Encapsulation Modes

You can configure ports within an STPD to accept specific BPDU encapsulations.

This STP port encapsulation is separate from the STP mode of operation. For example, you can configure a port to accept the PVST+ BPDU encapsulation while running in 802.1D mode.

An STP port has three possible encapsulation modes:

802.1D mode

Use this mode for backward compatibility with previous STP versions and for compatibility with third-party switches using IEEE standard 802.1D. BPDUs are sent untagged in 802.1D mode. Because of this, any given physical interface can have only one STPD running in 802.1D mode. The default port mode for user-created STP domains for Dot1d and Dot1w operation mode is Dot1d.

This encapsulation mode supports the following STPD modes of operation: 802.1D, 802.1w, and MSTP.
Extreme Multiple Instance Spanning Tree Protocol (EMISTP) mode

EMISTP mode is proprietary to Extreme Networks and is an extension of STP that allows a physical port to belong to multiple STPDs by assigning the port to multiple VLANs. EMISTP adds significant flexibility to STP network design. BPDUs are sent with an 802.1Q tag having an STPD instance Identifier (STPD ID) in the VLAN ID field.

This encapsulation mode supports the following STPD modes of operation: 802.1D and 802.1w.
Per VLAN Spanning Tree (PVST+) mode

This mode implements PVST+ in compatibility with third-party switches running this version of STP. The STPDs running in this mode have a one-to-one relationship with VLANs and send and process packets in PVST+ format.

This encapsulation mode supports the following STPD modes of operation: 802.1D and 802.1w.

These encapsulation modes are for STP ports, not for physical ports. When a physical port belongs to multiple STPDs, it is associated with multiple STP ports. It is possible for the physical port to run in different modes for different domains to which it belongs.

If configured in MSTP mode, an STPD uses the 802.1D BPDU encapsulation mode by default. To ensure correct operation of your MSTP STPDs, do not configure EMISTP or PVST+ encapsulation mode for MSTP STPDs.

To configure the BPDU encapsulation mode for one or more STP ports, use the command:
- configure stpd stpd_name ports mode [dot1d | emistp | pvst-plus] port_list
To configure the default BPDU encapsulation mode on a per STPD basis, use the command:
- configure stpd stpd_name default-encapsulation [dot1d | emistp | pvst-plus]

Instead of accepting the default encapsulation modes of dot1d for the default STPD s0 and for all other STPDs, this command allows you to specify the type of BPDU encapsulation to use for all ports added to the STPD (if not otherwise specified).