Cisco MDS 9000 Series Configuration Guide

FSPF provides the topology information to compute the distribution tree. Fibre Channel defines 256 multicast
groups and one broadcast address for each VSAN. Switches in the Cisco MDS 9000 Family only use broadcast
routing. By default, they use the principal switch as the root node to derive a loop-free distribution tree for
multicast and broadcast routing in a VSAN.
All switches in the fabric should run the same multicast and broadcast distribution tree algorithm to ensure
the same distribution tree.
Caution
To interoperate with other vendor switches (following FC-SW3 guidelines), the SAN-OS and NX-OS 4.1(1b)
and later software uses the lowest domain switch as the root to compute the multicast tree in interop mode.
About Multicast Root Switch
By default, the native (non-interop) mode uses the principal switch as the root. If you change the default, be
sure to configure the same mode in all switches in the fabric. Otherwise, multicast traffic could encounter
potential loop and frame-drop problems.
The operational mode can be different from the configured interop mode. The interop mode always uses the
lowest domain switch as the root.
Note
Use the mcast root lowest vsan command to change the multicast root from the principal switch to lowest
domain switch.
Setting the Multicast Root Switch
To use the lowest domain switch for the multicast tree computation, follow these steps:
Step 1 switch# config terminal
switch(config)#
Enters configuration mode.
Step 2 switch(config)# mcast root lowest vsan 1
Uses the lowest domain switch to compute the multicast tree.
Step 3 switch(config)# mcast root principal vsan 1
Defaults to using the principal switch to compute the multicast tree.
To display the configured and operational multicast mode and the selected root domain, use the show mcast command.
switch# show mcast vsan 1
Multicast root for VSAN 1
Configured root mode : Principal switch
Cisco MDS 9000 Series Fabric Configuration Guide, Release 8.x
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Configuring Fibre Channel Routing Services and Protocols
About Multicast Root Switch

Cisco MDS 9000 Series Specifications

General

Category	Switch
Operating System	Cisco NX-OS
Ports	Varies by model
Protocols	Fibre Channel (FC), Fibre Channel over IP (FCIP), iSCSI
Redundancy	Redundant supervisors, power supplies, and fans
Management	Cisco Data Center Network Manager (DCNM), CLI, SNMP
Virtualization Support	VSANs (Virtual SANs)
Security Features	Fibre Channel Security Protocol (FC-SP)
Hot Swappable Components	power supplies, fans
Power Supply Options	AC and DC options available