Convergence In A Complex Rstp Topology - Dell PowerConnect B-RX Configuration Manual

Bigiron rx series configuration guide v02.7.02

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Convergence in a complex RSTP topology

The following is an example of a complex RSTP topology.

Lines in the figure show the point-to-point connection to the bridges in the topology.

Switch 5 sends an RST BPDU that contains a proposal flag to Port5/Switch 2. When handshakes

are completed in Switch 5, Port5/Switch 2 is selected as the Root port on Switch 2. All other ports

on Switch 2 are given Designated port role with discarding states.

Port5/Switch 2 then sends an RST BPDU with an agreed flag to Switch 5 to confirm that it is the

new Root port and the port enters a forwarding state. Port7 and Port8 are informed of the identity

of the new Root port. RSTP algorithm selects Port7 as the Designated port while Port8 becomes

the Backup port.

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.

BigIron RX Series Configuration Guide

53-1001810-01

Complex RSTP topology

Bridge priority = 1000

Bridge priority = 300

57, Switch 5 is selected as the root bridge since it is the bridge with the highest priority.

Convergence in a complex RSTP topology

Bridge priority = 200

Bridge priority = 400

Bridge priority = 60

Bridge priority = 900

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