Avaya C360 - Manual (Page 130)

Avaya C360 Layer 2 Features
130 Installation and Configuration Guide Avaya C360 Multilayer Stackable Switches, version 4.5
Spanning Tree Implementation in the C360
RSTP is implemented in C360 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.
The balance of this section lists the conditions and limitations that govern the implementation of
Spanning Tree in the C360 family.
● 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 C360 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.
● RSTP is interoperable with C360 Port Redundancy and 802.1x applications. If either
RSTP or 802.1x put the port in blocking, its final state will be "blocking".
● You must manually configure uplink and backbone ports to be "non-edge" ports for both
STP and RST using the set port edge admin state CLI command.
● You must manually set the classification of uplink and backbone ports to "valuable" using
the set port classification CLI command.
● 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.