16- and 36-Port Ethernet Switch Module for Cisco 2600 Series, Cisco 3600 Series, and Cisco 3700 Series
Feature Overview
16
Cisco IOS Release 12.2(2)XT, 12.2(8)T, and 12.2(15)ZJ
Blocking State
A Layer 2 interface in the blocking state does not participate in frame forwarding, as shown in
Figure 5
.
After initialization, a BPDU is sent out to each Layer 2 interface in the switch. A switch initially assumes
it is the root until it exchanges BPDUs with other switches. This exchange establishes which switch in
the network is the root or root bridge. If only one switch is in the network, no exchange occurs, the
forward delay timer expires, and the ports move to the listening state. A port always enters the blocking
state following switch initialization.
Figure 5
Interface 2 in Blocking State
A Layer 2 interface in the blocking state performs as follows:
•
Discards frames received from the attached segment.
•
Discards frames switched from another interface for forwarding.
•
Does not incorporate end station location into its address database. (There is no learning on a
blocking Layer 2 interface, so there is no address database update.)
•
Receives BPDUs and directs them to the system module.
•
Does not transmit BPDUs received from the system module.
•
Receives and responds to network management messages.
Filtering
database
Frame
forwarding
System
module
Port 1
BPDUs
Segment
frames
Segment
frames
Forwarding
Blocking
BPDUs
Station
addresses
Network
management
and data frames
Port 2
S5692
Network
management
frames
Data
frames
