Avaya P332G-ML manual Spanning Tree Implementation in the P330 Family

Chapter 11 Avaya P330 Layer 2 Features

•Point-to-point Link ports — This port type applies only to ports interconnecting RSTP compliant switches and is used to define whether the devices are interconnected using shared Ethernet segment or point-to-point Ethernet link. RSTP convergence is faster when switches are connected using point-to-point links. The default setting for all ports – automatic detection of point-to-point link – is sufficient for most networks.

Spanning Tree Implementation in the P330 Family

RSTP is implemented in P330 family of products so that it is interoperable with the existing implementation of STP. In order to configure the switch to either common Spanning Tree or Rapid Spanning Tree protocol, use the set spantree version command.

•After upgrading to software version 4.0, the default is spanning tree version STP. The default after NVRAM INIT remains STP.

The balance of this section lists the conditions and limitations that govern the implementation of Spanning Tree in the P330 line.

•RSTP’s fast convergence benefits are lost when interacting with legacy (STP) bridges.

•When RSTP detects STP Bridge Protocol Data Units (BPDUs type 1) on a specific port, it will begin to “speak” 802.1d on this port only. Specifically, this means:

—802.1d bridges will ignore RSTP BPDUs and drop them.

—802.1d bridges will send 802.1d format BPDUs back to the switch.

—The switch will change to 802.1d mode for that port only.

The P330 configured to RSTP is therefore able to simultaneously work with other switches implementing either RSTP or STP without specific user intervention.

•Spanning Tree configuration is performed on the stack level.

•If you do not upgrade all switches in the stack to firmware version 4.0, spanning tree will continue its normal operation. However, configuring Spanning Tree will not be possible until all switches are upgraded to version 4.0.

•RSTP is interoperable with P330 Port Redundancy and PBNAC applications. If either RSTP or PBNAC put the port in blocking, its final state will be “blocking”.

•STP and Self Loop Discovery (SLD) are incompatible. However, If Spanning Tree is set to rapid-spanning-tree version, there is no need to use the Self-loop- discovery feature; the RSTP algorithm avoids loops generated by the IBM token ring cabling.

•The 802.1w standard defines differently the default path cost for a port compared to STP (802.1d). In order to avoid network topology change when migrating to RSTP, the STP path cost is preserved when changing the spanning tree version to RSTP. You can use the default RSTP port cost by using the CLI command set port spantree cost auto.

86 Avaya P332G-ML User’s Guide