Brocade Network OS Administrator’s Guide v4.1.1 - Manual (Page 152)

Multicast distribution tree-root selection
Network OS v4.0.0 software supports the following distribution tree behaviors.
• The root of the distribution tree is the switch with the lowest RBridge ID. The automated selection
process does not require any user intervention.
• Each switch in the cluster optionally carries a multicast root priority. This priority setting overrides
the automatically-selected multicast root. In deployments where a multicast root is required to be a
specific switch that does not have the lowest RBridge ID, then the priority setting on that switch can
override the root selection. If there are two switches with the same priority, then the switch with the
lower RBridge ID prevails.
• A back-up multicast root is pre-selected, which is the switch with the next lowest RBridge ID. The
back-up multicast root is automatically selected by all switches should the current multicast root fail.
Configuring priorities
As stated above, the root of the tree is auto-selected as the switch with the lowest RBridge ID. For
example, if you had a cluster with RBridge IDs 5, 6, 7, and 8, then 5 would be the root. If you then
added RBridge ID 1 to this fabric, the tree would be re-calculated with 1 as the root.
In order to avoid this behavior, you can set a priority (default is 1). The highest priority overrides the
lowest RBridge ID and becomes the root.
For example, to build a fabric with RBridge ID 7 or 8 as the root, set their priority to something higher
than 1 (priority values are 1 through 255). If there is a tie in priority, the lower RBridge is still chosen. If
RBridge ID 7 and 8 are both set to priority 1, 7 becomes the root.
Changing the priority
1. Connect to the switch and log in using an account assigned to the admin role.
2. Enter the fabric route mcast rbridge-id command.
Here is an example of changing an RBridge multicast priority:
switch(config)# fabric route mcast rbridge-id 12 priority 10
Displaying the running configuration
The show running-config fabric route mcast command allows you to display fabric route multicast
configuration information. The configuration currently effective on the switch is referred to as the
running configuration. Any configuration change you make while the switch is online is made to the
running configuration. The running configuration is nonpersistent.
NOTE
To save configuration changes, you must save the running-config file to a file, or you can apply the
changes by copying the running configuration to the startup configuration.
1. Connect to the switch and log in using an account assigned to the admin role.
2. Enter the show running-config fabric route mcast command.
switch# show running-config fabric route mcast priority
fabric route mcast rbridge-id 12 priority 10
Multicast distribution tree-root selection
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