H3C S12500X-AF Series, Руководство по настройке

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Table 9 Port state differences between RSTP and STP
STP port state
RSTP port
state Sends
BPDU Learns MAC
addresses Forwards user
data
Disabled Discarding No No No
Blocking Discarding No No No
Listening Discarding Yes No No
Learning Learning Yes Yes No
Forwarding Forwarding Yes Yes Yes
How RSTP works
During RSTP calculation, the following events occur:
•
If a port in discarding state becomes an alternate port, it retains its state.
•
If a port in discarding state is elected as the root port or designated port, it enters the learning
state after the forward delay. The port learns MAC addresses, and enters the forwarding state
after another forward delay.
{
A newly elected RSTP root port rapidly enters the forwarding state if the following
requirements are met:
−
The old root port on the device has stopped forwarding data.
−
The upstream designated port has started forwarding data.
{
A newly elected RSTP designated port rapidly enters the forwarding state if one of the
following requirements is met:
−
The designated port is configured as an edge port which directly connects to a user
terminal.
−
The designated port connects to a point-to-point link and receives a handshake
response from the directly connected device.
RSTP BPDU processing
In RSTP, a non-root bridge actively sends RSTP BPDUs at the hello time through designated ports
without waiting for the root bridge to send RSTP BPDUs. This enables RSTP to quickly detect link
failures. If a device fails to receive any RSTP BPDUs on a port within triple the hello time, the device
considers that a link failure has occurred. After the stored configuration BPDU expires, the device
floods RSTP BPDUs with the TC flag set to initiate a new RSTP calculation.
In RSTP, a port in blocking state can immediately respond to an RSTP BPDU with a lower priority
than its own BPDU.
As shown in Figure 27 , Device A is the root bridge. The priority of Device B is higher than the priority
of Device C. Port C2 on Device C is blocked.
When the link between Device A and Device B fails, the following events occur:
1.
Device B sends an RSTP BPDU with itself as the root bridge to Device C.
2.
Device C compares the RSTP BPDU with its own BPDU.
3.
Because the RSTP BPDU from Device B has a lower priority, Device C sends its own BPDU to
Device B.
4.
Device B considers that Port B2 is the root port and stops sending RSTP BPDUs to Device C.