MDF & IDF
The “heart” of the network at a facility is the MDF – the Main Distribution Frame. Although most facilities we work with only have the MDF, some will occasionally have an IDF – an Intermediate Distribution Frame. These are the rooms at a building where the hub of a network equipment is.
In the MDF, the external circuit from the Internet Service Provider (ISP) generally come in and is plugged into the firewall. This is the Demarc zone for us – the ISP is responsible for their equipment being setup and configured properly and plugging into our firewall, as well as everything “behind” that (that is, on the outside). We’re responsible for the firewall and everything “inside” the network.
At smaller facilities, the MDF is the only network room. It will have the firewall, ISP equipment, switches (for larger facilities), any servers and other computing hardware, and the patch panels. The patch panels are outlets where cables will run from the networking equipment into the panels. From the back of the panel, more permanent wires run into the walls/ceilings/other plenum spaces and throughout the building to wall ports around the facility. Those wall ports will, in turn, have the client devices plugged into them.
Larger & multi-story or multi-building locations will have an IDF per floor or building. The size of this varies, but it’s usually a smaller version of the MDF that will only have the switches and patch panels. These are connected back to the MDF typically by fiber cables which can handle the larger distance and higher bandwidth needs that a single Ethernet cable can’t. We generally run fiber through underground conduit. From the IDF, the patch panels and permanent cabling function the same.
Physical Security
Both of these rooms – the MDF & and IDFs – should have locks on the door with access limited to those who need access. We have uncounted numbers of issues where end users attempt to troubleshoot a network problem OR “tidy up some cables” and bring an entire facility down.
Network Racks
As much as possible, all of the networking equipment and servers are mounted into a rack – a large cabinet with mounting brackets following a standard size. Racks are measured in “U”s, with a U being a standard Unit of measurement for equipment. Equipment is measured in U’s – a switch is 1U, whereas a large server may be 2, 3, or more U’s. One side of the rack is designated the intake, and the other side the exhaust. The intake is the “cold” side where air conditioning provides cooling, while the exhaust is the “hot” side and is shunted away from the equipment to keep it from overheating.
Environmental & Power Consistency
In addition to environmental monitoring via air conditioning, as well as dehumidifiers that maintain a certain range of humidity (too much can cause moisture accumulation, while too little can cause static electricity buildup), consistent power is important. All equipment is on some type of Uninterruptible Power Supply, a battery which will kick in the moment power to the facility is interrupted. A PDU – power distribution unit – functions like a high-quality “power strip” which can include additional features like network monitoring and the ability to toggle individual power ports. For mission critical facilities, an outside gasoline generator is installed for longer outages.
Summary
This concludes a brief look at the physical network facilities. Power backup & strict environmental monitoring provides a good room for the rack-mounted network hardware to function. From the MDF hub, IDF spokes provide network access to more remote facilities. Proper physical security restricts the ability of uninformed or malicious actors from bringing an entire facility offline.
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