Table of Contents

• Background
  
• Policy
  
• Benefits
  
• Implementation Assistance
  

Background

The intent of this policy is not to further limit end-device connections to fan-out devices, but rather to insure that networks are not accidentally interconnected or multiply connected. UCDNet and Interim Network 21 have provided many connections for the campus. In some areas, more than one connection is available. Special care should be taken when connecting network devices in these areas. Problems of various severity may be experienced when making these connections. A simple problem may occur in connecting a machine to the wrong NAM. This would result in connecting to the wrong network. A very serious problem may occur if a multiport device like a hub or switch is connected to more than one NAM. This has the potential to disable the whole LAN or cause routing loops on the campus backbone networks if two different subnets are interconnected by the hub or switch. Serious problems may also occur if two buildings already connected to UCDNet or Network 21 are interconnected using a serial bridge or another LAN extending device. This may cause routing loops on the campus backbone networks.

Policy

UCDNet and Network 21 must only be interconnected at a few central locations for efficient and predictable routing. Bridges, Hubs, Switches and other multiport devices must only have a SINGLE connection to UCDNet or Network 21. Connection of other devices, such as computers and printers to the multiport device, is allowed but limited by previous policies regarding the use of fan-out devices. Sites currently connected by UCDNet or Network 21 shall not be interconnected by serial bridges or other devices that serve to extend a LAN to a remote site. IT/Communications Resources network design personnel shall be contacted to assist with projects that may cause sites to be interconnected by means other than UCDNet or Network 21 backbone routers. The attached drawing illustrates a simple scenario where a fan-out device is properly connected to a single NAM and several end devices such as computers and printers.

Benefits

This policy will prevent unexpected network outages that may occur as a result of interconnecting networks outside of the scope of UCDNet and Network 21 routing architectures. This policy also prevents network outages that will occur when connecting more than one port of a single device to a network. Hubs will cause excessive collisions and switches will cause broadcast storms when multiply connected to a single network.

Implementation Assistance

Network administrators may need to contact the Communications Resources Service Center to help with a network connection which might cause a delay in process of connection in a multiport device. However, simple fan-out devices connected to a single NAM may still be performed at a departments discretion within the limitations for fan-out devices set in the Network 21 Policy Document.