Brocade Network OS NETCONF Operations Guide v4.1.1 - Manual (Page 122)

90 Network OS NETCONF Operations Guide
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Fabric interface configuration management
8
Broadcast, unknown unicast, and multicast forwarding
All switches in a Brocade VCS Fabric share a single multicast tree rooted at the routing bridge with
the lowest RBridge ID (domain ID). All broadcast, unknown unicast, and multicast traffic between
two edge routing bridges is forwarded on this multicast tree inside the Brocade VCS Fabric. The
multicast tree includes all routing bridges in the Brocade VCS Fabric.
Multicast distribution tree-root selection
Network OS 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 backup multicast root is pre-selected, which is the switch with the next lowest RBridge ID.
The backup multicast root is automatically selected by all switches should the current
multicast root fail.
Priorities
As stated previously, 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 ID is
still chosen. If RBridge ID 7 and 8 are both set to priority 1, 7 becomes the root.
Changing the priority
To change the priority of a routing bridge, perform the following steps.
1. Issue the RPC to configure the node in the
urn:brocade.com:mgmt:brocade-fabric-service namespace.
2. Under the node, include the // hierarchy of node
elements.
3. Under the node element, include the following leaf elements.