Configuring Spanning Tree Protocol (STP) and IronSpan Features
December 2005
© Foundry Networks, Inc.
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Port3/Switch 5 sends an RST BPDU to Port3/Switch 6 with a proposal flag. When Port3/Switch 5 receives the
RST BPDU, handshake mechanisms select Port3 as the Root port of Switch 6. All other ports are given a
Designated port role with discarding states. Port3/Switch 6 then sends an RST BPDU with an agreed flag to Port3/
Switch 5 to confirm that it is the Root port. The Root port then goes into a forwarding state.
Now, Port4/Switch 6 receives RST BPDUs that are superior to what it can transmit; therefore, it is given the
Alternate port role. The port remains in discarding state.
Port5/Switch 6 receives RST BPDUs that are inferior to what it can transmit. The port is then given a Designated
port role.
Next Switch 2 sends RST BPDUs with a proposal flag to Port3/Switch 4. Port3 becomes the Root port for the
bridge; all other ports are given a Designated port role with discarding states. Port3/Switch 4 sends an RST BPDU
with an agreed flag to Switch 2 to confirm that it is the new Root port. The port then goes into a forwarding state.
Now Port4/Switch 4 receives an RST BPDU that is superior to what it can transmit. The port is then given an
Alternate port role, and remains in discarding state.
Likewise, Port5/Switch 4 receives an RST BPDU that is superior to what it can transmit. The port is also given an
Alternate port role, and remains in discarding state.
Port2/Switch 2 transmits an RST BPDU with a proposal flag to Port2/Switch 1. Port2/Switch 1 becomes the Root
port. All other ports on Switch 1 are given Designated port roles with discarding states.
Port2/Switch 1 sends an RST BPDU with an agreed flag to Port2/Switch 2 and Port2/Switch 1 goes into a
forwarding state.
Port3/Switch 1 receives an RST BPDUs that is inferior to what it can transmit; therefore, the port retains its
Designated port role and goes into forwarding state only after the forward delay timer expires twice on that port
while it is still in a Designated role.
Port3/Switch 2 sends an RST BPDU to Port3/Switch 3 that contains a proposal flag. Port3/Switch 3 becomes the
Root port, while all other ports on Switch 3 are given Designated port roles and go into discarding states. Port3/
Switch 3 sends an RST BPDU with an agreed flag to Port3/Switch 2 and Port3/Switch 3 goes into a forwarding
state.
Now, Port2/Switch 3 receives an RST BPDUs that is superior to what it can transmit so that port is given an
Alternate port state.
Port4/Switch 3 receives an RST BPDU that is inferior to what it can transmit; therefore, the port retains its
Designated port role.
Ports on all the bridges in the topology with Designated port roles that received RST BPDUs with agreed flags go
into forwarding states instantly. However, Designated ports that did not receive RST BPDUs with agreed flags
must wait until the forward delay timer expires twice on those port. Only then will these port move into forwarding
states.
The entire 802.1W topology converges in less than 300 msec and the essential connectivity is established
between the designated ports and their connected root ports.
Содержание FastIron Edge Switch X424
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