Handling Trunking in Switches

General

Some switches can be configured to treat two or more ports as if they were a single port. One reason for doing this is to get more bandwidth between two switches. Another reason is the result of 'load balancing'.

IntraVUE asks a managed switch for the port number of the MAC devices connected to it. In the case of trunking, the response could be any of the ports used for trunking. As a result IntraVUE will see the 'lower' switch as moving frequently between the trunked ports, and the IntraVUE display will redraw each time there is such a change.

A configuration file has been created that allows the IntraVUE administrator to inform the scanner of any trunking for switches being scanned.

'trunkingdefs.txt' is the default file name. It is located in the ...\intravue\autoip folder (file system details ) . The actual name used is user configurable in the ivserver.properties file, in the property 'scanner.trunk.data.file'. An administrator could then setup several different trunking files for testing and other purposes.

A side benefit of using the 'trunkingdefs.txt' file is the ability to renumber ports to suit the users view of the switch, see Example 3.

The 'trunkingdefs.txt' File

This file is read and interpreted to both combine ports for trunking purposes and also to change the port numbers assigned to a switch for display purposes.

The format is simple. A switch is designated using square braces, [ ], around its IP address. This is followed by one or more lines of port assignments until the next set of square braces.

The port assignments are done using a two character separator "->". On the left is the port as known to the switch. On the right is how IntraVUE should treat and display that port.

Many ports on the left can be assigned to the same number on the right. If a number is repeated on the left, the last one will be used.

Example 1 - Normal Case

The 10.1.2.3 switch has ports 2 and 3 trunked to ports 5 and 6 of switch 10.1.2.4. We want IntraVUE to consider ports 2 and 3 on the 10.1.2.3 to both be treated as port 2 and ports 5 and 6 on the other switch to be treated as port 5.

    [10.1.2.3]
    2->2
    3->2

    [10.1.2.4]
    5->5
    6->5

Example 2 - Showing different port numbers for Stacked Switches

When two 24 port switches are stacked, the port numbers of the second switch are changed internally so they do not conflict with the first switch. On some switches the first port of the second switch might be numbered 25, or 27 if there are some internal ports, or even a high number like 950.

This example shows the second stacked 8 port switch that has been renumbered for display purposes.

    [10.1.2.3]
    10->1
    11->2
    12->3
    13->4
    14->5
    15->6
    16->7
    17->8

Example 3 - A Switch with misnumbered ports

In this example the label on a switch numbers the ports 1 thru 12, but internally the ports are 12 to 1. IntraVUE reports the port number used by the switch internally and this leads to confusion. A Cisco 2955 is an example of such a switch.

    [10.1.2.3]
    1->12
    2->11
    3->10
    4->9
    5->8
    6->7
    7->6
    8->5
    9->4
    10->3
    11->2
    12->1