Extreme Networks ExtremeWare 7.7, Command Reference Manual

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ExtremeWare 7.7 Command Reference Guide 1579
Encapsulation Modes
You can configure ports within an STPD to accept and transmit 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
This mode is used 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, on any given physical interface there can be only
one STPD running in 802.1d mode.
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 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 (StpdID) in the VLANid field.
This encapsulation mode supports the following STPD modes of operation: 802.1D and 802.1w.
• 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 port 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.
MSTP STPDs use only 802.1D BPDU encapsulation mode. To ensure correct operation of your MSTP
STPDs, do not configure EMISTP or PVST+ encapsulation mode for MSTP STPDs.