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    Understanding the Spanning Tree Protocol

    Starting in Junos OS Release 15.1X49-D70, the Spanning Tree Protocol (STP) is supported on SRX300, SRX320, SRX340, SRX345, SRX550M, and SRX1500 devices.

    Spanning Tree Protocol (STP) is not supported from Junos Os Release 15.1X49-D40 to Junos OS Release 15.1X49-D60.

    Spanning Tree Protocol (STP), defined in IEEE 802.1D, creates a tree of links in the Ethernet switched network. Links that cause loops in the network are disabled, thereby providing a single active link between any two devices.

    Rapid Spanning Tree Protocol (RSTP), originally defined in IEEE 802.1w and later merged into IEEE 802.1D, facilitates faster spanning-tree convergence after a topology change.

    Multiple Spanning Tree Protocol (MSTP), initially defined in IEEE 802.1s and later included in IEEE 802.1Q, supports mapping of multiple VLANs onto a single spanning-tree instance. This reduces the number of spanning-tree instances required in a switched network with many VLANs.

    Juniper Networks devices provide Layer 2 loop prevention through STP, RSTP, and MSTP. You can configure bridge protocols data unit (BPDU) protection on interfaces to prevent them from receiving BPDUs that could result in STP misconfigurations, which could lead to network outages.

    For STP configuration parameters, see Table 1.

    Table 1: STP Configuration Parameters

    Field

    Function

    Action

    Protocol Name

    Displays the spanning-tree protocol.

    View only.

    Disable

    Disables STP on the interface.

    To enable this option, select the check box.

    BPDU Protect

    Specifies that BPDU blocks are to be processed.

    To enable this option, select the check box.

    Bridge Priority

    Specifies the bridge priority. The bridge priority determines which bridge is elected as the root bridge. If two bridges have the same path cost to the root bridge, the bridge priority determines which bridge becomes the designated bridge for a LAN segment.

    Select a value.

    Forward Delay

    Specifies the number of seconds an interface waits before changing from spanning-tree learning and listening states to the forwarding state.

    Enter a value from 4 through 30 seconds.

    Hello Time

    Specifies time interval in seconds at which the root bridge transmits configuration BPDUs.

    Enter a value from 1 through 10 seconds.

    Max Age

    Specifies the maximum aging time in seconds for all MST instances. The maximum aging time is the number of seconds a switch waits without receiving spanning-tree configuration messages before attempting a reconfiguration.

    Enter a value from 6 through 40 seconds.

    For RSTP configuration parameters, see Table 2.

    Table 2: RSTP Configuration Parameters

    Field

    Function

    Action

    Protocol Name

    Displays the spanning-tree protocol.

    View only.

    Disable

    Specifies whether RSTP must be disabled on the interface.

    To enable this option, select the check box.

    BPDU Protect

    Specifies that BPDU blocks are to be processed.

    To enable this option, select the check box.

    Bridge Priority

    Specifies the bridge priority. The bridge priority determines which bridge is elected as the root bridge. If two bridges have the same path cost to the root bridge, the bridge priority determines which bridge becomes the designated bridge for a LAN segment.

    Select a value.

    Forward Delay

    Specifies the number of seconds a port waits before changing from its spanning-tree learning and listening states to the forwarding state.

    Enter a value from 4 through 30 seconds.

    Hello Time

    Specifies the hello time in seconds for all MST instances.

    Enter a value from 1 through 10 seconds.

    Max Age

    Specifies the maximum aging time in seconds for all MST instances. The maximum aging time is the number of seconds a switch waits without receiving spanning-tree configuration messages before attempting a reconfiguration.

    Enter a value from 6 through 40 seconds.

    For MSTP configuration parameters, see Table 3.

    Table 3: MSTP Configuration Parameters

    Field

    Function

    Action

    Protocol Name

    Displays the spanning-tree protocol.

    View only.

    Disable

    Specifies whether MSTP must be disabled on the interface.

    To enable this option, select the check box.

    BPDU Protect

    Specifies that BPDU blocks are to be processed.

    To enable this option, select the check box.

    Bridge Priority

    Specifies the bridge priority. The bridge priority determines which bridge is elected as the root bridge. If two bridges have the same path cost to the root bridge, the bridge priority determines which bridge becomes the designated bridge for a LAN segment.

    Select a value.

    Forward Delay

    Specifies the number of seconds a port waits before changing from its spanning-tree learning and listening states to the forwarding state.

    Enter a value from 4 through 30 seconds.

    Hello Time

    Specifies the hello time in seconds for all MST instances.

    Enter a value from 1 through 10 seconds.

    Max Age

    Specifies the maximum aging time for all MST instances. The maximum aging time is the number of seconds a switch waits without receiving spanning-tree configuration messages before attempting a reconfiguration.

    Enter a value from 6 through 40 seconds.

    Configuration Name

    MSTP region name carried in the MSTP bridge protocol data units (BPDUs).

    Enter a name.

    Max Hops

    Maximum number of hops a BPDU can be forwarded in the MSTP region.

    Enter a value from 1 through 255.

    Revision Level

    Revision number of the MSTP region configuration.

    Enter a value from 0 through 65,535.

    MSTI tab

    MSTI Id

    Specifies the multiple spanning-tree instance (MSTI) identifier. MSTI IDs are local to each region; because of which you can reuse the same MSTI ID in different regions.

    Click one:

    • Add—Creates a MSTI.
    • Edit—Edits an existing MSTI.
    • Delete—Deletes an existing MSTI.

    Bridge Priority

    Specifies the bridge priority. The bridge priority determines which bridge is elected as the root bridge. If two bridges have the same path cost to the root bridge, the bridge priority determines which bridge becomes the designated bridge for a LAN segment.

    Select a value.

    VLAN

    Specifies the VLANs for the MSTI.

    Click one:

    • Add—Selects VLANs from the list.
    • Remove—Deletes the selected VLAN.

    Interfaces

    Specifies the interface for the MSTP protocol.

    Click one:

    • Add—Selects interfaces from the list.
    • Edit—Edits the selected interface.
    • Remove—Deletes the selected interface.

    For spanning-tree port configuration details, see Table 4.

    Table 4: Spanning-Tree Ports Configuration Details

    Field

    Function

    Action

    Interface Name

    Specifies the interface for the spanning-tree protocol type.

    Select an interface.

    Cost

    Specifies the link cost to control which bridge is the designated bridge and which interface is the designated interface.

    Enter a value from 1 through 200,000,000.

    Priority

    Specifies the interface priority to control which interface is elected as the root port.

    Select a value.

    Edge

    Configures the interface as an edge interface. Edge interfaces immediately transition to a forwarding state.

    Select to configure the interface as an edge interface.

    Mode

    Specifies the link mode.

    Select one:

    • Point to Point—For full-duplex links, select this mode.
    • Shared—For half-duplex links, select this mode.

    Modified: 2017-11-13