific VLANs. MAAS creates a default fabric (‘fabric-0’) for each detected subnet during installation.
Last updated 11 hours ago.