STP Rules and Restrictions

This section summarizes the rules and restrictions for configuring STP (Spanning Tree Protocol) are:

The carrier VLAN (Virtual LAN) must span all ports of the STPD (Spanning Tree Domain). (This is not applicable to MSTP (Multiple Spanning Tree Protocol).)
The StpdID must be the VLAN ID of the carrier VLAN; the carrier VLAN cannot be partitioned. (This is not applicable to MSTP.)
A default VLAN cannot be partitioned. If a VLAN traverses multiple STPDs, the VLAN must be tagged.
An STPD can carry, at most, one VLAN running in PVST+ mode, and its STPD ID must be identical with that VLAN ID. In addition, the PVST+ VLAN cannot be partitioned.
The default VLAN of a PVST+ port must be identical to the native VLAN on the PVST+ device connected to that port.
If an STPD contains both PVST+ and non-PVST+ ports, that STPD must be enabled. If that STPD is disabled, the BPDUs are flooded in the format of the incoming STP port, which may be incompatible with those of the connected devices.
The 802.1D ports must be untagged and the EMISTP/PVST+ ports must be tagged in the carrier VLAN.
STP and network login operate on the same port as follows:
- STP (802.1D), RSTP (802.1w), and MSTP (802.1s) support both network login and STP on the same port.
- At least one VLAN on the intended port should be configured both for STP and network login.
- STP and Network Login operate together in both Network Login ISP mode and campus mode starting with Extreme 22.2.
- When STP blocks a port, network login does not process authentication requests. All network traffic, except STP BPDUs, is blocked.
- When STP places a port in forwarding state, all network traffic is allowed and network login starts processing authentication requests.
STP cannot be configured on the following ports:
- FDB (forwarding database) flush does not occur on STP- and NetLogin-enabled ports during the topology changes.
- A mirroring target port.
- A software-controlled redundant port.
When you are using the older method of enabling STP instead of using EAPSv2 to block the super loop in a shared-port environment, you can continue to do so. In all other scenarios, it is not recommended to use both STP and EAPS on the same port.
MSTP and 802.1D STPDs cannot share a physical port.
Only one MSTP region can be configured on a switch.
In an MSTP environment, a VLAN can belong to one of the MSTIs.
A VLAN can belong to only one MSTP domain.
MSTP is not interoperable with PVST+.
No VLAN can be bound to the CIST.
Starting with ExtremeXOS 22.2, under the following two conditions, these attributes are preserved with autobind being used to bind the STPD domain to the VLAN: STP enable, Cost, Priority, LinkType, Edge-Sage-Guard, BPDU Restrict, Restrict Role, ActiveRole, LoopProtect, LoopProtect-Partner, AutoEdge, Restricted TCN:
- With sharing and STP configurations established, disabling sharing no longer removes the STP port configuration for the configured master port and it preserves certain configuration attributes and restores them when the port is recreated.
- Configured port's STP properties are preserved when the port is moved from one VLAN to another, provided the new port gets associated with same STP domain.
MLAG is not supported with STP (802.1D).

Published March 2020prev | next

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