User's Manual

Table Of Contents
243
Users Manual of CS-6306R
20.1.1.3 BPDU Filter
The BPDU filtering feature can be globally enabled on the switch or can be enabled per interface, but the
feature operates with some differences.
In SSTP/PVST mode, if a Port Fast port with BPDU filter configured receives the BPDU, the features BPDU
Filter and Port Fast at the port will be automatically disabled, resuming the port as a normal port. Before
entering the Forwarding state, the port must be in the Listening state and Learning state.
The BPDU Filter feature can be configured in global configuration mode or in port configuration mode. In
global configuration mode, run the command spanning-tree portfast bpdufilter to block all ports to send
BPDU out. The port, however, can still receive and process BPDU.
20.1.1.4 Uplink Fast
The feature Uplink Fast enables new root ports to rapidly enter the Forwarding state when the connection
between the switch and the root bridge is disconnected.
A complex network always contains multiple layers of devices, as shown in figure 1.2. Both aggregation
layer and the access layer of the switch have redundancy connections with the upper layer. These
redundancy connections are normally blocked by the STP to avoid loops.
Figure 1.2 Switching network topology
Suppose the connection between a switch and the upper layer is disconnected (called as Direct Link Failure),
the STP chooses the Alternate port on the redundancy line as the root port. Before entering the Forwarding
state, the Alternate port must be in the Listening state and Learning state. If the Uplink Fast feature is
configured by running the command spanning-tree uplinkfast in global configuration mode, new root port
can directly enter the forwarding state, resuming the connection between the switch and the upper layer.
Figure 1.3 shows the working principle of the Uplink Fast feature. The port for switch C to connect switch B is
the standby port when the port is in the original state. When the connection between switch C and root switch
A is disconnected, the previous Alternate port is selected as new root port and immediately starts forwarding.