Foundry NetIron M2404C and M2404F Metro Access Switches
Configuring STP (Rev. 03)
Spanning Tree Protocol (STP)
© 2008 Foundry Networks, Inc.
Page 12 of 38
STP Address Management
IEEE 802.1D specifies 17 multicast addresses, ranging from 0x0180C2000000 to
0x0180C2000010, to be used by different bridge protocols. These addresses are static addresses
that cannot be removed.
Regardless of the STP state, the device receives but does not forward packets destined for
addresses between 0x0180c2000000 and 0x0180C200000F.
If STP is enabled, the device CPU receives packets destined for 0x0180C2000000 and
0x0180C2000010. If STP is disabled, the device forwards those packets as unknown multicast
addresses.
STP and Redundant Connectivity
A redundant backbone can be created with STP by connecting two device ports to another device
or to two different devices. STP automatically disables one port but enables it if the other one fails,
as shown in
Figure 5
. If one link is high-speed and the other is low-speed, the low-speed link is
always disabled. If the speeds are the same, the port priority and port ID are added together, and
STP disables the link with the lowest value.
Figure 5: STP and Redundant Connectivity
Topology Change Detection
From the device point of view, the locations of workstations appear to change when the spanning
tree topology is changed. This requires the address tables on all devices to be flushed and the new
data path to be relearned on all the network devices.