Rstp Bpdu Processing; Pvst; Pvst Protocol Frames - H3C S5560S-EI Series Configuration Manual

− The designated port connects to a point-to-point link and receives a handshake

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
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.
Figure 22 BPDU processing in RSTP

PVST

In an STP- or RSTP-enabled LAN, all bridges share one spanning tree. Traffic from all VLANs is
forwarded along the spanning tree, and ports cannot be blocked on a per-VLAN basis to prune loops.
PVST allows every VLAN to have its own spanning tree, which increases usage of links and
bandwidth. Because each VLAN runs RSTP independently, a spanning tree only serves its VLAN.
A PVST-enabled H3C device can communicate with a third-party device that is running Rapid PVST
or PVST. The PVST-enabled H3C device supports fast network convergence like RSTP when
connected to PVST-enabled H3C devices or third-party devices enabled with Rapid PVST.

PVST protocol frames

As shown in
differences:
response from the directly connected device.
Figure 22, Device A is the root bridge. The priority of Device B is higher than the priority
Figure 23, a PVST BPDU uses the same format as an RSTP BPDU except the following
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