Alteon Application Switch Operating System Application Guide
Spanning Tree Protocol
Document ID: RDWR-ALOS-V2900_AG1302
105
Two spanning tree instances are configured in this example. To identify the STG a VLAN is
participating in for each Alteon, see
Multiple Spanning Tree Groups per VLAN Example, page 105
Table 12 provides a summary of this example:
Alteon-Centric Spanning Tree Protocol
In
Figure 9 - Four-Alteon Topology with a Multiple Spanning Tree, page 104
, VLAN 2 is shared by
Alteons A and B on ports 8 and 1 respectively. Alteon A identifies VLAN 2 in STG2 and Alteon B
identifies VLAN 2 in STG1. An STG is Alteon-centric. It is used to identify the VLANs participating in
the STGs. The STG ID is not transmitted in the BPDU. Each spanning tree decision is based on the
configuration of that Alteon.
VLAN Participation in Spanning Tree Groups
The VLAN participation for each STG in
Figure 9 - Four-Alteon Topology with a Multiple Spanning
is summarized as follows:
•
VLAN 1 Participation—If Alteon A is the root bridge, then Alteon A transmits the BPDU for
VLAN 1 on ports 1 and 2. Alteon C receives the BPDU on its port 2 and Alteon D receives the
BPDU on its port 1. Alteon D blocks port 8 or Alteon C blocks port 1 depending on the
information provided in the BPDU.
•
VLAN 2 Participation—Alteon A, the root bridge generates another BPDU for STG2 and
forwards it out from port 8. Alteon B receives this BPDU on its port 1. Port 1 on Alteon B is on
VLAN 2, STG1. Because Alteon B has no additional ports participating in STG1, this BPDU is not
be forwarded to any additional ports and Alteon A remains the designated root.
•
VLAN 3 Participation—For VLAN 3 you can have Alteon B or C to be the root bridge. If Alteon
B is the root bridge for VLAN 3, STG2, then Alteon B transmits the BPDU out from port 8. Alteon
C receives this BPDU on port 8 and is identified as participating in VLAN 3, STG2. Since Alteon C
has no additional ports participating in STG2, this BPDU is not forwarded to any additional ports
and Alteon B remains the designated root.
Rapid Spanning Tree Protocol
Rapid Spanning Tree Protocol (RSTP) provides rapid convergence of the spanning tree and provides
for the fast reconfiguration critical for networks carrying delay-sensitive traffic such as voice and
video. RSTP significantly reduces the time to reconfigure the active topology of the network when
changes occur to the physical topology or its configuration parameters. RSTP reduces the bridged-
LAN topology to a single spanning tree.
RSTP parameters are configured in STG1. STP Groups 2 through 32 do not apply to RSTP, and must
be cleared. There are new STP parameters to support RSTP, and some values to existing parameters
are different.
Table 12: Multiple Spanning Tree Groups per VLAN Example
Alteon
VLAN 1
VLAN 2
VLAN 3
Alteon A
STG1
Ports 1 and 2
STG2
Port 8
Alteon B
STG1
Port 1
STG2
Port 8
Alteon C
STG1
Ports 1 and 2
STG2
Port 8
Alteon D
STG1
Ports 1 and 8
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