Dell PowerConnect J-EX4200-24T Software Manual page 786

Dell PowerConnect J-Series Ethernet Switch Complete Software Guide for Junos OS
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configurations can merge. The members use the following rules to determine whether
a merge is possible:
If the Virtual Chassis configurations have the same Virtual Chassis ID, then the
configurations can merge. If the two Virtual Chassis were formed as the result of a
split, they will have the same Virtual Chassis ID.
If the Virtual Chassis IDs are different, then the two configurations can merge only if
both are active (inactive configurations cannot merge, ensuring that members removed
from one Virtual Chassis configuration do not become members of another Virtual
Chassis configuration). If the configurations to merge are both active and one of them
has a user-configured Virtual Chassis ID, this ID becomes the ID of the merged Virtual
Chassis. If neither Virtual Chassis has a user-configured Virtual Chassis ID, then the
Virtual Chassis ID of the configuration with the highest mastership priority becomes
the ID of the merged Virtual Chassis. The resulting merged Virtual Chassis configuration
will be active.
When you connect two Virtual Chassis configurations, the following events occur:
Connecting the two split Virtual Chassis configurations triggers the shortest-path-first
1.
(SPF) algorithm. The SPF algorithm computes the network topology and then triggers
the master election algorithm. The master election algorithm waits for the members
to synchronize the topology information before running.
The master election algorithm merges the Virtual Chassis IDs of all the members.
2.
Each member runs the master election algorithm to select a master and a backup
3.
from among all members with the same Virtual Chassis IDs. For more information,
see "Understanding How the Master in a Virtual Chassis Configuration Is Elected" on
page 698.
The master determines whether the Virtual Chassis configuration is active or inactive.
4.
(See "What Happens When a Virtual Chassis Configuration Splits" on page 712.)
If the Virtual Chassis configuration is active, the master assigns roles to all members.
5.
If the Virtual Chassis configuration is inactive, the master assigns all members the
role of linecard.
When the other members receive their role from the master, they change their role to
6.
backup or linecard. They also use the active or inactive state information sent by the
master to set their own state to active or inactive and to construct the Virtual Chassis
member list from the information sent by the master.
If the Virtual Chassis state is active, the master waits for messages from the members
7.
indicating that they have changed their roles to the assigned roles, and then the master
changes its own role to master.