How PE units join a Campus Fabric domain

A PE unit cannot join a CB unless the CB has been enabled. Refer to Enabling and configuring the control bridge.

PE discovery starts when a link is detected on a CB or PE port with a potential link to another PE-capable unit. Each PE unit has two reconfigurable SPX ports or LAGs over which LLDP exchanges messages with the CB. When a port in a standalone CB or a CB stack receives a join (LLDP Port-Extension) request from the SPX ports or LAGs of a potential PE unit, the connection process is initiated. When an SPX port on a PE is configured as part of a PE trunk, the join request is sent on all ports in the trunk.

During a PE join, the following PE information is sent to the CB and stored as unit configuration:

  • Module information
  • Ports on which the PE is joining
  • SPX ports
  • SPX LAGs
  • Software image version

How the CB applies a reserved configuration

If the CB has a reserved PE configuration for the same PE ID that does not match the physical configuration of the joining PE, the following scenarios result in different actions:

  • The modules are different (for example, the PE has a 24-port base module, and the reserved configuration has a 48-port module). The joined PE is put into a nonoperational state. The user can configure the no spx unit number command to remove the reserved configuration, and the CB learns the PE properly.
  • The PE has extra modules. The CB learns the extra modules.
  • The reserved PE configuration has extra modules. The CB keeps the extra modules.
  • The reserved PE configuration has different SPX ports or LAGs from the PE. The CB uses the reserved PE configuration and pushes it to the PE, but if reserved PE configuration might break connections, the CB learns the physical connections.

If the PE unit has no reserved configuration

After a PE joins, if the assigned PE ID does not have a reserved configuration, the CB creates an spx unit number configuration that contains the PE module along with SPX port and LAG information. The information is retained in memory unless the user enters the write memory command on the CB to save the configuration to the startup configuration file.

If the PE unit has a different software image

The CB checks the software image version to make sure the CB and the PE unit are running compatible images. If the PE unit is running a different image version, it is put in a nonoperational state. The CB can copy the correct image to a nonoperational unit. Refer to SPX image upgrade for more information.

Parent topic: Campus Fabric Manual Configuration