Stp And Ieee 802.1Q Trunks - Cisco 7609 Configuration Manual

Understanding How STP Works
Disabled State
A Layer 2 LAN port in the disabled state does not participate in frame forwarding or STP, as shown in
Figure
Figure 15-7 Interface 2 in Disabled State
A disabled Layer 2 LAN port performs as follows:
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STP and IEEE 802.1Q Trunks

802.1Q trunks impose some limitations on the STP strategy for a network. In a network of Cisco network
devices connected through 802.1Q trunks, the network devices maintain one instance of STP for each
VLAN allowed on the trunks. However, non-Cisco 802.1Q network devices maintain only one instance
of STP for all VLANs allowed on the trunks.
When you connect a Cisco network device to a non-Cisco device through an 802.1Q trunk, the Cisco
network device combines the STP instance of the 802.1Q VLAN of the trunk with the STP instance of
the non-Cisco 802.1Q network device. However, all per-VLAN STP information is maintained by Cisco
network devices separated by a cloud of non-Cisco 802.1Q network devices. The non-Cisco 802.1Q
cloud separating the Cisco network devices is treated as a single trunk link between the network devices.
For more information on 802.1Q trunks, see
Cisco 7600 Series Router Cisco IOS Software Configuration Guide—12.1E
15-12
15-7. A Layer 2 LAN port in the disabled state is virtually nonoperational.
All segment
frames
Port 1
Station
addresses
BPDUs
Filtering System
database module
Data
frames
Port 2
Disabled
Discards frames received from the attached segment.
Discards frames switched from another port for forwarding.
Does not incorporate end station location into its address database. (There is no learning, so there is
no address database update.)
Does not receive BPDUs.
Does not receive BPDUs for transmission from the system module.
Forwarding
Network
management
and data frames
Frame
forwarding
Network
management
frames
All segment
frames
Chapter 7, "Configuring LAN Ports for Layer 2 Switching."
Chapter 15 Configuring STP and IEEE 802.1s MST
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