H3C S6850 Series Configuration Guide

53
1. Port A1 can only receive BPDUs and cannot send BPDUs to Port B1.
2. Port B1 does not receive BPDUs from Port A1 for a certain period of time.
3. Device B determines itself as the root bridge.
4. Port B1 sends its BPDUs to Port A1.
5. Port A1 determines the received BPDUs are inferior to its own BPDUs. A dispute is detected.
6. Dispute guard is triggered and blocks Port A1 to prevent a loop.
Figure 19 Dispute guard triggering scenario (on a designated port)
As shown in Figure 20, in normal conditions, Device A is the root bridge, and Port B1 and Port C1 are
root ports. When the links between Device A and Device B become unidirectional (the links fail in the
direction of Port A1 to Port B1), the following events occur:
1. Device B cannot receive BPDUs from Device A.
2. Device B determines itself as the root bridge.
3. Port B1 sends BPDUs in which the root bridge is Device B to Port C1.
4. Port C1 receives BPDUs from two root bridges, Device A and Device B. A dispute is detected.
5. Dispute guard is triggered and blocks Port C1 to avoid a loop.
Device A
Device B
Root
Root port
Designated port
Normal link
Blocked link
Blocked port
Port A1 Port A2
Port B1 Port B2
Device A
Device B
Root
Port A1 Port A2
Port B1 Port B2
Normal condition
Unidirectional link
occurs
Device A
Device B
Root
Port A1
Port B1 Port B2
Dispute guard is
triggered
Port A2
Unidirectional link

H3C S6850 Series Specifications

General

Brand	H3C
Model	S6850 Series
Category	Switch
Language	English