Rack type and mounting bracket hole spacing

Use a four-post rack or a two-post rack. You can mount the router on any four-post or two-post rack that provides bracket holes or hole patterns spaced at 1 U (1.75-in./4.44-cm) increments and that meets the size and strength requirements specified in this table.

A U is the standard rack unit defined in Cabinets, Racks, Panels, and Associated Equipment (document number EIA-310–D) published by the Electronics Industry Association (http://www.eia.org).

Rack size and strength

• Ensure that the rack is a 19-in. rack as defined in Cabinets, Racks, Panels, and Associated Equipment (document number EIA-310–D) published by the Electronics Industry Association (http://www.eia.org).
• Ensure that the rack is one of the following standard lengths:
  • 23.62 in. (600 mm)
  • 30.0 in. (762 mm)
  • 21.5 in. (800 mm)
• The rack rails must be spaced widely enough to accommodate the router chassis's external dimensions: 20.75 in. (52.71 cm) high, 24.3 in. (61.7 cm) deep, and 17.43 in. (44.3 cm) wide. The outer edges of the mounting brackets extend the width to 19 in. (48.3 cm). The spacing of rails and adjacent racks must also allow for the clearances around the router and rack that are specified in M120 Clearance Requirements for Airflow and Hardware Maintenance.
• All mounting options require you to install the supplied large mounting shelf. The supplied small mounting shelf is needed for a front-mount four-post rack or cabinet.
• If a front-mount rack is used, you must support the back of the router with the large mounting shelf included with your shipment, or some other structure.
• For a front-mount rack, you use the front-mounting flanges on the front of the chassis instead of the mounting brackets. The flanges have holes for rack-mounting screws, spaced at 3.5 in. (8.89 cm). In addition, if you are mounting the router in a four-post rack or cabinet, you must install the spacer bars on the rack before you mount the chassis. For instructions about installing the mounting hardware, see Installing the Mounting Hardware for a Front-Mount Four-Post Rack or Cabinet, Installing the Mounting Hardware for a Front-Mount Open-Frame Rack, or Installing the Mounting Hardware for a Center-Mount Open-Frame Rack.
• The chassis height of 20.75 in. (52.71 cm) is approximately 12 U. A U is the standard rack unit defined in Cabinets, Racks, Panels, and Associated Equipment (document number EIA-310-D) published by the Electronics Industry Association. You can stack four M120 routers in a rack that has at least 48 U (84 in. or 2.1 m) of usable vertical space.
• The rack must be strong enough to support the weight of the fully configured router, up to 225 lb (102.1 kg). If you stack four fully configured routers in one rack, it must be capable of supporting about 900 lb (408.4 kg).
• Ensure that the spacing of rails and adjacent racks allows for the proper clearance around the switch and rack as specified in M120 Clearance Requirements for Airflow and Hardware Maintenance.

Rack connection to the building structure

• Secure the rack to the building structure.
• If earthquakes are a possibility in your geographical area, secure the rack to the floor.
• Secure the rack to the ceiling brackets as well as wall or floor brackets for maximum stability.