Routing Administrative Distance is a feature originally used by Cisco routing to select the best path when two or more paths exist, using two or more protocols that can forward packets to a given destination. Because NetMRI is not a router, Routing Distance provides for two specific use cases:

• Determine the preferred protocol used for the NetMRI appliance for receiving and transmitting packets. For example, an appliance might reside on a network that runs both OSPF and RIP. The Cisco default administrative distance for OSPF is 110, and the administrative distance default for RIP is 120, making OSPF the ‘preferred’ routing protocol for forwarding network traffic. The lower a Distance value, the more preferred or ‘reliable’ the system considers the protocol;
• For Topology, Administrative Distance has effects on how Path Analysis conducts calculations between any two points in the network. Under Path Analysis, a path could use two or more dynamic routing protocols (BGP4 and OSPF, for example). The Routing Distance settings determine how NetMRI reports its analyzed paths, indicating the protocol that takes precedence in the analyzed path.

Under Routing Distance, the values used by NetMRI reflect the Cisco-defined default values. You can change these values for the local NetMRI appliance or Operations Center system. Changing these values only has an effect on the local NetMRI appliance’s calculations for Path Analysis if the appliance is one of the endpoints, or is an intermediate node in a path being calculated.

To edit admin distance:

1. Go to the Settings icon > General Settings > Path Analysis.
2. Click in the cell under the Admin Distance column for each chosen protocol.

Entering a value of 255 as the Admin Distance will cause the protocol to be ignored by the device and not use the protocol.

The Routing Distance feature also may be useful for Operations Centers and their associated Collectors.

Specifying Path Calculations

In a large network, more than one possible path my exist between two devices. You can control the number of path calculations performed for the same Source/Destination pair. The default number of simultaneous path calculations is 2, with a maximum value of 10. Go to Settings icon –> General Settings –> Path Analysis and edit the Number of Calculated Paths setting. Avoid setting this value to too high a number, as multiple active path calculations can affect performance.