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:
|
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:
|
Interfaces | Specifies the interface for the MSTP protocol. | Click one:
|
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:
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