AOS-W 6.5.3.x | User Guide RSTP | 651
Chapter 24
RSTP
The AOS-W implementation of Rapid Spanning Tree Protocol (RSTP) is as specified in 802.1w, with backward
compatibility to legacy Spanning Tree (STP) 802.1D. RSTP takes advantage of point-to-point links and provides
rapid convergence of the spanning tree. RSTP is enabled by default on all Alcatel-Lucent switches.
Topics in this chapter include:
n Understanding RSTP Migration and Interoperability on page 651
n Working with Rapid Convergence on page 651
n Configuring RSTP on page 652
n Troubleshooting RSTP on page 654
Understanding RSTP Migration and Interoperability
The AOS-W RSTP implementation interoperates with PVST (Per VLAN Spanning Tree 802.1D) and Rapid-PVST
(802.1w) implementation on industry-standard routers/switches. Alcatel-Lucent only supports global instances
of STP and RSTP. Therefore, the ports on industry-standard routers/switches must be on the default or
untagged VLAN for interoperability with Alcatel-Lucent switches.
AOS-W supports RSTP on the following interfaces:
n FastEthernet IEEE 802.3: fastethernet
n Gigabitethernet IEEE 802.3:gigabitethernet
n Port Channel ID: port-channel
Working with Rapid Convergence
Since RSTP is backwards compatible with STP, it is possible to configure both bridges in the same network.
However, such mixed networks may not always provide rapid convergence. RSTP provides rapid convergence
when interfaces are configured as either:
n Edge ports: These are the interfaces/ports connected to hosts. These interfaces are immediately moved to
the forwarding state. In this mode, an interface forwards frames by default until it receives a BPDU (Bridge
Protocol Data Units), indicating that it should behave otherwise. It does not go through the Listening and
Learning states.
n Point-to-Point links: These are the interfaces/ports connected directly to neighboring bridges over a
point-to-point link. RSTP negotiates with the neighbor bridge for rapid convergence/transition only when
the link is point-to-point.
STP (802.1d)
Port State
RSTP (802.1w)
Port State
Disabled Discarding
Blocking Discarding
Listening Discarding
Table 143: Port State Comparison
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