Extreme Networks ExtremeWare 7.2e, Installation And User Manual

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Spanning Tree Domains
ExtremeWare 7.2e Installation and User Guide 197
Port Modes
An STP port has two modes of operation:
• 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, on any given physical interface there can be only one STPD running in 1D mode.
• Limited Support for Extreme Multiple Instance Spanning Tree Protocol (EMISTP) mode
Normally EMISTP mode is an extension of STP that allows a physical port to belong to multiple
STPDs by assigning the port to multiple VLANs. BPDUs are sent with an 802.1Q tag having an
STPD instance Identifier (StpdID) in the VLANid field.
With this implementation on the Summit 400, EMISTP is limited to supporting a single EMISTP
domain per physical port, called Compatibility Mode. Compatibility mode is supported to allow other
switches using the full EMISTP mode to interoperate with the Summit 400.
• Limited Support for 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.
With this implementation on the Summit 400, PVST+ is also limited to supporting a single PVST+
domain per physical port, called Compatibility Mode. Compatibility mode is supported to allow other
switches using the full PVST+ mode to interoperate with the Summit 400.
These port modes are for STP ports, not for physical ports. The Summit 400 restricts each physical port
to a single STPD.
STPD Identifier
An StpdID is used to identify each STP domain. You assign the StpdID when configuring the domain,
and that 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.
STPD BPDU Tunneling
You can configure ExtremeWare to allow a BDPU to traverse a VLAN without being processed by STP,
even if STP is enabled on the port. This is known as BPDU tunneling.
To enable and disable BPDU tunneling on a VLAN, use one of the following commands:
enable ignore-bpdu vlan <vlan name>
disable ignore-bpdu vlan <vlan name>
If you have a known topology and have switches outside of your network within your STPD, use this
feature to keep the root bridge within your network.