Extreme Networks ExtremeWare XOS 10.1, Manual

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Spanning Tree Domains
ExtremeWare XOS 10.1 Concepts Guide 139
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
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 1D mode. Because of
this, any given physical interface can have only one STPD running in 1D mode.
•
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.
• 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.
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.
To configure the BPDU encapsulation mode for one or more STP ports, use the following 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 following 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
emistp
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).
STPD Identifier
An StpdID is used to identify each STP domain. You assign the StpdID when configuring the domain,
and that carrier VLAN cannot belong to another STPD.
An StpdID must be identical to the VLANid of one of the member VLANs in that STP domain.
NOTE
If an STPD contains at least one port not in 1D mode, the STPD must be configured with an StpdID.