HP A5120 EI Series Configuration Guide

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Note the following rules:
 A device has independent roles in different MSTIs. It can act as the root bridge or a secondary root
bridge of one MSTI and the root bridge or a secondary root bridge of another MSTI. However, one
device cannot be the root bridge and a secondary root bridge in the same MSTI at the same time.
 There is only one root bridge in effect in a spanning tree instance. If two or more devices have been
designated as root bridges of the same spanning tree instance, MSTP selects the device with the
lowest MAC address as the root bridge.
 When the root bridge of an instance fails or is shut down, the secondary root bridge (if you have
specified one) can take over the role of the primary root bridge. However, if you specify a new
primary root bridge for the instance then, the one you specify, not the secondary root bridge will
become the root bridge. If you have specified multiple secondary root bridges for an instance, when
the root bridge fails, MSTP will select the secondary root bridge with the lowest MAC address as the
new root bridge.
Configuring the current device as the root bridge of a specific spanning tree
Follow these steps to configure the current device as the root bridge of a specific spanning tree:
To do...
Use the command...
Remarks
Enter system view
system-view
—
Configure the current device as
the root bridge of a specific
spanning tree
stp [ instance instance-id ] root
primary
Required
By default, a device does not
function as the root bridge of any
spanning tree.
Configuring the current device as a secondary root bridge of a specific spanning tree
Follow these steps to configure the current device as a secondary root bridge of a specific spanning tree:
To do...
Use the command...
Remarks
Enter system view
system-view
—
Configure the current device as a
secondary root bridge of a
specific spanning tree
stp [ instance instance-id ] root
secondary
Required
By default, a device does not
function as a secondary root
bridge.
NOTE:
 After specifying the current device as the root bridge or a secondary root bridge, you cannot change the priority
of the device.
 Alternatively, you can configure the current device as the root bridge by setting the priority of the device to 0. For
the device priority configuration, see ―Configuring the priority of a device.‖
Configuring the work mode of an MSTP device
MSTP and RSTP are mutually compatible and can recognize each other’s protocol packets. However, STP
cannot recognize MSTP packets. For hybrid networking with legacy STP devices, and for full
interoperability with RSTP-enabled devices, MSTP supports the following work modes: STP-compatible
mode, RSTP mode, and MSTP mode.
 In STP-compatible mode, all ports of the device send STP BPDUs,

HP A5120 EI Series Specifications

General

Uplink Ports	4 x SFP
Stacking	No
Management	CLI, Web, SNMP
Routing Protocols	RIP, OSPF
Power Supply	AC
MAC Address Table Size	16K
Dimensions	440 x 430 x 44 mm
Operating Temperature	0°C to 45°C
Operating Humidity	10% to 90% non-condensing
Model	HP A5120-24G EI Switch (JG234A)
VLANs	4094